SULFUR-CYCLING MICROBIAL MATS OF THE PALOS VERDES HYDROTHERMAL VENT FIELD, AN ANALOG FOR DEEP-SEA VENTS: IMPLICATIONS FOR SULFUR BIOGEOCHEMISTRY, EARLY EARTH AND CLIMATE CHANGE

Microbial mats are diverse communities often found in extreme environments on the modern Earth. This project focuses on the sulfur-cycling microbial mats of the Palos Verdes (PV) Peninsula hydrothermal vent field. Here, through a paired microbiological (FISH microscopy) and microgeochemical (sulfur radioisotope rate measurements) approach, this investigation aims to link the micron-scale physical variations in microbial community structure with the activity of microbial sulfur-cycling in these communities. I hypothesize that the mutualistic metabolic activities and close physical interactions between sulfur-oxidizing bacteria (SOXB) and sulfate-reducing bacteria (SRB), drive tightly coupled sulfur cycling in the PV mat ecosystem.

The PV microbial mat community was characterized using molecular sequencing techniques. This analysis revealed a highly diverse microbial assemblage. Natural fiber strings and glass slides have been deployed at the field site. String samples have been harvested for sulfate reduction activity measurements (SRR). The single step radiotracer method was utilized for SRR. Initial SRR results indicate that biological sulfate reduction is occurring within these mat communities. Control incubations were also employed to confirm that the measured sulfate reduction was of biological origin. Glass slide samples were utilized for FISH. Additionally, specific probes for lineages of SOXB (e.g. Thiothrix) and SRB (e.g. Desulfomusa) are being designed using the developed 16S rRNA sequence libraries.

The PV vents are a modern day analog for deep-sea hydrothermal systems and an excellent laboratory to study sulfur-cycling microbial populations and their influence on biogeochemical processes. This study also has implications for coastal habitats, especially in oxygen minimum zones, which are becoming more widespread due to the changing climate. Reduced-sulfur sequestration affects many biogeochemical cycles and atmospheric concentrations of CO₂ and O₂ over geologic time. Thus, a better understanding of “thiobiotic” communities and how their metabolic relationships shield them from unfavorable environmental conditions would have implications for climate change/eutrophication studies.