Diversity of culturable heterotrophic aerobic bacteria in pristine stream bed sediments

More than 900 culturable, heterotrophic aerobic isolates were obtained from the sediments of a forested, pristine stream and analyzed using three classical microbiological tests: API 20E, amplified ribosomal DNA restriction analysis (ARDRA), and fatty acid analysis. Gram-negative bacteria comprised most of the heterotrophic aerobic isolates (66.7%), similar to other oligotrophic environments. The isolates were assigned to the genus level as Pseudomonas, Flavobacterium, Micrococcus, Bacillus, Chromobacterium, Acinetobacter, Alcaligenes, Aeromonas, Methylobacterium, Enterobacter, Corynebacterium, and Sporolactobacillus. Genotypic analysis by ARDRA facilitated the comparison among strains within Pseudomonas, Bacillus, and Enterobacter groups. Temperature and predation may influence the survival of bacteria during seasons, as shown previously by others. Our results showed that the number of heterotrophic aerobic bacteria, especially Enterobacter, Alcaligenes, and Aeromonas, and Gram-positive bacteria, decreased in winter compared to summer conditions.