Effect of organic amendments on bacterial multiplication in lake water.

In Cayuga Lake water amended with 30 micrograms of glucose or amino acids per ml, an added strain of Pseudomonas fluorescens and indigenous bacteria grew extensively, Pseudomonas sp. B4 and two rhizobia multiplied at a moderate extent, and introduced Escherichia coli and Klebsiella pneumoniae multiplied but to only a slight degree. The amendments did not enhance growth of Micrococcus flavus and Arthrobacter citreus, and an asporogenous strain of Bacillus subtilis decreased in numbers. The pseudomonads, rhizobia, E. coli and K. pneumoniae multiplied extensively when inoculated into sterile lake water amended with amino acids, A. citreus grew to a slight extent, but the numbers of M. flavus and B. subtilis did not change appreciably. In nonsterile lake water amended with 30 micrograms of Trypticase soy broth per ml, the indigenous bacteria greatly increased in abundance, the pseudomonads, rhizobia, and E. coli developed to a lesser extent, the numbers of K. pneumoniae, A. citreus and M. flavus showed little increase, and B. subtilis decreased in numbers. Tests in pure culture containing 2 to 64 micrograms of Trypticase soy broth per ml demonstrated good growth of P. fluorescens, Pseudomonas sp. B4, and the rhizobia at all concentrations; an initial decline followed by growth of E. coli, K. pneumoniae and R. leguminosarum biovar phaseoli at low concentrations; little or no growth or decline at the low levels but multiplication at the high levels by A. citreus and B. subtilis; and decline of M. flavus. It is proposed that the apparent Ks value, mumax value, length of lag phase and resistance to stress can be used to predict behavior of bacteria in lake water receiving low levels of organic nutrients.