Trophic complexity in aqueous systems: bacterial species richness and protistan predation regulate dissolved organic carbon and dissolved total nitrogen removal

The coupling effects of carbon fractions, bacteria, and protists on carbon emissions among various ditch levels in the Lower Yellow River

Inland waters are receiving increasing attention due to their importance in the global carbon cycle. However, the dynamics of CO2 emissions and the related mechanisms from ditches remain unclear. In this study, field sampling and an incubation experiment were conducted to explore the effects and mechanisms, especially the coupling effects between carbon fractions, bacteria, and protists on carbon dynamics of different ditch levels (sublateral ditch, farm ditch, and lateral ditch) and sediment depths (0-20cm, 20-40cm) in the Lower Yellow River. Results indicated that sublateral ditches nearest to farmland had the highest accumulative carbon mineralization (0-20 cm 1.38 g C kg-1; 20-40 cm 0.89 g C kg-1), equivalent to that of farmland, followed by the lateral ditch (0-20 cm 0.84 g C kg-1; 20-40 cm 0.50 g C kg-1) and the farm ditch (0-20 cm 0.67 g C kg-1; 20-40 cm 0.26 g C kg-1). Carbon emissions from ditches are mainly regulated by SOC (36.97 %), bacteria (29.2 %), and protists (18.95 %). Specifically, the mineralization of flooded lateral ditches is attributed to protist diversity. SOC, bacterial and protistan diversity in the farm ditch significantly impacted carbon emissions, with SOC as the dominant factor, while the bacterial composition and SOC contributed more to CO2 emissions in the sublateral ditch. Our results highlight the importance of carbon emissions from ditches, especially those closest to farmland. This study provides new insights into the construction and management of farmland irrigation and drainage in the aspects of carbon sequestration.

Metatranscriptomic outlook on green and brown food webs in acid mine drainage

Acid mine drainages (AMDs), metal-rich acidic effluents generated by mining activities, are colonized by prokaryotic and eukaryotic microorganisms widely distributed among different phyla. We compared metatranscriptomic data from two sampling stations in the Carnoulès AMD and from a third station in the nearby Amous River, focussing on processes involved in primary production and litter decomposition. A synergistic relationship between the green and brown food webs was favoured in the AMD sediments by the low carbon content and the availability of mineral nutrients: primary production of organic matter would benefit C-limited decomposers whose activity of organic matter mineralization would in turn profit primary producers. This balance could be locally disturbed by heterogeneous factors such as an input of plant debris from the riparian vegetation, strongly boosting the growth of Tremellales which would then outcompete primary producers. In the unpolluted Amous River on the contrary, the competition for limited mineral nutrients was dominated by the green food web, fish and bacterivorous protists having a positive effect on phytoplankton. These results suggest that in addition to direct effects of low pH and metal contamination, trophic conditions like carbon or mineral nutrient limitations also have a strong impact on assembly and activities of AMDs' microbial communities.

Food Webs and Ecosystems: Linking Species Interactions to the Carbon Cycle

All species within ecosystems contribute to regulating carbon cycling because of their functional integration into food webs. Yet carbon modeling and accounting still assumes that only plants, microbes, and invertebrate decomposer species are relevant to the carbon cycle. Our multifaceted review develops a case for considering a wider range of species, especially herbivorous and carnivorous wild animals. Animal control over carbon cycling is shaped by the animals’ stoichiometric needs and functional traits in relation to the stoichiometry and functional traits of their resources. Quantitative synthesis reveals that failing to consider these mechanisms can lead to serious inaccuracies in the carbon budget. Newer carbon-cycle models that consider food-web structure based on organismal functional traits and stoichiometry can offer mechanistically informed predictions about the magnitudes of animal effects that will help guide new empirical research aimed at developing a coherent understanding of the interactions and importance of all species within food webs.

