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Listeria monocytogenes is a facultative intracellular gram-positive bacterium responsible for severe opportunistic infections in humans and animals. We had previously identified a gene encoding a putative UDP-N-acetylglucosamine 2-epimerase, a precursor of the teichoic acid linkage unit, in the genome of L monocytogenes strain EGD-e. This gene, now designated lmo2537, encodes a protein that shares 62% identity with the cognate epimerase MnaA of Bacillus subtilis and 55% identity with Cap5P of Staphylococcus aureus. Here, we addressed the role of lmo2537 in L. monocytogenes pathogenesis by constructing a conditional knockout mutant. The data presented here demonstrate that lmo2537 is an essential gene of L. monocytogenes that is involved in teichoic acid biogenesis. In vivo, the conditional mutant is very rapidly eliminated from the target organs of infected mice and thus is totally avirulent.

Sortases are transamidases that covalently link proteins to the peptidoglycan of gram-positive bacteria. The genome of the pathogenic bacterium Listeria monocytogenes encodes two sortases genes, srtA and srtB. The srtA gene product anchors internalin and some other LPXTG-containing proteins to the listerial surface. Here, we focus on the role of the second sortase, SrtB. Whereas SrtA acts on most of the proteins in the peptidoglycan fraction, SrtB appears to target minor amounts of surface polypeptides. We identified one of the SrtB-anchored proteins as the virulence factor SvpA, a surface-exposed protein which does not contain the LPXTG motif. Therefore, as in Staphylococcus aureus, the listerial SrtB represents a second class of sortase in L. monocytogenes, involved in the attachment of a subset of proteins to the cell wall, most likely by recognizing an NXZTN sorting motif. The [DELTA]srtB mutant strain does not have defects in bacterial entry, growth, or motility in tissue-cultured cells and does not show attenuated virulence in mice. SrtB-mediated anchoring could therefore be required to anchor surface proteins involved in the adaptation of this microorganism to different environmental conditions.

Research has been conducted on the bacteriophage lambda that interacts with cell-surface receptor LamB. The fusion of the C-terminal portion of the tail fiber protein of lambda to maltose-binding protein is described.

The levanase operon of Bacillus subtilis was found to be also inducible by mannose and to enhance mannose uptake in B. subtilis as well as in Escherichia coli. Also, B. subtilis cytoplasmic components IIC(super Fru) and IID(super Fru) could substitute for their E. coli mannose homologs to permit phage lambda DNA injection. In contrast, a series of other bacteriophages, also using the LamB protein as a cell surface receptor, do not need the mannose transporter for infection.

Topological analysis of an integral membrane protein LamB from Escherichia coli porin has detected nine external loops, five of which were identified by random and directed epitope tagging. Data confirmed four periplasmic loops that have been predicted in previous studies. A membrane protein topological model has been developed to represent the topology of the E. coli outer membrane protein.

LamB, the integral outer membrane protein and cell receptor site for bacteriophage lambda in E. coli K12, is a 42-amino acid polypeptide. Residue 151 of LamB forms the accessibility gate closest to the phage binding site. The residue at site 151 affects changes in the entry of phage to the binding site according to the size of the substitute side chain. The phage block by the accessibility gate is relieved by a series of amino acid changes in the distal part of J genes of extended host-range mutants of lambda.

J protein mutated residues maybe involved in overcoming the LamB mutation-induced phage adsorption blockage. The J protein distal part contains seven residues involved in lambda mutants host range properties, indicating the participation of the final C-terminal region in the phage adsorption on LamB. The two-step extended host range mutants exhibit double or triple point mutations at the J protein C-terminal.