Biology subjects

Grim, S. L.

Publications and source records attributed to Grim, S. L..

3 recordsLinked to original sources

bioRxiv2026

Habitat and Hydrodynamics Influence Coral Reef and Seagrass Microbial and Exometabolite Dynamics

Coral reef and seagrass ecosystems provide critical storm protection and economic revenue to tropical coastal communities. Effective monitoring and restoration strategies are essential given increasing impacts from climate change and human development. Microorganisms, and the metabolites they produce and consume, are key drivers of coastal ecosystem function. However, microbially-mediated metabolite recycling remains poorly understood, limiting its inclusion in conservation and restoration strategies. Here we examine how seawater exometabolites and microorganisms in coastal ecosystems vary in relation to habitat (seagrass or coral reef), temporal scales and hydrodynamics. We characterized benthic seawater from two St. John, U.S. Virgin Islands coral reefs (Yawzi and Tektite) and one seagrass meadow at dawn and mid-day over four consecutive days. Using quantitative metabolomics and SSU rRNA gene amplicon sequencing, we found that habitat served as the primary driver of exometabolite and microbial community composition, while daily changes and hydrodynamics strongly influenced system variability. Hydrodynamic modeling indicated offshore water intrusion at mid-day at Yawzi reef, likely driving exometabolite and microbial shifts towards oligotrophic taxa (e.g., SAR11, SAR86). In contrast, a high percentage of coastal source water in the seagrass habitat maintained stable exometabolite pools and supported diverse microbial communities. These findings demonstrate that coastal habitat and hydrodynamics strongly influence exometabolite and microbial assemblages, with lesser contributions from temporal changes. Integrating exometabolites, microorganisms, and hydrodynamics provides new insights into coastal ecosystem functioning useful for habitat monitoring and restoration strategies.

ecology↗

bioRxiv2023

Microbial abundance and diversity in 64-74 Ma subseafloor igneous basement from the Louisville Seamount Chain

The aquifer in subseafloor igneous basement is a massive, continuous microbial substrate, yet sparingly little is known about life in this habitat. The work to date has focused largely on describing microbial diversity in young basement (<10 Ma) at oceanic spreading regions and ridge flanks, where the basaltic crust is still porous and fluid flow through it is active. While the prevailing belief used to be that fluid flow through older parts of the seafloor was non-existent, recent heat flow models predict that fluid moves through subseafloor basement >65 Ma, and that seamounts can act as mid-plate conduits for fluids into and out of the subsurface aquifer in older crustal settings. Here we test the hypothesis that microbial life exists in subseafloor basement >65Ma using samples collected from the Louisville Seamount Chain via seafloor drilling. Cell biomass was heterogeneous in nature and ranged from below detection to [~]104 cells cm-3. Bacterial 16S rRNA genes from core samples and enrichment incubations are dominated by lineages putatively carrying out hydrocarbon oxidation and nitrogen, sulfur and metal redox processes. Samples from two different seamounts were statistically different, indicating some degree of biogeography. Archaea were not detected via quantitative polymerase chain reaction, indicating they are rare in the Louisville subsurface. Taken together, the data indicate that microbial life is indeed present in subseafloor igneous basement >65 Ma, which significantly expands the range of the subseafloor biosphere where microbial life is known to exist. Impact StatementThe aquifer in subseafloor igneous basement is the largest continuous microbial substrate on Earth, but it is difficult to access and therefore understudied. We here collected samples from the Louisville Seamount Chain using seafloor drilling to determine if microbial life exists in the >65 Ma subseafloor basement made at these seamounts. A low biomass environment dominated by Bacteria potentially capable of using the Fe and S inherent in subseafloor basalt was detected, including Bacteria that were revived in enrichment experiments. This discovery expands the range of seafloor where confirmed microbial life exists and indicates the interior of seamounts is habitable.

ecology↗

bioRxiv2023

Seasonal Shifts in Community Composition and Proteome Expression in a Sulfur-Cycling Cyanobacterial Mat

Seasonal changes in light and physicochemical conditions have strong impacts on cyanobacteria, but how they affect community structure, metabolism, and biogeochemistry of cyanobacterial mats remains unclear. Light may be particularly influential for cyanobacterial mats exposed to sulfide by altering the balance of oxygenic photosynthesis and sulfide-driven anoxygenic photosynthesis. We studied temporal shifts in irradiance, water chemistry, and community structure and function of microbial mats in Middle Island Sinkhole (MIS), where anoxic and sulfate-rich groundwater provides habitat for cyanobacteria that conduct both oxygenic and anoxygenic photosynthesis. Seasonal changes in light and groundwater chemistry were accompanied by shifts in bacterial community composition, with a succession of dominant cyanobacteria from Phormidium to Planktothrix, and an increase in diatoms, sulfur-oxidizing bacteria, and sulfate-reducing bacteria from summer to autumn. Differential abundance of cyanobacterial light harvesting proteins likely reflects a physiological response of cyanobacteria to light level. Beggiatoa sulfur oxidation proteins were more abundant in autumn. Correlated abundances of taxa through time suggest interactions between sulfur oxidizers and sulfate reducers, sulfate reducers and heterotrophs, and cyanobacteria and heterotrophs. These results support the conclusion that seasonal change, including light availability, has a strong influence on community composition and biogeochemical cycling of sulfur and O2 in cyanobacterial mats. Originality-Significance StatementCyanobacterial mats are found in terrestrial and aquatic environments on modern Earth and their fossil remains are present throughout the geologic record. They are biogeochemical oases that underpin diverse metabolic interactions, transform key nutrients and fix carbon, and can thrive in extreme environments. Mat-forming cyanobacteria can be metabolically versatile and conduct both oxygenic and anoxygenic photosynthesis using sulfide (OP and AP), thereby participating in both oxygen and sulfur cycling. The effect of seasonality on ecological factors constraining photosynthetic production and geochemical cycling in extreme cyanobacterial mats is not well known. In this study, we surveyed the mat community composition via bacterial 16S rRNA genes, microbial activity via metaproteomics, and water physico- and geochemistry over multiple seasons and years of the cyanobacterial mat in Middle Island Sinkhole, an O2-poor benthic sinkhole in Lake Huron, Michigan. We found that higher availability of sulfate-rich groundwater, together with higher light intensity, coincided with dominance of the metabolically flexible cyanobacterium Phormidium during the summer. Diverse sulfur cycling bacteria were more successful in other seasons when the mat experienced lower light and sulfate availability. These results provide insights into how seasonal environmental dynamics can shape the community structure and metabolisms of microbial mats, ultimately controlling biogeochemical cycling in these ecological hotspots.

microbiology↗