Biofilms attached to Myriophyllum spicatum play a dominant role in nitrogen removal in constructed wetland mesocosms with submersed macrophytes: Evidence from 15N tracking, nitrogen budgets and metagenomics analyses

The mechanisms behind nitrogen removal by the submersed macrophyte-biofilm complex in wetlands remain to be fully elucidated. This study investigated the role of Myriophyllum spicatum and the biofilm on their leaves in nitrogen removal in mesocosm experiments. ¹⁵N tracking showed that 61.9% and 30% of the ¹⁵N, respectively, was removed from the system and assimilated by the macrophyte-biofilm complex after loading with 5.4 mg L^-115N labelled NH₄⁺ for 17 days. Nitrogen budget results showed that about 0.2%, 0.2% and 3.6% of the nitrogen were emitted as water-, HCl- and NaOH-soluble nitrogen-gas species, respectively. Bacteria (76.7-91.8%) were the predominant domain in all samples, followed by eukaryotes (8.0-23.0%), archaea and viruses. Network analyses showed that there were positive- and negative-correlative relationships among nitrogen-cycling genes and nitrifiers and denitrifiers. Our data highlight the important role of biofilm on submersed macrophytes for nitrogen removal.

Synthetic Fertilizer Increases Denitrifier Abundance and Depletes Subsoil Total N in a Long-Term Fertilization Experiment

Chronic synthetic nitrogen (N) application can result in a significant accumulation of nitrate in the subsoil, which could alter subsoil N cycle and subsequently affect subsoil N levels. To understand how elemental interactions affect the cycle and storage of subsoil N, we examined the soils receiving no fertilizer control (CK), 30-year applications of synthetic fertilizer (CF), and CF plus organic manure (CF + OM). The N cycling microbial groups and activity were investigated through analyzing abundance of bacteria, nitrifiers and denitrifiers, potential nitrification (PNA) and denitrification (DEA) rates in the topsoil (0–20 cm) and subsoil depths (20–80 cm). Compared with the CK, the CF application increased subsoil nitrate but reduced or did not change subsoil microbial biomass N and total N. Corresponding to the increased nitrate, the abundances of denitrifiers increased in the CF subsoils. By contrast, the abundances of nitrifiers increased in the CF topsoil. Significant correlation between the abundances of nitrifiers and soil PNA was found in the topsoil, while significant correlation was also found in the subsoil between the abundances of nirS- and/or nirK-type denitrifiers and DEA. These results suggest that the depleted or less changed subsoil total N by CF application might be partly related to the enriched denitrifiers groups and the related potential activity. The contrasting responses of nitrifiers and denitrifiers in the CF subsoil indicate a decoupling of both processes. Our findings highlight that the leached nitrate by synthetic fertilizer addition not only occurs as an environmental risk causing groundwater contamination but may also alter the subsoil N cycle through the denitrifier groups.

Differences in substrate use linked to divergent carbon flow during litter decomposition

Discovering widespread microbial processes that create variation in soil carbon (C) cycling within ecosystems may improve soil C modeling. Toward this end, we screened 206 soil communities decomposing plant litter in a common garden microcosm environment and examined features linked to divergent patterns of C flow. C flow was measured as carbon dioxide (CO2) and dissolved organic carbon (DOC) from 44-days of litter decomposition. Two large groups of microbial communities representing ‘high’ and ‘low’ DOC phenotypes from original soil and 44-day microcosm samples were down-selected for fungal and bacterial profiling. Metatranscriptomes were also sequenced from a smaller subset of communities in each group. The two groups exhibited differences in average rate of CO2 production, demonstrating that the divergent patterns of C flow arose from innate functional constraints on C metabolism, not a time-dependent artefact. To infer functional constraints, we identified features – traits at the organism, pathway or gene level – linked to the high and low DOC phenotypes using RNA-Seq approaches and machine learning approaches. Substrate use differed across the high and low DOC phenotypes. Additional features suggested that divergent patterns of C flow may be driven in part by differences in organism interactions that affect DOC abundance directly or indirectly by controlling community structure.

