The cell wall (CW) of bacteria is an intricate arrangement of macromolecules, at least constituted of peptidoglycan (PG) but also of (lipo)teichoic acids, various polysaccharides, polyglutamate and/or proteins. During bacterial growth and division, there is a constant balance between CW degradation and biosynthesis. The CW is remodeled by bacterial hydrolases, whose activities are carefully regulated to maintain cell integrity or lead to bacterial death. Each cell wall hydrolase (CWH) has a specific role regarding the PG: (i) cell wall amidase (CWA) cleaves the amide bond between N-acetylmuramic acid and L-alanine residue at the N-terminal of the stem peptide, (ii) cell wall glycosidase (CWG) catalyses the hydrolysis of the glycosidic linkages, whereas (iii) cell wall peptidase (CWP) cleaves amide bonds between amino acids within the PG chain. After an exhaustive overview of all known conserved catalytic domains responsible for CWA, CWG, and CWP activities, this review stresses that the CWHs frequently display a modular architecture combining multiple and/or different catalytic domains, including some lytic transglycosylases as well as CW binding domains. From there, direct physiological and collateral roles of CWHs in bacterial cells are further discussed.

The microbial spoilage of meat and seafood products with short shelf lives is responsible for a significant amount of food waste. Food spoilage is a very heterogeneous process, involving the growth of various, poorly characterized bacterial communities. In this study, we conducted 16S ribosomal RNA gene pyrosequencing on 160 samples of fresh and spoiled foods to comparatively explore the bacterial communities associated with four meat products and four seafood products that are among the most consumed food items in Europe. We show that fresh products are contaminated in part by a microbiota similar to that found on the skin and in the gut of animals. However, this animal-derived microbiota was less prevalent and less abundant than a core microbiota, psychrotrophic in nature, mainly originated from the environment (water reservoirs). We clearly show that this core community found on meat and seafood products is the main reservoir of spoilage bacteria. We also show that storage conditions exert strong selective pressure on the initial microbiota: alpha diversity in fresh samples was 189±58 operational taxonomic units (OTUs) but dropped to 27 ± 12 OTUs in spoiled samples. The OTU assemblage associated with spoilage was shaped by low storage temperatures, packaging and the nutritional value of the food matrix itself. These factors presumably act in tandem without any hierarchical pattern. Most notably, we were also able to identify putative new clades of dominant, previously undescribed bacteria occurring on spoiled seafood, a finding that emphasizes the importance of using culture-independent methods when studying food microbiota.

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We report the existence of eight different interleukin-15 receptor ␣-chain (IL-15R␣) transcripts resulting from exon-splicing mechanisms within the IL-15R␣ gene. Two main classes of transcripts can be distinguished that do or do not (⌬2 isoforms) contain the exon 2-coding sequence. Both classes were expressed in numerous cell lines and tissues (including peripheral blood lymphocytes) at comparable levels and could be transcribed in COS-7 cells, and the proteins were expressed at the cell surface. Both receptor forms displayed numerous glycosylation states, reflecting differential usage of a single N-glycosylation site as well as extensive O-glycosylations. Whereas IL-15R␣ bound IL-15 with high affinity, ⌬2IL-15R␣ was unable to bind IL-15, thus revealing the indispensable role of the exon 2-encoded domain in cytokine binding. A large proportion of IL-15R␣ was expressed at the nuclear membrane with some intranuclear localization, supporting a potential direct action of the IL-15⅐IL-15R␣ complex at the nuclear level. In sharp contrast, ⌬2IL-15R␣ was found only in the non-nuclear membrane compartments, indicating that the exon 2-encoded domain (which is shown to contain a potential nuclear localization signal) plays an important role in receptor post-translational routing. Together, our data indicate that exon 2 splicing of human IL-15R␣ is a natural process that might play regulatory roles at different levels.

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Food safety is a major concern for consumers and a major issue for industry which has become aware of the importance of the starter safety assessment. In the European Union, the Food Safety Authority has introduced the Qualified Presumption of Safety (QPS) approach for safety assessment of microorganisms throughout the food chain. This assessment relies on: taxonomy, familiarity, pathogenicity and end use. Productions of toxins as well as biogenic amines by food isolates are both of major concern as they can lead to food poisoning. The other important criterion is the presence of transmissible antibiotic resistance markers. This review underlined that the main hazard of bacteria involved in food fermentations concerns antibiotic resistance and particularly the presence of transferable genetic determinants that may present a risk for public health. Selection of starter strains should consider this hazard. Following the QPS approach, a list of bacteria has been acknowledged acceptable for consumption.

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The migration of keratinocytes plays an important role in the re-epithelialization of cutaneous wounds. Zinc, copper and manganese are used in vivo for their healing properties and their mechanism of action is still only partially known. Thus, they have been shown both to promote keratinocyte proliferation and to modulate integrins expression. The aim of this study was to determine if trace elements induce an increase of the migration of keratinocytes and if this effect is related to the modulation of integrins. Two independent migration assays were used to study keratinocyte migration: the scratch assay using normal human keratinocytes and the modified Boyden chamber using HaCaT cells. Inhibition studies using function-blocking antibodies directed to alpha3, alpha6, alpha(v) and beta1 subunits were performed to investigate the modulator effect of trace elements on integrin function. In this way, zinc and copper gluconates increased alpha3, alpha(v) and beta1 function whereas manganese gluconate seems mainly able to modulate the function of alpha3 and beta1. The stimulating effect of these trace elements on keratinocyte migration does not appear related to alpha6 subunit. Thus, zinc, copper and manganese enhanced keratinocyte migration and one of the mechanisms was going through a modulation of integrin functions.