Host-Synthesized Secondary Compounds Influence the In Vitro Interactions between Fungal Endophytes of Maize

Maize produces a suite of allelopathic secondary metabolites, the benzoxazinoids. 2,4-Dihydroxy-7-methoxy-2H-1,4-benzoxazin-3-one and 2,4-dihydroxy-2H-1,4-benzoxazin-3-one reside as glucosides in plant tissue and spontaneously degrade to 6-methoxy-2-benzoxazolinone (MBOA) and 2-benzoxazolinone (BOA) upon plant cell disruption. Several maize-associated fungi in the genus Fusarium can metabolize MBOA and BOA. BOA tolerance levels in 10 species of Fusarium and in the maize endophytes Nigrospora oryzae, Acremonium zeae, and Periconia macrospinosa were characterized. BOA tolerance ranged from 0.25 to 1.10 mg/ml among species. The influence of substrate alteration by one species on the subsequent growth of another species was assessed in the presence and absence of BOA. The colony area of the secondary colonizer in heterospecific interactions was compared to that in autospecific interactions (one isolate follows itself). In the presence of BOA, four of six secondary colonizers had greater growth (facilitation) when primary colonizers had higher BOA tolerance than the secondary colonizer. When the primary colonizer had lower tolerance than the secondary, three of six secondary colonizers were inhibited (competition) and three not significantly affected. In BOA-free medium, the number of isolates that were facilitated or inhibited was the same regardless of the tolerance level of the primary colonizer. Two of six secondary colonizers were facilitated, two inhibited, and two not significantly affected. This study provides some support for facilitation in stressful conditions under the Menge-Sutherland model. The results are not consistent with the corresponding prediction of competition in the absence of stress. The hypothesis drawn from these data is that in the presence of a toxin, fungal species that detoxify their substrate can enhance the colonization rate of less tolerant fungi.     

Short-term succession of marine microbial fouling communities and the identification of primary and secondary colonizers

Microbial succession during the initial stages of marine biofouling has been rarely studied, especially in the Arabian Gulf. This study was undertaken to follow temporal shifts in biofouling communities in order to identify primary and secondary colonizers. Quantitative analysis revealed a significant increase in total biomass, coverage of macrofoulers, chlorophyll a concentrations, and bacterial counts with time. The relative abundance of the adnate diatoms increased with time, whereas it decreased in the case of the plocon diatoms. Non-metric multidimensional scaling (NMDS) ordination based on MiSeq data placed the bacterial communities in three distinct clusters, depending on the time of sampling. While the relative abundance of Alphaproteobacteria and Flavobacteriia decreased with time, suggesting their role as primary colonizers, the relative abundance of Actinobacteria and Planctomycetia increased with time, suggesting their role as secondary colonizers. Biofouling is a dynamic process that involves temporal quantitative and qualitative shifts in the micro- and macrofouling communities.     

Cross-Ocean Distribution of Rhodobacterales Bacteria as Primary Surface Colonizers in Temperate Coastal Marine Waters

Bacterial surface colonization is a universal adaptation strategy in aquatic environments. However, neither the identities of early colonizers nor the temporal changes in surface assemblages are well understood. To determine the identities of the most common bacterial primary colonizers and to assess the succession process, if any, of the bacterial assemblages during early stages of surface colonization in coastal water of the West Pacific Ocean, nonnutritive inert materials (glass, Plexiglas, and polyvinyl chloride) were employed as test surfaces and incubated in seawater off the Qingdao coast in the spring of 2005 for 24 and 72 h. Phylogenetic analysis of the 16S rRNA gene sequences amplified from the recovered surface-colonizing microbiota indicated that diverse bacteria colonized the submerged surfaces. Multivariate statistical cluster analyses indicated that the succession of early surface-colonizing bacterial assemblages followed sequential steps on all types of test surfaces. The Rhodobacterales, especially the marine Roseobacter clade members, formed the most common and dominant primary surface-colonizing bacterial group. Our current data, along with previous studies of the Atlantic coast, indicate that the Rhodobacterales bacteria are the dominant and ubiquitous primary surface colonizers in temperate coastal waters of the world and that microbial surface colonization follows a succession sequence. A conceptual model is proposed based on these findings, which may have important implications for understanding the structure, dynamics, and function of marine biofilms and for developing strategies to harness or control surface-associated microbial communities.     

