Transcriptional profiling of Legionella pneumophila biofilm cells and the influence of iron on biofilm formation.

International audienceIn aquatic environments, biofilms constitute an ecological niche where Legionella pneumophila persists as sessile cells. However, very little information on the sessile mode of life of L. pneumophila is currently available. We report here the development of a model biofilm of L. pneumophila strain Lens and the first transcriptome analysis of L. pneumophila biofilm cells. Global gene expression analysis of sessile cells as compared to two distinct populations of planktonic cells revealed that a substantial proportion of L. pneumophila genes is differentially expressed, as 2.3 % of the 2932 predicted genes exhibited at least a twofold change in gene expression. Comparison with previous results defining the gene expression profile of replicative- and transmissive-phase Legionella suggests that sessile cells resemble bacteria in the replicative phase. Further analysis of the most strongly regulated genes in sessile cells identified two induced gene clusters. One contains genes that encode alkyl hydroperoxide reductases known to act against oxidative stress. The second encodes proteins similar to PvcA and PvcB that are involved in siderophore biosynthesis in Pseudomonas aeruginosa. Since iron has been reported to modify biofilm formation in other species, we further focused on iron control of gene expression and biofilm formation. Among the genes showing the greatest differences in expression between planktonic cells and biofilm, only pvcA and pvcB were regulated by iron concentration. A DeltapvcA L. pneumophila mutant showed no changes in biofilm formation compared to the wild-type, suggesting that the pvcA product is not mandatory for biofilm formation. However, biofilm formation by L. pneumophila wild-type and a DeltapvcA strain was clearly inhibited in iron-rich conditions

Genetic Basis of Exploiting Ecological Opportunity During the Long-Term Diversification of a Bacterial Population

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The biology of lantibiotics from the lacticin 481 group is coming of age.

International audienceLantibiotics are antimicrobial peptides from the bacteriocin family, secreted by Gram-positive bacteria. These peptides differ from other bacteriocins by the presence of (methyl)lanthionine residues, which result from enzymatic modification of precursor peptides encoded by structural genes. Several groups of lantibiotics have been distinguished, the largest of which is the lacticin 481 group. This group consists of at least 16 members, including lacticin 481, streptococcin A-FF22, mutacin II, nukacin ISK-1, and salivaricins. We present the first review devoted to this lantibiotic group, knowledge of which has increased significantly within the last few years. After updating the group composition and defining the common properties of these lantibiotics, we highlight the most recent developments. The latter concern: transcriptional regulation of the lantibiotic genes; understanding the biosynthetic machinery, in particular the ability to perform in vitro prepeptide maturation; characterization of a novel type of immunity protein; and broad application possibilities. This group differs in many aspects from the best known lantibiotic group (nisin group), but shares properties with less-studied groups such as the mersacidin, cytolysin and lactocin S groups

Microbiota-Derived Extracellular Vesicles Detected in Human Blood from Healthy Donors

International audienceThe microbiota constitutes an important part of the holobiont in which extracellular vesicles (EVs) are key players in health, especially regarding inter- and intra-kingdom communications. Analysis of EVs from the red blood cell concentrates of healthy donors revealed variable amounts of OmpA and LPS in 12 of the 14 analyzed samples, providing indirect experimental evidence of the presence of microbiota EVs in human circulating blood in the absence of barrier disruption. To investigate the role of these microbiota EVs, we tracked the fusion of fluorescent Escherichia coli EVs with blood mononuclear cells and showed that, in the circulating blood, these EVs interacted almost exclusively with monocytes. This study demonstrates that bacterial EVs constitute critical elements of the host–microbiota cellular communication. The analysis of bacterial EVs should thus be systematically included in any characterization of human EVs

Ecological and evolutionary dynamics of coexisting lineages during a long-term experiment with Escherichia coli.

International audienceClosely related organisms usually occupy similar ecological niches, leading to intense competition and even extinction. Such competition also can promote rapid phenotypic evolution and ecological divergence. This process may end with the stable occupation of distinct niches or, alternatively, may entail repeated bouts of evolution. Here we examine two Escherichia coli lineages, called L and S, that coexisted for more than 30,000 generations after diverging from a common ancestor. Both lineages underwent sustained phenotypic evolution based on global transcription and resource utilization profiles, with L seeming to encroach over time on the catabolic profile of S. Reciprocal invasion experiments with L and S clones from the same or different generations revealed evolutionary changes in their interaction, including an asymmetry that confirmed the encroachment by L on the niche of the S lineage. In general, L and S clones from the same generation showed negative frequency-dependent effects, consistent with stable coexistence. However, L clones could invade S clones from both earlier and later generations, whereas S clones could invade only L clones from earlier generations. In this system, the long-term coexistence of competing lineages evidently depended on successive rounds of evolution, rather than on initial divergence followed by a static equilibrium

Nitric oxide inhibits Shiga-toxin synthesis by enterohemorrhagic Escherichia coli.

