Impacts of fungi on marine organisms and human health : the 2009 Australian dust storm associated Aspergillus sydowii bloom

The incidence of massive Aspergillus sydowii marine “fungal slicks” along the east coast of Australia between Brisbane and Sydney in the wake of the 2009 dust storm, covering an area 25-times the surface of England, has raised concerns about marine ecosystem as well as human health impacts. Our current knowledge on the impacts of fungi on marine organisms and human health through seafood consumption is very limited. The present study aimed at: i) Elucidation of pathogenicity of A. sydowii against the coral endosymbiont Symbiodinium as a model to elucidate the cause of sea fan coral aspergillosis; ii) Impacts of emerging mycotoxins on marine organisms using a fish gill cell line model (RT-gillW1); and iii) Assessment of combined toxicity of mycotoxins and phycotoxins on human cell line models (intestinal HT-29 and neuroblastoma SH-SY5Y). Dust originated (ASBS), terrestrial (FRR5068) and sea fan coral pathogenic (FK1) A. sydowii fungal strains all produced the same set of known A. sydowii metabolites, including sydowinin A, sydowinin B, sydowinol, sydonic acid, hydroxysydonic acid and sydonol, but minor metabolites differed between strains. Sydowic acid, sydowinol and sydowinin A adversely affected photophysiological performance (Fv/Fm) of the coral reef dinoflagellate endosymbiont Symbiodinium. Moreover, different Symbiodinium clades exhibited varying sensitivities to these fungal metabolites, mimicking sensitivity to coral bleaching phenomena in sea fan coral aspergillosis. Re-evaluation of the 2009 dust storm silks confirmed the dominance of A. sydowii (73.7%), with varying metabolite profiles, but these all produced sydonic acid. Other minor fungal isolates newly found in this study included Cladosporium, Penicillium and other Aspergillus species, which suggests potential secondary colonisation of the 2009 dust storm rafts. Shellfish and 2009 dust storm associated mycotoxins (e.g. patulin, alamethicin, gliotoxin and major A. sydowii metabolites) exhibited significant cytotoxicity to the fish gill cell (RT-gillW1) cell line with IC50 (inhibitory concentration 50%) values of 0.098 – 103.7 μM. Previously reported combined effect of alamethicin and domoic acid using a larval Diptera bioassay, was not observed when using RT-gillW1 cells. The current study also evaluated the cytotoxicity of shellfish and dust storm associated mycotoxins and algal toxin okadaic acid (responsible for the syndrome of Diarrhetic Shellfish Poisoning), either alone or in combination, when challenged against human intestinal (HT-29) and neuroblastoma (SH-SY5Y) cell lines. Combinations of okadaic acid, sydowinin A, alamethicin, patulin, and gliotoxin exhibited shifts from antagonism to additive/synergistic interactions with increasing cytotoxicity, with okadaic acid–sydowinol displaying an antagonistic relationship against HT-29 cells. Furthermore, only the okadaic acid–sydowinin A combination showed synergism, while okadaic acid combined with sydowinol, alamethicin, patulin, or with gliotoxin demonstrated antagonism against SH-SY5Y. While Diarrhetic Shellfish Poisoning from okadaic acid and analogues in many parts of the world is considered to be a comparatively minor seafood toxin syndrome, our human cell model studies provide the first insights that synergisms with mycotoxin may aggravate human health impacts. These findings highlight the shortcomings of current regulatory approaches, which do not regulate for mycotoxins in shellfish and treat seafood toxins as if they occur as single toxins.