Bacterial survival in a dilute environment

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Abstract
Bacteria were isolated from lake water and their ability to remain viable in a dilute, nutrient-deficient environment was tested by a method that permits suspension of test bacteria between 2 appressed microporous membranes in an aqueous environment. This approach permitted separation of the lake isolates into 2 categories. Members of the tribe Klebsielleae had a prolonged survival rate of 40% or better after 24 h; nonsurvivors were not viable for much longer than 24 h. These nonsurvivors belonged to the genera Acinetobacter, Aeromonas, Alcaligenes, Erwinia, Escherichia, Flavobacterium and Pseudomonas. Differences in RNase and ATPase levels between Escherichia coli (nonsurvivor) and Klebsiella (survivor) cells were detected. At pH 7.5, stressed E. coli cells contained 14% of the ATPase activity detected in the control; at pH 5.5, in the presence of Ca ions, these same cells contained 50% of the control ATPase levels. At pH 7.2, E. coli cells were strongly inhibited by an ATPase inhibitor, bathophenanthroline (88%); oligomycin (64%); and the proton ionophore carbonyl cyanide-m-chlorophenyl hydrazone (67%). Sodium azide and valinomycin were only moderately inhibitory (15 and 28%, respectively). Although the ability to scavenge internal endogenous reserves seems important, certain enteric bacteria seem capable of using acidic conditions (pH 5.5) as an electrochemical gradient to generate necessary high-energy intermediates for prolongation of survival beyond that possible in environments of near-neutral pH.