Comparative transcriptome analysis of Listeria monocytogenes strains of the two major lineages reveals differences in virulence, cell wall, and stress response

Listeria monocytogenes is a food-borne, opportunistic, bacterial pathogen causing a wide spectrum of diseases, including meningitis, septicemia, abortion, and gastroenteritis, in humans and animals. Among the 13 L. monocytogenes serovars described, human listeriosis is mostly associated with strains of serovars 4b, 1/2b, and 1/2a. Within the species L. monocytogenes, three phylogenetic lineages are described. Serovar 1/2a belongs to phylogenetic lineage I, while serovars 4b and 1/2b group in phylogenetic lineage II. To explore the role of gene expression in the adaptation of L. monocytogenes strains of these two major lineages to different environments, as well as in virulence, we performed whole-genome expression profiling of six L. monocytogenes isolates of serovars 4b, 1/2b, and 1/2a of distinct origins, using a newly constructed Listeria multigenome DNA array. Comparison of the global gene expression profiles revealed differences among strains. The expression profiles of two strains having distinct 50% lethal doses, as assessed in the mouse model, were further analyzed. Gene ontology term enrichment analysis of the differentially expressed genes identified differences in protein-, nucleic acid-, carbon metabolism-, and virulence-related gene expression. Comparison of the expression profiles of the core genomes of all strains revealed differences between the two lineages with respect to cell wall synthesis, the stress-related sigma B regulon and virulence-related genes. These findings suggest different patterns of interaction with host cells and the environment, key factors for host colonization and survival in the environment.     

Variation in the effectors of the type III secretion system among Photorhabdus species as revealed by genomic analysis

Entomopathogenic bacteria of the genus Photorhabdus harbor a type III secretion system. This system was probably acquired prior to the separation of the species within this genus. Furthermore, the core components of the secretion machinery are highly conserved but the predicted effectors differ between Photorhabdus luminescens and P. asymbiotica, two highly related species with different hosts.     

Effect of Tobacco Control Policies on Information Seeking for Smoking Cessation in the Netherlands: A Google Trends Study

Background

The impact of tobacco control policies on measures of smoking cessation behaviour has often been studied, yet there is little information on their precise magnitude and duration. This study aims to measure the magnitude and timing of the impact of Dutch tobacco control policies on the rate of searching for information on smoking cessation, using Google Trends search query data.

Methods

An interrupted time series analysis was used to examine the effect of two types of policies (smoke-free legislation and reimbursement of smoking cessation support (SCS)) on Google searches for ‘quit smoking’. Google Trends data were seasonally adjusted and analysed using autoregressive integrated moving average (ARIMA) modelling. Multiple effect periods were modelled as dummy variables and analysed simultaneously to examine the magnitude and duration of the effect of each intervention. The same analysis was repeated with Belgian search query data as a control group, since Belgium is the country most comparable to the Netherlands in terms of geography, language, history and culture.

Results

A significant increase in relative search volume (RSV) was found from one to four weeks (21–41%) after the introduction of the smoking ban in restaurants and bars in the Netherlands in 2008. The introduction of SCS reimbursement in 2011 was associated with a significant increase of RSV (16–22%) in the Netherlands after 3 to 52 weeks. The reintroduction of SCS in 2013 was associated with a significant increase of RSV (9–21%) in the Netherlands from 3 to 32 weeks after the intervention. No effects were found in the Belgian control group for the smoking ban and the reintroduction of SCS in 2013, but there was a significant increase in RSV shortly before and after the introduction of SCS in 2011.

Conclusions

These findings suggest that these tobacco control policies have short-term or medium-term effects on the rate of searching for information on smoking cessation, and therefore potentially on smoking cessation rates.     

Whole-genome comparison between Photorhabdus strains to identify genomic regions involved in the specificity of nematode interaction

The bacterium Photorhabdus establishes a highly specific association with Heterorhabditis, its nematode host. Photorhabdus strains associated with Heterorhabditis bacteriophora or Heterorhabditis megidis were compared using a Photorhabdus DNA microarray. We describe 31 regions belonging to the Photorhabdus flexible gene pool. Distribution analysis of regions among the Photorhabdus genus identified loci possibly involved in nematode specificity.     

Characterization of Arabidopsis ABCG11/WBC11, an ATP binding cassette (ABC) transporter that is required for cuticular lipid secretion

ABCG11/WBC11, an ATP binding cassette (ABC) transporter from Arabidopsis thaliana, is a key component of the export pathway for cuticular lipids. Arabidopsis wbc11 T-DNA insertional knock-out mutants exhibited lipidic inclusions inside epidermal cells similar to the previously characterized wax transporter mutant cer5, with a similar strong reduction in the alkanes of surface waxes. Moreover, the wbc11 knock-out mutants also showed defects not present in cer5, including post-genital organ fusions, stunted growth and a reduction in cutin load on the plant surface. A mutant line previously isolated in a forward genetics screen, called permeable leaves 1 (pel1), was identified as an allele of ABCG11/WBC11. The double knock-out wbc11 cer5 exhibited the same morphological and biochemical phenotypes as the wbc11 knock-out. A YFP-WBC11 fusion protein rescued a T-DNA knock-out mutant and was localized to the plasma membrane. These results show that WBC11 functions in secretion of surface waxes, possibly by interacting with CER5. However, unlike ABCG12/CER5, ABCG11/WBC11 is important to the normal process of cutin formation.     

Identification, Characterization, and Regulation of a Cluster of Genes Involved in Carbapenem Biosynthesis in Photorhabdus luminescens

The luminescent entomopathogenic bacterium Photorhabdus luminescens produces several yet-uncharacterized broad-spectrum antibiotics. We report the identification and characterization of a cluster of eight genes (named cpmA to cpmH) responsible for the production of a carbapenem-like antibiotic in strain TT01 of P. luminescens. The cpm cluster differs in several crucial aspects from other car operons. The level of cpm mRNA peaks during exponential phase and is regulated by a Rap/Hor homolog identified in the P. luminescens genome. Marker-exchange mutagenesis of this gene in the entomopathogen decreased antibiotic production. The luxS-like signaling mechanism of quorum sensing also plays a role in the regulation of the cpm operon. Indeed, luxS, which is involved in the production of a newly identified autoinducer, is responsible for repression of cpm gene expression at the end of the exponential growth phase. The importance of this carbapenem production in the ecology of P. luminescens is discussed.