A biogenic weathering-microenvironment on the mineral surface: Knufia petricola and its polymer matrix (shown carotenoid mutant Δphd1 on olivine).
Source: BAM
atRock-dwelling fungi have been colonising rocks for millions of years and perform important tasks on these surfaces: important nutrients are extracted through mineral weathering. Biologically enhanced mineral weathering (e.g., of olivine) takes place particularly effectively when biofilms adhere to the mineral surfaces.
The principle of action of the rock-attacking black fungi is known, but the decoding of the particularly important and active "weathering substances" is still pending. How does one find out which substances are particularly important? To do this, an analytical approach and organisms that can be genetically manipulated in the laboratory were brought together.
Take: a fungus that adheres well to rocks and other solid materials exposed to the air, e.g., by producing extracellular polymeric substances (EPS). Create several genetic variants of it. These fungal mutants, which lack some metabolites, are grown as air-exposed biofilms. The EPS, responsible for the contact with the mineral, were extracted, quantified and characterized.
The absence of the protective pigment melanin affected the amount and composition of EPS produced: mutants lacking melanin synthesized more EPS with fewer pullulan-related glycosidic bonds. The adhesion capacity of these pullulan-related bonds explains the reduced fungal attachment to and weathering of the mineral of these mutants. Melanin-producing strains on the other hand adhered more strongly to the mineral olivine - while also dissolving it at a higher rate. Mineral dissolution was further enhanced by the release of iron-binding metabolites which prevents the dissolution-inhibiting capacities of iron oxides.
The genetics-assisted analytical approach of Breitenbach et al. can be broadly applied: the biofilm-created microenvironment is relevant not only to rocks, but also to many energy-related contexts of microbially influenced corrosion.
The role of extracellular polymeric substances of fungal biofilms in mineral attachment and weathering
Romy Breitenbach, Ruben Gerrits, Polina Dementyeva, Nicole Knabe, Julia Schumacher, Ines Feldmann, Jörg Radnik, Masahiro Ryo & Anna A. Gorbushina
published in npj Materials Degradation, Vol. 6, article 42, 2022
BAM division Materials and the Environment
BAM division Materials and Air Pollutants
BAM division Surface Analysis and Interfacial Chemistry