Abstract
Eight strains of chemoorganotrophic bacteria were isolated from the water column of Lake Hoare, McMurdo Dry Valleys, Antarctica, using cold enrichment temperatures. The isolates were Alpha-, Beta-, and Gammaproteobacteria and Actinobacteria spp. All isolates grew at 0 degrees C, and all but one grew at subzero temperatures characteristic of the water column of Lake Hoare. Growth temperature optima varied among isolates, but the majority showed optima near 15 degrees C, indicative of cold-active phenotypes. One isolate was truly psychrophilic, growing optimally around 10 degrees C and not above 20 degrees C. Half of the isolates grew at 2% salt while the other half did not, and all but one isolate grew at 2 atm of O(2). Our isolates are the first prokaryotes from the water column of Lake Hoare to be characterized phylogenetically and physiologically and show that cold-active species of at least two major phyla of Bacteria inhabit Lake Hoare.