Genes encoding the candidate enzyme for anaerobic activation of n ‐alkanes in the denitrifying bacterium, strain HxN1

Abstract

Summary Strain HxN1, a member of the Betaproteobacteria , can grow anaerobically by denitrification with n ‐alkanes. n ‐Alkanes are apparently activated by subterminal carbon addition to fumarate yielding (1‐methylalkyl)succinates, the postulated enzyme being (1‐methylalkyl)succinate synthase (Mas). Genes encoding this enzyme ( mas ) were searched for via proteins that were specifically formed in n ‐hexane‐grown cells (in comparison with caproate‐grown cells), as revealed by two‐dimensional gel electrophoresis. Partial amino acid sequencing and subsequent probe development for hybridization of restricted DNA led to the identification of a gene cluster. Deduced proteins are similar to the subunits of benzylsuccinate synthase (Bss), the toluene‐activating enzyme in other anaerobic bacteria and its activase. The tentative (1‐methylalkyl)succinate synthase is presumably a heterotrimer (MasDEC) which, like benzylsuccinate synthase, contains a motif (in MasD, the large subunit) characteristic of glycyl radical‐bearing sites. Based on amino acid sequence comparison, the tentative (1‐methylalkyl)succinate synthase branches outside of the phylogenetic cluster of benzylsuccinate synthases from different organisms and represents a separate line of descent within glycyl radical enzymes. n ‐Hexane‐induced co‐transcription of the mas genes and additional genes of an apparent operon was demonstrated by Northern hybridization experiments.

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