We report the isolation of a pinnacle-forming cyanobacterium isolated from a microbial mat covering the sediment surface at Little Salt Spring - a flooded sinkhole in Florida with a perennially microoxic and sulfidic water column. The draft genome of the isolate encodes all of the enzymatic machinery necessary for both oxygenic and anoxygenic photosynthesis, as well as genes for methylating hopanoids at the C-2 position. The physiological response of the isolate to H 2 S is complex: (i) no induction time is necessary for anoxygenic photosynthesis; (ii) rates of anoxygenic photosynthesis are regulated by both H 2 S and irradiance; (iii) O 2 production is inhibited by H 2 S concentrations as low as 1 μM and the recovery rate of oxygenic photosynthesis is dependent on irradiance; (iv) under the optimal light conditions for oxygenic photosynthesis, rates of anoxygenic photosynthesis are nearly double those of oxygenic photosynthesis. We hypothesize that the specific adaptation mechanisms of the isolate to H 2 S emerged from a close spatial interaction with sulfate-reducing bacteria. The new isolate, Leptolyngbya sp. strain hensonii, is not closely related to other well-characterized Cyanobacteria that can perform anoxygenic photosynthesis, which further highlights the need to characterize the diversity and biogeography of metabolically versatile Cyanobacteria. The isolate will be an ideal model organism for exploring the adaptation of Cyanobacteria to sulfidic conditions.
Bibliographical noteFunding Information:
Sampling at Little Salt Spring was carried out in cooperation with divers T White (Pennsylvania State University), K Broad (University of Miami/RSMAS), S Koski (University of Miami/RSMAS), R Riera-Gomez (University of Miami/ RSMAS) and C Coy (Florida Aquarium). We are grateful to S Koski for help with field operations. We are grateful to the technicians of the microsensor group and staff at the Max Planck Institute for Marine Microbiology in Bremen, Germany for microsensor construction. We thank L Pole-recky and D Bryant for fruitful discussions. We thank A Czaja, A Gangidine and C Schuler for assistance with microscopy. This project was funded by grants to JLM from the National Science Foundation (NSF EAR-0525503) and the NASA Astrobiology Institute (PSARC, NNA04CC06A), and by the PSU Science Diving Program. Microsensor work was carried out, while JLM was a Fellow at the Hanse Wissenschaftskolleg (HWK), Delmenhorst, Germany. TLH graciously acknowledges support from the NAI Postdoctoral Program and the University of Cincinnati.