Interactions between the diatom Thallasiosira pseudonanna and an associated pseudomonad in a mariculture system.

The marine diatom Thallasiosira pseudonanna (3H) and several bacteria associated with it were isolated from batch cultures at the University of Delaware mariculture facility. The interaction between the algae and each of the bacteria was investigated. One of the isolates, T827/2B (Pseudomonas sp.), was incapable of surviving in f/2 culture medium unless the algae were present. When the algae and T827/2B were grown together in the f/2 medium, the bacterial growth was stimulated and the algal growth was inhibited. Bacterial filtrate had a similar effect on the algae, indicating that the bacterial effect is an indirect one most likely resulting from the excretion of a harmful compound into the medium. Preliminary characterization of the material excreted by the bacteria indicates that it s proteinaceous in nature. The interactions observed does not fit into any single category of interactions but can be explained as a combination of competition and indirect parasitism.     

Interactions between the diatom Thallasiosira pseudonanna and an associated pseudomonad in a mariculture system

The marine diatom Thallasiosira pseudonanna (3H) and several bacteria associated with it were isolated from batch cultures at the University of Delaware mariculture facility. The interaction between the algae and each of the bacteria was investigated. One of the isolates, T827/2B (Pseudomonas sp.), was incapable of surviving in f/2 culture medium unless the algae were present. When the algae and T827/2B were grown together in the f/2 medium, the bacterial growth was stimulated and the algal growth was inhibited. Bacterial filtrate had a similar effect on the algae, indicating that the bacterial effect is an indirect one most likely resulting from the excretion of a harmful compound into the medium. Preliminary characterization of the material excreted by the bacteria indicates that it s proteinaceous in nature. The interactions observed does not fit into any single category of interactions but can be explained as a combination of competition and indirect parasitism.     

Metabolic relationships of uncultured bacteria associated with the microalgae Gambierdiscus

Microbial communities inhabit algae cell surfaces and produce a variety of compounds that can impact the fitness of the host. These interactions have been studied via culturing, single-gene diversity and metagenomic read survey methods that are limited by culturing biases and fragmented genetic characterizations. Higher-resolution frameworks are needed to resolve the physiological interactions within these algal–bacterial communities. Here, we infer the encoded metabolic capabilities of four uncultured bacterial genomes (reconstructed using metagenomic assembly and binning) associated with the marine dinoflagellates Gambierdiscus carolinianus and G. caribaeus. Phylogenetic analyses revealed that two of the genomes belong to the commonly algae-associated families Rhodobacteraceae and Flavobacteriaceae. The other two genomes belong to the Phycisphaeraceae and include the first algae-associated representative within the uncultured SM1A02 group. Analyses of all four genomes suggest these bacteria are facultative aerobes, with some capable of metabolizing phytoplanktonic organosulfur compounds including dimethylsulfoniopropionate and sulfated polysaccharides. These communities may biosynthesize compounds beneficial to both the algal host and other bacteria, including iron chelators, B vitamins, methionine, lycopene, squalene and polyketides. These findings have implications for marine carbon and nutrient cycling and provide a greater depth of understanding regarding the genetic potential for complex physiological interactions between microalgae and their associated bacteria.     

ALGAL EXCRETION AND BACTERIAL ASSIMILATION IN HOT SPRING ALGAL MATS1

Benthic algal-bacterial mats are present in the effluents of alkaline hot springs at temperatures between 50 and 73 C. The thin surface layer is composed of the unicellular blue-green alga Synechococcus lividus. Also present in the surface layer and forming thick, orange mats beneath it, are filamentous, phototrophic, gliding bacteria of the genus Chloroflexis, also capable of heterotrophic growth. The very low species diversity and the constancy of the hot spring environment, make these mats a good ecosystem for studying the transfer of nutrients from the algae to the bacteria. To determine whether the alga might supply organic materials to the bacterium, excretion by natural populations of S. lividus was studied in the field by means of short-term radioisotope experiments. Under optimal conditions for photosynthesis, between 3 and 12% of the total ¹⁴C fixed was excreted as ¹⁴C-labeled organic compounds. Variations in cell density at concentrations of S. lividus approximating those found in the mat had no effect on the percentage excretion. However, at cell densities below a threshold, level, the percentage excretion increased with diminishing cell density. Except at very low light intensities the percentage of fixed carbon excreted, was very similar for all light intensities tested. Excretion at temperatures approaching the upper limit for growth was not significantly different from the percentage excretion values observed at lower temperatures. ¹⁴C-labeled organic compounds excreted during algal photosynthesis could be subsequently assimilated by natural populations of the bacteria present in the mat.     

