Comparative genomics sheds new light on the microbiology of the whiskey fungus Baudoinia

Baudoinia compniacensis is a melanized saprobic fungus that causes blackening of surfaces in the vicinity of spirit maturation warehouses, commercial bakeries, or distilleries that are exposed to low levels of ethanol vapour; with the fungus growing on the ethanol in the vapour. The surfaces that are most affected are those that are highly exposed and undergo extreme diurnal temperature fluctuations. This review focuses on the currently available physiological and genomic data to facilitate a comparative analysis of Baudoinia compniacensis with the genomes of a panel of fungi representing a broad spectrum of lifestyles, stress-tolerance strategies, ecological specializations and convergent adaptations that parallel those of Baudoinia, together with fungi with ethanol tolerance. By anchoring Baudoinia within this rationally selected comparative framework, this review attempts to differentiate traits that are widely shared among melanized and extremotolerant fungi from those that are unique in helping to enable the fungus colonize ethanol-rich, anthropogenic surfaces. The review also provides insights into a number of potential adaptive genetic traits that are likely to underpin the ecological success of Baudoinia, including genes involved in carbon and pentose phosphate metabolism, carbohydrate-active enzymes, genes involved in peroxisome and mitochondrial fatty-acid metabolism, together with calcium signalling and in melanin biosynthesis. We place these traits in comparative perspective, noting that many are shared across the broader oligotrophic, melanized black-fungal guild and that ethanol appears to act as a multifunctional, concentration-dependent input — germination cue, carbon source and stressor — rather than as a uniquely defining resource, with wood- and plant-derived carbohydrates likely to supplement ethanol as carbon sources. We also identify priority avenues for future work, including the sequencing of confirmed B. compniacensis, systematic survey of natural (non-industrial) reservoirs, and experimental separation of the signalling and nutritional roles of ethanol, together with direct characterisation of carbon metabolism on lignocellulosic (wood-cask) substrates.