Community structure and diversity of the microbiomes of two microhabitats at the root-soil interface: implications of meta-analysis of the root-zone soil and root endosphere microbial communities in Xiong'an New Area

The diversity of the microbial compositions of the root-zone soil (the rhizosphere-surrounding soil) and root endosphere (all inner root tissues) of Pinus tabulaeformis Carr. and Ginkgo biloba L. were evaluated in Xiong'an New Area using high-throughput sequencing; the influence of the soil edaphic parameters on microbial community compositions was also evaluated. Our results showed that both the taxonomic and phylogenetic diversities of the root endosphere were lower than those of the root-zone soil, but the variation in the endosphere microbial community structure was remarkably higher than that of the root-zone soil. Spearman correlation analysis showed that the soil organic matter, total nitrogen, total phosphate, total potassium, ratio of carbon to nitrogen, and pH significantly explained the α-diversity of the bacterial community and that total nitrogen differentially contributed to the α-diversity of the fungal community. Variation partitioning analysis showed that plant species had a greater influence on microbial composition variations than did any other soil property, although soil chemical parameters explained more variation when integrated. Together, our results suggest that both plant species and soil chemical parameters played a critical role in shaping the microbial community composition.

More Than the Sum of Its Parts: Microbiome Biodiversity as a Driver of Plant Growth and Soil Health

Microorganisms drive several processes needed for robust plant growth and health. Harnessing microbial functions is thus key to productive and sustainable food production. Molecular methods have led to a greater understanding of the soil microbiome composition. However, translating species or gene composition into microbiome functionality remains a challenge. Community ecology concepts such as the biodiversity–ecosystem functioning framework may help predict the assembly and function of plant-associated soil microbiomes. Higher diversity can increase the number and resilience of plant-beneficial functions that can be coexpressed and unlock the expression of plant-beneficial traits that are hard to obtain from any species in isolation. We combine well-established community ecology concepts with molecular microbiology into a workable framework that may enable us to predict and enhance soil microbiome functionality to promote robust plant growth in a global change context.

Changes in Plant Rhizosphere Microbial Communities under Different Vegetation Restoration Patterns in Karst and Non-karst Ecosystems

Understanding how patterns of recovery and geological conditions affect microbial communities is important for determining the stability of karst ecosystems. Here, we investigated the diversity and composition of microorganisms in karst and non-karst environments under natural restoration and artificial rehabilitation conditions. The results showed no significant differences in soil microbial diversity, but the microbial communities associated with geological conditions and tree species differed significantly. Variation partitioning analysis (VPA) showed that a total of 77.3% of the variation in bacteria and a total of 69.3% of the variation in fungi could be explained by vegetation type and geological background. There were significant differences in six bacterial classes (Actinobacteria, Alphaproteobacteria, Ktedonobacteria, TK10, Gammaproteobacteria, and Anaerolineae) and nine fungal classes (Eurotiomycetes, Agaricomycetes, unclassified _p_Ascomycota, Sordariomycetes, Tremellomycetes, norank_k_Fungi, Pezizomycetes, Leotiomycetes and Archaeorhizomycetes) among the soils collected from six plots. A Spearman correlation heatmap showed that the microbial community was affected by the major soil properties. Principal coordinates analysis indicated that the microbial community of Pinus yunnanensis in the artificial forest, which was established for the protection of the environment was most similar to that in the natural secondary forest in the karst ecosystem. These findings further our understanding of microbial responses to vegetation restoration and geological conditions.

Numerical calculations of environmental impacts for deep sea mining activities

With the expected dramatic increase of mineral resources consumption, deep sea mining (DSM) was proposed as a method supplying the running of world economy by cooperating with or compensating for the terrestrial mining industry. However, its industrialization process is hindered by various reasons including the technological feasibility, economic profitability, and the DSM environmental impacts. The objective of this paper is to calculate the DSM environmental impacts based on a DSM environmental impact framework, which was selected through a systematic literature review in earlier work. The numerical calculations focus on the initial DSM disturbances and plume source, species disturbance, sediment plume and tailings. More importantly, the interconnection between the sediment plume and the species disturbances is also analysed particularly in this paper. The research quantifies the environmental impacts into a systematic framework, which could be helpful to assess the comprehensive environmental performances of a DSM activity and to promote the DSM industrialization process in the future.

