THE ROLE OF VOCs IN MICROFUNGAL COLONIZATION BIOLOGY:

The phenomenon known as "warehouse staining" refers to the growth of dark fungi on exterior surfaces that are subjected to low level exposure to ethanol vapour, specifically around distilleries and spirit maturation facilites. Many fungi are involved in this growth, however, one fungus, which has been called Torula compniacensis, is responsible for initiating the growth; in other words, it is the "founding colonist".  Torula compniacensis, was described by the French mycologist Richon in 1881 (Richon and Petit 1881) who remarked on the presence of darkly coloured fungal growth on stone walls of buildings neighboring distilleries in Cognac, France. The species name "compniacensis" is the Latin work for Cognac, so Richon's fungus literally meant "the Torula of Cognac".  But the name Torula was a bad choice.  Torula dates back to the Swedish mycologist Elias Fries in the 1820s, who used Torula to refer to any fungus that was darkly coloured and yeast-like.  In recent times, scientists have realized, not surprisingly, that all things that are darkly coloured and yeasty are not necessarily related. Thus, for the past 100 years or so, species that were formerly assigned to the genus Torula have slowly been re-assigned to other, more suitable genera.  In 2001, Dr. Lee Crane summarized the current status of species that have been described in the genus Torula (Mycotaxon 80: 109-162), noting that T. compniacensis was one of the species still awaiting transfer to a new, more appropriate genus.

In collaboration with Prof. Wendy Untereiner from Brandon University in Manitoba and with the kind assistance of Dr. Stanley Hughes, we have untangled some of the taxonomic complexities of this group and published a new genus, Baudoinia, to accommodate T. compniacensis; hence, the proper name of the warehouse staining fungus is now Baudoinia compniacensis (Scott et al. 2007).  We chose the generic name to honour Antonin Baudoin, a French pharmacist who first brought the then-unnamed fungus to the attention of the French Botanical Society in 1878.  In an upcoming paper we shall describe several additional species from similar habitats in other parts of the world.

The ecology of warehouse staining is very interesting.  Species of Baudoinia require high relative humidity during at least some parts of the year to support colonization.  Once Baudoinia has started to grow, other fungi become entangled or are dispersed within its mycelium. Thus, at maturity, the colonized surface is polymicrobial. However, the interruption of colonization must target the prevention of the founding colonist, Baudoinia spp.  It is worth noting that Baudoinia spp. are not exclusively associated with spirit maturation.  We have successfully recovered isolates from other habitats (e.g. near commercial bakeries) using a novel semiselective medium (Ewaze et al. 2008a), and confirmed their identites by gene sequencing.  Although species of Baudoinia are able to use ethyl alcohol for their carbon nutrition, colonies of Baudoinia accumulate much greater biomass than can be explained if ethanol were their sole source of nutrition.  We have confirmed that the fungus relies on other readily available organic materials to satisfy its carbon and nitrogen nutrition (see Ewaze et al. 2007), and further discovered that ethanol vapour exerts growth promotive effects that are independent of nutrition.  In particular, we have found two such effects.  Firstly, ethanol vapour provides a germination stimulus for the fungus.  Similar effects have been observed in fungi that cause post-harvest spoiling of ripe fruits.  Secondly, ethanol vapour stimulates the formation of special heat-protective proteins that prevent cells from being killed by exposure to high temperatures (such as those that develop on roofing materials and exterior siding surfaces during full sun exposure in the summertime).  Our newly released paper discusses details of the ethanol physiology of Baudoinia (Ewaze et al. 2008b).

Despite the remarkable world-wide prevalence of this fungus, it has received very little scientific consideration.  Apart from our studies and the original paper of Richon and Petit (1881) (summarized by Roumeguère 1881), the only two non-taxonomic scientific publication to mention this fungus included a very interesting yet obscure paper by Prof. Annelise Kjøller in the Danish journal Botanisk Tidsskrift discussing germination events (Kjøller 1961), and a brief re-description of the warehouse staining phenomenon by Mme. Auger-Barreau (France) (Auger-Barreau 1966).  Our current projects on Baudoinia continue to examine the physiological role of vapour-phase ethanol in the stimulation of growth.  We have a simultaneous phylogenetic study underway examining strains from a variety of geographic regions to explore the extent of genotypic diversity of this fungus, and to describe several additional species in the genus. Our work on Baudoinia was featured on the front cover of the March 2009 issue of MICROBE and described in an accompanying editorial. The full story of the Baudoinia discovery and naming in detailed in a feature article in the June 2011 issue of Wired Magazine