On the diversity of fungi from soda soils

Abstract

The diversity of filamentous fungi that can grow at high ambient pH values (i.e., 8–11) remains largely understudied. Here we study 100 alkalitolerant and alkaliphilic isolates from the soils around the basin of soda lakes in Asia and Africa to assess the major evolutionary lineages and morphologies pertinent to the alkaliphilic trait in filamentous fungi. The Emericellopsis lineage (Hypocreales, Hypocreomycetidae), along with Plectosphaerellaceae (Hypocreomycetidae), Pleosporaceae (Dothideomycetes), Chaetomiaceae (Sordariomycetidae) families appeared to be overrepresented with strong alkalitolerants and effective alkaliphiles. In particular, Sodiomyces species (Plectosphaerellaceae), Acrostalagmus luteoalbus (Plectosphaerellaceae), Emericellopsis alkalina (Hypocreales), Thielavia sp. (Chaetomiaceae), and Alternaria sect. Soda (Pleosporaceae) grew best at high ambient pH. The pH tolerance of Chordomyces antarcticum, Acrostalagmus luteoalbus and some other species was largely affected by the presence of extra Na+ in the growth medium. Moderate alkalitolerants included Scopulariopsis members (Microascales), Fusarium, Cladosporium, and many asexual acremonium-like species from Bionectriaceae. Weak alkalitolerants were represented by sporadic isolates of Penicillium, Purpureocillium lilacinum, and Alternaria alternata species, with the growth optimum at neutral or acidic pH. Weak alkalitolerants develop loose dry chains of spores easily dispersed by air. Their presence at low frequency with the growth optimum at neutral or acidic pH leads us to treat them as transient species in the alkaline soils, as those are also ubiquitous saprobes in normal soils. Our phylogenetic analyses show that the alkaliphilic trait in filamentous fungi has evolved several times. Several lineages harboring strong alkalitolerants derived from the known marine-borne fungi (Emericellopsis, Alternaria sect. Phragmosporae), or fall within the fungi associated with halophytic grasses (Pleosporaceae). Soda soils contain a diversity of fungi that range from weak alkalitolerant to alkaliphilic, which in few cases is associated with darkly pigmented mycelium and formation of microsclerotia. The alkaliphilic trait is spread throughout the Ascomycota, and usually juxtaposes with slime-covered polyphyletic acremonium-, verticillium-, gliocladium-types of asexual morphology, hyphae aggregating in chords, and enclosed fruit bodies.