The role of extracellular polymeric substances of fungal biofilms in mineral attachment and weathering

Abstract

The roles extracellular polymeric substances (EPS) play in mineral attachment and weathering were studied using genetically modified biofilms of the rock-inhabiting fungus Knufia petricola strain A95. Mutants deficient in melanin and/or carotenoid synthesis were grown as air-exposed biofilms. Extracted EPS were quantified and characterised using a combination of analytical techniques. The absence of melanin affected the quantity and composition of the produced EPS: mutants no longer able to form melanin synthesised more EPS containing fewer pullulan-related glycosidic linkages. Moreover, the melanin-producing strains attached more strongly to the mineral olivine and dissolved it at a higher rate. We hypothesise that the pullulan-related linkages, with their known adhesion functionality, enable fungal attachment and weathering. The released phenolic intermediates of melanin synthesis in the Δsdh1 mutant might play a role similar to Fe-chelating siderophores, driving olivine dissolution even further. These data demonstrate the need for careful compositional and quantitative analyses of biofilm-created microenvironments.

Identification and Biosynthesis of DHN-melanin Related Pigments in the Pathogenic Fungi Monilinia laxa, M. fructicola, and M. fructigena

“…Fungi can biosynthesize melanin by two different pathways: either through the L-3,4 dihydroxyphenylalanine (L-DOPA) pathway, which is found primarily in basidiomycetes [ 11 ] and human pathogens [ 12 ], or through the 1,8-dihydroxynaphthalene (DHN) pathway, which is usually found in ascomycetes [ 13 , 14 ], such as fungi belonging to the Sclerotiniaceae family. It is believed that the L-DOPA pathway is spontaneously activated after initiating the oxidation by a laccase [ 15 ].…”

The contribution of living organisms to rock weathering in the critical zone

“…through the study of gene deletion mutants 198,199 (see also ref. 200 in this issue). On the other hand, the application of nm-resolved techniques to the study of microbially weathered surfaces 91,123,192,201 should help characterize imprints of microbial process left behind at mineral surfaces and in the geological record.…”

Seasonal Variations in Fungal Communities on the Surfaces of Lan Na Sandstone Sculptures and Their Biodeterioration Capacities

“…For example, Cladosporium an d Knufia , which can produce extracellular melanin–polysaccharide complexes, which are compounds belonging to the group of extracellular polymeric substances (EPSs) [ 61 , 62 ]. EPSs lend stability to the biofilm by mediating cellular aggregation and bringing the cells in close contact with the substrate via adhesion [ 63 ], encouraging themselves and fungi to attach more strongly to the substrate and deteriorating it at a fast rate. In addition, it was reported that Xylaria were predominantly identified from mycelium particles of a biofilm biomass on the surface of a Mayan building [ 64 ].…”