Identification of a Gene Cluster EnablingLactobacillus caseiBL23 To Utilizemyo-Inositol

Abstract

Genome analysis of Lactobacillus casei BL23 revealed that, compared to L. casei ATCC 334, it carries a 12.8-kb DNA insertion containing genes involved in the catabolism of the cyclic polyol myo-inositol (MI). Indeed, L. casei ATCC 334 does not ferment MI, whereas strain BL23 is able to utilize this carbon source. The inserted DNA consists of an iolR gene encoding a DeoR family transcriptional repressor and a divergently transcribed iolTABCDG1G2EJK operon, encoding a complete MI catabolic pathway, in which the iolK gene probably codes for a malonate semialdehyde decarboxylase. The presence of iolK suggests that L. casei has two alternative pathways for the metabolism of malonic semialdehyde: (i) the classical MI catabolic pathway in which IolA (malonate semialdehyde dehydrogenase) catalyzes the formation of acetyl-coenzyme A from malonic semialdehyde and (ii) the conversion of malonic semialdehyde to acetaldehyde catalyzed by the product of iolK. The function of the iol genes was verified by the disruption of iolA, iolT, and iolD, which provided MI-negative strains. By contrast, the disruption of iolK resulted in a strain with no obvious defect in MI utilization. Transcriptional analyses conducted with different mutant strains showed that the iolTABCDG1G2EJK cluster is regulated by substrate-specific induction mediated by the inactivation of the transcriptional repressor IolR and by carbon catabolite repression mediated by the catabolite control protein A (CcpA). This is the first example of an operon for MI utilization in lactic acid bacteria and illustrates the versatility of carbohydrate utilization in L. casei BL23.myo-Inositol (MI) is the most abundant stereoisomer of inositol (1,2,3,4,5,6-cyclohexanehexol). It is common in soils, and it is a constituent of phytic acid (inositol hexaphosphate), which in the form of various salts (phytates) provides a major phosphate storage molecule in plant seeds. Several microorganisms, mostly inhabitants of soil, can utilize MI as a carbon source. For bacteria, the MI catabolic pathway has been elucidated for Enterobacter aerogenes (formerly Aerobacter aerogenes) (3). MI is important for the establishment of symbiosis in legume nodules. The metabolism of MI in Sinorhizobium fredii and Rhizobium leguminosarum is required for efficient nitrogen fixation and nodulation of soybeans (9, 15). MI dehydrogenase genes (e.g., iolG) and inosose dehydratase genes (iolE) have been characterized in S. fredii and Sinorhizobium meliloti (10, 15, 36), and iolA and iolDEB genes have been studied in R. leguminosarum (9). An MI utilization gene cluster has also been described for Clostridium perfringens, which was induced by MI via the IolR regulator (16), and recently, transcriptome analysis permitted the identification of an iol cluster which allowed the rapid growth of Corynebacterium glutamicum on MI (19). However, the first MI catabolic gene cluster was characterized in Bacillus subtilis, and detailed molecular data are available only for this bacterium. The B. subtilis iolRS and iolABC...

myo-Inositol Catabolism in Bacillus subtilis

“…However, its 1 H NMR spectra clearly revealed that the product was DKGP (compound [8]) in Figs. 1 and 3; 1 H 5DG (α-amoner) IolD reaction products turned out to be an equimolar mixture of compound [12] and [13] (with carbon and proton numbering).…”

“…viciae (4), Sinorhizobium meliloti (5), Sinorhizobium fredii (6), Corynebacterium glutamicum (7), and Lactobacillus casei (8) can grow on MI as the sole carbon source. MI catabolism in A. aerogenes was studied biochemically, and a pathway of the catabolism finally yielding acetyl-CoA and dihydroxyacetone phosphate (DHAP) was proposed (9).…”

myo-Inositol transport by Salmonella enterica serovar Typhimurium

“…Genetic comparison and computational analysis of iol divergons have been performed recently (Boutte et al, 2008;Kröger & Fuchs, 2009). A phylogenetic analysis of iol genes from L. casei is also available (Yebra et al, 2007). We investigated whether, and to what degree of similarity, IolT homologues are present in other bacterial genomes.…”

“…Two proteins belonging to the major facilitator superfamily (MFS), IolT and IolF, have been identified as the major and minor inositol transporters of B. subtilis, and IolR has been revealed to inhibit the transcription of iolT (Yoshida et al, 2002). MI degradation has also been studied in Corynebacterium glutamicum (Krings et al, 2006), Clostridium perfringens (Kawsar et al, 2004) and Lactobacillus casei (Yebra et al, 2007).…”

GntR family regulator SCO6256 is involved in antibiotic production and conditionally regulates the transcription of myo-inositol catabolic genes in Streptomyces coelicolor A3(2)

“…Although the regulation of myo-inositol catabolism has been extensively studied in some bacteria (Boutte et al, 2008;Yebra et al, 2007;Yoshida et al, 1999), the regulatory mechanism is poorly understood in Streptomyces. In our previous works, the myo-inositol catabolic gene cluster has been identified in Strep.…”