Identification and characterization of a new beta-glucoside utilization system in Bacillus subtilis

Abstract

A new catabolic system in Bacillus subtilis involved in utilization of ␤-glucosidic compounds has been investigated. It consists of five genes encoding phosphotransferase system (PTS) enzyme II (licB and licC) and enzyme IIA (licA), a presumed 6-phospho-␤-glucosidase (licH), as well as a putative regulator protein (licR). The genes map around 334؇ of the B. subtilis chromosome, and their products are involved in the uptake and utilization of lichenan degradation products. These five genes are organized in two transcriptional units. A weak promoter precedes gene licR, and transcription is obviously terminated at a secondary structure immediately downstream of the reading frame, as shown by Northern RNA blot analysis. Genes licB, licC, licA, and licH constitute an operon. Initiation of transcription at the promoter in front of this operon presumably requires activation by the gene product of licR. The LicR protein shows an unusual domain structure, i.e., similarities to (i) the conserved transcriptional antiterminator BglG family signature and (ii) PTS enzyme II. Using RNA techniques and transcriptional lacZ fusions, we have shown that the expression of the licBCAH operon is inducible by products of lichenan hydrolysis, lichenan and cellobiose. The presence of excess glucose prevents the induction of this operon, indicating the control by carbon catabolite repression. Moreover, the expression of the operon requires the general PTS components and seems to be negatively controlled by the specific lic PTS enzymes.

Carbon Catabolite Control of the Metabolic Network inBacillus subtilis

“…Inactivation of pstI and ptsH completely prevented LicR activity, whereas mutants devoid of LicA (EIIA Cel ) or LicB (EIIB Cel ) exhibited constitutive expression from the lic promoter. 150) B. subtilis MtlR is the regulator of the mtlAFD operon encoding the PTS for mannitol, 151) and it specifically interacts with DNA regions containing the mtl promoter. 152) Disruption of the mtlR gene prevented the utilization of mannitol, indicating that MtlR functions as a transcription activator of the mtlAFD operon.…”

The LicT protein acts as both a positive and a negative regulator of loci within the bgl regulon of Streptococcus mutans

“…b-Glucoside-utilization systems have been described in several bacteria, including Escherichia coli (Ausubel et al, 2001), Erwinia chrysanthemi (el Hassouni et al, 1990), Clostridium longisporum (Brown & Thomson, 1998), Lactobacillus plantarum (Marasco et al, 2000), Bacillus subtilis (Le Coq et al, 1995;Tobisch et al, 1997) and Streptococcus mutans (Cote et al, 2000). These organisms rely on the phosphoenolpyruvate-dependent phosphotransferase system (PTS) (Postma & Lengeler, 1985) for the transport and the subsequent utilization of various b-glucosides.…”

“…Antiterminator proteins are believed to be involved in the transcriptional regulation of b-glucoside-specific genes from Escherichia coli (Hall & Xu, 1992), Erwinia chrysanthemi (el Hassouni et al, 1990), Lactococcus lactis (Bardowski et al, 1994), Lactobacillus plantarum (Marasco et al, 2000), B. subtilis (Le Coq et al, 1995;Tobisch et al, 1997) and C. longisporum (Brown & Thomson, 1998). It is believed that these antiterminator proteins would bind to a ribonucleic antiterminator (RAT) site present in a specific mRNA secondary structure and would prevent the formation of a hairpin terminator structure that terminates transcription (Rutberg, 1997).…”

Molecular analysis of the mannitol operon of Clostridium acetobutylicum encoding a phosphotransferase system and a putative PTS-modulated regulator

“…MtlR of C. acetobutylicum exhibits greatest identity (25n4 %) to the MtlR protein of B. stearothermophilus (Henstra et al, 1999). Similar transcriptional regulators are encoded within the lic (lichenan) operon of B. subtilis (LicR ; Tobisch et al, 1997), by the ydaA gene of B. subtilis, for which the name mtlR has recently been proposed (Stu$ lke et al, 1998), and by the mtlR and srlR genes of the Streptococcus mutans mannitol and sorbitol operons respectively (Honeyman & Curtiss, 2000 ;Boyd et al, 2000). The central part of MtlR comprises two PTS regulatory domains (PRDs), which are found in each of these proteins, as well as in the B. subtilis transcriptional regulator LevR and in transcriptional antiterminator proteins of the BglG family (Tortosa et al, 1997 ;Stu$ lke et al, 1998).…”