Multilocus sequence analysis of homologous recombination and diversity in Arthrobacter sensu lato named species and glacier-inhabiting strains

Members of the bacterial genus Arthrobacter sensu lato are Gram-positive actinomycetes distributed worldwide and found in numerous environments including soil, water, glacier ice, and sewage. Homologous recombination is an important driving force in bacterial evolution, but its impact on Arthrobacter sensu lato evolution is poorly understood. We evaluated homologous recombination among 41 Arthrobacter sensu lato named species, using multilocus sequence analysis (MLSA). A high level of recombination was found, associated with strong diversification and a reticulate evolutionary pattern of Arthrobacter sensu lato. We also collected a total of 31 cold-adapted Arthrobacter sensu lato strains from two cold glaciers located in northwest China and two temperate glaciers in southwest China, and evaluated their diversity and population structure by MLSA. The glacier strains displayed high diversity, but rates of recombination among the four glacier groups were quite low, indicating that barriers to homologous recombination formed in the past among the populations on different glaciers. Our findings indicate that historical glaciation events shaped the contemporary distributions, taxonomic relationships, and phylogeographic patterns of Arthrobacter sensu lato species on glaciers.     

Chlorophycean parasite on a marine fish,Sillago japonica (Japanese sillago)

A green spotted Japanese sillago (Sillago japonica) was caught by a fisherman and brought to the laboratory for pathological inspection. The green spots were abundant on the lateral line and more extensively so within the mouth cavity. In both sites, green spots were embedded within the fish flesh and formed 2–3 mm dome-shaped colonies. SEM revealed these colonies to harbor numerous unknown cells with small, surface warts (ornamentations). Molecular analysis showed the cells were Desmodesmus (D. komarekii), a common freshwater coccoid green alga found in ponds and rivers worldwide. It is uncertain how the host fish came to be infected with the alga which was not merely attached externally but embedded within the flesh and inside the mouth cavity. This is the first case of parasitic form of coccoid green algae in marine fish and provides new insights into the variable nature of green algae.     

Bacterial biodiversity from Roopkund Glacier, Himalayan mountain ranges, India

The bacterial diversity of two soil samples collected from the periphery of the Roopkund glacial lake and one soil sample from the surface of the Roopkund Glacier in the Himalayan ranges was determined by constructing three 16S rRNA gene clone libraries. The three clone libraries yielded a total of 798 clones belonging to 25 classes. Actinobacteria was the most predominant class (>10% of the clones) in the three libraries. In the library from the glacial soil, class Betaproteobacteria (24.2%) was the most predominant. The rarefaction analysis indicated coverage of 43.4 and 41.2% in the samples collected from the periphery of the lake thus indicating a limited bacterial diversity covered; at the same time, the coverage of 98.4% in the glacier sample indicated most of the diversity was covered. Further, the bacterial diversity in the Roopkund glacier soil was low, but was comparable with the bacterial diversity of a few other glaciers. The results of principal component analysis based on the 16S rRNA gene clone library data, percentages of OTUs and biogeochemical data revealed that the lake soil samples were different from the glacier soil sample and the biogeochemical properties affected the diversity of microbial communities in the soil samples.     

Comparative ecophysiology of three Placopsis species, pioneer lichens in recently exposed Chilean glacial forelands

Lichen species belonging to the genus Placopsis are early colonisers on snow free moraines of exposed land surfaces in the subantarctic region of Tierra de Fuego, South Chile. The physiological performance of three co-occurring species, P. pycnotheca, (terricolous), and P. perrugosa, and P. stenophylla (both saxicolous) was studied. All, possess green algal photobionts but have cyanobacteria in cephalodia. It was found that there was (i) a strong positive correlation between the acetylene reduction rate (AR) and the maximum photosynthetic rate (Amax), between the N content and the AR rate, and between the N and P contents, and (ii) the relationship between the CO₂-exchange rates and the responses obtained in the laboratory reflected the ecology of these three lichens in the field. The results provide new information about the dynamics of some of the fastest growing crustose lichens. We hypothesize that the performance of these three species may have developed as a response to growing in an unstable environment that resulted from frequent glacial fluctuations.     

