Moisture and material shape microbial communities in the built environment through disturbance-productivity relationships

The built environment houses diverse microbial communities whose diversity and composition differ among building materials and environmental conditions. Ecological theory makes predictions about how productivity and diversity shape communities, and experiments in the built environment provide an opportunity to test these predictions. We manipulated moisture (constant or repeated wet-dry cycling) on three common building materials to test hypotheses that environmental disturbance interacts with the potential productivity of building materials to influence alpha and beta diversity.

Coupons of different building materials, medium density fiberboard, gypsum wallboard and oriented strand board, were sterilized before passive inoculation, then kept wet or periodically air-dried before rewetting. Microbial communities were sampled using swabs every 14 days for 7-week period. Productivity was measured using bacterial cell counts, fungal hyphal length, and fungal spore density, and microbial diversity was determined via community amplicon sequencing using universal bacterial (16S) and fungal (ITS) primers.

The most productive material (oriented strand board) supported the highest bacterial alpha and beta diversity, and these diversity levels were reduced by repeated drying disturbances. Diversity patterns for fungi were more variable, with the highest alpha diversity on low-moderate productivity material (gypsum wallboard). Fungal beta diversity was reduced by disturbance on high productivity material but increased on the other materials. These patterns were driven largely by members of Bacillaceae, Sphingomonadaceae, and Aspergillaceae that reached high abundances in some treatments.

Disturbance regime interacted with building material, so disturbance effects depended on material type. There were also differences between bacteria and fungi, which may be due to the scale-dependence of productivity-diversity relationships, but this pattern was not uniform. Network analysis found evidence of multi-species complexes of bacteria and fungi known to form biofilms, as well as evidence of competitive exclusion on specific materials and conditions. Together, these results indicate that disturbances can interact with building materials, and that these disturbances may be strongly mediated by biotic interactions.