Gene cloning system for sulfonamide-mineralizing Microbacterium sp. strain BR1.

The wide application of sulfonamide (SA) antibiotics in human and veterinary medicine contributes to the accumulation of these antibiotics in the environment and the corresponding onset of antibiotic resistance among bacteria. Microbacterium sp. BR1 is capable of mineralizing sulfamethoxazole and other SAs via a novel mechanism. The genetic basis of SA elimination by BR1 remains unknown. Development of an efficient plasmid transfer protocol for Microbacterium sp. BR1 is highly desirable, as it would open the door to genetic analysis and manipulation of its genome. Here we report that intergeneric Escherichia coli-Microbacterium spp. BR1 conjugation is an efficient way to introduce various plasmids into BR1. The generated transconjugants were stable in the presence of antibiotics and the plasmids showed no signs of rearrangements. Nevertheless, the plasmids were rapidly lost in the absence of selection. We also show that the cumate-inducible beta-glucuronidase reporter gene functions in BR1 and is strictly regulated. Our results set the working ground for further genetic manipulations of BR1, such as the overexpression of sulfonamide degradation genes or the selection of strong microbacterial promoters.

The degradation of alkylphenols by Sphingomonas sp. strain TTNP3 - a review on seven years of research.

Over the past seven years, we have been working with Sphingomonas sp. strain TTNP3, a bacterium capable of growing on numerous alkylphenolic compounds as a source of carbon and energy. We succeeded in elucidating an unusual pathway involving an attack at the quaternary alpha-carbon atom of the substrate, a position previously thought to be highly resistant to biodegradation. Combining analytical and bioanalytical methods, a good understanding of the reaction mechanisms, the enzymes catalysing them and the organization of the genes encoding them could be gained. First studies on the use of Sphingomonas sp. strain TTNP3 in wastewater treatment have been performed revealing promising results.

Identification of the flavin monooxygenase responsible for ipso substitution of alkyl and alkoxyphenols in Sphingomonas sp. TTNP3 and Sphingobium xenophagum Bayram.

We previously showed that opdA from Sphingomonas sp. PWE1 encodes a putative flavin monooxygenase capable of transforming octylphenol (OP) via type II ipso substitution. Here, we demonstrate that an opdA homolog is responsible for OP and related alkyl/alkoxyphenol degradation in the nonylphenol degrader Sphingomonas sp. TTNP3. PCR and Southern blot analyses revealed that TTNP3 contained an opdA homolog, while a TTNP3 derivative unable to grow on nonylphenol (TTNP3d) did not. OpdA expression was confirmed in wild-type TTNP3 via two dimensional gel electrophoresis. Activity was restored to TTNP3d following complementation with opdA. Sequence analysis of an opdA homolog from another nonylphenol degrader, Sphingobium xenophagum Bayram, revealed that the predicted protein sequences from PWE1 and Bayram were identical, but differed from TTNP3 by four amino acids. In order to assess differences, we heterologously expressed the two unique opdA homologs and compared their effect on the disappearance of five alkyl/alkoxyphenol substrates and subsequent appearance of hydroquinone. For all substrates, except OP, the levels of substrate disappearance and hydroquinone appearance were significantly lower in cultures expressing odpA (TTNP3) than those expressing opdA (PWE1/Bayram). These differences in substrate specificity were consistent with an in silico model which predicted that two of the amino acid differences between odpA (TTNP3) and opdA (PWE1/Bayram) lay in a putative substrate binding pocket. While these strains are known to use the same type II ipso substitution mechanism for alkylphenol degradation, this work provides the first preliminary evidence that opdA homologs also encode the type I ipso substitution activity responsible for the degradation of alkoxyphenols.

Degradation pathway of bisphenol A: does ipso substitution apply to phenols containing a quaternary alpha-carbon structure in the para position?

The degradation of bisphenol A and nonylphenol involves the unusual rearrangement of stable carbon-carbon bonds. Some nonylphenol isomers and bisphenol A possess a quaternary alpha-carbon atom as a common structural feature. The degradation of nonylphenol in Sphingomonas sp. strain TTNP3 occurs via a type II ipso substitution with the presence of a quaternary alpha-carbon as a prerequisite. We report here a new degradation pathway of bisphenol A. Consequent to the hydroxylation at position C-4, according to a type II ipso substitution mechanism, the C-C bond between the phenolic moiety and the isopropyl group of bisphenol A is broken. Besides the formation of hydroquinone and 4-(2-hydroxypropan-2-yl)phenol as the main metabolites, further compounds resulting from molecular rearrangements consistent with a carbocationic intermediate were identified. Assays with resting cells or cell extracts of Sphingomonas sp. strain TTNP3 under an (18)O(2) atmosphere were performed. One atom of (18)O(2) was present in hydroquinone, resulting from the monooxygenation of bisphenol A and nonylphenol. The monooxygenase activity was dependent on both NADPH and flavin adenine dinucleotide. Various cytochrome P450 inhibitors had identical inhibition effects on the conversion of both xenobiotics. Using a mutant of Sphingomonas sp. strain TTNP3, which is defective for growth on nonylphenol, we demonstrated that the reaction is catalyzed by the same enzymatic system. In conclusion, the degradation of bisphenol A and nonylphenol is initiated by the same monooxygenase, which may also lead to ipso substitution in other xenobiotics containing phenol with a quaternary alpha-carbon.