A. radioresistens S13 was isolated in our laboratories from the soil surrounding an activated sludge pilot plant because of its ability to quickly degrade phenol (P) and selected for bioremediation applications. Among aromatic molecules it also can metabolize benzoate (B): both aromatic compounds can be used as the sole carbon and energy source and are degraded through the -ketoadipate pathway. It was previously established that a double set of genes, one for B and the other for P catabolism, is present and two isozymes of catechol 1,2-dioxygenase (C1,2O) have been characterized. Kinetic analysis of A. radioresistens S13 growth shows that P (qp max = 53.8 Cmmol g-1 h-1, YX/phenol = 16.31 g/Cmol) is degraded faster and more efficiently than B (qb max = 49.3 Cmmol g-1 h-1, YX/benzoate = 9.79 g/Cmol). In order to establish whether these differences are due to different expression patterns or rather to different catalytic properties of the catabolic enzymes involved, functional proteomics and transcripts analyses were performed. Both approaches show that the presence of an aromatic substrate is essential to activate biosynthesis of the enzymes of the -ketoadipate route. Surprisingly B induces higher amounts of both isoenzymes of the C1,2O, of muconolactone isomerase (MLI) and of -ketoadipil-CoA thiolase than P, in spite of its lower degradative rate. We therefore hypothesized that the slow B degradation is determined by either a low catalytic efficiency of BD and DHBDH (the enzymes converting B to catechol) or maybe to a too high catalytic efficiency of them leading to an accumulation of catechol which can be toxic for the cell. This accumulation would justify the need of biosynthesizing high amounts of both C1,2O isozymes during growth on B. In spite of its low degradation rate, B is the preferred carbon source when bacteria are grown on binary (B + P) or ternary substrates mixtures (B + P + acetate). These results suggest that some P or acetate (A) catabolites could play a synergistic role, together with B, in activating the expression of genes involved in B degradation. P degradation , on the contrary, is inhibited by the presence of both A and/or B. Kinetic parameters suggest that the presence of alternative carbon sources (or their catabolites) could repress the expression of the phenol catabolic genes.
Combined proteomic and trascripts analysis to study catabolism of aromatic compounds in acinetobacter radioresistens S13.
MAZZOLI, Roberto;GIUNTA, Carlo;PESSIONE, Enrica
2004-01-01
Abstract
A. radioresistens S13 was isolated in our laboratories from the soil surrounding an activated sludge pilot plant because of its ability to quickly degrade phenol (P) and selected for bioremediation applications. Among aromatic molecules it also can metabolize benzoate (B): both aromatic compounds can be used as the sole carbon and energy source and are degraded through the -ketoadipate pathway. It was previously established that a double set of genes, one for B and the other for P catabolism, is present and two isozymes of catechol 1,2-dioxygenase (C1,2O) have been characterized. Kinetic analysis of A. radioresistens S13 growth shows that P (qp max = 53.8 Cmmol g-1 h-1, YX/phenol = 16.31 g/Cmol) is degraded faster and more efficiently than B (qb max = 49.3 Cmmol g-1 h-1, YX/benzoate = 9.79 g/Cmol). In order to establish whether these differences are due to different expression patterns or rather to different catalytic properties of the catabolic enzymes involved, functional proteomics and transcripts analyses were performed. Both approaches show that the presence of an aromatic substrate is essential to activate biosynthesis of the enzymes of the -ketoadipate route. Surprisingly B induces higher amounts of both isoenzymes of the C1,2O, of muconolactone isomerase (MLI) and of -ketoadipil-CoA thiolase than P, in spite of its lower degradative rate. We therefore hypothesized that the slow B degradation is determined by either a low catalytic efficiency of BD and DHBDH (the enzymes converting B to catechol) or maybe to a too high catalytic efficiency of them leading to an accumulation of catechol which can be toxic for the cell. This accumulation would justify the need of biosynthesizing high amounts of both C1,2O isozymes during growth on B. In spite of its low degradation rate, B is the preferred carbon source when bacteria are grown on binary (B + P) or ternary substrates mixtures (B + P + acetate). These results suggest that some P or acetate (A) catabolites could play a synergistic role, together with B, in activating the expression of genes involved in B degradation. P degradation , on the contrary, is inhibited by the presence of both A and/or B. Kinetic parameters suggest that the presence of alternative carbon sources (or their catabolites) could repress the expression of the phenol catabolic genes.
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