Art und Menge der Ausscheidung 14C-markierter Verbindungen bei Chlorella pyrenoidosa unter dem Einfluss des osmotischen Drucks der Nährlösung

Chlorella pyrenoidosa was labelled by ¹⁴CO₂ and the nature and amount of excreted organic compounds in nutrient media of different osmotic pressure were determined after a 24 h period. The total rate of excretion of organic bound ¹⁴C was about 4 μg ¹⁴C per mg harvested algal dry matter or 1% of the total ¹⁴C content of the algae at the beginning of the excretion period. The main compounds found in the excretions were unidentified substances with a molecular weight higher than 700, amino acids, organic acids and sugars. The osmotic pressure of the nutrient medium did not affect the total amount of the organic excretions. However, the excreted amounts of some specific compounds differed in respect to the osmotic conditions of the nutrient medium.     

Physiological Diversity and Distributions of Heterotrophic Bacteria in Deep Cretaceous Sediments of the Atlantic Coastal Plain

A series of 23 intact core segments was obtained from two distinct deep subsurface geological formations, the Middendorf and the Cape Fear formations, underlying the southeastern coastal plain of South Carolina. The Middendorf formation in this region consists of permeable, saturated, sandy sediments; the Cape Fear formation consists mainly of less permeable sediments. The core segments were separated by vertical distances ranging from several centimeters to 48 m. Aerobic chemoheterotrophic bacteria were enumerated on a dilute medium, and populations ranged from 3.1 to 6.4 log CFU g of sediment^-1 in the Middendorf cores and from below detection to 4.3 log CFU g^-1 in the Cape Fear cores. A total of 198 morphologically distinct colony types were isolated, purified, and subjected to 108 different physiological measurements. The isolates from the two formations were distinct (i.e., they produced substantially different response patterns to the various physiological measurements), as were those in different core samples from the same formation. Cluster analysis revealed 21 different biotypes based on similarities of 75% or higher in response patterns to 21 physiological assays. One biotype contained 57 (29%) of the subsurface isolates, 10 biotypes contained 5 or more isolates, and the remainder had 4 or fewer. The organic compounds that were most commonly metabolized by the subsurface bacteria included Tween 40 (85%) and β-hydroxybutyric acid (60%). Organic acids, in general, were also commonly metabolized by the subsurface bacteria. Isolates from the Cape Fear core segments were capable of metabolizing a higher percentage of the substrates than were bacteria isolated from the Middendorf formation. Although the heterogeneous distributions of bacteria in deep subsurface sediments may make it difficult to use aquifer microcosms to predict in situ biotransformation rates, the diversity of the physiological properties of these organisms offers promise for in situ remediation of contaminants.     

Plants secrete substances that mimic bacterial N-acyl homoserine lactone signal activities and affect population density-dependent behaviors in associated bacteria

In gram-negative bacteria, many important changes in gene expression and behavior are regulated in a population density-dependent fashion by N-acyl homoserine lactone (AHL) signal molecules. Exudates from pea (Pisum sativum) seedlings were found to contain several separable activities that mimicked AHL signals in well-characterized bacterial reporter strains, stimulating AHL-regulated behaviors in some strains while inhibiting such behaviors in others. The chemical nature of the active mimic compounds is currently unknown, but all extracted differently into organic solvents than common bacterial AHLs. Various species of higher plants in addition to pea were found to secrete AHL mimic activities. The AHL signal-mimic compounds could prove to be important in determining the outcome of interactions between higher plants and a diversity of pathogenic, symbiotic, and saprophytic bacteria.     