Abundance of Microbes Involved in Nitrogen Transformation in the Rhizosphere of Leucanthemopsis alpina (L.) Heywood Grown in Soils from Different Sites of the Damma Glacier Forefield

Glacier forefields are an ideal playground to investigate the role of development stages of soils on the formation of plant–microbe interactions as within the last decades, many alpine glaciers retreated, whereby releasing and exposing parent material for soil development. Especially the status of macronutrients like nitrogen differs between soils of different development stages in these environments and may influence plant growth significantly. Thus, in this study, we reconstructed major parts of the nitrogen cycle in the rhizosphere soil/root system of Leucanthemopsis alpina (L.) Heywood as well as the corresponding bulk soil by quantifying functional genes of nitrogen fixation (nifH), nitrogen mineralisation (chiA, aprA), nitrification (amoA AOB, amoA AOA) and denitrification (nirS, nirK and nosZ) in a 10-year and a 120-year ice-free soil of the Damma glacier forefield. We linked the results to the ammonium and nitrate concentrations of the soils as well as to the nitrogen and carbon status of the plants. The experiment was performed in a greenhouse simulating the climatic conditions of the glacier forefield. Samples were taken after 7 and 13 weeks of plant growth. Highest nifH gene abundance in connection with lowest nitrogen content of L. alpina was observed in the 10-year soil after 7 weeks of plant growth, demonstrating the important role of associative nitrogen fixation for plant development in this soil. In contrast, in the 120-year soil copy numbers of genes involved in denitrification, mainly nosZ were increased after 13 weeks of plant growth, indicating an overall increased microbial activity status as well as higher concentrations of nitrate in this soil.     

Mutualistic Biofilm Communities Develop with Porphyromonas gingivalis and Initial,Early, and Late Colonizers of Enamel

