Bacterial community associated with the dry-rot fungus Serpula lacrymans is dominated by Firmicutes and Proteobacteria

Abstract

The dry-rot fungus Serpula lacrymans causes enormous structural damage by decaying construction timber thereby resulting in tremendous financial loss. Dry-rot fungi decompose cellulose and hemicellulose and, if the wood remains wet, are often accompanied by a succession of bacteria and other fungi. Bacterial-fungal interactions have considerable impact on all interaction partners ranging from antagonistic to beneficial relationships. However, little is known about possible interaction partners of S. lacrymans. Here we show that S. lacrymans has many co-existing, mainly Gram-positive bacteria. By investigating differences in the bacterial community associated with fruiting bodies, mycelia and rhizomorphs, we provide evidence of preferential colonization of S. lacrymans tissues by certain bacterial phyla. Bacteria isolated from fruiting bodies and mycelia were dominated by Firmicutes, while bacteria isolated from rhizomorphs were dominated by Proteobacteria. Actinobacteria and Bacteroidetes were found in lower abundances. In situ fluorescence hybridization (FISH) analysis revealed that bacteria were not present biofilm-like, but occurred as independent cells, sometimes also attached to fungal spores. In co-culture, single bacterial isolates caused growth inhibition of S. lacrymans and vice versa. Additionally, certain bacteria induced pigment production in the fungus. Our results provide first insights for a better understanding of the holobiont S. lacrymans and give hints that bacteria are able to influence the behavior, e.g. growth and secondary metabolite production, of S. lacrymans in culture. ImportanceSerpula lacrymans is a very effective dry-rot causing fungus, specialized in degradation of coniferous timber in houses. The initial colonization is favored by water damage, and after establishment, the fungus starts to destruct cellulose and hemicellulose. It is among the most feared wood-rotting fungi in the built environment as the remediation of S. lacrymans damaged buildings is expensive and tedious. After improper renovation, the possibility of a recolonization by S. lacrymans is likely. As bacteria influence fungal establishment on wood, the need to investigate the bacterial community associated with S. lacrymans is apparent. The significance of our research is in identifying and characterizing bacteria associated with S. lacrymans. This will allow the assessment of their influence on fungal life style, leading to a broader understanding of the properties that make S. lacrymans so extraordinarily aggressive at decaying wood compared to other indoor wood destroyers.