Dextransucrase Expression Is Concomitant with that of Replication and Maintenance Functions of the pMN1 Plasmid in Lactobacillus sakei MN1

Abstract

The exopolysaccharide synthesized by Lactobacillus sakei MN1 is a dextran with antiviral and immunomodulatory properties of potential utility in aquaculture. In this work we have investigated the genetic basis of dextran production by this bacterium. Southern blot hybridization experiments demonstrated the plasmidic location of the dsrLS gene, which encodes the dextransucrase involved in dextran synthesis. DNA sequencing of the 11,126 kbp plasmid (pMN1) revealed that it belongs to a family which replicates by the theta mechanism, whose prototype is pUCL287. The plasmid comprises the origin of replication, repA, repB, and dsrLS genes, as well as seven open reading frames of uncharacterized function. Lb. sakei MN1 produces dextran when sucrose, but not glucose, is present in the growth medium. Therefore, plasmid copy number and stability, as well as dsrLS expression, were investigated in cultures grown in the presence of either sucrose or glucose. The results revealed that pMN1 is a stable low-copy-number plasmid in both conditions. Gene expression studies showed that dsrLS is constitutively expressed, irrespective of the carbon source present in the medium. Moreover, dsrLS is expressed from a monocistronic transcript as well as from a polycistronic repA-repB-orf1-dsrLS mRNA. To our knowledge, this is the first report of a plasmid-borne dextransucrase-encoding gene, as well as the first time that co-transcription of genes involved in plasmid maintenance and replication with a gene encoding an enzyme has been established.

Sucrose-Induced Proteomic Response and Carbohydrate Utilization of Lactobacillus sakei TMW 1.411 During Dextran Formation

“…Nevertheless, it was reported to be a stably inherited low-copy number plasmid, which was attributed to its repA/B based replication mechanism and a possible toxin-antitoxin system. The dextransucrase gene has been proposed to have integrated through a transposition process (Nácher-Vázquez et al, 2017b ). This might once have led to a selective advantage in habitats, where sucrose is the predominant carbon source, such as in plants or in e.g., plant sap sucking insects.…”

“…and Weissella spp. the expression of glucansucrases (e.g., dextransucrases) has been shown to be most often specifically induced by sucrose, many other LAB express glucansucrases independently of sucrose (Kralj et al, 2004 ; Arsköld et al, 2007 ; Bounaix et al, 2010 ; Gänzle and Follador, 2012 ; Harutoshi, 2013 ; Nácher-Vázquez et al, 2017b ).…”

“…This clearly suggested a sucrose-independent expression and agreed with previous experiments, where dextran synthesis by L. sakei TMW 1.411 in buffer solutions was possible even if the cells had been previously cultivated in glucose containing mMRS medium (Prechtl et al, 2018 ). Furthermore, it was demonstrated by gene expression analyses that the plasmid-encoded dextransucrase DsrLS of L. sakei MN1 was constitutively expressed and connected to replication and maintenance functions of the plasmid pMN1 (Nácher-Vázquez et al, 2017b ). Since pMN1 and p-1.411_1 were shown to be more or less identical (Table 2 ), these results should be transferable to the expression of Dsr1411 in L. sakei TMW 1.411.…”

Different Modes of Regulation of the Expression of Dextransucrase in Leuconostoc lactis AV1n and Lactobacillus sakei MN1

“…mesenteroides NRRL B-512F dsrLM gene and not of the Lb. sakei MN1 dsrLS gene takes place (Quirasco et al, 1999; Nácher-Vázquez et al, 2017b).…”

Oenococcus oeni Exopolysaccharide Biosynthesis, a Tool to Improve Malolactic Starter Performance

“…The dextransucrase gene dsrO is not induced by sucrose, contrarily to what described in Leuconostoc mesenteroides or other glycoside hydrolase in lactic bacteria (Neely and Nott, 1962 ; Quirasco et al, 1999 ; Schwab and Gänzle, 2006 ) and O. oeni behave similarly Lactobacillus sakei or Weisella confusa (Bounaix et al, 2010 ; Nácher-Vázquez et al, 2017 ), or even Leuconostoc mesenteroides NRRL_1299 for minor dextransucrases (Dols et al, 1998 ). Taking into consideration the unusual presence of sucrose in the usual environment of O. oeni , the constitutive expression of dsrO is quite surprising and suggests that O. oeni must always be prepared to produce dextran and that dextran is very useful for the bacteria.…”