Microbial Composition of Freshwater Marsh Sediment Responds more Strongly to Microcosm Seawater Addition than Simulated Nitrate or Phosphate Eutrophication.

As sea level rise impacts coastal wetlands, saltmarsh will overtake coastal freshwater marsh in many areas, but changes in the sediment microbiome in response to saltwater intrusion are difficult to predict. Coastal freshwater marsh sediment was exposed to ambient, brackish, and saline conditions as well as to elevated nitrate and phosphate to model the combined stresses of saltwater intrusion and coastal eutrophication. Initially, sediment prokaryotic composition was similar to prior studies of freshwater marsh but diverged over time, reflecting the magnitude of increase in saltwater.

Microbial Communities in Saltpan Sediments Show Tolerance to Mars Analog Conditions, but Susceptibility to Chloride and Perchlorate Toxicity.

Brines at or near the surface of present-day Mars are a potential explanation for seasonally recurring dark streaks on the walls of craters, termed recurring slope lineae (RSL). Deliquescence and freezing point depression are possible drivers of brine stability, attributable to the high salinity observed in martian regolith including chlorides and perchlorates. Investigation of life, which may inhabit RSL, and the cellular mechanisms necessary for survival, must consider the tolerance of highly variable hydration, freeze-thaw cycles, and high osmolarity in addition to the anaerobic, oligotrophic, and irradiated environment.

The Saltpan Microbiome is Structured by Sediment Depth and Minimally Influenced by Variable Hydration.

Saltpans are a class of ephemeral wetland characterized by alternating periods of inundation, rising salinity, and desiccation. We obtained soil cores from a saltpan on the Mississippi Gulf coast in both the inundated and desiccated state. The microbiomes of surface and 30 cm deep sediment were determined using Illumina sequencing of the V4 region of the 16S rRNA gene.

The gut microbiome of freshwater Unionidae mussels is determined by host species and is selectively retained from filtered seston.

Freshwater mussels are a species-rich group of aquatic invertebrates that are among the most endangered groups of fauna worldwide. As filter-feeders that are constantly exposed to new microbial inoculants, mussels represent an ideal system to investigate the effects of species or the environment on gut microbiome composition. In this study, we examined if host species or site exerts a greater influence on microbiome composition.