Low-temperature sensors in bacteria

Bacteria are ubiquitous colonizers of various environments and host organisms, and they are therefore often subjected to drastic temperature alterations. Temperature alterations set demands on these colonizers, in that the bacteria need to readjust their biochemical constitution and physiology in order to survive and resume growth at the new temperature. Furthermore, temperature alteration is also a main factor determining the expression or repression of bacterial virulence functions. To cope with temperature variation, bacteria have devices for sensing temperature alterations and a means of translating this sensory event into a pragmatic gene response. While such regulatory cascades may ultimately be complicated, it appears that they contain primary sensor machinery at the top of the cascade. The functional core of such machinery is usually that of a temperature-induced conformational or physico-chemical change in the central constituents of the cell. In a sense, a bacterium can use structural alterations in its biomolecules as the primary thermometers or thermostats.     

Microbial communities ofPyrenophora-infested wheat straw as examined by multivariate analysis

Winter wheat straw naturally infested withPyrenophora triticirepentis andSeptoria nodorum was incubated in the field in one of three placements: buried in the soil, placed directly on the soil surface, or placed 2 cm above the soil within a straw layer. Periodically between June and April, straws from each treatment were collected and assayed by dilution plating to determine microbial populations in the following categories: total yeasts, total actinomycetes, total other bacteria, and genera or species of fungi. The data were analyzed by the multivariate procedures of ordination and classification, using detrended correspondence analysis (DCA) and cluster analysis, respectively. The major DCA axis displayed a gradient starting with pioneer colonizer communities of above-soil straw (dominated byPyrenophora, Septoria, Alternaria, andCladosporium), through on-soil straws (colonized by secondary saprophytes such asAcremonium strictum, Diplodia, Fusarium, and bacteria) to buried straws (dominated by actinomycetes, bacteria, and soil-inhabiting fungi). The second DCA axis showed a gradient separating different types of late secondary communities. In vitro tests for degradative abilities of straw-inhabiting organisms showed that low-temperature cellulolysis is characteristic of pioneer and early secondary colonizers, whereas chitin degradation is limited to secondary colonizers, particularly soil inhabitants. The results suggest the vulnerability ofPyrenophora andSeptoria to displacement by secondary colonists in an active microbial community, and indicate a number of organisms that may be useful in biological control of these plant parasites through exploitative or interference competition in plant residues.     

Activities of chitinolytic enzymes during primary and secondary colonization of wood by basidiomycetous fungi

The nitrogen (N) content of wood is usually suboptimal for fungal colonization. During decomposition of wood, an increasing fraction of the N becomes incorporated into fungal mycelium. Between 5 and 50% of the N in wood-degrading mycelium may be incorporated into chitin. Chitinolytic enzymes render this N available for re-utilization. Here, the activities of chitinolytic enzymes produced by wood-rotting fungi during degradation of spruce (Picea abies) wood were quantified in situ using fluorogenic 4-methylumbelliferyl substrates. A new method was developed that enables spatial quantification of enzyme activities on solid surfaces. All of the three tested fungi produced endochitinases, chitobiosidases and N-acetylhexosaminidases during colonization of wood. N-acetylhexosaminidase activity, and in some cases also chitobiosidase and endochitinase activities, were higher during secondary overgrowth of another fungus than during primary colonization of noncolonized wood. The results suggest that wood-degrading fungi degrade their own cell walls as well as the hyphae of earlier colonizers. Recycling of cell wall material within single mycelia and between fungal individuals during succession may lead to retention of N within woody debris.     

Insects as stem engineers: interactions mediated by the twig-girdler Oncideres albomarginata chamela enhance arthropod diversity

Background

Ecosystem engineering may influence community structure and biodiversity by controlling the availability of resources and/or habitats used by other organisms. Insect herbivores may act as ecosystem engineers but there is still poor understanding of the role of these insects structuring arthropod communities.

