Pathogenic threats and probiotic use in larviculture of the scallop, Pecten maximus

During a series of experiments, bacteriological elements in scallop larval rearing were investigated: larvae susceptibility to pathogens as a function of their age, and the use of probiotic bacteria during larviculture. Younger larvae (d5 PF) were highly more susceptible to pathogenic-challenge than their older siblings, which were challenged at an older age (d15 PF). A challenge with 104 CFU mL−1 of V. pectenicida killed 100% of d5 PF larvae 7 days following challenge, yet killed only 9% of d15 PF larvae 9 days following challenge. Use of the probiotics Phaeobacter gallaeciensis, Alteromonas macleodii 0444 and Neptunomonas sp. 0536, provided for larger larvae, a high yield of competent larvae and, perhaps more importantly, protection against pathogen-challenge similar to levels achieved from antibiotic use. When challenged with V. pectenicida, d29 survivals were 20.3%, 85.1% and 75.0% respectively for control (no probiotic), antibiotic treated, and ‘probiotic mix’ administered larvae. Use of potential probiotic Pseudoalteromonas sp. D41 appeared to hinder scallop larvae. Future use of probiotics in scallop larval rearing would benefit from combined use of P. gallaeciensis, A. macleodii 0444 and Neptunomonas sp. 0536

Establishment of microbiota in larval culture of Pacific oyster, Crassostrea gigas

00000 ăWOS:000383370300057International audienceThis study has two main objectives: (1) to implement a recycling aquaculture system (RS) for the larvae of the oyster Crassostrea gigas, and (2) to characterise the bacterial communities established in different compartments of this system. An RS with 25% fresh seawater addition per hour and another with no addition (0%) were compared with a flow-through system (FT). Larval survival was equivalent in RS and FT, but growth rate was 17% slower in RS than in FT. The physical chemical parameters remained stable, except for pH that decreased to 7.75 and salinity that increased to 37.5% in the RS 0%. In both systems, the cultivable bacteria were present in similar numbers in seawater (around 10(5) ml(-1)) and in larvae (10(3) larva(-1)) on day 15. Bacterial assemblages, characterised by 454 pyrosequencing of the V1-V3 region of 16S rRNA, were highly similar (50-65%) for compartments, regardless of rearing system and sampling time, but the compartments were clearly different from one another. At the beginning of rearing, larval microbiota was mostly composed of Proteobacteria (similar to 90%), with 47% Rhodobacteraceae (gamma-Proteobacteria). beta-Proteobacteria, including Pseudoalteromonas, Alteromonas and a few vibrios, declined in the rearing period (25% on day 7 to 9% on day 15). At the end of rearing, colonisation by two members of the Burkholderiales (beta-Proteobacteria), 45% on average on day 15, had decreased overall diversity. Seawater microbiota was more stable with in all batches as one unclassified bacterium present in all batches (27 +/- 7%), 42 OTUs of alpha-Proteobacteria (19 +/- 7%) and 26 of gamma-Proteobacteria (14%). Change was due notably to a species of Cryomorphaceae (Flavobacteria) that reached 15 +/- 7% on day 15. Predatory bacteria, Bdellovivrio spp. and Bacteriovorax spp. were present (3-12%) and could participate in the regulation of bacterial populations. Bacterial assemblages in RS bioreactors remained stable and were mainly composed of Rhodobacteraceae, Rhizobiales and Planctomycetes. Only a few nitrite oxidisers were detected and no ammonia oxidisers, although nitrification was efficient in RS without addition of new water. The larval microbiota was made up of bacteria growing in seawater, but some such as the Burkholderiales could have come from the broodstock. Several bacteria predominant in seawater were first harboured in the algal culture. Finally, despite sanitary measures in the hatchery (UV treatment and frequent cleaning), the diversity of microbiota remained high, and it did not contain pathogenic bacteria. The presence of this microbiota might even be indispensable to ensure normal ontogenesis, as suggested by the holobiont concept. Statement of relevance RAS and control of microbiota should improve bivalve larval culture

Characterization of endospore-forming bacteria producing extracellular enzymes isolated from the Djurdjura Mountains in Algeria

Biodiversity in mountains in Algeria appears scanty and has not been thoroughly investigated. However, the mountain soil has been shown as an  almost entire reserve of novel enzymes with interesting properties for industrial and environmental applications. In the present study, thirty  bacterial strains were isolated from the Djurdjura Mountains in Kabylia (Algeria) and were studied for their ability to produce enzymes to be possibly  used in biotechnological processes such as amylase, caseinase, and chitinase. The characterization of these isolates was carried out using  morphological, physiological, and biochemical characteristics. All the data obtained with regards to the phenotypical properties of the isolates,  confirmed that the strains belonged to the Bacillus group. In addition, the 16S rRNA gene of the two retained strains KA15 and LK-DZ15 was also  amplified and sequenced. Phylogenetic tree was, afterwards, constructed. The nucleotide sequences and blast analyses confirmed that the KA15  and LK-DZ15 strains were closely related to those of the Bacillus altitudinis (accession n°.: MK874318) and Paenibacillus timonensis (accession n°.:  MK734103) strains. The presence of amylases, proteases, and chitinases in KA15 and LK-DZ15 isolates are an indicator of their pivotal application in  a variety of biotechnological processes.&nbsp

Determination of stocking density limits for Crassostrea gigas larvae reared in flow-through and recirculating aquaculture systems and interaction between larval density and biofilm formation

WOS:000407887300001International audienceThe first aim of this study was to determine the stocking density limits for Pacific oyster Crassostrea gigas larvae reared in flow-through system (FTS) and recirculating aquaculture systems (RAS). The second aim was to examine biofilm formation on the larval tank wall and its interaction with larvae growth. Three larvae concentrationswere tested: 50, 150, and 300mL(-1). Chemical parameters and larvae performance were measured. The biofilm was observed by scanning electron microscopy, and its bacterial composition was investigated by pyrosequencing analysis of part of the 16S rRNA gene. The highest growth (13 mu mday(-1)), survival (87%) and metamorphosis (50%) rates were observed in FTS at 50 larvaemL(-1), while lower and similar performances occurred at 150 larvaemL(-1) in both systems. At 300 larvaemL(-1), performances dropped with occurrence of mortality. Biofilm thickness increased with larval density. The pioneer bacteria were coccobacilli followed by filamentous bacteria. The latter constituted abundant braids at the end of rearing at high larval concentrations. The first colonizers were mainly Rhodobacteraceae (alpha-Proteobacteria). The filamentous bacteria were Saprospirae (Bacteroidetes) and Anaerolineae (Chloroflexi). The biofilm was also made up of other minor groups, including Actinobacteria, Planctomycetes, delta-, gamma-Proteobacteria, and Flavobacteriales. The biofilm'scompositionwas more similar to that found in a sewage reactor than in open-sea collectors, which might negatively influence larval rearing due to potential metabolites. This first study on biofilms provides insights into the interaction between rearing density and larvae performance