Dynamics of competitive population abundance of Lactobacillus plantarum ivi gene mutants in faecal samples after passage through the gastrointestinal tract of mice

AIM: This study aims to evaluate the impact of mutation of previously identified in vivo-induced (ivi) genes on the persistence and survival of Lactobacillus plantarum WCFS1 in the gastrointestinal (GI) tract of mice. METHODS AND RESULTS: Nine Lact. plantarum ivi gene replacement mutants were constructed, focussing on ivi genes that encode proteins with a predicted role in cell envelope functionality, stress response and regulation. The in vitro growth characteristics of the mutants appeared identical to those observed for the wild-type strain, which agrees with the recombination-based in vivo expression technology suggestion that these genes are not transcribed in the laboratory. Quantitative PCR experiments demonstrated differences in the relative population dynamics of the Lact. plantarum ivi mutants in faecal samples after passage through the GI tract of mice. CONCLUSIONS: The in situ competition experiments revealed a 100- to 1000-fold reduction of the relative abundance of three of the ivi gene mutants, harbouring deletions of genes predicted to encode a copper transporter, an orphan IIC cellobiose PTS and a cell wall anchored extracellular protein. SIGNIFICANCE AND IMPACT OF THE STUDY: These experiments clearly establish that the proteins encoded by these three genes play a key role in Lact. plantarum performance during passage of the GI tract.     

Biodiversity-based identification and functional characterization of the mannose-specific adhesin of Lactobacillus plantarum

Lactobacillus plantarum is a frequently encountered inhabitant of the human intestinal tract, and some strains are marketed as probiotics. Their ability to adhere to mannose residues is a potentially interesting characteristic with regard to proposed probiotic features such as colonization of the intestinal surface and competitive exclusion of pathogens. In this study, the variable capacity of 14 L. plantarum strains to agglutinate Saccharomyces cerevisiae in a mannose-specific manner was determined and subsequently correlated with an L. plantarum WCFS1-based genome-wide genotype database. This led to the identification of four candidate mannose adhesin-encoding genes. Two genes primarily predicted to code for sortase-dependent cell surface proteins displayed a complete gene-trait match. Their involvement in mannose adhesion was corroborated by the finding that a sortase (srtA) mutant of L. plantarum WCFS1 lost the capacity to agglutinate S. cerevisiae. The postulated role of these two candidate genes was investigated by gene-specific deletion and overexpression in L. plantarum WCFS1. Subsequent evaluation of the mannose adhesion capacity of the resulting mutant strains showed that inactivation of one candidate gene (lp_0373) did not affect mannose adhesion properties. In contrast, deletion of the other gene (lp_1229) resulted in a complete loss of yeast agglutination ability, while its overexpression quantitatively enhanced this phenotype. Therefore, this gene was designated to encode the mannose-specific adhesin (Msa; gene name, msa) of L. plantarum. Domain homology analysis of the predicted 1,000-residue Msa protein identified known carbohydrate-binding domains, further supporting its role as a mannose adhesin that is likely to be involved in the interaction of L. plantarum with its host in the intestinal tract.     

Novel screening assay for in vivo selection of Klebsiella pneumoniae genes promoting gastrointestinal colonisation

ABSTRACT: BACKGROUND: Klebsiella pneumoniae is an important opportunistic pathogen causing pneumonia, sepsis and urinary tract infections. Colonisation of the gastrointestinal (GI) tract is a key step in the development of infections; yet the specific factors important for K. pneumoniae to colonize and reside in the GI tract of the host are largely unknown. To identify K. pneumoniae genes promoting GI colonisation, a novel genomic-library-based approach was employed. RESULTS: Screening of a K. pneumoniae C3091 genomic library, expressed in E. coli strain EPI100, in a mouse model of GI colonisation led to the positive selection of five clones containing genes promoting persistent colonisation of the mouse GI tract. These included genes encoding the global response regulator ArcA; GalET of the galactose operon; and a cluster of two putative membrane-associated proteins of unknown function. Both ArcA and GalET are known to be involved in metabolic pathways in Klebsiella but may have additional biological actions beneficial to the pathogen. In support of this, GalET was found to confer decreased bile salt sensitivity to EPI100. CONCLUSIONS: The present work establishes the use of genomic-library-based in vivo screening assays as a valuable tool for identification and characterization of virulence factors in K. pneumoniae and other bacterial pathogens.     