Microbial communities in the saturated groundwater environment II: Diversity of bacterial communities in a Pleistocene sand aquifer and their in vitro activities

Bacterial cell numbers obtained from 103 water and sediment samples from a Pleistocene sandy aquifer in the Lower Rhine region (Bocholt, FRG) were determinated on P-agar and by direct count. Below 5 m under the surface, colony-forming unit (cfu) numbers in water samples were less than 100/ml, and in many cases less than 50/ml. In sediment samples, they were 10- to 100-fold higher (10²–10⁴ cfu/g dry wt), but changing markedly between different depths. Direct cell counts yielded numbers two to three orders of magnitude higher.About 2,700 strains of bacteria from 60 samples were isolated randomly and characterized by morphological and physiological properties. Of all the isolates, 71.6% were gram-negative, and 52.2% were gram-negative straight rods. Water communities, with one exception, had low proportions of gram-positive bacteria (<11%), whereas in all but one of the sediment communities percentages of gram-positive isolates were three- to sevenfold higher (35–43%). Water and sediment communities, as well as communities from different sampling sites and communities from different depths of the same sampling site, differed in their qualitative and quantitative morphotype composition and physiological capabilities.The in vitro activities of strains within a single community were quite different, indicating that each community is composed of many diverse bacteria, several having extremely different capabilities. Thus, each community has its own specific activity pattern. Gram-positive bacteria showed on an average lower total activities than did gram-negative bacteria. Grampositive bacteria as well as gram-negative bacteria from sediment had higher values of in vitro activities than the corresponding groups isolated from water. Many water and sediment bacteria preferred the same substrates which were utilized at high rates. However, there were differences in the degradation of the various other substrates present, and each community showed preferences for particular substrates, which they degraded best.The results of cell morphology and physiology studies indicated that all eight characterized communities were very different from one another and very diversely structured.     

Bacterial Growth on Coral Mucus

Coral mucus-degrading bacteria were isolated by an enrichment culture procedure. The isolates were able to grow as pure cultures on 10% sterilized mucus in seawater, yielding 10⁸ CFU/ml. The isolates, mostly Vibrio strains, were classified by classical and molecular methods. When carbon, nitrogen, and phosphorus compounds were added separately to the mucus medium, there was no increase in CFUs; however, when they were added together, there was a large increase in cell yield. The indigenous bacterial population of coral mucus increased from 10³ to 10⁸ CFU/ml when incubated at 30°C for 11 h, changing from a heterogeneous community to a Vibrio-dominated population. Factors which regulate the abundance and diversity of coral mucus bacteria are discussed.     

Bacterial response to spatial gradients of algal-derived nutrients in a porous microplate

Photosynthetic microalgae are responsible for 50% of the global atmospheric CO₂ fixation into organic matter and hold potential as a renewable bioenergy source. Their metabolic interactions with the surrounding microbial community (the algal microbiome) play critical roles in carbon cycling, but due to methodological limitations, it has been challenging to examine how community development is influenced by spatial proximity to their algal host. Here we introduce a copolymer-based porous microplate to co-culture algae and bacteria, where metabolites are constantly exchanged between the microorganisms while maintaining physical separation. In the microplate, we found that the diatom Phaeodactylum tricornutum accumulated to cell abundances ~20 fold higher than under normal batch conditions due to constant replenishment of nutrients through the porous structure. We also demonstrate that algal-associated bacteria, both single isolates and complex communities, responded to inorganic nutrients away from their host as well as organic nutrients originating from the algae in a spatially predictable manner. These experimental findings coupled with a mathematical model suggest that host proximity and algal culture growth phase impact bacterial community development in a taxon-specific manner through organic and inorganic nutrient availability. Our novel system presents a useful tool to investigate universal metabolic interactions between microbes in aquatic ecosystems.Subject terms: Microbial ecology, Microbial ecology, Microbial ecology     

