N-acylhomoserine lactone-degrading bacteria isolated from hatchery bivalve larval cultures

Abstract

The health of marine bivalve larvae is greatly affected by bacteria in the environment particularly when reared in marine hatcheries. This is generally because high stocking densities resulting in high organic loads of both food and faeces, can support increased bacterial growth and biomass levels. Increased bacterial load can lead to larval disease referred to as bacillary necrosis (BN) leading in turn to rapid larval mortality and loss of production. Despite more than 50 years since the first detailed description of BN, we still do not fully understand its causes and mechanisms. Through the manipulation of a model larval culture of the Australian blue mussels (Mytilus galloprovincialis), we determined that BN is linked with rapid and systematic changes in the bacterial community. Early investigation of larval mortality in bivalve larval cultures in the 1950s reported mortality associated with infection by gram negative bacilli that necrotised larval tissues, leading to the descriptive term bacillary necrosis (BN) 1. The disease is capable of causing total collapse of larval cultures (larval crash) in a period of 24-48 hours and is today, the most prevalent hatchery disease worldwide, affecting more than 20 bivalve species. Whilst it is difficult to quantify the impact of BN in shellfish hatcheries, frequent recurrence can severely impact hatchery production with repercussions often felt throughout the supply chains. The prevailing view that BN is an opportunistic disease leads to the emphasis on sound husbandry practices primarily to reduce excess build-up of organic matter. However, whether and how enriched organic conditions are linked with development of BN is unclear. Efforts to study BN have also been complicated by the unpredictable nature of the outbreaks. To address this problem, we deliberately overfed a series of identical small-scale larval cultures with microalgae to create an environment that would increase the incidence of the disease. In cultures that developed mass mortal-ities, automated ribosomal intergenic spaces analysis (ARISA) demonstrated that BN involves rapid and systematic changes in the bacterial community, firstly in the seawater, then rapidly proceeding to the larvae as the disease progresses and necrosis occurs (Figure 1). This study shows that, at least within the system analysed here, BN is a condition of abnormal changes in seawater-associated communities that are capable of affecting the larvae, suggestive of seawater-to-larvae infectivity. The similarity of bacterial communities in seawater and larvae at the onset of mortality suggest swamping by outgrowth of particular bacteria. Bacterial diversity examination using Illumina MiSeq sequencing of 16S rRNA ampli-cons showed that mortality in the model systems was linked with a bacterial community increasingly dominated by Psychroserpens, Polaribacter, Marinomonas, and members of the Candidatus phylum Gracilibacteria. The observation that BN did not occur in all overfed cultures suggests variability in causation made it difficul...

N-Acyl Dehydrotyrosines, Tyrosinase Inhibitors from the Marine Bacterium Thalassotalea sp. PP2-459

“…based on 16S rRNA sequence comparison (European Nucleotide Archive; accession number LN898116). 20 It has been deposited in the Spanish Type Culture Collection (CECT) under restricted access. Cultures were maintained in YP seawater medium (1 g yeast extract, 5 g peptone, 22.5 g Instant Ocean (Spectrum Brands, Blacksburg, VA) per liter of deionized water) at 25 °C and shaking at 200 rpm.…”

“…PP2-459, a strain isolated from a carpet-shell clam ( Ruditapes decussata ) harvested in a bivalve hatchery located in Galicia (NW Spain). 20 PP2-459 was previously determined to have quorum quenching ability against key bivalve aquaculture pathogens, including Vibrio anguillarum . 20 Hence, PP2-459 has been proposed as a candidate for probiotic applications in aquaculture.…”

“…20 PP2-459 was previously determined to have quorum quenching ability against key bivalve aquaculture pathogens, including Vibrio anguillarum . 20 Hence, PP2-459 has been proposed as a candidate for probiotic applications in aquaculture. Due to structural similarity with known tyrosinase inhibitors such as N -acylated tyrosines, 1 – 5 were evaluated for their inhibition of the tyrosinase enzyme.…”

New Insights into Pathogenic Vibrios Affecting Bivalves in Hatcheries: Present and Future Prospects

“…The use of AHL-degrading bacteria has been successful in increasing the survival of turbot ( Scophthalmus maximus ) and freshwater prawn have ( Macrobrachium rosenbergii ) larvae (Tinh et al, 2008; Nhan et al, 2010). Torres et al (2013) detected and isolated AHL-degrading bacteria from a bivalve hatchery, including representatives of genera Alteromonas and Thalassomonas (further reclassified as belonging to genus Thalassotalea ) (Deering et al, 2016), pointing out their potential to be employed to attenuate the production of virulence factors by bivalve pathogens. Since new agents for controlling bacterial diseases can be considered only when their efficacy is demonstrated using different challenge tests, further research is needed in order to elucidate the in vivo interactions of quorum-quenching microorganisms with aquaculture pathogens and animals.…”

Ontogeny of bivalve immunity: assessing the potential of next‐generation sequencing techniques

“…To make advancements in the field of bivalve immunology, we need to improve our understanding of the factors that influence and stimulate stress responses (Fitzgerald-Dehoog et al 2012;Guerra et al 2012). Mortalities affecting hatchery facilities cause economic hardship (Roch 1999); they are usually due to infections associated with microorganisms (Ren et al 2013b;Torres et al 2013) and sometimes amplified by genomic aberrations (Mart ın-G omez et al 2013). To stabilize short-term farm production and promote long-term performance, it is essential to simultaneously improve our knowledge of immune defence mechanisms and successfully develop targeted genetic approaches.…”