Methodology/Principal Findings

We evaluated the effect of ecosystem engineering by the stem-borer Oncideres albomarginata chamela on the arthropod community of a tropical dry forest for three consecutive years. The results showed that ecosystem engineering by O. albomarginata chamela had strong positive effects on the colonization, abundance, species richness and composition of the associated arthropod community, and it occurred mainly through the creation of a habitat with high availability of oviposition sites for secondary colonizers. These effects cascade upward to higher trophic levels. Overall, ecosystem engineering by O. albomarginata chamela was responsible for nearly 95% of the abundance of secondary colonizers and 82% of the species richness.

Conclusions/Significance

Our results suggest that ecosystem engineering by O. albomarginata chamela is a keystone process structuring an arthropod community composed by xylovores, predators and parasitoids. This study is the first to empirically demonstrate the effect of the ecosystem engineering by stem-boring insects on important attributes of arthropod communities. The results of this study have important implications for conservation.     

Effects of attack of saprobic fungi on twig litter decomposition by endophytic fungi

Endophytic fungi of healthy twig tissues act as dominant primary colonizers of twig litters and are exposed to the attacks of saprobic secondary colonizers. In the present study, we examined the effect of interspecific interactions on the decay rate of twigs in laboratory experiments using two endophytic ascomycetes (Phomopsis sp. and Xylaria sp.) and two saprobic basidiomycetes (Mycena polygramma and Phanerochaete filamentosa) on twigs of Japanese beech (Fagus crenata) as a model system. Both endophytes were defensive against two saprobes on 2% malt agar, and were not replaced by the saprobes in the twigs during the incubation period. However, inoculation of the saprobes reduced the mass loss of twig components (acid-unhydrolyzable residue (AUR), holocellulose, soluble carbohydrate, and polyphenol). Especially when the twigs previously inoculated with Xylaria sp. or Phomopsis sp. were successively inoculated with M. polygramma the net weight of AUR increased, which was probably due to the synthesized melanin in hyphae of the endophytes. Our findings indicate that interspecific interactions between endophytic and saprobic fungi do affect the total mass of humic substances produced during the litter decay process.     

Study of fungi on decaying leaves of Saccharum munja by differential washing technique

Summary This study reports that the primary fungal colonizers of decaying leaves, which were rarely recorded with the last fungal colonizers in the pattern of succession in later stage of decaying, were persistent in dead tissues in the form of dormant mycelia and were unable to sporulate due to competition with last colonizers for nutrition and space in substrates. The presence of such fungi in suppressed and dormant condition in the sustrate is confirmed by transference of washed bits of leaves onto nutrient media which allowed them to grow and sporulate freely.A part of Ph.D. thesis approved by the Banaras Hindu University, 1968.     

Mycoflora of cave cricket Troglophilus neglectus cadavers

By using different techniques and media, microfungi were isolated from cadavers of the cave cricket Troglophilus neglectus, collected on the walls of a Slovenian cave. The isolated mycobiota was consistently different for adult and larval stages of T. neglectus cadavers. Fungi isolated with the highest frequency from the larval stage were represented by five different species of the genus Mucor, the prevailing one being a newly described species, M. troglophilus. The dominating fungus isolated from the adult stage was the well-known fungal entomopathogen Beauveria bassiana. The other isolated fungi were mainly primary and secondary saprotrophic colonizers. This revised version was published online in June 2006 with corrections to the Cover Date.     

