Baudoinia compniacensis growing on various surfaces (Credits: James Scott)

Baudoinia compniacensis (Credits: James Scott)

The extremophilic sooty mold Baudoinia compniacensis is the prominent pioneering species in the primary successional community known as “warehouse staining”, where darkly pigmented microbes form dry biofilms on outdoor surfaces periodically subjected to low level exposure to ethyl alcohol vapour, such as those around distilleries, spirit maturation facilities (“bond warehouses”) and commercial bakeries. Pronounced blackening often extends considerable distances from alcohol emission source, indiscriminately colonizing exposed surfaces ranging from vegetation to built structures, sign posts and fences (including those made from glass and stainless steel). Mature colonies are crust-like and scorched in appearance, sometimes reaching 1—2 cm in thickness.

Baudoinia compniacensis is world-wide in its distribution, reported from most geographic localities where spirits are manufactured and aged. In addition to ethanolic vapour, it requires high relative humidity during at least some parts of the year to support its colonization. Baudoinia compniacensis can assimilate ethyl alcohol but not other simple alcohols; however, the fungus relies on other more metabolically lucrative organic materials including carbohydrates and proteins to satisfy its carbon nutrition. Moreover, the role of ethanol in the colonization biology of the fungus appears to be non-nutritional, facilitating growth regulation by acting as a germination initiator (similar effects have been observed in fungi that cause post-harvest spoiling of ripe fruits). Ethanol exposure also stimulates the expression of heat-protective proteins that protect cells against high temperature (such as those that develop on roofing materials and exterior walls subject to full sun exposure during summertime).

Microscopically, B. compniacensis is characterized by thick-walled, rugulose, darkly-pigmented hyphae that disarticulate to form irregularly globose to barrel-shaped conidia. Laboratory cultures can be cultivated on a range of growth media, but develop extremely slowly. A homothallic mating system appears to be present but non-functional, consistent with the absence of a reported teleomorph. Sequencing studies have shown Baudoinia to be phylogenetic Teratosphaereaceae (Capnodiales: Dothideomycetes), closely related to Friedmanniomyces, a genus of psychrophilic lithobionts. Baudoinia compniacensis is unique in the Capnodiales in its clear association with allogenic environmental factors, particularly industrial processes. This feature, coupled with its manifest lack of animal or plant pathogenicity make B. compniacensis an interesting candidate for comparative genomic analysis.