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A novel bacterial strain that was capable of growing on the [beta]-tripeptide H-[beta]hVal-[beta]hAla-[beta]hLeu-OH as the sole carbon and nitrogen source was isolated from an enrichment culture. On the basis of physiological characterization, partial 16S rRNA sequencing, and fatty acid analysis, strain 3-2W4 was identified as a member of the family Sphingomonadaceae. Growth on the [beta]-tripeptide and the [beta]-dipeptide H-[beta]hAla-[beta]hLeu-OH was observed, and emerging metabolites were characterized. Small amounts of a persisting metabolite, the N-acetylated [beta]-dipeptide, were identified in both media. According to dissolved organic carbon measurements, 74 to 80% of the available carbon was dissimilated. The [beta]-peptide-degrading enzyme was purified from the crude cell extract of cells from strain 3-2W4 grown on complex medium. The enzyme was composed of two subunits, and the N-terminal sequences of both were determined. With this information, it was possible to identify the complete nucleotide sequence and to deduce the primary structure of the gene bapA. The gene encoded a [beta]-peptidyl aminopeptidase (BapA) of 402 amino acids that was synthesized as preprotein with a signal sequence of 29 amino acids. The enzyme was cleaved into two subunits (residues 30 to 278 and 279 to 402). It belonged to the N-terminal nucleophile (Ntn) hydrolase superfamily.

Two operons of the hbpCAD gene cluster are independently regulated and their expression is mediated by HbpR protein, which requires RNA polymerase-sigma(sup)54 and an integration host factor for complete activation. The transcriptional organization of the gene cluster facilitates orderly expression of the hbp genes and 2-hydroxybiphenyl degradation pathway.

Research has been conducted on the 2-hydroxybiphenyl and 2,2'-dihydroxybiphenyl degradationin Pseudomonas azelaica. The regulation of this degradation by the regulatory gene hbpR is discussed.

A study was conducted on whether Sphingomonas herbicidovorans initiates degradation of mecoprop by two alpha-ketoglutarate-dependent dioxygenase activities. The findings lend support to this hypothesis. Comparison of the conversion rates of different phenoxy herbicides showed that the two enzyme activities were distinct from that of TfdA, which catalyzes the first step in the degradation of 2,4-dichlorophenoxyacetic acid in Ralstonia eutropha JMP134.

Pseudomonas strain HBP1 cells cultured in a medium containing 2-hydroxy- or 2,2'-dihydroxybiphenyl was demonstrated to contain a functional monooxygenase activity dependent on NADH. Monooxygenase action on 2,2'-dihydroxybiphenyl yields 2,2',3-trihydroxybiphenyl which can also act as amonooxygenase substrate in a hydroxylation reaction that generates 2,2',3,3'-tetrahydroxybiphenyl. Catabolism of either 2,2',3-trihydroxybiphenyl or 2,2',3,3'-tetrahydroxybiphenyl is mediated via scission reactions. A characterization of the cleavage products is presented.