Metabolic Regulation of Copper Toxicity during Marine Mussel Embryogenesis.

The development of new tools for assessing the health of cultured shellfish larvae is crucial for aquaculture industries to develop and refine hatchery methodologies. We established a large-volume ecotoxicology/health stressor trial, exposing mussel (Perna canaliculus) embryos to copper in the presence of ethylenediaminetetraacetic acid (EDTA). GC/MS-based metabolomics was applied to identify potential biomarkers for monitoring embryonic/larval health and to characterise mechanisms of metal toxicity. Cellular viability, developmental abnormalities, larval behaviour, mortality, and a targeted analysis of proteins involved in the regulation of reactive oxygen species were simultaneously evaluated to provide a complementary framework for interpretative purposes and authenticate the metabolomics data. Trace metal analysis and speciation modelling verified EDTA as an effective copper chelator. Toxicity thresholds for P. canaliculus were low, with 10% developmental abnormalities in D-stage larvae being recorded upon exposure to 1.10 µg·L-1 bioavailable copper for 66 h. Sublethal levels of bioavailable copper (0.04 and 1.10 µg·L-1) caused coordinated fluctuations in metabolite profiles, which were dependent on development stage, treatment level, and exposure duration. Larvae appeared to successfully employ various mechanisms involving the biosynthesis of antioxidants and a restructuring of energy-related metabolism to alleviate the toxic effects of copper on cells and developing tissues. These results suggest that regulation of trace metal-induced toxicity is tightly linked with metabolism during the early ontogenic development of marine mussels. Lethal-level bioavailable copper (50.3 µg·L-1) caused severe metabolic dysregulation after 3 h of exposure, which worsened with time, substantially delayed embryonic development, induced critical oxidative damage, initiated the apoptotic pathway, and resulted in cell/organism death shortly after 18 h of exposure. Metabolite profiling is a useful approach to (1) assess the health status of marine invertebrate embryos and larvae, (2) detect early warning biomarkers for trace metal contamination, and (3) identify novel regulatory mechanisms of copper-induced toxicity.

Immune response in probiotic-fed New Zealand black-footed abalone (Haliotis iris) under Vibrio splendidus challenge.

Vibriosis disease is a major constraint for sustainable molluscan aquaculture. Development of strategies to enhance disease resistance during grow out would greatly reduce stock mortality and boost production yields. In this study, New Zealand black-footed abalone (Haliotis iris) were fed a commercial diet enhanced with multi-strain probiotics (Exiguobacterium JHEb1, Vibrio JH1 and Enterococcus JHLDc) for four months, then challenged with an injection of pathogenic Vibrio splendidus. Host immune responses in haemocytes were characterized using flow cytometry by measuring total haemocyte counts (THC) and viability, degree of apoptosis, and production of reactive oxygen species (ROS) 48 h post-challenge. Probiotic-fed abalone had significantly higher survival rates compared to control animals after the bacterial challenge. Infected probiotic-fed abalone also had significantly higher haemocyte viabilities, slightly lower proportions of haemocytes undergoing early apoptosis, and lower proportions of ROS-producing haemocytes compared to infected control-fed abalone. In addition, metabolite profiles of muscle tissues generated via gas chromatography-mass spectrometry (GC-MS) delivered complimentary evidence to support a perturbed ROS-regulatory system in infected abalone through changes in key metabolites associated with glutathione biosynthesis. The results of this study provide valuable information to assist in farm management practices, leading to enhance production and sustainability of the New Zealand abalone aquaculture industry.

Effects of depleting the essential central metabolic enzyme fructose-1,6-bisphosphate aldolase on the growth and viability of Candida albicans: implications for antifungal drug target discovery.

The central metabolic enzyme fructose-1,6-bisphosphate aldolase (Fba1p) catalyzes a reversible reaction required for both glycolysis and gluconeogenesis. Fba1p is a potential antifungal target because it is essential in yeast and because fungal and human aldolases differ significantly. To test the validity of Fba1p as an antifungal target, we have examined the effects of depleting this enzyme in the major fungal pathogen Candida albicans. Using a methionine/cysteine-conditional mutant (MET3-FBA1/fba1), we have shown that Fba1p is required for the growth of C. albicans. However, Fba1p must be depleted to below 5% of wild-type levels before growth is blocked. Furthermore, Fba1p depletion exerts static rather than cidal effects upon C. albicans. Fba1p is a relatively abundant and stable protein in C. albicans, and hence, Fba1p levels decay relatively slowly following MET3-FBA1 shutoff. Taken together, our observations can account for our observation that the virulence of MET3-FBA1/fba1 cells is only partially attenuated in the mouse model of systemic candidiasis. We conclude that an antifungal drug directed against Fba1p would have to be potent to be effective.