赤潮过程中“藻-菌”关系研究进展

微生物对促进海洋物质循环,维持水生环境的生态平衡具有重要作用。在赤潮事件中,基于微生物(尤其是细菌)的多样性和重要性,它们与藻类之间的相互关系成为了研究的热点。过去20年里,人们从不同角度对"藻-菌"间的关系进行了探索,包括物理学过程、生物学过程、环境过程以及化学过程。就化学过程而言,它作为一种较早出现的技术,在以往的研究中带给人们许多认识藻菌关系的方法。随着学科的渗透,化学法有了拓展与延伸,为人们认识藻菌关系带来了新的契机。从化学生态学领域来梳理"藻-菌"关系中涉及的现象和行为,包括菌对藻的有益面、菌对藻的有害面、以及藻类应答细菌行为的化学途径;并从信号语言(群体感应、化感作用)的角度来阐释两者之间的互生或克生关系。通过文献综述的方式来解读藻菌关系的互作过程和机理,为认识赤潮的发生和防控方法提供借鉴。     

Heterotrophic bacteria associated with the green alga <Emphasis Type="Italic">Ulva rigida</Emphasis>: identification and antimicrobial potential

Heterotrophic bacteria associated with the green alga Ulva rigida, collected from the coast of Tunisia, were isolated and subsequently identified by their 16S rRNA gene sequences and by phylogenetic analysis. The 71 isolates belong to four phyla: Proteobacteria (Alpha-and Gamma- subclasses), Bacteroidetes, Firmicutes, and Actinobacteria. Most of the isolates belong to Proteobacteria. The Gram-positive Firmicutes and especially the genus Bacillus were well-represented at the surface of U. rigida, collected from the coast as well as from the lagoon, while Actinobacteria were represented only at the surface of algae collected from the coast of Cap Zebib. Bacteroidetes were more represented at the surface of algae collected from the Ghar El Melh lagoon. The bacterial community of the water surrounding the algae was different from that associated with the surface of the algae. Moreover, the abundance of bacteria in the surrounding water was much lower compared to the density of bacteria associated with the surface of the algae. Bacteria isolated from the algal surface were tested for their antimicrobial potential. The results show that ~?36% of the algae-associated bacterial isolates possess antibacterial activity whereas free-living bacteria, isolated from the surrounding water, did not show such activity. The surface of U. rigida was colonized by a high diversity of culturable and possibly novel epiphytic bacteria that may be an important source of antimicrobial compounds and are therefore of biotechnological interest.     

Diversity of culturable phyllosphere bacteria on beech and oak: the effects of lepidopterous larvae

The community composition of epiphytic heterotrophic bacteria on leaves of beech and oak, which were either damaged by lepidopterous larvae or remained undamaged, was investigated. In addition, the ability of these bacteria to utilize inorganic nitrogen was studied. The bacteria were isolated on nutrient agar and systematically identified with biochemical and physiological tests. Rarefaction plots and the Shannon-Wiener function revealed that species diversity was significantly higher on leaves of damaged beech compared to undamaged leaves, but no differences were found on leaves of oak. The portion of bacterial isolates showing a strong response to ammonia and nitrate was significantly larger on leaves of oak than on those of beech. Furthermore, significantly more isolates with a high capability to assimilate both nitrogen compounds were found on leaves attacked by the folivorous larvae compared to those not attacked on oak. It is suggested that the changes in the microbial community in response to folivorous insects might affect the extent of nutrient cycling exceeding eventually the scale of a leaf.     

