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 investi gated. The response of the organisms to P depended mainly on their aff inity for the available P. Thus, Corynebacterium sp. at an initial den sity of 3.3 x 10(4) cells ml(-1) readily degraded-10 mg l(-1) of PNP i n filter-sterilized Nile water supplemented with 22.8 mg l(-1) of P. T he same effect was observed when Pseudomonas cepacia was inoculated in to 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 r elated 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 N ile water inoculated with Pseudomonas sp. and amended with 10 mg l(-1) of 2,4-D did not stimulate the degradation compared with that obtaine d with the unsupplemented samples. The affinity of the three strains t o P was demonstrated in P-deficient medium amended with PNP or 2,4-D a s 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 wate r without added P. A slight enhancement of degradation was observed in water samples amended with a high concentration of P. The addition of P to non-sterile Nile water inoculated with Corynebacterium sp. and a mended with 10 mg l(-1) of PNP stimulated degradation, which was rapid and extensive in Nile water receiving 22.8 mg l(-1) of P. It is sugge sted that contaminated natural water with P limitation could be inocul ated with a degrading strain that has low affinity for P to bring abou t biodegradation.