AME 66:95-106 (2012)  -  DOI: https://doi.org/10.3354/ame01561

ABSTRACT: In nature, bacteria interact with each other in ways that do not occur in pure laboratory cultures. However, when bacteria are purified from environmental samples, the resulting colonies occasionally harbor diverse bacterial isolates, which we have termed ‘associated isolates’. Bacteria were obtained from a freshwater lake along a euphotic gradient (100, 10 and 1% light penetration). Surprisingly, 76 of the 1196 resulting colonies harbored between 2 and 5 associated isolates (for a total of 168 associated isolates), and 121 of these associated isolates were recovered as pure cultures. A portion of the isolates (47/168) was non-viable after re-streaking, suggesting an inability to survive and reproduce in the absence of their associates. Partial sequencing of 16S rDNA revealed that these isolates were affiliated with Proteobacteria, Firmicutes, Bacteroidetes, Actinobacteria and Deinococcus-Thermus, and represented 26 genera. Colonies harboring associated isolates and those that harbored the largest number of isolates were primarily sampled from the 1% euphotic gradient. Significant differences in the distribution of associated isolates along the euphotic gradient suggest that environmental factors are driving these associations.

KEY WORDS: Associated bacteria · Intracolony · Diversity · 16S rDNA · Freshwater