AbstractsBiology & Animal Science

The toxicity of arsenic is greatly dependent on its chemical form and only one arsenic compound is considered to be non-toxic, arsenobetaine (AB). The formation pathway for AB is still unknown despite being found in high concentrations and proportions in many marine organisms. AB is found in fewer organisms and at lower concentrations and proportions in the terrestrial environment with the exception of the fruiting bodies (FBs), or mushrooms, of terrestrial fungi. The present study interrogated AB formation pathways in the complete fungal organism (fungus and associated microbes) through a combination of fruiting body and substrate analysis, and culture experiments. The analytical methods used were reviewed and selected to include complementary high performance liquid chromatography ??? inductively coupled plasma mass spectrometry (HPLC-ICP- MS) and X-ray absorption spectroscopy (XAS), specifically x-ray absorption near edge structure (XANES) and XAS 2-dimensional imaging. A comprehensive survey of arsenic compounds in the mushrooms of 46 different fungus species over a diverse range of phylogenetic groups were collected from Canadian grocery stores and background (sites with lower arsenic concentrations) and arsenic-contaminated areas. The major arsenic compounds in mushrooms were found to be similar among phylogenetic groups, and AB was generally absent in log-growing mushrooms, suggesting the microbial community may influence arsenic speciation in mushrooms. The high proportion of AB in mushrooms with puffball or gilled morphologies may suggest that AB acts as an osmolyte in certain mushrooms to help maintain fruiting body structure. The mycelia of three different fungi species (targeting those containing AB, including Agaricus bisporus) were cultured axenically and exposed to AB, arsenate (As(V)) and dimethylarsinoyl acetic acid (DMAA, a potential AB precursor) for 60 days. The mycelia of all fungi species accumulated all arsenic compounds with two species (those whose fruiting bodies contain mostly AB) accumulating significantly more AB than other compounds, but few biotransformations were observed. Thus AB biosynthesis by fungus mycelium is unlikely. To investigate the involvement of reproductive life stage of Agaricus species (an AB-containing fungus) in AB formation growth substrate and fungi were collected and analyzed during the commercial growth of A. bisporus. AB was found to be the major arsenic compound in the fungus at the earliest growth stage of fruiting (the primordium). AB was revealed by two-dimensional imaging to be present only in fungal tissue and not in embedded substrate of an A. bisporus primordium grown on As(V) treated substrate, and in a mature A. campestris fruiting body stalk from arsenic contaminated mine tailings. These findings indicate AB formation is likely associated with the reproductive life stage of the fungus. To interrogate the contribution to AB formation of the microbial communities associated with mushrooms, 16s pyrosequencing techniques were used to reveal that phyla…