Antimicrobial activity observed among cultured marine epiphytic bacteria reflects their potential as a source of new drugs

The surfaces of marine eukaryotes provide a unique habitat for colonizing microorganisms where competition between members of these communities and chemically mediated interactions with their host are thought to influence both microbial diversity and function. For example, it is believed that marine eukaryotes may use their surface-associated bacteria to produce bioactive compounds in defence against competition and to protect the host against further colonization. With the increasing need for novel drug discovery, marine epibiotic bacteria may thus represent a largely underexplored source of new antimicrobial compounds. In the current study, 325 bacterial isolates were obtained from the surfaces of marine algae Delisea pulchra and Ulva australis . Thirty-nine showed to have antimicrobial activity and were identified via 16S rRNA gene sequencing. The majority of those isolates belonged to Alpha- and Gammaproteobacteria . Interestingly, the most commonly isolated bacterial strain, Microbulbifer sp., from the surface of D. pulchra has previously been described as an ecologically significant epibiont of different marine eukaryotes. Other antimicrobial isolates obtained in this study belonged to the phyla Actinobacteria , Firmicutes and Bacteroidetes . Phylogenetically, little overlap was observed among the bacteria obtained from surfaces of D. pulchra and U. australis . The high abundance of cultured isolates that produce antimicrobials suggest that culturing remains a powerful resource for exploring novel bioactives of bacterial origin.     

维生素B12在细菌与真核藻类相互作用中的功能研究进展

自然环境中细菌与藻类发生着直接或间接的相互作用,这些相互作用对双方的生理功能、群落组成、逆境抵御等方面具有重要影响。维生素B12 (VB12)是一种结构复杂、功能重要的维生素,是许多真核藻类所必需的生长因子。由于VB12在自然界中只能由产VB12的细菌合成,产VB12细菌对真核藻类的生理功能具有重要影响。本文将主要介绍近年来在细菌-真核藻类相互作用中VB12所参与的藻类生长调节、抗逆反应与基因表达调控等方面的研究进展,并讨论在细菌-真核藻类分子相互作用这一研究模式中应注重的发展方向。     

Fermentative and aerobic metabolism in Rhizobium etli.

Strains of Rhizobium etli, Rhizobium meliloti, and Rhizobium tropici decreased their capacity to grow after successive subcultures in minimal medium, with a pattern characteristic for each species. During the growth of R. etli CE 3 in minimal medium (MM), a fermentation-like response was apparent: the O2 content was reduced and, simultaneously, organic acids and amino acids were excreted and poly-beta-hydroxybutyrate (PHB) was accumulated. Some of the organic acids excreted into the medium were tricarboxylic acid (TCA) cycle intermediates, and, concomitantly, the activities of several TCA cycle and auxiliary enzymes decreased substantially or became undetectable. Optimal and sustained growth and a low PHB content were found in R. etli CE 3 when it was grown in MM inoculated at a low cell density with O2 maintained at 20% or with the addition of supplements that have an effect on the supply of substrates for the TCA cycle. In the presence of supplements such as biotin or thiamine, no amino acids were excreted and the organic acids already excreted into the medium were later reutilized. Levels of enzyme activities in cells from supplemented cultures indicated that carbon flux through the TCA cycle was maintained, which did not happen in MM. It is proposed that the fermentative state in Rhizobium species is triggered by a cell density signal that results in the regulation of some of the enzymes responsible for the flux of carbon through the TCA cycle and that this in turn determines how much carbon is available for the synthesis and accumulation of PHB. The fermentative state of free-living Rhizobium species may be closely related to the metabolism that these bacteria express during symbiosis.     

Direct and indirect influences of crustacean zooplankton on bacterioplankton of Lake Constance

Herbivorous crustacean zooplankton may influence bacterial populations of lakes directly by grazing on them or indirectly by grazing on algae. In Lake Constance a regularly observed decrease of bacterial density during periods of high abundance of cladocerans (clearwater phase) indicated bacterial grazing losses. However, cladoceran grazing on bacteria appeared to be less efficient than on algae. Moreover, cladocera reduced grazing pressure on bacteria by grazing on bacterivorous flagellates. Additionally, a shift of bacterial composition from an originally higher percentage of filamentous and aggregate growth forms towards a population of homogenously distributed small single celled bacteria was observed regularly at the beginning of the clearwater phase. Transient increases of bacterial abundance and productivity coinciding with the increase of cladocera at the end of the algal spring bloom were interpreted as field indications of indirect bacteria-zooplankton interactions due to crustacean grazing on phytoplankton. The release of organic carbon during grazing of crustacea on algae was considered as explanation for the observed stimulation of bacterial populations. Thereby, additional, otherwise inaccessible algal carbon would be made available to bacteria by zooplankton. Experimental support for this hypothesis was given by showing that bacteria were able to respond to crustacean grazing on algae by enhanced growth and activities. The possible impact of these direct and indirect crustacea-bacteria interactions on the abundance, activity and composition of bacterioplankton as well as on the structure and function of the total planktonic community is discussed.     

