Effects of turbulence on diatoms of the genus Pseudo-nitzschia spp. and associated bacteria.

Turbulence is one of the least investigated environmental factors impacting the ecophysiology of phytoplankton, both at the community and individual species level. Here, we investigated, for the first time, the effect of a turbulence gradient (Reynolds number, from Reλ = 0 to Reλ = 360) on two species of the marine diatom Pseudo-nitzschia and their associated bacterial communities under laboratory conditions. Cell abundance, domoic acid (DA) production, chain formation, and Chl a content of P.

Trajectories of nutrients concentrations and ratios in the French coastal ecosystems: 20 years of changes in relation with large-scale and local drivers.

Along with their important diversity, coastal ecosystems receive various amounts of nutrients, principally arising from the continent and from the related human activities (mainly industrial and agricultural activities). During the 20th century, nutrients loads have increased following the increase of both the global population and need of services. Alongside, climate change including temperature increase or atmospheric circulation change has occurred.

Underwater light climate and wavelength dependence of microalgae photosynthetic parameters in a temperate sea.

Studying how natural phytoplankton adjust their photosynthetic properties to the quantity and quality of underwater light (. light climate) is essential to understand primary production. A wavelength-dependent photoacclimation strategy was assessed using a multi-color pulse-amplitude-modulation chlorophyll fluorometer for phytoplankton samples collected in the spring at 19 locations across the English Channel.

Catalytic mechanism of MraY and WecA, two paralogues of the polyprenyl-phosphate N-acetylhexosamine 1-phosphate transferase superfamily.

The MraY transferase catalyzes the first membrane step of bacterial cell wall peptidoglycan biosynthesis, namely the transfer of the N-acetylmuramoyl-pentapeptide moiety of the cytoplasmic precursor UDP-MurNAc-pentapeptide to the membrane transporter undecaprenyl phosphate (C55P), yielding C55-PP-MurNAc-pentapeptide (lipid I). A paralogue of MraY, WecA, catalyzes the transfer of the phospho-GlcNAc moiety of UDP-N-acetylglucosamine onto the same lipid carrier, leading to the formation of C55-PP-GlcNAc that is essential for the synthesis of various bacterial cell envelope components. These two enzymes are members of the polyprenyl-phosphate N-acetylhexosamine 1-phosphate transferase superfamily, which are essential for bacterial envelope biogenesis.

Colicin M hydrolyses branched lipids II from Gram-positive bacteria.

Lipids II found in some Gram-positive bacteria were prepared in radioactive form from l-lysine-containing UDP-MurNAc-pentapeptide. The specific lateral chains of Enterococcus faecalis, Enterococcus faecium and Staphylococcus aureus (di-L-alanine, D-isoasparagine, and pentaglycine, respectively) were introduced by chemical peptide synthesis using the Fmoc chemistry. The branched nucleotides obtained were converted into the corresponding lipids II by enzymatic synthesis using the MraY and MurG enzymes.

Synthesis and biological evaluation of potential new inhibitors of the bacterial transferase MraY with a β-ketophosphonate structure.

Stable analogs of bacterial transferase MraY substrate or product with a pyrophosphate surrogate in their structure are described. β-ketophosphonates were designed as pyrophosphate bioisosteres and were investigated as UDP-GlcNAc mimics. The developed strategy allows introduction of structural diversity at a late stage of the synthesis.

Synthesis and biological evaluation of a diazepanone-based library of liposidomycins analogs as MraY inhibitors.

New inhibitors of the bacterial tranferase MraY are described. A scaffold strategy based on the diazepanone central core of liposidomycins, natural inhibitors of MraY has been developed. It involves the introduction of key structural fragments required for biological activity on enantiopure diazepanones by reductive amination, esterification and glycosylation.

Bacterial transferase MraY inhibitors: synthesis and biological evaluation.

New inhibitors of the bacterial transferase MraY are described. Their structure is based on an aminoribosyl-O-uridine like scaffold, readily obtained in two key steps. The amino group can be coupled with proline or guanylated.

Role of the amino acid invariants in the active site of MurG as evaluated by site-directed mutagenesis.

To evaluate their role in the active site of the MurG enzyme from Escherichia coli, 13 residues conserved in the sequences of 73 MurG orthologues were submitted to site-directed mutagenesis. All these residues lay within, or close to, the active site of MurG as defined by its tridimensional structure [Ha et al., Prot.

The essential peptidoglycan glycosyltransferase MurG forms a complex with proteins involved in lateral envelope growth as well as with proteins involved in cell division in Escherichia coli.

In Escherichia coli many enzymes including MurG are directly involved in the synthesis and assembly of peptidoglycan. MurG is an essential glycosyltransferase catalysing the last intracellular step of peptidoglycan synthesis. To elucidate its role during elongation and division events, localization of MurG using immunofluorescence microscopy was performed.

Purification and characterization of the bacterial MraY translocase catalyzing the first membrane step of peptidoglycan biosynthesis.

The MraY translocase catalyzes the first membrane step of bacterial cell wall peptidoglycan synthesis (i.e. the transfer of the phospho-N-acetylmuramoyl-pentapeptide motif onto the undecaprenyl phosphate carrier lipid), a reversible reaction yielding undecaprenylpyrophosphoryl-N-acetylmuramoyl-pentapeptide (lipid intermediate I).