Heterotrophic bacteria in the Ross Sea (Terra Nova Bay, Antarctica).

Microbial research on temporal variation of bacterial densities was carried out on seawater samples collected from two field stations at different depths during the Antarctic summer (oceanographic campaign 1989/1990). Bacterial densities evaluated on Marine Agar 2216 (Difco) and on TCBS Agar (Difco) after incubation at +4 degrees C for 21 days respectively ranged from 0 to 7.9 x 10(2) CFU/ml for heterotrophic bacteria and from 0 to 5.7 x 10(2) CFU/100ml for "presumptive vibrios". During the period of observation, Vibrio densities showed a higher variability than those of total heterotrophic bacteria. A high percentage of gelatinolytic and chitinolytic vibrios was observed. The qualitative composition of heterotrophic bacterial communities was studied on 38 morphological and biochemical characteristics of 152 strains isolated from the stations. The data were subsequently used to determine the structure and metabolic potentialities of bacterial communities in the two sites. Almost all the heterotrophic, psychrotrophic isolates were non fermentative Gram-negative rods, belonging to the genera Pseudomonas/Alcaligenes, Flavobacterium/Cytophaga. The bacterial communities in the two coastal habitats investigated were clearly different.