Microbial and Metabolic Succession on Common Building Materials Under High Humidity Conditions

Abstract

1Despite considerable efforts to characterize the ecology of bacteria and fungi in the built 2 environment (BE), the metabolic mechanisms underpinning their colonization and successional 3 dynamics remain unclear. Here, we applied bacterial/viral particle counting, qPCR, 16S and ITS 4 rRNA amplicon sequencing, and metabolomics to longitudinally characterize the ecological 5 dynamics of four commonly used building materials maintained at high humidity conditions 6 (~94% RH). We varied the natural inoculum provided to each material by placing them in different 7 occupied spaces, and we wet the surface of half of the samples of each material to simulate a 8 flooding event. As expected, different materials showed different bacterial and viral particle 9 abundance, with wet materials having higher growth rates and lower alpha diversity compared to 10 non-wetted materials. Wetting described the majority of the variance in bacterial, fungal and 11 metabolite structure, and material type only influenced bacterial and metabolic diversity, while 12 location of inoculation was only weakly associated with bacterial and fungal beta diversity. 13 Metabolites indicative of microbial activity were identified, as were those that were native to the 14 surface material. Glucose-phosphate was abundant on all materials (except mold-free gypsum) and 15 was correlated with Enterobacteriaceae, which could indicate a potential bacterial nutrient source. 16 A compound consistent with scopoletin, a plant metabolite with antimicrobial activity, was 17 significantly negatively correlated with Bacillus and positively correlated with Pseudomonas and 18 enriched in medium density fiberboard (MDF) materials. In wet samples, the alkaloids nigragillin 19 and fumigaclavine C, both with antimicrobial properties, were significantly positively correlated 20 with the fungal phylum Ascomycota. Nigragillin, was also negatively correlated with Bacillus and 21 Pseudomonas abundance. Thiabendazole and azoxystrobin (anti-fungal compounds) were highly 22 abundant on mold-resistant gypsum wallboard and likely directly influenced the decreased fungal 23 growth observed on this material. The mold-resistant gypsum material also showed a significant 24 increase in bacterial alpha diversity, and bacterial and viral particle abundance, as well as a 25 decrease in metabolite diversity, likely a result of reduced fungal growth. Penicillium taxa were 26 positively correlated with thiabendazole, which suggested the persistence of resistant strains. Also, 27 2 specific to the wet samples, Bacillus abundance was positively correlated with the azoxystrobin, 28 suggesting bi-directional competitive adaptation, and positively correlated with metabolites known 29 to interfere with Pseudomonas biofilm formation, which could explain the anti-correlation 30 between these taxa. As expected, high moisture conditions enabled faster growth of inoculating 31 microorganisms, whose composition, chemistry, and competition was shaped by surface material, 32 suggesting that...

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