The biomineralization of carbonate minerals, such as calcite, vaterite, aragonite, siderite, and dolomite, is an intensively studied phenomenon due to its practical application. This work aimed at studying carbonate-precipitating fungi isolated from a calthemite straw stalactite growing from a concrete ceiling of a building. The isolates were molecularly identified as the ascomycetes Paecilomyces inflatus and Plectosphaerella cucumerina. After 6 months of laboratory incubation, P. inflatus and P. cucumerina showed rates of CaCO3 precipitation of 15.68 and 16.28gL−1, respectively. A diffuse network of fungal hyphae, clothed with micrometric and wellformed crystals, was observed by SEM. XRD analysis of the precipitated crystals showed that vaterite and calcite crystals were associated withP.inflatushyphae, whereaspurecalcitecrystals were observedinthepresenceofP. cucumerina. P. inflatus and P. cucumerina grew within pH ranges of 3–11 and 4 to 12, respectively. Furthermore, both microorganisms were able to precipitate pyromorphite and hydrocerussite when cultivated in broth amended with Pb2+. Such strains seem to represent particularly suitable candidates for concrete healing, bioremediation processes and soil and sand consolidation. To our best knowledge, this is the first time that P. inflatus and P. cucumerina are described as fungal species capable of biomineralizing carbonates.

This work was supported by the project “Sostegno alla Ricerca Individuale di Ateneo per l'Anno 2015 e 2016” funded by Parthenope University of Naples and by the Italian Association for the Study of Clays.