Strategy of Pseudomonas pseudoalcaligenes C70 for effective degradation of phenol and salicylate.

Phenol- and naphthalene-degrading indigenous Pseudomonas pseudoalcaligenes strain C70 has great potential for the bioremediation of polluted areas. It harbours two chromosomally located catechol meta pathways, one of which is structurally and phylogenetically very similar to the Pseudomonas sp. CF600 dmp operon and the other to the P. stutzeri AN10 nah lower operon. The key enzymes of the catechol meta pathway, catechol 2,3-dioxygenase (C23O) from strain C70, PheB and NahH, have an amino acid identity of 85%. The metabolic and regulatory phenotypes of the wild-type and the mutant strain C70ΔpheB lacking pheB were evaluated. qRT-PCR data showed that in C70, the expression of pheB- and nahH-encoded C23O was induced by phenol and salicylate, respectively. We demonstrate that strain C70 is more effective in the degradation of phenol and salicylate, especially at higher substrate concentrations, when these compounds are present as a mixture; i.e., when both pathways are expressed. Moreover, NahH is able to substitute for the deleted PheB in phenol degradation when salicylate is also present in the growth medium. The appearance of a yellow intermediate 2-hydroxymuconic semialdehyde was followed by the accumulation of catechol in salicylate-containing growth medium, and lower expression levels and specific activities of the C23O of the sal operon were detected. However, the excretion of the toxic intermediate catechol to the growth medium was avoided when the growth medium was supplemented with phenol, seemingly due to the contribution of the second meta pathway encoded by the phe genes.

Cadmium increases catechol 2,3-dioxygenase activity in Variovorax sp. 12S, a metal-tolerant and phenol-degrading strain.

A Gram-negative bacterium, designated as strain 12S, was isolated from a heavy metal-polluted soil. According to the biochemical characteristics, FAME analysis, and 16S rRNA gene sequence analysis, the isolated strain was identified as Variovorax sp. 12S. In the presence of 0.1 mM cadmium, 12S was able to completely utilize up to 1.5 mM of phenol as the sole carbon and energy source in an MSM-TRIS medium. Degradation of phenol was accompanied by a slow bacterial growth rate and an extension of the lag phase. The cells grown on phenol showed catechol 2,3-dioxygenase (C23O) activity. The activity of C23O from 12S cultivated in medium with Cd(2+) was almost 20 % higher than in the control. Since environmental contamination with aromatic compounds is often accompanied by the presence of heavy metals, Variovorax sp. 12S and its C23O appear to be very powerful and useful tools in the biotreatment of wastewaters and soil decontamination.