A variable response of degrading bacteria to phosphorus added to natural water.

The effect of inorganic phosphorus (P) on the degradation of 10 mg l-1 of para-nitrophenol (PNP) or 2,4-dichlorophenoxyacetic acid (2,4-D) by three test bacteria inoculated into Nile water samples was investigated. The response of the organisms to P depended mainly on their affinity for the available P. Thus, Corynebacterium sp. at an initial density of 3.3 x 10(4) cells ml-1 readily degraded 10 mg l-1 of PNP in filter-sterilized Nile water supplemented with 22.8 mg l-1 of P. The same effect was observed when Pseudomonas cepacia was inoculated into Nile water amended with PNP and supplemented with 2.28-22.8 mg l-1 of P. The bacteria grew in Nile water and the final densities were related to the level of the added P. On the other hand, the addition of P, at concentrations ranging from 2.28 to 22.8 mg l-1, to sterile Nile water inoculated with Pseudomonas sp. and amended with 10 mg l-1 of 2,4-D did not stimulate the degradation compared with that obtained with the unsupplemented samples. The affinity of the three strains to P was demonstrated in P-deficient medium amended with PNP or 2,4-D as a sole carbon source. The pH of the medium was adjusted with 0.1 mol l-1 Tris buffer. Pseudomonas sp. at an initial density of 3.3 x 10(4) cells ml-1 degraded 10 mg l-1 of 2,4-D in non-sterile Nile water without added P. A slight enhancement of degradation was observed in water samples amended with a high concentration of P.(ABSTRACT TRUNCATED AT 250 WORDS)