Introduction

1. Virginia Tech University of NC-Wilmington University of Miami Anhydrophilic, Halotolerant Microbial Mats of San Salvador, Bahamas Anhydrophilic, Halotolerant Microbial Mats of San Salvador, Bahamas Tim Steppe & UNC-CH Institute of Marine Sciences tim_steppe@unc.edu Hans Paerl hans_paerl@unc.edu Alan DechoUSC-ColumbiaDept. of Environmental adecho@sph.sc.edu Health Sciences Jay PinckneyTexas A&MDept. of Oceanography pinckney@ocean.tamu.edu Diversity Sites and Organisms Introduction Typical of many Bahamian Islands, San Salvador Island (24o05’N, 74o30’W) contains numerous hypersaline (45 to 200‰) lakes and ponds. The lakes are subject to intense irradiance (>2100 µE m-2 s-1), high temperatures (> 30° C) and chronic nutrient depletion. Highly productive microbial mats blanket the shallow sediments in many of these lakes. In addition to the osmotic stress induced by the hypersaline conditions, the mats are subjected to an additional water stress, desiccation, as lake levels recede during the dry season (December to April). Many of these organisms are found in mats throughout the world. However, the relative isolation of San Salvador, its extreme climatic conditions, and diversity of organisms increases the likelihood that novel organisms possessing unique adaptive mechanisms inhabit the mats and lakes. One of our primary goals is to isolate and characterize anhydrophilic microorganisms from the mats and lakes. Field work is based out of the Bahamian Field Station (BFS) on San Salvador Island. Every year, the BFS hosts students and researchers from many institutions in the United Sates and abroad. In cooperation with the BFS staff, a prime focus for this project will be the establishment of educational and research opportunities for students wishing to better understand the structure and function of halotolerant microbial mat communities of San Salvador. a A phylogenetic tree created from amino acid translations of the nifH gene. The tree shows some of the sequences obtained from the ‘pie mound’ or ectoplasm mats. Similar to other mats the ectoplasm contains a diverse assemblage of diazotrophs. In addition to nifH, we will characterize cyano- bacteria using 16S rRNA genes and sulfate -reducing bacteria using the dissimilatory reductase gene (dsr). This will allow us to characterize the organisms involved in the major biogeochemical processes. Initially, the major effort will be to characterize the organisms along a desiccation gradient (see below) established in Salt Pond. Frankia alni G+ Highborne Cay Culture #06 Synechococcus sp. Phormidium sp. S.L. Ecto 04 AD Culture 01 S.L Ecto 14 j b Nostoc muscorum Hetero Anabaena oscillariodes Exuma Heterocyst. #01 BS Cyano Cyanobacteria S.L. Ecto 05 Xenococcus sp. S.L. Ecto 09 S.L. Ecto 01 Plectonema boryanum Lyngbya lagerhaemii S.L. Ecto 17 c i Highborne Cay Culture #02 Highborne Cay Culture #05 AEROBIC Symploca chtonoplastes GM26 Azotobacter vinelandii BS LM 51 Marichromatium purpurtum Alpha Klebsiella pneumoniae S.L Ecto 16 B.S. UM 01 Rhizobium meliloti Beta/ Gamma Rhodobacter capsulatus d h Azospirillum brasilense Rhizobium japonicum Bacillus azotofixans G+ S.L. Ecto 03 S.L. Ecto 08 BS LM 29 Desulfovibrio gigas S.L. Ecto 24 Halodule wrightii #02 S.L. Ecto 20 Anaerobic BS UM 113 e g Objectives The overall research objective of this study is to assess the influence water availability has on structural diversification, community composition, production, and carbon sequestration in microbial mats. The specific goals for this observatory are to: 1) Isolate and characterize desiccation tolerant organisms. 2) Describe the structural and microbial diversity of the mat communities in relation to water availability. 3) Assess the influence water availability has on primary production extracellular polymeric substances (EPS) production, and EPS degradation. 4) Develop a conceptual model linking climate and water budget data, water availability, and primary production. S.L. Ecto 07 BS LM J7 Desulfovibrio salexigens HB Lactate Enrichment 01 BS Um 413 BS UM 913 Clostridium pasteurianum 01 Clostridium pasteurianum 02 G+ Desulfotomaculum sp. Clostridium cellobioparum Clostridium pasteurianum 03 Rhodobacter capsulatus ANF/ Meth. voltae f Meth. thermolithotrophicus ARCHAE Ecophysiology along a desiccation gradient Two lakes have been chosen as our main study sites: Storr’s Lake (b) & Salt Pond (j). Storr’s Lake possesses many mat types including ~1.0 m high stromatolites in the deeper portions and the ‘pie mound mats’ (e). The mat (g) in Salt Pond continuously covers the bottom of the shallow lake from the eastern edge to ~35 m from the edge. There are a great diversity of microorganisms on Sal Salvador. We are in the process of culturing both cyanobacteria and heterotrophic bacteria, which we will screen for the ability to withstand desiccation. Organisms arranged clockwise from the top include: mix of organisms from Salt Pond Mat (a), Aphanothece sp. (major planktonic organism in Salt Pond) (c), Lyngbya sp. (cosmopolitan diazotrophic mat organism) (d), Johannesbaptista sp.(f), benthic diatom (although eukaryotic, diatoms are significant phototrophs in the mats) (h), and Microcoleus sp. (another cosmopolitan mat cyanobacterium) (i). Three transects across a desiccation gradient, 26 m in length and 15 m apart, have been established in Salt Pond. These transects cover areas of the mat that range from infrequently hydrated to those that are permanently submerged. While the phototrophic community composition did not vary, the carotenoid pigment ratios shifted from being primarily photoprotective in the more desiccated mats to ones associated with photoacclimation responses in the more submerged mats. Oxygen microelectrode measurements of photosynthesis (not shown) showed that the highest rates of oxygenic photosynthesis occurred in the middle part of the transect. The results suggest that changes in the ecophysiology of the mats are good indicators of the degree and frequency of desiccation. Significance & Impact Water is indispensable for life. The proposed work addresses a fundamental mechanism that is essential to all life on earth, the ability to conserve water and balance ions. Anhydrophilic communities exist under ‘feast or famine’ conditions with regards to water availability. The mechanisms of cell survival as it enters the air-dried state, remains desiccated for extended periods (months to years), and then rehydrates, are poorly understood. Monitoring the physiological responses of pristine, anhydrophilic communities over time and under different conditions of water availability will provide information necessary to understanding how long and short term climatic oscillations impact critical biogeochemical cycles. Water Chemistry (Salt Pond) Photosynthesis and Nitrogenase Activity www.SanSalMO.net Collaborators Participants Salinity effects on CO2 fixation and nitrogenase activity. Salt Pond mat pieces were incubated for 2-3 days in seawater. Rates were compared to mat pieces similarly incubated in Salt Pond water. Diel patterns of CO2 fixation and nitrogenase acitivity. Similar to many mats, oxygen sensitive nitrogen fixation is temporally separated from photosynthesis. Salt Pond mat.