Changes in Trophic Groups of Protists With Conversion of Rainforest Into Rubber and Oil Palm Plantations

Protists, abundant but enigmatic single-celled eukaryotes, are important soil microbiota providing numerous ecosystem functions. We employed high-throughput sequencing of environmental DNA, targeting the V4 region of the 18S rRNA gene, to characterize changes in their abundance, species richness, and community structure with conversion of lowland rainforest into rubber agroforest (jungle rubber), and rubber and oil palm plantations; typical agricultural systems in Sumatra, Indonesia. We identified 5,204 operational taxonomic units (OTUs) at 97% identity threshold of protists from 32 sites. Protists species richness was similar in rainforest, jungle rubber and oil palm plantations but significantly lower in rubber plantations. After standardization, 4,219 OTUs were assigned to five trophic groups, and inspected for effects of land-use change, and potential biotic and abiotic driving factors. The most abundant trophic group was phagotrophs (52%), followed by animal parasites (29%), photoautotrophs (12%), plant parasites (1%), and symbionts (<1%). However, the relative abundance and OTU richness of phagotrophs and photoautotrophs increased significantly with increasing land-use intensity. This was similar, but less pronounced, for the relative abundance of symbionts. Animal and plant parasites decreased significantly in abundance and species richness with increasing land-use intensity. Community compositions and factors affecting the structure of individual trophic groups differed between land-use systems. Parasites were presumably mainly driven by the abundance and species richness of their hosts, while phagotrophs by changes in soil pH and increase in Gram-positive bacteria, and photoautotrophs by light availability. Overall, the results show that relative species richness, relative abundance, and community composition of individual trophic groups of protists in tropical lowland rainforest significantly differ from that in converted ecosystems. This is likely associated with changes in ecosystem functioning. The study provides novel insight into protist communities and their changes with land-use intensity in tropical lowland ecosystems. We show, that trophic groups of protists are powerful indicators reflecting changes in the functioning of ecosystems with conversion of rainforest into monoculture plantations.

Bacterial Subspecies Variation and Nematode Grazing Change P Dynamics in the Wheat Rhizosphere

Low phosphorus soils are thought to constitute the majority of soils worldwide and cannot support intensive agriculture without high fertilizer inputs. Rhizobacteria are well-known to modify P dynamics and an increased bacterial diversity normally has a positive impact on various process rates. However, it is not known how variation in bacterial diversity at the subspecies level could influence trophic interactions in the rhizosphere and its consequences on plant P nutrition. We therefore hypothesized that the interactions between closely related P solubilizing bacteria and their grazing nematodes could improve plant P dynamics from an unavailable P source. We isolated four Pseudomonas poae strains and extracted nematodes from a Saskatchewan wheat field soil sample. The potential of all bacterial isolates with and without nematodes for increasing P availability in the wheat rhizosphere was tested in controlled microcosms with Ca₃(PO₄)₂ as sole P source. Liberated P, phosphatase activity, plant P and bacterial abundance based on phnX gene copies were determined. Phosphorus solubilization efficiency of isolates varied between isolates whereas phosphatase enzyme activity was only detected under nematodes grazing and during the first 15 days of the experiment. Nematodes grazing upon individual Pseudomonas poae increased phosphatase enzyme activity, bacterial abundance, but decreased plant P concentration compared to non-grazed system. In contrast, the treatment combining all Pseudomonas poae isolates together with nematodes resulted in significant increases in P availability and plant P concentration. Diverse P-solubilizing efficiency and interaction with nematodes within the same bacterial "species" suggest that P dynamics might be linked to micro variation in soil diversity that would not accurately be picked up using common tools such as 16S rRNA gene sequencing.