Adhesin receptors of human oral bacteria and modeling of putative adhesin-binding domains

Adherence by bacteria to a surface is critical to their survival in the human oral cavity. Many types of molecules are present in the saliva and serous exudates that form the acquired pellicle, a coating on the tooth surface, and serve as receptor molecules for adherent bacteria. The primary colonizing bacteria utilize adhesins to adhere to specific pellicle receptor molecules, then may adhere to other primary colonizers via adhesins, or may present receptor molecules to be utilized by secondary colonizing species. The most common primary colonizing bacteria are streptococci, and six streptococcal cell wall polysaccharide receptor molecules have been structurally characterized. A comparison of the putative adhesin disaccharide-binding regions of the six polysaccharides suggests three groups. A representative of each group was modeled in molecular dynamics simulations. In each case it was found that a loop formed between the galactofuranoseß (Galfß) and an oxygen of the nearest phosphate group on the reducing side of the Galfß, that this loop was stabilized by hydrogen bonds, and that within each loop resides the putative disaccharide-binding domain.Abbreviations used are as follows f furanose - Fuc d-fucose - Gal d-galactose - GalNAc N-Acetyl-d-Galactosamine - Glc d-glucose - Glyc glycerol - HPLC high-performance liquid chromatography - HPTLC high-performance thin-layer chromatography - HF hydrofluoric acid - LacCer lactosyl ceramide - NeuAc N-Acetyl neuraminic acid - NMR nuclear magnetic resonance - PRG proline-rich glycoproteins - PRP proline-rich proteins - p pyranose - Rha l-rhamnose - RMSD root-mean-square differences     

Fungal successions on pine needles fallen at different seasons: The succession of surface colonizers

Field experiments were carried out to investigate influences of seasonal change on the fungal succession occurring on the surface of decaying pine needles at a moder site in Japan. At different seasons, the needles fallen for a short period were collected and marked, then placed on the surface of the O horizon. The needles were removed at intervals and their fungal communities were examined by using a washing technique. Unlike the successions of interior colonizers studied at the same time, those of surface colonizers observed on the fallen needles at four different times are roughly similar to each other.Thysanophora penicillioides was the major first colonizer on the sample needles from the O horizon, andTrichoderma species followed it. In an experiment started in late autumn, three dematiaceous fungi,Chloridium viride var.chlamydosporis, Sporidesmium omahutaense, andChalara sp., commonly occurred and contributed to the darkening of colonized needles. Seasonal variation in climate may have a stronger effect on internal colonizers than external colonizers of needles. Contributions from Sugadaira Montane Research Center, No. 165.     

Regeneration niche differentiates functional strategies of desert woody plant species

Plant communities vary dramatically in the number and relative abundance of species that exhibit facilitative interactions, which contributes substantially to variation in community structure and dynamics. Predicting species’ responses to neighbors based on readily measurable functional traits would provide important insight into the factors that structure plant communities. We measured a suite of functional traits on seedlings of 20 species and mature plants of 54 species of shrubs from three arid biogeographic regions. We hypothesized that species with different regeneration niches—those that require nurse plants for establishment (beneficiaries) versus those that do not (colonizers)—are functionally different. Indeed, seedlings of beneficiary species had lower relative growth rates, larger seeds and final biomass, allocated biomass toward roots and height at a cost to leaf mass fraction, and constructed costly, dense leaf and root tissues relative to colonizers. Likewise at maturity, beneficiaries had larger overall size and denser leaves coupled with greater water use efficiency than colonizers. In contrast to current hypotheses that suggest beneficiaries are less “stress-tolerant” than colonizers, beneficiaries exhibited conservative functional strategies suited to persistently dry, low light conditions beneath canopies, whereas colonizers exhibited opportunistic strategies that may be advantageous in fluctuating, open microenvironments. In addition, the signature of the regeneration niche at maturity indicates that facilitation expands the range of functional diversity within plant communities at all ontogenetic stages. This study demonstrates the utility of specific functional traits for predicting species’ regeneration niches in hot deserts, and provides a framework for studying facilitation in other severe environments.     