Porphyromonas gingivalis is present in dental plaque as early as 4 h after tooth cleaning, but it is also associated with periodontal disease, a late-developing event in the microbial successions that characterize daily plaque development. We report here that P. gingivalis ATCC 33277 is remarkable in its ability to interact with a variety of initial, early, middle, and late colonizers growing solely on saliva. Integration of P. gingivalis into multispecies communities was investigated by using two in vitro biofilm models. In flow cells, bacterial growth was quantified using fluorescently conjugated antibodies against each species, and static biofilm growth on saliva-submerged polystyrene pegs was analyzed by quantitative real-time PCR using species-specific primers. P. gingivalis could not grow as a single species or together with initial colonizer Streptococcus oralis but showed mutualistic growth when paired with two other initial colonizers, Streptococcus gordonii and Actinomyces oris, as well as with Veillonella sp. (early colonizer), Fusobacterium nucleatum (middle colonizer), and Aggregatibacter actinomycetemcomitans (late colonizer). In three-species flow cells, P. gingivalis grew with Veillonella sp. and A. actinomycetemcomitans but not with S. oralis and A. actinomycetemcomitans. Also, it grew with Veillonella sp. and F. nucleatum but not with S. oralis and F. nucleatum, indicating that P. gingivalis and S. oralis are not compatible. However, P. gingivalis grew in combination with S. gordonii and S. oralis, demonstrating its ability to overcome the incompatibility when cultured with a second initially colonizing species. Collectively, these data help explain the observed presence of P. gingivalis at all stages of dental plaque development.Removal of dental plaque by routine oral hygiene procedures is followed by a repetition of a species succession that starts with initially colonizing streptococci and actinomyces (5, 16). Other species follow as early, middle, and late colonizers, which establishes the following developmental process: successive attachment of saliva-suspended species to already attached bacteria and formation of multispecies communities.Attachment is a critical event essential to preventing the bacteria from being swallowed by salivary flow. Initial colonizers bind to host-derived receptors in the salivary pellicle coating of the tooth enamel. The remainder of typical plaque development occurs by accretion of saliva-suspended species and growth of attached bacteria, thereby increasing the microbial diversity. Adherence of suspended single cells to attached cells is called coadhesion (1). Some suspended cells are already coaggregated and adhere to attached cells as coaggregates; coaggregation is defined as the specific cell-to-cell recognition and adherence of genetically distinct cell types (8). All human oral bacterial species exhibit coaggregation. For example, Streptococcus oralis coaggregates with Streptococcus gordonii (intrageneric coaggregation). Both species pair with Actinomyces oris (intergeneric coaggregation), and all of them coaggregate with Fusobacterium nucleatum (multigeneric coaggregation). Multispecies communities composed of coaggregating species characterize dental plaque biofilms in vivo (3, 17, 18).To increase our understanding of interactions among species, we have employed two in vitro model systems and are testing numerous combinations of seven species for their ability to grow on saliva as their sole nutritional source (20, 21). First, we reported that F. nucleatum (middle colonizer) failed to grow when paired with S. oralis but grew well when A. oris was included in the three-species biofilm (20), indicating specificity by F. nucleatum for the presence of a particular initial colonizer. Recently, we showed that Aggregatibacter actinomycetemcomitans (late colonizer and periodontopathogen) exhibited mutualistic relationships with F. nucleatum and Veillonella sp. (early colonizer and commensal organism), illustrating the ability of commensals and pathogens to grow together (21).Porphyromonas gingivalis, another periodontopathogen, forms three-species communities with F. nucleatum and S. gordonii (11). Proteomics of P. gingivalis in this three-species community revealed a broad increase in proteins involved in protein synthesis, suggesting that a multispecies relationship is advantageous for the porphyromonad (11). This research group had previously reported the presence of differentially regulated porphyromonad genes when P. gingivalis and S. gordonii were together in biofilms (22). Thus, P. gingivalis responds to the presence of other oral species.P. gingivalis is detected in dental plaque samples within 6 h after professional tooth cleaning (5, 13), and its numbers increase in periodontally diseased sites (15). It forms biofilms with S. gordonii but not with Streptococcus mutans (12) or Streptococcus cristatus (23). P. gingivalis required a preformed streptococcal substratum for its incorporation into a biofilm (12). Partner specificity was also noted among four fresh isolates of P. gingivalis, which showed no coaggregation with a variety of oral actinomyces, aggregatibacteria, capnocytophagae, and streptococci (9) but coaggregated with F. nucleatum (7, 10). We show here that P. gingivalis exhibits widespread mutualism with initial, early, middle, and late colonizers but also shows specificity with initially colonizing streptococci, which could help explain its early appearance in the development of dental plaque biofilms. The relationship of porphyromonads with initial, early, middle, and later colonizers during biofilm growth on saliva as a sole nutritional source has not been explored previously. We hypothesize that the ability of P. gingivalis to coaggregate with S. gordonii and A. oris (initial colonizers), Veillonella sp. (early colonizer), F. nucleatum (middle colonizer), and A. actinomycetemcomitans (late colonizer) allows these bacteria to form multispecies biofilm communities.     