The use of listeriolysin to identify in vivo induced genes in the gram-positive intracellular pathogen Listeria monocytogenes

Listeria monocytogenes is capable of growth within the cytoplasm of infected host cells. Escape from the host cell phagosome is mediated primarily through secretion of listeriolysin, a haemolytic factor which functions to actively lyse the phagosomal membrane. Listeriolysin negative mutants of L. monocytogenes are non-haemolytic on blood agar plates and demonstrate a significant reduction of virulence in the mouse model of infection. We have developed a system for the identification of in vivo induced genes in L. monocytogenes which utilizes the listeriolysin gene, hly, as both a reporter of gene expression and as a means of selection of promoter elements expressed in vivo. The system is analogous to in vivo expression technology (IVET) first reported for Salmonella, however, as listeriolysin functions in the environment of the host phagosome the loci identified in this study are most likely expressed during residence in the phagosome. The system was successfully tested using the promoter of the inducible virulence gene plcA. A bank was created by fusing a promoterless copy of hly to random promoter elements in a listeriolysin negative IVET host. Sequential inoculations of mice with this bank resulted in the isolation of clones with increased survival potential in the mouse model relative to a negative control, but which remained haemolysin negative on blood agar plates. Nine in vivo induced loci were identified including genes encoding a DNA topoisomerase III, a cellobiose transporter and a fumarase. Two isolates represented fusions to proteins of unknown function and three isolates contained no significant homologues in the database. A mutant in the fumarase gene demonstrated reduced virulence for mice and an inability to grow in cultured mouse phagocytes.     

Proteomic analysis of log to stationary growth phase Lactobacillus plantarum cells and a 2-DE database

Lactobacillus plantarum is part of the natural microbiota of many food fermentations as well as the human gastro-intestinal tract. The cytosolic fraction of the proteome of L. plantarum WCFS1, whose genome has been sequenced, was studied. 2-DE was used to investigate the proteins from the cytosolic fraction isolated from mid- and late-log, early- and late-stationary phase cells to generate reference maps of different growth conditions offering more knowledge of the metabolic behavior of this bacterium. From this fraction, a total of 200 protein spots were identified by MALDI-MS and a proteome production map was constructed to facilitate further studies such as detection of suitable biomarkers for specific growth conditions. More than half (57%) of the identified proteins were predicted to be involved in metabolic pathways of the bacterium. The protein profile changed during the growth of the bacteria such that 29% of the identified proteins involved in anabolic pathways were at least twofold up-regulated throughout the mid- and late-exponential and early-stationary phases. In the late-stationary phase, six proteins involved in stress or with a potential role for survival during starvation were up-regulated significantly.     

Ralstonia solanacearum genes induced during growth in tomato: an inside view of bacterial wilt

The phytopathogen Ralstonia solanacearum has over 5000 genes, many of which probably facilitate bacterial wilt disease development. Using in vivo expression technology (IVET), we screened a library of 133 200 R. solanacearum strain K60 promoter fusions and isolated approximately 900 fusions expressed during bacterial growth in tomato plants. Sequence analysis of 307 fusions revealed 153 unique in planta-expressed (ipx) genes. These genes included seven previously identified virulence genes (pehR, vsrB, vsrD, rpoS, hrcC, pme and gspK) as well as seven additional putative virulence factors. A significant number of ipx genes may reflect adaptation to the host xylem environment; 19.6%ipx genes are predicted to encode proteins with metabolic and/or transport functions, and 9.8%ipx genes encode proteins possibly involved in stress responses. Many ipx genes (18%) encode putative transmembrane proteins. A majority of ipx genes isolated encode proteins of unknown function, and 13% were unique to R. solanacearum. The ipx genes were variably induced in planta; beta-glucuronidase reporter gene expression analysis of a subset of 44 ipx fusions revealed that in planta expression levels were between two- and 37-fold higher than in culture. The expression of many ipx genes was subject to known R. solanacearum virulence regulators. Of 32 fusions tested, 28 were affected by at least one virulence regulator; several fusions were controlled by multiple regulators. Two ipx fusion strains isolated in this screen were reduced in virulence on tomato, indicating that gene(s) important for bacterial wilt pathogenesis were interrupted by the IVET insertion; mutations in other ipx genes are necessary to determine their roles in virulence and in planta growth. Collectively, this profile of ipx genes suggests that in its host, R. solanacearum confronts and overcomes a stressful and nutrient-poor environment.     

Identification and characterization of host factors interacting with Bombyx mori nucleopolyhedrovirus ORF8

The orf8 gene (Bm8) in Bombyx mori nucleopolyhedrovirus (BmNPV) is one of 17 genes unique to group I NPVs and is expressed as an early gene. We have reported that Bm8 may play an important role during viral infection and that Bm8 protein co-localized with IE1 to specific nuclear foci throughout infection. It was also demonstrated that both IE1 and BmNPV hr facilitate this localization of Bm8. To investigate further, host proteins interacting with Bm8 were screened using a yeast two-hybrid system. We identified 6 host clones as Bm8-interacting partners from three cDNA libraries derived from BmN cells or B. mori larvae. Further assays showed that the N-terminal region of Bm8 is important for the interaction with most host clones and that two of the clones can associate with IE1. Cloning and sequencing of full-length cDNAs revealed that most of the clones potentially encode either membrane-bound proteins or secreted proteins. Quantitative RT-PCR analysis revealed that some of these host genes were slightly induced during the early stage of infection in BmN cells, and that the expression of all genes was markedly reduced during the late stage of infection. Generation of mutant BmNPVs over-expressing these host genes also identified a gene that potentially functions as a negative factor during BmNPV infection. These features of Bm8-interacting host proteins strongly support that Bm8 is a multifunctional protein involved in multiple signaling pathways in host cells.