Traits-Based Integration of Multi-Species Inoculants Facilitates Shifts of Indigenous Soil Bacterial Community

Microbial co-inoculation is considered to be an innovative approach and had been applied worldwide. However, the underlying mechanisms of microbial co-inoculants constructions, especially the trait-based combination of distinctly different microbial species remains poorly understood. In this study, we constructed two microbial co-inoculants with the same three strains with emphasis on the microbial, soil and plant traits. Microbial co-inoculants 1 (M1) were constructed according to soil fertility, microbial activity and cucumber nutrient requirement with a 2:1:2 ratio (Ensifer sp. NYM3, Acinetobacter sp. P16 and Flavobacterium sp. KYM3), while microbial co-inoculants 2 (M2) were constructed according to soil fertility and cucumber nutrient requirement with a 1:10:1 ratio without considering the difference in the nutrient supply capability of microbial species. The results showed that M1 and M2 both obviously increased cucumber yields. The M1 had significant highest pH value, total nitrogen (TN) and invertase activity (IA). The M2 had significant highest available phosphate (AP), NO₃-N, urea activity (UA), and alkaline phosphatase activity (APA). Gammaproteobacteria, Acidobacteria, Nitrospirae, and Armatimonadetes were significantly increased, while Actinobacteria and Firmicutes were significantly decreased by microbial co-inoculations (M1 and M2). The bacterial lineages enriched in M1 were Gammaproteobacteria and TM7. Acidobacteria, Bacteroidetes, and Deltaproteobacteria were enriched in M2. Principal coordinate analysis (PCoA) analysis showed that the bacterial communities were strongly separated by the different microbial inoculation treatments. The functional groups of intracellular_parasites were highest in M1. The functional groups of phototrophy, photoautotrophy, nitrification, fermentation, cyanobacteria, oxygenic_photoautotrophy, chitinolysis and animal_parasites_or_symbionts were highest in M2. Based on correlation analysis, it inferred that the M1 and M2 might promote cucumber yields by mediating bacterial community structure and function about nitrogen fixing and urea-N hydrolysis, respectively. Collectively, these results revealed that microbial co-inoculants had positive effects on cucumber yields. Trait-based integration of different microbial species had significant effects on soil properties and bacterial communities. It indicated that microbial activity should be considered in the construction of microbial co-inoculants. This will expand our knowledge in bacteria interaction, deepen understanding of microbial inoculants in improving plant performance, and will guide microbial fertilizer formulation and application in future.

Rhizosphere Bacterial Communities Differ According to Fertilizer Regimes and Cabbage (Brassica oleracea var. capitata L.) Harvest Time, but Not Aphid Herbivory

Rhizosphere microbial communities are known to be highly diverse and strongly dependent on various attributes of the host plant, such as species, nutritional status, and growth stage. High-throughput 16S rRNA gene amplicon sequencing has been used to characterize the rhizosphere bacterial community of many important crop species, but this is the first study to date to characterize the bacterial and archaeal community of Brassica oleracea var. capitata. The study also tested the response of the bacterial community to fertilizer type (organic or synthetic) and N dosage (high or low), in addition to plant age (9 or 12 weeks) and aphid (Myzus persicae) herbivory (present/absent). The impact of aboveground herbivory on belowground microbial communities has received little attention in the literature, and since the type (organic or mineral) and amount of fertilizer applications are known to affect M. percicae populations, these treatments were applied at agricultural rates to test for synergistic effects on the soil bacterial community. Fertilizer type and plant growth were found to result in significantly different rhizosphere bacterial communities, while there was no effect of aphid herbivory. Several operational taxonomic units were identified as varying significantly in abundance between the treatment groups and age cohorts. These included members of the S-oxidizing genus Thiobacillus, which was significantly more abundant in organically fertilized 12-week-old cabbages, and the N-fixing cyanobacteria Phormidium, which appeared to decline in synthetically fertilized soils relative to controls. These responses may be an effect of accumulating root-derived glucosinolates in the B. oleracea rhizosphere and increased N-availability, respectively.

