Genetic characterization of the CcpA-dependent, cellobiose-specific PTS system comprising CelB, PtcB and PtcA that transports lactose in Lactococcus lactis IL1403

Abstract

Lactose metabolism is one of the most important areas of research on Lactic Acid Bacteria (LAB). In rapidly acidifying industrial Lactococcus lactis strains, lactose is transported by a lactose-specific phosphotransferase system (PTS) encoded by a plasmid. However, an alternative lactose catabolic pathway was evidenced in the plasmid-cured, and thus initially lactose-negative L. lactis IL1403. We showed that in this strain the chromosomally-encoded cellobiose-specific PTS system comprising the celB, ptcB and ptcA genes is also able to transport lactose. By expression studies in the wild type IL1403 strain and IBB550, its ccpA-deficient derivative, we demonstrated that celB, ptcB and ptcA are tightly regulated by the general catabolite repression system, whereas celB additionally requires the presence of cellobiose to be fully induced. The comparison of expression levels of sugar catabolic genes indicated that the efficiency of CcpA-mediated catabolic repression depends on conservation of the cre sequence, and that in the case of perfect matching with the cre consensus, CcpA still drives a strong repression even under non-repressing conditions.

Lactose and β-Glucosides Metabolism and Its Regulation in Lactococcus lactis: A Review

“…4.A.3), which includes several lactose porters of Gram-positive bacteria as well as the E. coli and Borrelia burgdorferi N,N'-diacetylchitobiose (Chb) porters (according to http://www.tcdb.org/). The involvement of CelB and CelB/PtcC permeases in cellobiose transport has been experimentally confirmed in L. lactis IL1403 and MG1363, respectively (Aleksandrzak-Piekarczyk et al, 2011;Campelo et al, 2011). Although L. lactis IL1403 has such a large number of -glucosidesspecific PTS systems, CelB is the only permease operative in cellobiose uptake in this strain (Aleksandrzak-Piekarczyk et al, 2011) (Fig.…”

“…The involvement of CelB and CelB/PtcC permeases in cellobiose transport has been experimentally confirmed in L. lactis IL1403 and MG1363, respectively (Aleksandrzak-Piekarczyk et al, 2011;Campelo et al, 2011). Although L. lactis IL1403 has such a large number of -glucosidesspecific PTS systems, CelB is the only permease operative in cellobiose uptake in this strain (Aleksandrzak-Piekarczyk et al, 2011) (Fig. 1), whereas in L. lactis MG1363 also another PTS permease, namely PtcC, seems to participate in the transport of this sugar, albeit to a much lesser extent than CelB (Campelo et al, 2011).…”

“…It is well known from sugar fermentation characteristics that L. lactis strains of different origin can utilize a variety of -glucosides (e.g., Aleksandrzak-Piekarczyk et al, 2011;Bardowski et al, 1995;Fernández et al, 2011;Siezen et al, 2008). The metabolic potential for catabolism of these sugars can be chromosomally encoded by more than one genetic system, as was shown for L. lactis IL1403.…”

“…On the other hand, the EIIAB components, namely PtcA and PtcB, seem to be more versatile, being involved in the metabolism of numerous sugars (arbutin, cellobiose, glucose, lactose, salicin) in L. lactis (Aleksandrzak-Piekarczyk et al, 2011;Castro et al, 2009;Pool et al, 2006). No other PTS systems dedicated to transport of other -glucosides have yet been described in detail in any L. lactis strain.…”

“…It exerts its regulatory role in carbon catabolite repression (CCR) by binding to DNA sites called cres, which occur in the vicinity of CcpAregulated genes (Weickert & Chambliss, 1990). In L. lactis the known targets of CcpA are the gal operon for galactose utilization (Luesink et al, 1998), the fru operon for fructose utilization (Barrière et al, 2005), the ptcABC operon for cellobiose utilization , and cel-lac genes for cellobiose and lactose utilization (Aleksandrzak-Piekarczyk et al, 2011). Thus, one could speculate that in L. lactis IL1403 cellobiose-inducible chromosomal alternative lactose utilization genes are under the negative control of CcpA, and, therefore, inactivation of the ccpA gene could result in their derepression and ability to assimilate lactose by the IL1403 ccpA mutant.…”