MORPHOGENESIS OF THE SPORANGIUM OF COMATRICHA

Goodwin , Donna C. (State U. Iowa, Iowa City.) Morphogenesis of the sporangium of Comatricha. Amer. Jour. Bot. 48(2): 148–154. IIlus. 1961.—Three species of the myxomycete genus, Comatricha, were studied: Comatricha nigra, C. fimbriata, and C. elegans. The sporangia developed on living bark of Ulmus americana in moist chamber. The hypothallus is formed under the homogeneous protoplasmic mass of the sporangial initial. The fibrous threads of the hypothallus bend upward, lengthening at the apices to become the fibers of the stalk and columella. The undifferentiated protoplasm is carried upward as the stalk elongates. When the columella has attained its mature height, threads bend out from the columella and grow toward the periphery of the sporangium. These threads form the capillitium. Simultaneous with the appearance of the capillitial initials, the peridium, a delicate membrane, forms. After the capillitium is mature, the protoplast cleaves into many cells, the future spores. The peridium evanesces early in the stage of spore maturation. Cellulose is present in the stalk, capillitium, and spore walls but is not found in the peridium or hypothallus. The capillitium of these species follows a developmental pattern designated as the “Comatricha-type” by Ross (1957) from a study of Comatricha typhoides. The taxonomic implications of the sporangial developmental pattern are discussed.     

High-Level Diversity of Tailed Phages,Eukaryote-Associated Viruses,and Virophage-Like Elements in the Metaviromes of Antarctic Soils

The metaviromes of two distinct Antarctic hyperarid desert soil communities have been characterized. Hypolithic communities, cyanobacterium-dominated assemblages situated on the ventral surfaces of quartz pebbles embedded in the desert pavement, showed higher virus diversity than surface soils, which correlated with previous bacterial community studies. Prokaryotic viruses (i.e., phages) represented the largest viral component (particularly Mycobacterium phages) in both habitats, with an identical hierarchical sequence abundance of families of tailed phages (Siphoviridae > Myoviridae > Podoviridae). No archaeal viruses were found. Unexpectedly, cyanophages were poorly represented in both metaviromes and were phylogenetically distant from currently characterized cyanophages. Putative phage genomes were assembled and showed a high level of unaffiliated genes, mostly from hypolithic viruses. Moreover, unusual gene arrangements in which eukaryotic and prokaryotic virus-derived genes were found within identical genome segments were observed. Phycodnaviridae and Mimiviridae viruses were the second-most-abundant taxa and more numerous within open soil. Novel virophage-like sequences (within the Sputnik clade) were identified. These findings highlight high-level virus diversity and novel species discovery potential within Antarctic hyperarid soils and may serve as a starting point for future studies targeting specific viral groups.     

Acetic Acid Bacterial Biota of the Pink Sugar Cane Mealybug, Saccharococcus sacchari, and Its Environs

Saccharococcus sacchari is the primary colonizer of the developing “sterile” tissue between the leaf sheath and stem of sugar cane. The honeydew secreted by the mealybugs is acidic (about pH 3) and supports an atypical epiphytic microbiota dominated by acetobacter-like bacteria and acidophilic yeast species. However, Erwinia and Leuconostoc species predominate within the leaf sheath pocket region when the mealybugs die out. The unidentified acetobacters were readily isolated from S. sacchari throughout its life cycle and from other genera of mealybugs on sugar cane and various other plants, both above and below ground. No other insect present on sugar cane was a significant vector of acetic acid bacteria. The major factors restricting microbial diversity within the environs of mealybugs were considered to be yeast activity along with bacterial production of acetic acid, ketogluconic acids, and gamma-pyrones, in association with their lowering of pH. The microbial products may aid in suppressing the attack by the parasitic mold Aspergillus parasiticus on mealybugs but could act as attractants for the predatory fruit fly Cacoxenus perspicax.     

Benthic Trophic Interactions in an Antarctic Shallow Water Ecosystem Affected by Recent Glacier Retreat