Mechanism of facilitation by sedge and cotton-grass tussocks on seedling establishment in a post-mined peatland

In stressful and disturbed ecosystems, seedling establishment may be facilitated by early colonizing plants. We examined the mechanism of such facilitation by tussock-forming species (Carex middendorffii and Eriophorum vaginatum), focusing on the independent and interactive effects of tussock litter and tussock mound substrate. Shading by litter on tussock mounds provides a stable but dryer substrate that may negatively affect early colonizers, owing to the co-occurrence of light deficiency and limited water availability, but positively affect late colonizers by subsequent amelioration of water availability. We used seed sowing and seedling transplant experiments with un-manipulated tussocks and manipulated shading?×?tussock mounds to examine seedling emergence, survival, and the biomass of early (Moliniopsis japonica) and late (Lobelia sessilifolia) colonizers in a post-mined peatland in northern Japan. Carex and Eriophorum tussocks facilitated seedling emergence and the growth of M. japonica and L. sessilifolia. Manipulation experiments indicated that the major positive effect was in providing stable substrates for seeds and seedlings. While the survival and growth of both colonizers were unaffected by shading alone and were negatively affected by tussock mounds alone, shading on tussock mounds decreased both the survival and growth in M. japonica but increased it in L. sessilifolia. Overall, tussock mounds with litter shading accelerated seedling establishment, especially that of late colonizers, in post-mined peatland. Our results indicate that the importance of facilitation mechanisms, for early successional plant composition that result from independent and interactive processes that co-occur as environmental conditions change.     

Composition and Dynamics of Functional Groups of Trees During Tropical Forest Succession in Northeastern Costa Rica

We compared the functional type composition of trees ≥10 cm dbh in eight secondary forest monitoring plots with logged and unlogged mature forest plots in lowland wet forests of Northeastern Costa Rica. Five plant functional types were delimited based on diameter growth rates and canopy height of 293 tree species. Mature forests had significantly higher relative abundance of understory trees and slow-growing canopy/emergent trees, but lower relative abundance of fast-growing canopy/emergent trees than secondary forests. Fast-growing subcanopy and canopy trees reached peak densities early in succession. Density of fast-growing canopy/emergent trees increased during the first 20 yr of succession, whereas basal area continued to increase beyond 40 yr. We also assigned canopy tree species to one of three colonization groups, based on the presence of seedlings, saplings, and trees in four secondary forest plots. Among 93 species evaluated, 68 percent were classified as regenerating pioneers (both trees and regeneration present), whereas only 6 percent were classified as nonregenerating pioneers (trees only) and 26 percent as forest colonizers (regeneration only). Slow-growing trees composed 72 percent of the seedling and sapling regeneration for forest colonizers, whereas fast-growing trees composed 63 percent of the seedlings and saplings of regenerating pioneers. Tree stature and growth rates capture much of the functional variation that appears to drive successional dynamics. Results further suggest strong linkages between functional types defined based on adult height and growth rates of large trees and abundance of seedling and sapling regeneration during secondary succession.
Abstract in Spanish is available at http://www.blackwell-synergy.com/loi/btp     

Phenotype–environment mismatches reduce connectivity in the sea

The connectivity of marine populations is often surprisingly lower than predicted by the dispersal capabilities of propagules alone. Estimates of connectivity, moreover, do not always scale with distance and are sometimes counterintuitive. Population connectivity requires more than just the simple exchange of settlers among populations: it also requires the successful establishment and reproduction of exogenous colonizers. Marine organisms often disperse over large spatial scales, encountering very different environments and suffering extremely high levels of post-colonization mortality. Given the growing evidence that such selection pressures often vary over spatial scales that are much smaller than those of dispersal, we argue that selection will bias survival against exogenous colonizers. We call this selection against exogenous colonizers a phenotype–environment mismatch and argue that phenotype–environment mismatches represent an important barrier to connectivity in the sea. Crucially, these mismatches may operate independently of distance and thereby have the potential to explain the counterintuitive patterns of connectivity often seen in marine environments. We discuss how such mismatches might alter our understanding and management of marine populations.
Ecology Letters (2010) 13: 128–140     

