Transcriptional changes in Crassostrea gigas oyster spat following a parental exposure to the herbicide diuron.

The Pacific oyster Crassostrea gigas is the main oyster species produced in the world, and a key coastal economic resource in France. High mortalities affect Pacific oysters since 2008 in France and Europe. Their origins have been attributed to a combination of biotic and abiotic factors, underlining the importance of environment quality. The impact of water pollution has been pointed out and one of the pollutants, the genotoxic herbicide diuron, occurs at high concentrations all along the French coasts. Previous work has revealed that a parental exposure to diuron had a strong impact on hatching rates and offspring development even if spats were not exposed to diuron themselves. In this study, we explored for the first time the transcriptional changes occurring in oyster spats (non exposed) originating from genitors exposed to an environmentally relevant concentration of diuron during gametogenesis using the RNAseq methodology. We identified a transcriptomic remodeling revealing an effect of the herbicide. Different molecular pathways involved in energy production, translation and cell proliferation are particularly disturbed. This analysis revealed modulated candidate genes putatively involved in response to oxidative stress and mitochondrial damage in offspring of genitors exposed to diuron. Complementary measures of the activity of enzymes involved in these latter processes corroborate the results obtained at the transcriptomic level. In addition, our results suggested an increase in energy production and mitotic activity in 5-month-spats from diuron-exposed genitors. These results could correspond to a "catch-up growth" phenomenon allowing the spats from diuron-exposed genitors, which displayed a growth delay at 3 months, to gain a normal size when they reach the age of 6 months. These results indicate that exposure to a concentration of diuron that is frequently encountered in the field during the oyster's gametogenesis stage can impact the next generation and may result in fitness disturbance.

Proteobacteria from the human skin microbiota: Species-level diversity and hypotheses.

The human skin microbiota is quantitatively dominated by Gram-positive bacteria, detected by both culture and metagenomics. However, metagenomics revealed a huge variety of Gram-negative taxa generally considered from environmental origin. For species affiliation of bacteria in skin microbiota, clones of 16S rRNA gene and colonies growing on diverse culture media were analyzed. Species-level identification was achieved for 81% of both clones and colonies. Fifty species distributed in 26 genera were identified by culture, mostly belonging to Actinobacteria and Firmicutes, while 45 species-level operational taxonomic units distributed in 30 genera were detected by sequencing, with a high diversity of Proteobacteria. This mixed approach allowed the detection of 100% of the genera forming the known core skin Gram-negative microbiota and 43% of the known diversity of Gram-negative genera in human skin. The orphan genera represented 50% of the current skin pan-microbiota. Improved culture conditions allowed the isolation of Roseomonas mucosa, Aurantimonas altamirensis and Agrobacterium tumefaciens strains from healthy skin. For proteobacterial species previously described in the environment, we proposed the existence of skin-specific ecotypes, which might play a role in the fine-tuning of skin homeostasis and opportunistic infections but also act as a shuttle between environmental and human microbial communities. Therefore, skin-associated proteobacteria deserve to be considered in the One-Health concept connecting human health to the health of animals and the environment.

Schistosoma mansoni: developmental arrest of miracidia treated with histone deacetylase inhibitors.

In the present study, we examined the effect of the histone deacetylase (HDAC) inhibitors trichostatin A (TSA), valproic acid (VA) and sodium-butyrate on the metamorphosis of larvae of the human blood-fluke Schistosoma mansoni from the free-swimming miracidia into the intramolluskal sporocyst. We show that HDAC inhibitors block transformation in concentration dependant manner. TSA reversibly blocks this developmental process: only 13+/-11% of TSA treated miracidia transform into sporocysts in-vitro, compared to 92+/-3% in the mock-treated control. Other enzyme inhibitors such as cycloheximide or hydroxyurea had no effect on metamorphosis. For treatment of up to 4 h, the effect of TSA was completely reversible. Our data indicates that HDAC activity is necessary for the transformation of S. mansoni miracidia during infection of the snail host.

Isolation, free-living capacities, and genome structure of "Candidatus Glomeribacter gigasporarum," the endocellular bacterium of the mycorrhizal fungus Gigaspora margarita.

"Candidatus Glomeribacter gigasporarum" is an endocellular beta-proteobacterium present in the arbuscular mycorrhizal (AM) fungus Gigaspora margarita. We established a protocol to isolate "Ca. Glomeribacter gigasporarum" from its host which allowed us to carry out morphological, physiological, and genomic investigations on purified bacteria. They are rod shaped, with a cell wall typical of gram-negative bacteria and a cytoplasm rich in ribosomes, and they present no flagella or pili. Isolated bacteria could not be grown in any of the 19 culture media tested, but they could be kept alive for up to 4 weeks. PCR-based investigations of purified DNA from isolated bacteria did not confirm the presence of all genes previously assigned to "Ca. Glomeribacter gigasporarum." In particular, the presence of nif genes could not be detected. Pulsed-field gel electrophoresis analyses allowed us to estimate the genome size of "Ca. Glomeribacter gigasporarum" to approximately 1.4 Mb with a ca. 750-kb chromosome and a 600- to 650-kb plasmid. This is the smallest genome known for a beta-proteobacterium. Such small genome sizes are typically found in endocellular bacteria living permanently in their host. Altogether, our data suggest that "Ca. Glomeribacter gigasporarum" is an ancient obligate endocellular bacterium of the AM fungus G. margarita.

Penaeidins, antimicrobial peptides with chitin-binding activity, are produced and stored in shrimp granulocytes and released after microbial challenge.

Penaeidins are members of a new family of antimicrobial peptides isolated from a crustacean, which present both Gram-positive antibacterial and antifungal activities. We have studied the localization of synthesis and storage of penaeidins in the shrimp Penaeus vannamei. The distribution of penaeidin transcripts and peptides in various tissues reveals that penaeidins are constitutively synthesized and stored in the shrimp haemocytes. It was shown by immunocytochemistry, at both optical and ultrastructural levels, that the peptides are localized in granulocyte cytoplasmic granules. The expression and localization of penaeidins were further analysed in shrimp subjected to microbial challenge. We found that (1) penaeidin mRNA levels decrease in circulating haemocytes in the first 3 hours following stimulation and (2) an increase in plasma penaeidin concentration occurs after microbial challenge, together with (3) a penaeidin immunoreactivity in cuticular tissue, which can be related to the chitin-binding activity we demonstrate here for penaeidins.