Molecular mechanisms of genetic adaptation to xenobiotic compounds.

THE EFFECT OF POLYCYCLIC AROMATIC HYDROCARBONS ON THE DEGRADATION OF BENZO[a]PYRENE BY MYCOBACTERIUM SP. STRAIN RJGII-135

“…strain KR2 [35]. Organization of catabolic enzymes into upper and lower pathways is well characterized in bacterial isolates that degrade low-molecularweight compounds [6,[37][38][39], as is the positive regulation of upper pathways by downstream, intermediate metabolites [40,41].…”

“…Biodegradation is the main route of PAH removal from the environment. Although numerous microorganisms have been isolated that degrade PAHs that contain three aromatic rings or less, only a few have been found that can break down structures with four or more rings [3][4][5][6]. Isolation of these organisms through enrichment isolation methods for four-and five-ring degrading bacteria has often resulted in isolation of mycobacteria [4,[7][8][9][10][11][12].…”

Biodegradation of chlorobenzene by indigenous bacteria

“…Our survey of four long-term CB-contaminated sites showed that CB-degrading bacteria were readily isolated from areas of moderate CB contamination, in marked con trast to the finding of no CB-degrading organisms in nearby, but uncontaminated, control wells Selection periods of short duration (one-three weeks) were required for the isolation of CB degrading bacteria from these sites, as opposed to the six to 14 months previously reported for isolation of bacteria able to degrade mono-and dichlorobenzenes [25-301 The brief selection periods indicate that the CB-degrading bacteria were present in the contaminated soil and water at the time the samples were taken and did not develop as a result of evolutionary processes during the lab selection Contamination by CB-degrading organisms during the sampling pro cess is unlikely because no CB-degrading organisms could be recovered from control samples, and the wide variety of deg radative phenotypes that were obtained from contaminated wells would preclude a single contarnination event The above observations led us to the conclusion that indigenous degradative populations develop where there is chronic CB contamination of soil and ground water The question then arises of how the degradative population came to be at the contaminated sites Although the answers are beyond the scope of this study, we can speculate about two possible mechanisms the transport of degradative organisms from elsewhere or the evolution of catabolic phenotypes in situ Ultimately all subsurface bacteria must have originated elsewhere, but recent studies of subsurface bacteria indicate that a large variety of catabolic phenotypes can be found in both contaminated and pristine aquifers [7, In deep subsurface samples from the coastal plain of South Carolina, comparisons of antibiotic resistances [42], physiological responses [43], and G + C values [44] of bacterial isolates from various depths have demonstrated that distinct bacterial communities exist in the subsurface that are not derived from transport from the surface through drill muds Thus catabolic phenotypes may develop in indigenous subsurface communities that are genetically isolated from surface com munities If the degradative capabilities did not originate through transport of or contact with foreign microorganisms, we are left with the possibility of evolution of the catabolic phenotype at the contaminated site We have established that organisms able to degrade CB existed in the microbial communities of the contaminated wells As neither contamination during the sampling process nor evolution during lab selection for CB degraders is likely to have occurred, we are left with two possibilities that adaptation [45] to CB had occurred as a result of the contamination through selection for CB-degrading bacteria or that CB-degrading organisms were present in the contaminant spill Although this last possibility cannot be disproved here, it would require that the CB-degrading bacteria be able to withstand exposure to pure CB and that they be transported into the ground water with the CB The unlikelihood of those two events favors the genetic adaptation mechanism Similar patterns of degradation of creosote components were reported for creosote-contaminated but not for pristine subsurface materials [46] This result supports the suggestion that adaptation to specific contaminants occurs as a result of the contamination When bioreactors were installed at a site that had a long history of CB contamination, they were quickly colonized by indigenous CB degrading bacteria When supplemented with appropriate nutrients and 02, the bior...…”

The use of mutants to discern the degradation pathway of 3,4′-dichlorobiphenyl in Pseudomonas acidovorans M3GY

“…The detection of 3-CC as an intermediate in the degradation of 3,4P-DCBP by Tn5 insertion mutant P. acidovorans strain M3GY-9 indicates that the clc genes are relevant in the metabolism of this substrate by wild-type strain M3GY. Productive ring ¢ssion of 3-CC involves intradiol cleavage by chlorocatechol 1,2-dioxygenase [16], which is encoded by the clc genes. In contrast, 2,3-extradiol cleavage of 3-CC leads to lethal production of 5-chloroformyl-2-hydroxypenta-2,4-dienoic acid, which is a potent inhibitor of meta-pyrocatechases [17].…”