The western Antarctic Peninsula is experiencing strong environmental changes as a consequence of ongoing regional warming. Glaciers in the area are retreating rapidly and increased sediment-laden meltwater runoff threatens the benthic biodiversity at shallow depths. We identified three sites with a distinct glacier-retreat related history and different levels of glacial influence in the inner part of Potter Cove (King George Island, South Shetland Islands), a fjord-like embayment impacted since the 1950s by a tidewater glacier retreat. We compared the soft sediment meio- and macrofauna isotopic niche widths (δ¹³C and δ¹⁵N stable isotope analysis) at the three sites to investigate possible glacier retreat-related influences on benthic trophic interactions. The isotopic niches were locally shaped by the different degrees of glacier retreat-related disturbance within the Cove. Wider isotopic niche widths were found at the site that has become ice-free most recently, and narrower niches at the older ice-free sites. At an intermediate state of glacier retreat-related disturbance (e.g. via ice-growler scouring) species with different strategies could settle. The site at the earliest stage of post-retreat development was characterized by an assemblage with lower trophic redundancy. Generally, the isotopic niche widths increased with increasing size spectra of organisms within the community, excepting the youngest assemblage, where the pioneer colonizer meiofauna size class displayed the highest isotopic niche width. Meiofauna at all sites generally occupied positions in the isotopic space that suggested a detrital-pool food source and/or the presence of predatory taxa. In general ice scour and glacial impact appeared to play a two-fold role within the Cove: i) either stimulating trophic diversity by allowing continuous re-colonization of meiofaunal species or, ii) over time driving the benthic assemblages into a more compact trophic structure with increased connectedness and resource recycling.     

Carbohydrates in the hypothallus and areolae of the crustose lichen <Emphasis Type="Italic">Rhizocarpon geographicum</Emphasis> (L.) DC.

Carbohydrate concentrations in the marginal hypothallus and areolae of the crustose lichen Rhizocarpon geographicum (L.) DC. were measured in north Wales, U.K. using gas chromatography. Ribitol, arabitol, and mannitol were the most abundant carbohydrates while α- glucose β-glucose, fructose, sucrose, and trehalose were present in smaller amounts. The concentrations of arabitol, ribitol, mannitol, fructose, and α-glucose were greater in the areolae while the concentration of trehalose was greater in the hypothallus. Concentrations of carbohydrates varied little between sample days. Concentrations of polyols in the hypothallus were not correlated with those in the areolae. These results suggest: 1) the hypothallus has a lower demand for carbohydrates than the areolae or there is limited transport from areolae to hypothallus, 2) increased trehalose in the non-lichenised hypothallus may be an adaptation to withstand stress and desiccation, and 3) polyols are partitioned differently in the hypothallus and areolae.     

Trends in soil characteristics along a recently deglaciated foreland on Anvers Island,Antarctic Peninsula

We assessed patterns in soil development at a recently deglaciated foreland on Anvers Island on the Antarctic Peninsula. Soil samples were collected along transects extending 35 m over bare ground from the edge of a receding glacier; the far end of these transects has been ice free for approximately 20 years. We also compared soils at the far end of these transects under bare ground to those under canopies of isolated individuals of Deschampsia antarctica, a caespitose grass, that had recently colonized the site (established for <6 years). In addition, we compared soils at this young foreland to those in a well-developed tundra island that has been ice free for at least several hundred years. At the foreland site, soil moisture was greatest near the glacier, consistent with proximity to meltwater, and declined with distance from the glacier. This decline in soil moisture may explain the decrease in litter decomposition rates and the greater soil nitrate (NO₃ ⁻) concentrations that we observed with distance from the glacier. The greater soil moisture near the glacier likely promoted leaching and transport of NO₃ ⁻ to drier soils away from the glacier. The presence of D. antarctica at the glacier foreland had little effect on soil properties, which is not surprising considering it had only colonized sampling areas during the previous 5 years. Compared to the foreland, which contained only mineral soil, soil at the older tundra site had a 2.5- to 5-cm-thick organic horizon that had much higher concentrations of total carbon, nitrogen, and NO₃ ⁻.     

