Roof-Inhabiting Cousins of Rock-Inhabiting Fungi: Novel Melanized Microcolonial Fungal Species from Photocatalytically Reactive Subaerial Surfaces

Abstract

Subaerial biofilms (SAB) are an important factor in weathering, biofouling, and biodeterioration of bare rocks, building materials, and solar panel surfaces. The realm of SAB is continually widened by modern materials, and the settlers on these exposed solid surfaces always include melanized, stress-tolerant microcolonial ascomycetes. After their first discovery on desert rock surfaces, these melanized chaetothyrialean and dothidealean ascomycetes have been found on Mediterranean monuments after biocidal treatments, Antarctic rocks and solar panels. New man-made modifications of surfaces (e.g., treatment with biocides or photocatalytically active layers) accommodate the exceptional stress-tolerance of microcolonial fungi and thus further select for this well-protected ecological group. Melanized fungal strains were isolated from a microbial community that developed on highly photocatalytic roof tiles after a long-term environmental exposure in a maritime-influenced region in northwestern Germany. Four of the isolated strains are described here as a novel species, Constantinomyces oldenburgensis, based on multilocus ITS, LSU, RPB2 gene phylogeny. Their closest relative is a still-unnamed rock-inhabiting strain TRN431, here described as C. patonensis. Both species cluster in Capnodiales, among typical melanized microcolonial rock fungi from different stress habitats, including Antarctica. These novel strains flourish in hostile conditions of highly oxidizing material surfaces, and shall be used in reference procedures in material testing.

Keywords: Constantinomyces; microcolonial fungi; multilocus phylogeny; photocatalytic surfaces; stress tolerance; subaerial biofilms.

Figure 1

The roof of a residential house with indicated sampled tiles at the moment of sampling in May 2014—after 7.5 years of total exposure and 59 months of exposure beside each other. This area is free from shading by architectural elements and thus photocatalytic activity might occur at least during sun irradiation periods. (a) The position of the two sampled photocatalytically active tiles on the control part of the roof was “home” to those tiles for almost five years prior to the sampling. The photocatalytically active tiles have the visibly different subaerial biofilm that is more discoloring. (b) Sampled tile surface in a close-up showing dark-pigmented fungal colonies on the elevated surface area—the area where time of wetness is additionally reduced, leading to less pronounced algal growth. Fungal colonies that were sampled with sterile implements to isolate dominant subaerial settlers are indicated by the blue frame.

Figure 2

ML 3-genes multilocus phylogeny based on a selection of rock-inhabiting and plant pathogenic fungi in the order Capnodiales showing the phylogenetic placement of the new species described. The tree, based on 59 sequences and 1681 nucleotide positions, has been generated using a GTR + G(4) model calculated using ML in the software MrAIC. Bootstrap values above 80%, calculated from 1000 resampled data sets, are shown.

Figure 3

Appearance of the Constantinomyces oldenburgensis and Constantinomyces patonensis. (a–g) Constantinomyces oldenburgensis, strain T2.1. (a) Colony appearance. (b) Dark, spherical multicellular bodies. Scale bar 50 µm. (c) Irregular toruloid brown hyphae. Scale bar 25 µm. (d) Irregular toruloid brown hyphae with development of chlamydospore-like cells. Scale bar 25 µm. (e) Micronematous conidiophores and arthroconidia. Scale bar 25 µm. (f–g) Micronematous conidiophores and arthroconidia, details. Scale bars 10 µm. (h–j) Constantinomyces patonensis, strain TRN431. (h) Colony appearance. (i–j) Irregular toruloid brown hyphae. Scale bars 25 µm.