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Acid-inducible transcription of the operon encoding the citrate lyase complex of Lactococcus lactis Biovar diacetylactis CRL264.

ABSTRACT: Although Lactococcus is one of the most extensively studied lactic acid bacteria and is the paradigm for biochemical studies of citrate metabolism, little information is available on the regulation of the citrate lyase complex. In order to fill this gap, we characterized the genes encoding the subunits of the citrate lyase of Lactococcus lactis CRL264, which are located on an 11.4-kb chromosomal DNA region. Nucleotide sequence analysis revealed a cluster of eight genes in a new type of genetic organization. The citM-citCDEFXG operon (cit operon) is transcribed as a single polycistronic mRNA of 8.6 kb. This operon carries a gene encoding a malic enzyme (CitM, a putative oxaloacetate decarboxylase), the structural genes coding for the citrate lyase subunits (citD, citE, and citF), and the accessory genes required for the synthesis of an active citrate lyase complex (citC, citX, and citG). We have found that the cit operon is induced by natural acidification of the medium during cell growth or by a shift to media buffered at acidic pHs. Between the citM and citC genes is a divergent open reading frame whose expression was also increased at acidic pH, which was designated citI. This inducible response to acid stress takes place at the transcriptional level and correlates with increased activity of citrate lyase. It is suggested that coordinated induction of the citrate transporter, CitP, and citrate lyase by acid stress provides a mechanism to make the cells (more) resistant to the inhibitory effects of the fermentation product (lactate) that accumulates under these conditions.

SUBMITTER: Martin MG

PROVIDER: S-EPMC516808 | biostudies-literature | 2004 Sep

REPOSITORIES: biostudies-literature

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Acid-inducible transcription of the operon encoding the citrate lyase complex of Lactococcus lactis Biovar diacetylactis CRL264.

Martín Mauricio G MG Sender Pablo D PD Peirú Salvador S de Mendoza Diego D Magni Christian C

Journal of bacteriology 20040901 17

Although Lactococcus is one of the most extensively studied lactic acid bacteria and is the paradigm for biochemical studies of citrate metabolism, little information is available on the regulation of the citrate lyase complex. In order to fill this gap, we characterized the genes encoding the subunits of the citrate lyase of Lactococcus lactis CRL264, which are located on an 11.4-kb chromosomal DNA region. Nucleotide sequence analysis revealed a cluster of eight genes in a new type of genetic o ...[more]

PMID: 15317769

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Project description:BACKGROUND:Important industrial traits have been linked to plasmids in Lactococcus lactis. RESULTS:The dairy isolate L. lactis subsp. lactis biovar diacetylactis FM03P was sequenced revealing the biggest plasmidome of all completely sequenced and published L. lactis strains up till now. The 12 plasmids that were identified are: pLd1 (8277 bp), pLd2 (15,218 bp), pLd3 (4242 bp), pLd4 (12,005 bp), pLd5 (7521 bp), pLd6 (3363 bp), pLd7 (30,274 bp), pLd8 (47,015 bp), pLd9 (15,313 bp), pLd10 (39,563 bp), pLd11 (9833 bp) and pLd12 (3321 bp). Structural analysis of the repB promoters and the RepB proteins showed that eleven of the plasmids replicate via the theta-type mechanism, while only plasmid pLd3 replicates via a rolling-circle replication mechanism. Plasmids pLd2, pLd7 and pLd10 contain a highly similar operon involved in mobilisation of the plasmids. Examination of the twelve plasmids of L. lactis FM03P showed that 10 of the plasmids carry putative genes known to be important for growth and survival in the dairy environment. These genes encode technological functions such as lactose utilisation (lacR-lacABCDFEGX), citrate uptake (citQRP), peptide degradation (pepO and pepE) and oligopeptide uptake (oppDFBCA), uptake of magnesium and manganese (2 mntH, corA), exopolysaccharides production (eps operon), bacteriophage resistance (1 hsdM, 1 hsdR and 7 different hsdS genes of a type I restriction-modification system, an operon of three genes encoding a putative type II restriction-modification system and an abortive infection gene) and stress resistance (2 uspA, cspC and cadCA). Acquisition of these plasmids most likely facilitated the adaptation of the recipient strain to the dairy environment. Some plasmids were already lost during a single propagation step signifying their instability in the absence of a selective pressure. CONCLUSIONS:Lactococcus lactis FM03P carries 12 plasmids important for its adaptation to the dairy environment. Some of the plasmids were easily lost demonstrating that propagation outside the dairy environment should be minimised when studying dairy isolates of L. lactis.

Dataset Information

Acid-inducible transcription of the operon encoding the citrate lyase complex of Lactococcus lactis Biovar diacetylactis CRL264.

Publications

Acid-inducible transcription of the operon encoding the citrate lyase complex of Lactococcus lactis Biovar diacetylactis CRL264.

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