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

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 Delta sdh1 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.

Automated summary

The roles of extracellular polymeric substances (EPS) in mineral attachment and weathering were investigated using genetically modified biofilms of Knufia petricola strain A95. Mutants deficient in melanin and/or carotenoid synthesis were grown as air-exposed biofilms. The presence of melanin affected the quantity and composition of EPS, with melanin-producing strains showing stronger attachment to the mineral olivine and faster dissolution rates. The pullulan-related glycosidic linkages in EPS enable fungal attachment and weathering, while phenolic intermediates released by melanin synthesis may enhance olivine dissolution. These findings highlight the importance of compositional and quantitative analyses of biofilm microenvironments.