Biology subjects

Steven, B.

Publications and source records attributed to Steven, B..

3 recordsLinked to original sources

bioRxiv2018

Biogeography and Edaphic Factors Structure Coastal Sediment Microbial Communities More than Vegetation Removal by Sudden Vegetation Dieback

Development of sudden vegetation dieback (SVD), a phenomenon that causes the rapid mortality of salt marsh plants, specifically Spartina alterniflora, has affected large-scale alterations in Atlantic coastal systems, through the often-complete removal of vegetation. In this study, two wetlands that differ in the time since development of SVD were compared in order to study biogeographic and temporal patterns that structure coastal wetland microbial communities and their response to disturbance.\n\nBiogeographic and edaphic factors that distinguished the two wetlands, such as differing salinity, water content, and soil carbon and nitrogen between the sites were more strongly associated with sediment microbial community structure than either sampling date or SVD development. In fact, no OTUs differed in abundance due to the season samples were collected, or vegetation loss due to SVD. This is not to say that SVD did not alter the composition of the microbial communities. The taxonomic composition of sediment communities in SVD-affected sediments was more heterogeneous between samples and a small number of OTUs were enriched in the vegetated sediments. Yet, these data suggest that coastal wetland sediment communities are predominantly shaped by environmental conditions and are generally resilient to temporal cycles or ecosystem disturbances.\n\nImportanceOne of the challenges of microbial ecology is predicting how microbial communities will respond to ecosystem change. Yet, few studies have addressed whether microbial responses to disturbance are consistent over space or time. In this study we employ SVD as a natural vegetation removal experiment and compare the sediment microbial communities between two geographically separated wetlands (ca 125 km). In this manner, we uncover a hierarchical structuring of the microbial communities, being predominantly governed by biogeography, with lesser effects due to disturbance, or temporal dynamics.

microbiology↗

bioRxiv2018

Chronic Physical Disturbance Substantially Alters the Response of Biological Soil Crusts to a Wetting Pulse, as Characterized by Metatranscriptomic Sequencing

Biological soil crusts (biocrusts) are microbial communities that are a feature of arid surface soils worldwide. In drylands where precipitation is pulsed and ephemeral, the ability of biocrust microbiota to rapidly initiate metabolic activity is critical to their survival. Community gene expression was compared after a short duration (1 hour) wetting pulse in both intact and soils disturbed by chronic foot trampling.\n\nAcross the metatranscriptomes the majority of transcripts were cyanobacterial in origin, suggesting that cyanobacteria accounted for the bulk of the transcriptionally active cells. Chronic trampling substantially altered the functional profile of the metatranscriptomes, specifically resulting in a significant decrease in transcripts for nitrogen fixation. Soil depth (biocrust and below crust) was a relatively small factor in differentiating the metatranscriptomes, suggesting that the metabolically active bacteria were similar between shallow soil horizons. The dry samples were consistently enriched for hydrogenase genes, indicating that molecular hydrogen may serve as an energy source for the desiccated soil communities. The water pulse was associated with a restructuring of the metatranscriptome, particularly for the biocrusts. Biocrusts increased transcripts for photosynthesis and carbon fixation, suggesting a rapid resuscitation upon wetting. In contrast, the trampled surface soils showed a much smaller response to wetting, indicating that trampling altered the metabolic response of the community. Finally, several biogeochemical cycling genes in carbon and nitrogen cycling were assessed for their change in abundance due to wetting in the biocrusts. Different transcripts encoding the same gene product did not show a consensus response, with some more abundant in dry or wet biocrusts, highlighting the challenges in relating transcript abundance to biogeochemical cycling rates.\n\nThese observations demonstrate that metatranscriptome sequencing was able to distinguish alterations in the function of arid soil microbial communities at two varying temporal scales, a long-term ecosystems disturbance through foot trampling, and a short term wetting pulse. Thus, community metatranscriptomes have the potential to inform studies on the response and resilience of biocrusts to various environmental perturbations.

microbiology↗

bioRxiv2018

Axenic Aedes aegypti develop without live bacteria, but exhibit delayed development and reduced oviposition.

The mosquito gut microbiome plays an important role in mosquito development and fitness, providing a promising avenue for novel mosquito control strategies. Here we present a method for rearing axenic (bacteria free) Aedes aegypti mosquitoes, which will greatly facilitate mechanistic studies documenting the structure and function of the microbiome. Through feeding sterilized larvae agar plugs containing attenuated Escherichia coli, mosquito development was observed in the absence of living bacteria. Axenic larvae were capable of full development into adults, which laid eggs that were subsequently hatched. However, axenic mosquitoes exhibited delayed development time and reduced egg clutch size in comparison to bacterially colonized mosquitoes. These findings suggest that mosquito development is not dependent on live bacteria, but their phenotype is modulated by the presence of microorganisms. This axenic system offers a new tool in which the mosquito microbiome can be systematically manipulated for a deeper understanding of microbiome host interactions.

microbiology↗