Bacterial regeneration of ammonium and phosphate as affected by the carbon:nitrogen:phosphorus ratio of organic substrates.

The effect of carbon∶nitrogen∶phosphorus (C∶N∶P) ratio of organic substrates on the regeneration of ammonium and phosphate was investigated by growing natural assemblages of freshwater bacteria in mineral media supplemented with the simple organic C, N, and P sources (glucose, asparagine, and sodium glycerophosphate, respectively) to give 25 different substrate C∶N∶P ratios. Both ammonium and phosphate were regenerated when C∶N and N∶P atomic ratios of organic substrates were ≤10∶1 and ≤16∶1, respectively. Only ammonium was regenerated when C∶N and N∶P ratios were ≤10∶1 and ≥10-20∶1, respectively. On the other hand, neither ammonium nor phosphate was regenerated when C∶N and N∶P ratios were ≥15∶1 and ≥5∶1, respectively. In no case was phosphate alone regenerated. As bacteria were able to alter widely the C∶N∶P ratio of their biomass, the growth yield of bacteria appeared primarily dependent on the substrate carbon concentration, irrespective of a wide variation in the substrate C∶N∶P ratio.