Abstract
BackgroundThe amino acid-producing Gram-positive Corynebacterium glutamicum is auxotrophic for biotin although biotin ring assembly starting from the precursor pimeloyl-CoA is still functional. It possesses AccBC, the α-subunit of the acyl-carboxylases involved in fatty acid and mycolic acid synthesis, and pyruvate carboxylase as the only biotin-containing proteins. Comparative genome analyses suggested that the putative transport system BioYMN encoded by cg2147, cg2148 and cg2149 might be involved in biotin uptake by C. glutamicum.ResultsBy comparison of global gene expression patterns of cells grown with limiting or excess supply of biotin or with dethiobiotin as supplement replacing biotin revealed that expression of genes coding for enzymes of biotin ring assembly and for the putative uptake system was regulated according to biotin availability. RT-PCR and 5'-RACE experiments demonstrated that the genes bioY, bioM, and bioN are transcribed from one promoter as a single transcript. Biochemical analyses revealed that BioYMN catalyzes the effective uptake of biotin with a concentration of 60 nM biotin supporting a half-maximal transport rate. Maximal biotin uptake rates were at least five fold higher in biotin-limited cells as compared to cells grown with excess biotin. Overexpression of bioYMN led to an at least 50 fold higher biotin uptake rate as compared to the empty vector control. Overproduction of BioYMN alleviated biotin limitation and interfered with triggering L-glutamate production by biotin limitation.ConclusionsThe operon bioYMN from C. glutamicum was shown to be induced by biotin limitation. Transport assays with radio-labeled biotin revealed that BioYMN functions as a biotin uptake system. Overexpression of bioYMN affected L-glutamate production triggered by biotin limitation.
Highlights
The amino acid-producing Gram-positive Corynebacterium glutamicum is auxotrophic for biotin biotin ring assembly starting from the precursor pimeloyl-CoA is still functional
In E. coli, malonyl-CoA methyl ester is generated by SAM-dependent methyltransferase BioC as a primer molecule and afterwards elongated in fatty acid biosynthesis to yield methyl-pimeloyl-ACP which is demethylated by carboxylesterase BioH [5]
Parallel cultures of C. glutamicum WT were grown in CGXII with glucose and either with 1, 200, or 20,000 μg/l biotin (1 μg/l and 20,000 μg/l referred to below as biotin limitation and biotin excess, respectively)
Summary
The amino acid-producing Gram-positive Corynebacterium glutamicum is auxotrophic for biotin biotin ring assembly starting from the precursor pimeloyl-CoA is still functional. It possesses AccBC, the asubunit of the acyl-carboxylases involved in fatty acid and mycolic acid synthesis, and pyruvate carboxylase as the only biotin-containing proteins. In B. subtilis, pimeloyl-CoA is generated by interception of fatty acid biosynthesis by P450-dependent BioI, which yields pimeloyl-ACP chains by oxidative cleavage of long-chain acyl-ACPs [4]. In E. coli, malonyl-CoA methyl ester is generated by SAM-dependent methyltransferase BioC as a primer molecule and afterwards elongated in fatty acid biosynthesis to yield methyl-pimeloyl-ACP which is demethylated by carboxylesterase BioH [5]. Other sources of pimeloylCoA are externally added pimelic acid which is activated by pimeloyl-CoA synthetase as e.g. in B. subtilis, yet uncharacterized biosynthetic pathways as proposed e.g. for Desulfovibrio species [6] or degradation of benzene as e.g. in Rhodopseudomonas palustris [7]
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