Ancient colonization predicts recent naturalization in Anolis lizards

The distributions and characteristics of naturalized species may be explained by novel anthropogenous aspects of world biogeography such as the creation of favorable transport environments for propagules on ships. Conversely, the unprecedented connectivity of humans may simply accelerate omnipresent ecological and evolutionary forces, for example, ships may allow species that are generally good dispersers to disperse more quickly. As a null hypothesis, there may be no human component to species naturalization. The first hypothesis predicts that naturalized species will possess unusual characteristics specific to interactions with humans. The latter two hypotheses predict similarity between ancient colonizers and recently naturalized species. In this article, we present a test of the latter hypotheses and show how they may be reconciled with the former. We show that species of Anolis lizard that are ancient solitary colonizers share characteristics of size, shape, scalation, and phylogeny with naturalized species of Anolis. Characteristics of ancient solitary colonizers predict naturalization approximately as well as characteristics of naturalized species themselves. These results suggest the existence of a general colonizing type of Anolis, and that contemporary patterns of naturalization are at least partially explained by abilities that are unrelated to interactions with humans.     

Early stages in biofilm development in methanogenic fluidized-bed reactors

Summary Biofilm development in methanogenic fluidized-bed reactors with sand as the carrier was studied on a laboratory scale. The microorganisms present in consecutive layers of the biofilm of mature sludge granules were preliminarily characterized on the basis of their morphology, element composition and adhesion capacity and were compared to bacteria which take part in the initial colonization of sand. The early phase of biofilm development was monitored with reactors receiving waste-waters containing different mixtures of volatile fatty acids and inoculated with fluidized-bed reactor effluent for different lengths of time. The results obtained indicate that facultative anaerobic bacteria abundantly present in the outermost biofilm layers of mature sludge granules are probably the main primary colonizers of the sand. Methanothrix spp. or other methanogens were rarely observed among the primary colonizers. The course of biofilm formation was comparable under the various start-up conditions employed including variations in waste-water composition, inoculation and anaerobicity. However, omission of waste-water and thus of substrate resulted in rapid wash-out of the attached biomass. Offprint requests to: W. Heinen     

The Sialic Acid Binding Protein,Hsa, in Streptococcus gordonii DL1 also Mediates Intergeneric Coaggregation with Veillonella Species

Dental biofilm development involves initial colonization of the tooth’s surface by pioneer colonizers, followed by cell-cell coaggregation between the pioneer and later colonizers. Streptococcus gordonii is one of the pioneer colonizers. In addition to its role in oral biofilm development, S. gordonii also is a pathogen in infective endocarditis in susceptible humans. A surface adhesin, Hsa, has been shown to play a critical role in colonization of S. gordonii on the heart tissue; however, its role in oral biofilm development has not been reported. In this study we demonstrate that Hsa is essential for coaggregation between S. gordonii and Veillonella sp., which are bridging species connecting the pioneer colonizers to the late colonizers. Interestingly, the same domains shown to be required for Hsa binding to sialic acid on the human cell surface are also required for coaggregation with Veillonella sp. However, sialic acid appeared not to be required for this intergeneric coaggregation. This result suggests that although the same domains of Hsa are involved in binding to eukaryotic as well as Veillonella cells, the binding mechanism is different. The gene expression pattern of hsa was also studied and shown not to be induced by coaggregation with Veillonella sp.     

Pioneer dwarf willow may facilitate tree succession by providing late colonizers with compatible ectomycorrhizal fungi in a primary successional volcanic desert

To advance understanding of the contribution of ectomycorrhizal (ECM) fungi to tree successional processes, natural establishment patterns of secondary colonizing hosts and their ECM fungal communities were investigated with special reference to pioneer hosts. In the volcanic desert on Mount Fuji, Japan, vegetation is sparsely distributed, resembling islands in a sea of scoria. Of 509 vegetation islands in the research area, 161 contained Salix reinii (Salix), the first colonizing ECM host species. The spatial coincidence between secondary colonizing timber species and Salix was analysed, and ECM fungal communities were studied using molecular identification methods. I found 39 and 26 individuals of Betula ermanii and Larix kaempferi, respectively. Without exception, these individuals were all accompanied by Salix. The ECM fungal communities of these timber species showed high similarity to that of Salix and were dominated by generalists that were compatible with two or more plant families. In this desert, available ECM propagules are limited. Pioneer Salix may contribute to tree succession by providing adjacent late colonizers with compatible ECM fungal symbionts.