Detection and characterization of denitrifying bacteria from a permanently ice-covered Antarctic lake

Denitrifying bacterial strains were isolated from Lake Bonney, a permanently ice-covered and chemically stratified lake in the McMurdo dry valley region of Antarctica, using complex media at 4 degrees C. Three strains, identified as denitrifiers by their ability to produce nitrous oxide using nitrate or nitrite as a respiratory substrate, were characterized as to their temperature and salinity optima for aerobic growth in batch culture; all three were psychrophilic and moderately halophilic. Maximum growth rates of near 0.024 h(-1) were measured for all three strains. Growth rates projected to occur at in situ temperature and salinity imply generation times on the order of 100 h. Species specific polyclonal antisera were prepared against two of the strains, ELB 17 (from the east lobe of the lake at 17 m) and WLB20 (from the west lobe at 20 m). Both strains were subsequently detected and enumerated in the lake using the antisera. ELB 17 was present in both lobes below the chemocline, while WLB20 was present in the west lobe below the chemocline but only in surface waters of the east lobe. These distributions are related to the observed chemical distributions which imply the occurrence of denitrification in the west lobe of the lake and not in the east lobe.