Differential microbial uptake of dissolved amino acids and amino sugars in surface waters of the Atlantic Ocean

Nitrogen bioavailability is considered to limit the productivityof oceanic oligotrophic gyres, the largest biomes on Earth.In order to assess the microbial requirement for small organicnitrogen molecules in these and other waters, the microbialuptake rates of amino acids (leucine, methionine and tyrosine)and amino sugars (glucosamine and N-acetyl-glucosamine) as wellas glucose were compared using a bioassay technique of radiotracerdilution. The bioassays were carried out on four mid-Atlanticmeridional transects spanning a latitudinal range from 60°Nto 42°S. The mean concentrations of both bioavailable N-acetyl-glucosamineand glucose in the gyres were 1 nM, four times higher than themean leucine concentration. Despite its lower concentration,the mean turnover time of leucine in the gyres of 15 h was 90and 9 times shorter than the turnover time of N-acetyl-glucosamineand glucose, respectively. In addition, among amino acids, leucinewas taken up in the gyres at a rate of 1.5 times faster thanmethionine and 2.5 times faster than tyrosine. Hence, oceanicbacterioplankton as a community showed a clear preference foramino acids, particularly leucine, compared with amino sugars.The preferential uptake of amino acids to sugars challengesthe concept of microbial nitrogen or carbon limitation in theopen ocean.     

Light enhanced amino acid uptake by dominant bacterioplankton groups in surface waters of the Atlantic Ocean

(35)S-Methionine and (3)H-leucine bioassay tracer experiments were conducted on two meridional transatlantic cruises to assess whether dominant planktonic microorganisms use visible sunlight to enhance uptake of these organic molecules at ambient concentrations. The two numerically dominant groups of oceanic bacterioplankton were Prochlorococcus cyanobacteria and bacteria with low nucleic acid (LNA) content, comprising 60% SAR11-related cells. The results of flow cytometric sorting of labelled bacterioplankton cells showed that when incubated in the light, Prochlorococcus and LNA bacteria increased their uptake of amino acids on average by 50% and 23%, respectively, compared with those incubated in the dark. Amino acid uptake of Synechococcus cyanobacteria was also enhanced by visible light, but bacteria with high nucleic acid content showed no light stimulation. Additionally, differential uptake of the two amino acids by the Prochlorococcus and LNA cells was observed. The populations of these two types of cells on average completely accounted for the determined 22% light enhancement of amino acid uptake by the total bacterioplankton community, suggesting a plausible way of harnessing light energy for selectively transporting scarce nutrients that could explain the numerical dominance of these groups in situ.     

Origin and function of the two major tail proteins of bacteriophage SPP1

The majority of bacteriophages have a long non-contractile tail (Siphoviridae) that serves as a conduit for viral DNA traffic from the phage capsid to the host cell at the beginning of infection. The 160-nm-long tail tube of Bacillus subtilis bacteriophage SPP1 is shown to be composed of two major tail proteins (MTPs), gp17.1 and gp17.1*, at a ratio of about 3:1. They share a common amino-terminus, but the latter species has approximately 10 kDa more than gp17.1. A CCC.UAA sequence with overlapping proline codons at the 3' end of gene 17.1 drives a programmed translational frameshift to another open reading frame. The recoding event generates gp17.1*. Phages carrying exclusively gp17.1 or gp17.1* are viable, but tails are structurally distinct. gp17.1 and the carboxyl-terminus of gp17.1* have a distinct evolutionary history correlating with different functions: the polypeptide sequence identical in the two proteins is responsible for assembly of the tail tube while the additional module of gp17.1* shields the structure exterior exposed to the environment. The carboxyl-terminal extension is an elaboration present in some tailed bacteriophages. Different extensions were found to combine in a mosaic fashion with the MTP essential module in a subset of Siphoviridae genomes.     

Le BNP dans l’exploration de l’insuffisance cardiaque et le syndrome coronarien aigu

Le BNP, ou “Brain Natriuretic Peptide”, initialement mis en évidence au niveau de l’encéphale de porc, est aujourd’hui renommé “B-type natriuretic peptide” en raison de l’origine myocardique chez l’homme. Sa synthèse, principalement réalisée au niveau du ventricule gauche, à partir d’une pro-hormone, le Pro-BNP, est liée à l’état d’étirement de la paroi ventriculaire.     

Colon cancer stemness as a reversible epigenetic state: Implications for anticancer therapies

The recent discovery of cancer cell plasticity, i.e. their ability to reprogram into cancer stem cells (CSCs) either naturally or under chemotherapy and/or radiotherapy, has changed, once again, the way we consider cancer treatment. If cancer stemness is a reversible epigenetic state rather than a genetic identity, opportunities will arise for therapeutic strategies that remodel epigenetic landscapes of CSCs. However, the systematic use of DNA methyltransferase and histone deacetylase inhibitors, alone or in combination, in advanced solid tumors including colorectal cancers, regardless of their molecular subtypes, does not seem to be the best strategy. In this review, we first summarize the knowledge researchers have gathered on the epigenetic signatures of CSCs with the difficulty of isolating rare populations of cells. We raise questions about the relevant use of currently available epigenetic inhibitors (epidrugs) while the expression of numerous cancer stem cell markers are often repressed by epigenetic mechanisms. These markers include the three cluster of differentiation CD133, CD44 and CD166 that have been extensively used for the isolation of colon CSCs.and . Finally, we describe current treatment strategies using epidrugs, and we hypothesize that, using correlation tools comparing associations of relevant CSC markers with chromatin modifier expression, we could identify better candidates for epienzyme targeting.     

Inactivation of the Spirochete recA Gene Results in a Mutant with Low Viability and Irregular Nucleoid Morphology

Recently, we have shown the first evidence for allelic exchange in Leptospira spp. By using the same methodology, the cloned recA of Leptospira biflexa was interrupted by a kanamycin resistance cassette, and the mutated allele was then introduced into the L. biflexa chromosome by homologous recombination. The recA double-crossover mutant showed poor growth in liquid media and was considerably more sensitive to DNA-damaging agents such as mitomycin C and UV light than the wild-type strain. The efficiency of plating of the recA mutant was about 10% of that of the parent strain. In addition, microscopic observation of the L. biflexa recA mutant showed cells that are more elongated than those of the wild-type strain. Fluorescent microscopy of stained cells of the L. biflexa wild-type strain revealed that chromosomal DNA is distributed throughout most of the length of the cell. In contrast, the recA mutant showed aberrant nucleoid morphologies, i.e., DNA is condensed at the midcell. Our data indicate that L. biflexa RecA plays a major role in ensuring cell viability via mechanisms such as DNA repair and, indirectly, active chromosome partitioning.