Affiliation:
1. Faculty of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki, Japan
Abstract
ABSTRACT
The actinobacterium
Microbacterium maritypicum
splits riboflavin (vitamin B
2
) into lumichrome and
d
-ribose. However, such degradation by other bacteria and the involvement of a two-component flavin-dependent monooxygenase (FMO) in the reaction remain unknown. Here we investigated the mechanism of riboflavin degradation by the riboflavin-assimilating alphaproteobacterium
Devosia riboflavina
(formerly
Pseudomonas riboflavina
). We found that adding riboflavin to bacterial cultures induced riboflavin-degrading activity and a protein of the FMO family that had 67% amino acid identity with the predicted riboflavin hydrolase (RcaE) of
M. maritypicum
MF109. The
D. riboflavina
genome clustered genes encoding the predicted FMO, flavin reductase (FR), ribokinase, and flavokinase, and riboflavin induced their expression. This finding suggests that these genes constitute a mechanism for utilizing riboflavin as a carbon source. Recombinant FMO (rFMO) protein of
D. riboflavina
oxidized riboflavin in the presence of reduced flavin mononucleotide (FMN) provided by recombinant FR (rFR), oxidized FMN and NADH, and produced stoichiometric amounts of lumichrome and
d
-ribose. Further investigation of the enzymatic properties of
D. riboflavina
rFMO indicated that rFMO-rFR coupling accompanied O
2
consumption and the generation of enzyme-bound hydroperoxy-FMN, which are characteristic of two-component FMOs. These results suggest that
D. riboflavina
FMO is involved in hydroperoxy-FMN-dependent mechanisms to oxygenize riboflavin and a riboflavin monooxygenase is necessary for the initial step of riboflavin degradation.
IMPORTANCE
Whether bacteria utilize either a monooxygenase or a hydrolase for riboflavin degradation has remained obscure. The present study found that a novel riboflavin monooxygenase, not riboflavin hydrolase, facilitated this process in
D. riboflavina
. The riboflavin monooxygenase gene was clustered with flavin reductase, flavokinase, and ribokinase genes, and riboflavin induced their expression and riboflavin-degrading activity. The gene cluster is uniquely distributed in
Devosia
species and actinobacteria, which have exploited an environmental niche by developing adaptive mechanisms for riboflavin utilization.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
6 articles.
订阅此论文施引文献
订阅此论文施引文献,注册后可以免费订阅5篇论文的施引文献,订阅后可以查看论文全部施引文献