Predator and prey biodiversity relationship and its consequences on marine ecosystem functioning-interplay between nanoflagellates and bacterioplankton

The importance of biodiversity effects on ecosystem functioning across trophic levels, especially via predatory-prey interactions, is receiving increased recognition. However, this topic has rarely been explored for marine microbes, even though microbial biodiversity contributes significantly to marine ecosystem function and energy flows. Here we examined diversity and biomass of bacteria (prey) and nanoflagellates (predators), as well as their effects on trophic transfer efficiency in the East China Sea. Specifically, we investigated: (i) predator diversity effects on prey biomass and trophic transfer efficiency (using the biomass ratio of predator/prey as a proxy), (ii) prey diversity effects on predator biomass and trophic transfer efficiency, and (iii) the relationship between predator and prey diversity. We found higher prey diversity enhanced both diversity and biomass of predators, as well as trophic transfer efficiency, which may arise from more balanced diet and/or enhanced niche complementarity owing to higher prey diversity. By contrast, no clear effect was detected for predator diversity on prey biomass and transfer efficiency. Notably, we found prey diversity effects on predator-prey interactions; whereas, we found no significant diversity effect on biomass within the same trophic level. Our findings highlight the importance of considering multi-trophic biodiversity effects on ecosystem functioning in natural ecosystems.

Interactions between predation and disturbances shape prey communities

Ecological disturbances are important drivers of biodiversity patterns. Many biodiversity studies rely on endpoint measurements instead of following the dynamics that lead to those outcomes and testing ecological drivers individually, often considering only a single trophic level. Manipulating multiple factors (biotic and abiotic) in controlled settings and measuring multiple descriptors of multi-trophic communities could enlighten our understanding of the context dependency of ecological disturbances. Using model microbial communities, we experimentally tested the effects of imposed disturbances (i.e. increased dilution simulating density-independent mortality as press or pulse disturbances coupled with resource deprivation) on bacterial abundance, diversity and community structure in the absence or presence of a protist predator. We monitored the communities immediately before and after imposing the disturbance and four days after resuming the pre-disturbance dilution regime to infer resistance and recovery properties. The results highlight that bacterial abundance, diversity and community composition were more affected by predation than by disturbance type, resource loss or the interaction of these factors. Predator abundance was strongly affected by the type of disturbance imposed, causing temporary relief of predation pressure. Importantly, prey community composition differed significantly at different phases, emphasizing that endpoint measurements are insufficient for understanding the recovery of communities.

The Limnohabitans Genus Harbors Generalistic and Opportunistic Subtypes: Evidence from Spatiotemporal Succession in a Canyon-Shaped Reservoir

We studied the diversity of Limnohabitans using reverse line blot hybridization with Limnohabitans lineage-specific probes in the freshwater canyon-shaped Římov reservoir (Czech Republic). To examine the succession of distinct lineages, we performed (i) a study of an intensive spring sampling program at the lacustrine part of the Římov reservoir (from ice melt through a phytoplankton peak to the clear-water phase), and (ii) a seasonal study (April to November) when the occurrence of distinct Limnohabitans lineages was related to the inherent longitudinal heterogeneity of the reservoir. Significant spatiotemporal changes in the compositions of distinct Limnohabitans lineages allowed for the identification of "generalists" that were always present throughout the whole season as well as "specialists" that appeared in the reservoir only for limited periods of time or irregularly. Our results indicate that some phytoplankton groups, such as cryptophytes or cyanobacteria, and zooplankton composition were the major factors modulating the distribution and dynamics of distinct Limnohabitans lineages. The highest Limnohabitans diversity was observed during the spring algal bloom, whereas the lowest was during the summer cyanobacterial bloom. The microdiversity also markedly increased upstream in the reservoir, being highest at the inflow, and thus likely reflecting strong influences of the watershed.IMPORTANCE The genus Limnohabitans is a typical freshwater bacterioplankton and is believed to play a significant role in inland freshwater habitats. This work is unique in detecting and tracing different closely related lineages of this bacterial genus in its natural conditions using the semiquantitative reverse line blot hybridization method and in discovering the factors influencing the microdiversity, subtype alternations, and seasonality.

