Abstract
BackgroundIn the environment as well as in the vertebrate intestine, Listeriae have access to complex carbohydrates like maltodextrins. Bacterial exploitation of such compounds requires specific uptake and utilization systems.Methodology/Principal FindingsWe could show that Listeria monocytogenes and other Listeria species contain genes/gene products with high homology to the maltodextrin ABC transporter and utilization system of B. subtilis. Mutant construction and growth tests revealed that the L. monocytogenes gene cluster was required for the efficient utilization of maltodextrins as well as maltose. The gene for the ATP binding protein of the transporter was located distant from the cluster. Transcription analyses demonstrated that the system was induced by maltose/maltodextrins and repressed by glucose. Its induction was dependent on a LacI type transcriptional regulator. Repression by glucose was independent of the catabolite control protein CcpA, but was relieved in a mutant defective for Hpr kinase/phosphorylase.Conclusions/SignificanceThe data obtained show that in L. monocytogenes the uptake of maltodextrin and, in contrast to B. subtilis, also maltose is exclusively mediated by an ABC transporter. Furthermore, the results suggest that glucose repression of the uptake system possibly is by inducer exclusion, a mechanism not described so far in this organism.
Highlights
Listeriae are gram-positive rods, asporogenic and very robust
Similar results were obtained in tryptic soy broth without glucose (TSB) with 1.0 percent maltodextrin (Figure 2, lower panel). These results show that sustained growth of L. monocytogenes EGD-e in TSB is dependent on the addition and uptake of the supplemented carbon source and TSB is a suitable medium for such kind of investigations
It can be anticipated that the other genes in the operon are regulated in the same way. It has previously been suggested [46] that in L. monocytogenes EGD-e maltose is taken up and utilized by the proteins encoded by lmo0858–lmo0865. This assumption was based on a comparison of the genome organization of Lactococcus lactis, Lactobacillus plantarum and Listeria monocytogenes
Summary
Listeriae are gram-positive rods, asporogenic and very robust. They grow between pH 5 to 9, from 1–45uC and at salt concentrations up to 12%. Natural habitats of Listeriae are decaying plant material in soil and the intestine of healthy animals, including birds. The bacteria eventually gain access to sewage and water and may contaminate food processing environments. Uptake of contaminated food leads to the transmission of Listeria to humans [1,2]. In the environment as well as in the vertebrate intestine, Listeriae have access to complex carbohydrates like maltodextrins. Bacterial exploitation of such compounds requires specific uptake and utilization systems
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