The role of glacier mice in the invertebrate colonisation of glacial surfaces: the moss balls of the Fallj?kull, Iceland

Glacier surfaces have a surprisingly complex ecology. Cryoconite holes contain diverse invertebrate communities, while other invertebrates, such as Collembola, often graze on algae and windblown dead organic material on the glacier surface. Glacier mice (ovoid unattached moss balls) occur on some glaciers worldwide. Studies of these glacier mice have concentrated on their occurrence and mode of formation. There are no reports of the invertebrate communities. But, such glacier mice may provide a suitable favourable habitat and refuge for a variety of invertebrate groups to colonise the glacier surface. Here, we describe the invertebrate fauna of the glacier mice (moss balls) of the Fallj?kull, Iceland. The glacier mice were composed of Racomitrium sp. and varied in size from 8.0 to 10.0?cm in length. All glacier mice studied contained invertebrates. Two species of Collembola were present. Pseudisotoma sensibilis (Tullberg, 1876) was numerically dominant with between 12 and 73 individuals per glacier mouse, while Desoria olivacea (Tullberg, 1871) occurred but in far lower numbers. Tardigrada and Nematoda had mean densities of approximately 200 and 1,000, respectively. No Acari, Arachnida or Enchytraeidae were observed, which may be related to the difficulty these groups have in colonising the glacier mice. We suggest that glacier mice provide an unusual environmentally ameliorated microhabitat for an invertebrate community dwelling on a glacial surface. The glacier mice thereby enable an invertebrate fauna to colonise an otherwise largely inhospitable location with implications for carbon flow in the system.     

Soil microbial carbon and nitrogen transformations at a glacial foreland on Anvers Island, Antarctic Peninsula

Microbial communities can play a critical role in soil development and succession at glacial forelands through their contribution to soil carbon (C) and nitrogen (N) cycling. Using a combination of molecular fingerprinting techniques and metabolic rate measurements, we examined the soil microbial community composition and key transformations in the C and N cycles at a glacial foreland on Anvers Island along the Antarctic Peninsula. Soils were sampled along transects representing a chronosequence of <1 to approximately 10?years since deglaciation. The soil microbial community was active adjacent to the receding edge of the glacier, where soil had been ice-free for <1?year. A survey of the microbial community composition identified typical soil bacterial species such as Arthrobacter and Sphingomonas, as well as known Antarctic heterotrophs, cyanobacteria and fungi. The soil C cycle over this zone was dominated by phototrophic microbial activity, while the N cycle was dominated by heterotrophic N₂-fixation and not cyanobacterial N₂-fixation as found at other recently deglaciated forelands. Other N transformations such as ammonia oxidation and denitrification appeared to be of limited relevance.     

Community dominance patterns, not colonizer genetic diversity, drive colonization success in a test using grassland species

Successful colonization and/or invasion depend on characteristics of the invaded community and of the colonizer itself. Although many studies have documented a negative relationship between invasibility and biodiversity, the importance of community evenness is rarely examined and thus poorly understood. However, colonizer characteristics, including population genetic diversity, can also be important determinants of colonization success. We conducted a greenhouse experiment to assess the relative importance of community evenness and colonizer population genetic diversity using the weed Arabidopsis thaliana. We added seeds of A. thaliana (varying genetic diversity while keeping propagule pressure constant) to four types of constructed plant communities: those dominated by legumes, grasses or forbs, or with equal abundances of all three functional groups. We selected community members from a large pool of species to avoid the confounding effects of species identity. We also assessed the success of multiple seedbank colonizers to assess generality in the effects of our evenness treatments. Equal-abundance communities were no better at suppressing colonization than communities dominated by a single functional group. Forb-dominated communities suppressed A. thaliana colonization better than grass-dominated communities and suppressed seedbank colonizers better than legume-dominated communities. Equal-abundance communities were similar to forb-dominated ones in their eventual composition and in their invasibility, suggesting that forbs drove colonizer suppression in that treatment rather than high evenness itself. Most of our forbs grew quickly, yielding productive forb-dominated communities; this points to the importance of growth and colonization phenology in our system. A. thaliana genetic diversity did not affect colonization success, perhaps because strong interspecific competition substantially limited A. thaliana seedling emergence.     