International audienceShiga-toxin (Stx) is the cardinal virulence factor of enterohemorrhagic Escherichia coli (EHEC). The genes encoding Stx are carried by a lambdoid phage integrated in the bacterial genome and are fully expressed after a bacterial SOS response induced by DNA-damaging agents. Because nitric oxide (NO) is an essential mediator of the innate immune response of infected colonic mucosa, we aimed to determine its role in Stx production by EHEC. Here we demonstrate that chemical or cellular sources of NO inhibit spontaneous and mitomycin C-induced stx mRNA expression and Stx synthesis, without altering EHEC viability. The synthesis of stx phage is also reduced by NO. This inhibitory effect apparently occurs through the NO-mediated sensitization of EHEC because mutation of the NO sensor nitrite-sensitive repressor results in loss of NO inhibiting activity on stx expression. Thus our findings identify NO as an inhibitor of stx expressing-phage propagation and Stx release and thus as a potential protective factor limiting the development of hemolytic syndromes

Plasticity of Promoter-Core Sequences Allows Bacteria to Compensate for the Loss of a Key Global Regulatory Gene

International audienceTranscription regulatory networks (TRNs) are of central importance for both short-term phenotypic adaptation in response to environmental fluctuations and long-term evolutionary adaptation, with global regulatory genes often being targets of natural selection in laboratory experiments. Here, we combined evolution experiments, whole-genome resequencing, and molecular genetics to investigate the driving forces, genetic constraints, and molecular mechanisms that dictate how bacteria can cope with a drastic perturbation of their TRNs. The crp gene, encoding a major global regulator in Escherichia coli, was deleted in four different genetic backgrounds, all derived from the Long-Term Evolution Experiment (LTEE) but with different TRN architectures. We confirmed that crp deletion had a more deleterious effect on growth rate in the LTEE-adapted genotypes; and we showed that the ptsG gene, which encodes the major glucose-PTS transporter, gained CRP (cyclic AMP receptor protein) dependence over time in the LTEE. We then further evolved the four crp-deleted genotypes in glucose minimal medium, and we found that they all quickly recovered from their growth defects by increasing glucose uptake. We showed that this recovery was specific to the selective environment and consistently relied on mutations in the cis-regulatory region of ptsG, regardless of the initial genotype. These mutations affected the interplay of transcription factors acting at the promoters, changed the intrinsic properties of the existing promoters, or produced new transcription initiation sites. Therefore, the plasticity of even a single promoter region can compensate by three different mechanisms for the loss of a key regulatory hub in the E. coli TRN

Data from: Ecological and evolutionary dynamics of coexisting lineages during a long-term experiment with E. coli

Closely related organisms usually occupy similar ecological niches, leading to intense competition and even extinction. Such competition also can promote rapid phenotypic evolution and ecological divergence. This process may end with the stable occupation of distinct niches or, alternatively, may entail repeated bouts of evolution. Here we examine two Escherichia coli lineages, called L and S, that coexisted for more than 30,000 generations after diverging from a common ancestor. Both lineages underwent sustained phenotypic evolution based on global transcription and resource utilization profiles, with L seeming to encroach over time on the catabolic profile of S. Reciprocal invasion experiments with L and S clones from the same or different generations revealed evolutionary changes in their interaction, including an asymmetry that confirmed the encroachment by L on the niche of the S lineage. In general, L and S clones from the same generation showed negative frequency-dependent effects, consistent with stable coexistence. However, L clones could invade S clones from both earlier and later generations, whereas S clones could invade only L clones from earlier generations. In this system, the long-term coexistence of competing lineages evidently depended on successive rounds of evolution, rather than on initial divergence followed by a static equilibrium

Lacticin 481: an antimicrobial peptide of the lantibiotic family produced by Lactococcus lactis.

Lacticin 481 is an antimicrobial peptide secreted by some strains of the lactic acid bacterium Lactococcus lactis. This peptide contains two lanthionines, one 3-methyllanthionine and one 2,3-didehydrobutyrine. Such unusual residues are specifically found in lantibiotics and are created by enzymatic modification of some amino acids included into a precursor peptide. The latter is encoded by a structural gene. Several groups of lantibiotics have been distinguished and lacticin 481 is representative the so-called lacticin 481 group. Here, we present an overview of the data accumulated on lacticin 481, including its properties and spectrum of action, its genetic determinants, its maturation pathway, the immunity system protecting the producer strains from their own lantibiotic, and potential applications