Bacillus subtilis can utilize maltose and maltodextrins that are derived from polysaccharides, like starch or glycogen. In this work, we show that maltose is taken up by a member of the phosphoenolpyruvate-dependent phosphotransferase system and maltodextrins are taken up by a maltodextrin-specific ABC transporter. Uptake of maltose by the phosphoenolpyruvate-dependent phosphotransferase system is mediated by maltosespecific enzyme IICB (MalP; synonym, GlvC), with an apparent K m of 5 M and a V max of 91 nmol · min ؊1 · (10 10 CFU) ؊1 . The maltodextrin-specific ABC transporter is composed of the maltodextrin binding protein MdxE (formerly YvdG), with affinities in the low micromolar range for maltodextrins, and the membranespanning components MdxF and MdxG (formerly YvdH and YvdI, respectively), as well as the energizing ATPase MsmX. Maltotriose transport occurs with an apparent K m of 1.4 M and a V max of 4.7 nmol · min ؊1

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MalT is the central transcriptional activator of all mal genes in Escherichia coli. Its activity is controlled by the inducer maltotriose. It can be inhibited by the interaction with certain proteins, and its expression can be controlled. We report here a novel aspect of mal gene regulation: the effect of cytoplasmic glucose and glucokinase (Glk) on the activity and the expression of MalT. Amylomaltase (MalQ) is essential for the metabolism of maltose. It forms maltodextrins and glucose from maltose or maltodextrins. We found that glucose above a concentration of 0.1 mM blocked the activity of the enzyme. malQ mutants when grown in the absence of maltodextrins are endogenously induced by maltotriose that is derived from the degradation of glycogen. Therefore, the fact that glk malQ ؉ mutants showed elevated mal gene expression finds its explanation in the reduced ability to remove glucose from MalQ-catalyzed maltodextrin formation and is caused by a metabolically induced MalQ ؊ phenotype. However, even in mutants lacking glycogen, Glk controls endogenous induction. We found that overexpressed Glk due to its structural similarity with Mlc, the repressor of malT, binds to the glucose transporter (PtsG), releasing Mlc and thus increasing malT repression. In addition, even in mutants lacking Mlc (and glycogen), the overexpression of glk leads to a reduction in mal gene expression. We interpret this repression by a direct interaction of Glk with MalT concomitant with MalT inhibition. This repression was dependent on the presence of either maltodextrin phosphorylase or amylomaltase and led to the inactivation of MalT.The Escherichia coli maltose system (4, 52) is geared for the efficient utilization of maltose and maltodextrins. Ten mal genes encode proteins found in all compartments of the cell. The lambda receptor in the outer membrane (43,49) facilitates the diffusion of maltodextrins into the periplasmic space, where they are taken up into the cytoplasm via a bindingprotein-dependent ABC transporter (32, 55). There are two main enzymes catalyzing the degradation of maltose and maltodextrins to glucose and ␣-glucose-1-phosphate. Amylomaltase (MalQ) (29), a maltodextrin glucanotransferase (41, 59), forms from any maltodextrin, including maltose, larger maltodextrins, and glucose (16,34,60). Maltotetraose and longer maltodextrins are substrates of the maltodextrin phosphorylase (MalP) (53, 58), yielding by phosphorolysis ␣-glucose-1-phosphate and smaller maltodextrins. Two other enzymes are a periplasmic amylase (MalS) (20, 51) and a cytoplasmic maltodextrin glucosidase (MalZ) that are not essential for maltose or maltodextrin utilization (44,51,57). While MalS produces preferentially maltohexaose from longer maltodextrins in the periplasm, MalZ degrades longer maltodextrins by cleaving glucose from the reducing end of the dextrins in the cytoplasm. The smallest substrate of MalZ is maltotriose, producing maltose and glucose. All mal genes are under the positive control of MalT (45), which in turn is activated by the...

A gene coding for a putative α-glucosidase has been identified in the open reading frame yvdL (now termed malL), which was sequenced as part of the Bacillus subtilis genome project. The enzyme was overproduced in Escherichia coliand purified. Further analyses indicate that MalL is a specific oligo-1,4-1,6-α-glucosidase (sucrase-maltase-isomaltase). MalL expression in B. subtilis requires maltose induction and is subject to carbon catabolite repression by glucose and fructose. Insertional mutagenesis of malL resulted in a complete inactivation of the maltose-inducible α-glucosidase activity in crude protein extracts and a Mal− phenotype.