Microbial Community Succession in an Unvegetated,Recently Deglaciated Soil

Primary succession is a fundamental process in macroecosystems; however, if and how soil development influences microbial community structure is poorly understood. Thus, we investigated changes in the bacterial community along a chronosequence of three unvegetated, early successional soils (∼20-year age gradient) from a receding glacier in southeastern Peru using molecular phylogenetic techniques. We found that evenness, phylogenetic diversity, and the number of phylotypes were lowest in the youngest soils, increased in the intermediate aged soils, and plateaued in the oldest soils. This increase in diversity was commensurate with an increase in the number of sequences related to common soil bacteria in the older soils, including members of the divisions Acidobacteria, Bacteroidetes, and Verrucomicrobia. Sequences related to the Comamonadaceae clade of the Betaproteobacteria were dominant in the youngest soil, decreased in abundance in the intermediate age soil, and were not detected in the oldest soil. These sequences are closely related to culturable heterotrophs from rock and ice environments, suggesting that they originated from organisms living within or below the glacier. Sequences related to a variety of nitrogen (N)-fixing clades within the Cyanobacteria were abundant along the chronosequence, comprising 6–40% of phylotypes along the age gradient. Although there was no obvious change in the overall abundance of cyanobacterial sequences along the chronosequence, there was a dramatic shift in the abundance of specific cyanobacterial phylotypes, with the intermediate aged soils containing the greatest diversity of these sequences. Most soil biogeochemical characteristics showed little change along this ∼20-year soil age gradient; however, soil N pools significantly increased with soil age, perhaps as a result of the activity of the N-fixing Cyanobacteria. Our results suggest that, like macrobial communities, soil microbial communities are structured by substrate age, and that they, too, undergo predictable changes through time.     

The Effect of Arthrobotrys conoides on Meloidogyne incognita Population Densities in Corn as Influenced by Temperature,Fungus Inoculum Density,and Time of Fungus Introduction in the Soil

In greenhouse experiments, the effect of Arthrobotrys conoides on Meloidogyne incognita population densities as affected by soil temperature, inoculum density, and green alfalfa was determined. The effect on M. incognita population densities was greater at a soil temperature of 25 C than at 18 or 32 C. Nematode control by A. conoides was most effective when the fungus was introduced into the soil 2 wk prior to nematode inoculation and planting of corn. Inoculum density of A. conoides was positively correlated with plant shoot weight (r = 0.81) and negatively correlated with numbers of Meloidogyne juveniles (r = -0.96), eggs (-0.89) and galls per gram of root (-0.91). A. conoides was not isolated from green alfalfa, but was isolated from alfalfa-amended soil to which no fungus had been added.     

Structure of a microbiol mat at Great Sippewissett Marsh, Cape Cod, Massachusetts

The microzination of phototrophic bacteria in a flat laminated microbiol mat at Great Sippewissett Salt Marsh on Cape Cod, Massachusetts, was studied using a combination of scanning and transmission electron microscopy, light microscopy and photosynthetic pigment analysis. Comparison of pigment content and ultrastructural information from electron microscopy of thin sections allowed us to determine the major groups of photosynthetic bacteria present. The approximately 1-cm-thick mat is located in sandy intertidal sediments of the marsh and comprised four to five distinctly colored layers. The uppermost brown layer contained Lyngbya, Nostoc, Phormidium (cyanobacteria) and Navicula (diatom) species. An intermediate bluish-green layer was dominated by Oscillatoria species. A central pink layer contained purple sulfur bacteria such as Amoebobacter, Thiocapsa, Chromatium and Thiocystis species, Below this was a distinctive orange layer, formed largely by one species of purple sulfur bacteria, Thiocapsa pfennigii. The lowermost and thinnest layer contained green sulfur bacteria of the genus Prosthecochloris, a very small prosthecate species with numerous knobby projections; this layer was not always present. Below this, where pigments were generally absent, were dark gray and black iron sulfide-rich sediments. Remnants of older decayed mats could be found deeper in the sediment. Extensive production of microbial extracellular polymers in all layers appeared to be responsible for attachment of cells to sand grains, for lamination of layers and for structural integrity of the mat as a whole. Below the layer of green sulfur bacteria, binding of sediment by microbial polymers ceased abruptly. Possibly in response to decreasing light penetration, the mean size of bacterial cells decreased in successively deeper layers. In the lowest layer where light penetration was very low, green sulfur bacteria with highly convoluted surfaces occurred. The increase in cell surface area-to-volume ratio may allow such organisms to survive at low light levels.     