Growth and nutritional characteristics of cowpea rhizobia

Summary Twenty-five slow-growing strains of cowpea rhizobia were examined for growth and nutritional characteristics. Growth and nutritional data of these isolates were surprisingly homogeneous given their proposed genetic diversity. Most strains tested were capable of anaerobic growth in the presence of nitrate and all were found capable of autotrophic growth in a defined atmosphere of CO₂ and H₂ with oxygen or nitrate as terminal electron acceptors. These isolates grew heterotrophically with various carbohydrates and organic acids. Nitrogen utilization was consistent with that of other slow-growing rhizobia. Medium composition strongly affected the final pH of the culture. Cowpea rhizobia generally did not require vitamins; those requiring vitamins exhibited good growth when biotin was supplemented to the medium.     

The microbial diversity of a storm cloud as assessed by hailstones

Being an extreme environment, the atmosphere may act as a selective barrier for bacterial dispersal, where only most robust organisms survive. By remaining viable during atmospheric transport, these cells affect the patterns of microbial distribution and modify the chemical composition of the atmosphere. The species evenness and richness, and the community composition of a storm cloud were studied applying cultivation-dependent and cultivation-independent techniques to a collection of hailstones. In toto 231 OTUs were identified, and the total species richness was estimated to be about 1800 OTUs. The diversity indices - species richness and evenness - suggest a functionally stable community, capable of resisting environmental stress. A broad substrate spectrum of the isolates with epiphytic origin (genus Methylobacterium) implied opportunistic ecologic strategy with high growth rates and fast growth responses. These may grow in situ despite their short residence times in cloud droplets. In addition, epiphytic isolates utilized many atmospheric organic compounds, including a variety of carboxylic acids. In summary, the highly diverse bacterial community, within which the opportunistic bacteria may be particularly important in terms of atmospheric chemistry, is likely to remain functional under stressful conditions. Overall our study adds important details to the growing evidence of active microbial life in clouds.     

The microbial ecology of the Great Salt Lake

The Great Salt Lake is actually two lakes. A highly saline (330-gml^–1) northern arm and a moderately saline (120-gml^–1) southern arm separated by a semipermeable rock causeway. The lake, particularly the northern arm, has a massive accumulation of organic matter resulting from more than 100,000 years of productivity, cycling from a freshwater to a saline lake, plus the influence of human industry and agriculture in more recent times. The north arm planktonic and attached community consists principally of, in order of biomass: bacteria of at least two genera,Halobacterium andHalococcus; two algae,Dunaliella salina andD. viridis; the brine shrimp,Anemia salina; and, two species of brine fly,Ephydra gracilis andE. hians and possibly one more species. The algae and the bacteria appear to depend on each other for nutrients. The bacteria use organic matter produced by the algae and the algae use ammonia produced by the bacteria and possibly the brine shrimp. The production of ammonia appears to be the rate-limiting step although there is no shortage of other forms of nitrogen in the north arm. Based on aquarium studies, the potential for biomass production of algae and bacteria is much higher than actually observed in the north arm, leading to the postulation of two additional factors controlling population; the grazing of the algae by invertebrates with the excretion of compounds rich in nitrogen, and the effect of a low habitat temperature and winter cold on the bacteria, reducing their metabolic activities to nearly zero. Some aspects of the various organisms and their metabolism are discussed. A comparison is made with recent work on the Dead Sea.