BSocial: Deciphering Social Behaviors within Mixed Microbial Populations

Ecosystem functionality depends on interactions among populations, of the same or different taxa, and these are not just the sum of pairwise interactions. Thus, know-how of the social interactions occurring in mixed-populations are of high interest, however they are commonly unknown due to the limitations posed in tagging each population. The limitations include costs/time in tediously fluorescent tagging, and the number of different fluorescent tags. Tag-free strategies exist, such as high-throughput sequencing, but ultimately both strategies require the use of expensive machinery. Our work appoints social behaviors on individual strains in mixed-populations, offering a web-tool (BSocialhttp://m4m.ugr.es/BSocial.html) for analyzing the community framework. Our quick and cheap approach includes the periodic monitoring of optical density (OD) from a full combinatorial testing of individual strains, where number of generations and growth rate are determined. The BSocial analyses then enable us to determine how the addition/absence of a particular species affects the net productivity of a microbial community and use this to select productive combinations, i.e., designate their social effect on a general community. Positive, neutral, or negative assignations are applied to describe the social behavior within the community by comparing fitness effects of the community against the individual strain. The usefulness of this tool for selection of optimal inoculum in biofilm-based methyl tert-butyl ether (MTBE) bioremediation was demonstrated. The studied model uses seven bacterial strains with diverse MTBE degradation/growth capacities. Full combinatorial testing of seven individual strains (triplicate tests of 127 combinations) were implemented, along with MTBE degradation as the desired function. Sole observation of highest species fitness did not render the best functional outcome, and only when strains with positive and neutral social assignations were mixed (Rhodococcus ruber EE6, Agrobacterium sp. MS2 and Paenibacillus etheri SH7), was this obtained. Furthermore, the use of positive and neutral strains in all its combinations had a significant higher degradation mean (x1.75) than exclusive negative strain combinations. Thus, social microbial processes benefit bioremediation more than negative social microbial combinations. The BSocial webtool is a great contributor to the study of social interactions in bioremediation processes, and may be used in other natural or synthetic habitat studies.

Microbial Interactions in the Phyllosphere Increase Plant Performance under Herbivore Biotic Stress

The phyllosphere supports a tremendous diversity of microbes and other organisms. However, little is known about the colonization and survival of pathogenic and beneficial bacteria alone or together in the phyllosphere across the whole plant life-cycle under herbivory, which hinders our ability to understand the role of phyllosphere bacteria on plant performance. We addressed these questions in experiments using four genetically and biogeographically diverse accessions of Arabidopsis thaliana, three ecologically important bacterial strains (Pseudomonas syringae DC3000, Xanthomonas campestris, both pathogens, and Bacillus cereus, plant beneficial) under common garden conditions that included fungus gnats (Bradysia spp.). Plants supported greater abundance of B. cereus over either pathogenic strain in the phyllosphere under such greenhouse conditions. However, the Arabidopsis accessions performed much better (i.e., early flowering, biomass, siliques, and seeds per plant) in the presence of pathogenic bacteria rather than in the presence of the plant beneficial B. cereus. As a group, the plants inoculated with any of the three bacteria (Pst DC3000, Xanthomonas, or Bacillus) all had a higher fitness than uninoculated controls under these conditions. These results suggest that the plants grown under the pressure of different natural enemies, such as pathogens and an herbivore together perform relatively better, probably because natural enemies induce host defense against each other. However, in general, a positive impact of Bacillus on plant performance under herbivory may be due to its plant-beneficial properties. In contrast, bacterial species in the mixture (all three together) performed poorer than as monocultures in their total abundance and host plant growth promotion, possibly due to negative interspecific interactions among the bacteria. However, bacterial species richness linearly promoted seed production in the host plants under these conditions, suggesting that natural enemies diversity may be beneficial from the host perspective. Collectively, these results highlight the importance of bacterial community composition on plant performance and bacterial abundance in the phyllosphere.