The responses of an early (<Emphasis Type="Italic">Rhynchospora alba</Emphasis>) and a late (<Emphasis Type="Italic">Molinia japonica</Emphasis>) colonizer to solar radiation in a boreal wetland after peat mining

The responses of seedlings to solar radiation, including ultraviolet (UV), were investigated for Rhynchospora alba, an early colonizer, and Molinia japonica, a late colonizer, in a mined peatland in northern Japan. The solar radiation and rainfall were, respectively, higher and lower in 2008 than in 2009 during the field surveys. The seedlings were transplanted to bare ground, and measurements were made of the biomass, the allocation of biomass to shoots and roots, the absorbance of ultraviolet A and ultraviolet B, and the concentrations of anthocyanin and chlorophyll. R. alba did not change its biomass in response to any solar radiation treatment in 2008 and decreased shoot biomass with low UV and decreased root biomass with shade in 2009. Additionally, M. japonica did not change its biomass in 2008 but decreased its root biomass with low UV in 2009. The chlorophyll concentration of R. alba did not change in 2008 or 2009, whereas the chlorophyll concentration of M. japonica increased with decreased solar radiation, including UV. The UV absorbance of R. alba decreased under shade and with high peat moisture. In contrast, the content of UV-absorbing substances remained unchanged in M. japonica. Therefore, R. alba, the early colonizer, adapted more to strong solar radiation by changing its shoot-root allometry and producing UV-absorbing substances, whereas M. japonica, the late colonizer, tended to respond more to peat moisture. These differing responses to solar radiation and peat moisture may explain the temporal patterns of species replacement from early to late colonizers.     

Fumarole-Supported Islands of Biodiversity within a Hyperarid, High-Elevation Landscape on Socompa Volcano, Puna de Atacama, Andes

Fumarolic activity supports the growth of mat-like photoautotrophic communities near the summit (at 6,051 m) of Socompa Volcano in the arid core of the Andes mountains. These communities are isolated within a barren, high-elevation landscape where sparse vascular plants extend to only 4,600 m. Here, we combine biogeochemical and molecular-phylogenetic approaches to characterize the bacterial and eucaryotic assemblages associated with fumarolic and nonfumarolic grounds on Socompa. Small-subunit rRNA genes were PCR amplified, cloned, and sequenced from two fumarolic soil samples and two reference soil samples, including the volcanic debris that covers most of the mountain. The nonfumarolic, dry, volcanic soil was similar in nutrient status to the most extreme Antarctic Dry Valley or Atacama Desert soils, hosted relatively limited microbial communities dominated by Actinobacteria and Fungi, and contained no photoautotrophs. In contrast, modest fumarolic inputs were associated with elevated soil moisture and nutrient levels, the presence of chlorophyll a, and ¹³C-rich soil organic carbon. Moreover, this soil hosted diverse photoautotroph-dominated assemblages that contained novel lineages and exhibited structure and composition comparable to those of a wetland near the base of Socompa (3,661-m elevation). Fumarole-associated eucaryotes were particularly diverse, with an abundance of green algal lineages and a novel clade of microarthropods. Our data suggest that volcanic degassing of water and ¹³C-rich CO₂ sustains fumarole-associated primary producers, leading to a complex microbial ecosystem within this otherwise barren landscape. Finally, we found that human activities have likely impacted the fumarolic soils and that fumarole-supported photoautotrophic communities may be exceptionally sensitive to anthropogenic disturbance.