Microbes and associated soluble and volatile chemicals on periodically wet household surfaces

Abstract

Background: Microorganisms influence the chemical milieu of their environment, and chemical metabolites can affect ecological processes. In built environments, where people spend the majority of their time, very little is known about how surface-borne microorganisms influence the chemistry of the indoor spaces. Here, we applied multidisciplinary approaches to investigate aspects of chemical microbiology in a house.

Methods: We characterized the microbial and chemical composition of two common and frequently wet surfaces in a residential setting: kitchen sink and bathroom shower. Microbial communities were studied using culture-dependent and independent techniques, including targeting RNA for amplicon sequencing. Volatile and soluble chemicals from paired samples were analyzed using state-of-the-art techniques to explore the links between the observed microbiota and chemical exudates.

Results: Microbial analysis revealed a rich biological presence on the surfaces exposed in kitchen sinks and bathroom shower stalls. Microbial composition, matched for DNA and RNA targets, varied by surface type and sampling period. Bacteria were found to have an average of 25× more gene copies than fungi. Biomass estimates based on qPCR were well correlated with measured total volatile organic compound (VOC) emissions. Abundant VOCs included products associated with fatty acid production. Molecular networking revealed a diversity of surface-borne compounds that likely originate from microbes and from household products.

Conclusions: Microbes played a role in structuring the chemical profiles on and emitted from kitchen sinks and shower stalls. Microbial VOCs (mVOCs) were predominately associated with the processing of fatty acids. The mVOC composition may be more stable than that of microbial communities, which can show temporal and spatial variation in their responses to changing environmental conditions. The mVOC output from microbial metabolism on kitchen sinks and bathroom showers should be apparent through careful measurement, even against a broader background of VOCs in homes, some of which may originate from microbes in other locations within the home. A deeper understanding of the chemical interactions between microbes on household surfaces will require experimentation under relevant environmental conditions, with a finer temporal resolution, to build on the observational study results presented here.

Keywords: Bathroom tiles; Built environment; Chemical ecology; Emissions; Indoors; Metabolites; Microbiota; Stainless steel coupons; Volatile organic compounds.

Fig. 1

Removable kitchen coupons (a) and bathroom tiles (b) were installed in an occupied home for approximately 4 weeks, after which time they were analyzed for their microbial and chemical content. There were two clusters of kitchen coupons, referred to as “front” and “side” kitchen sink samples

Fig. 2

a Low-magnification image of bacterial growth on a stainless-steel coupon stained with SYTO BC (green fluorescent nucleic acid stain). Scale bar is 100 μm. Arrows indicate a trail of bacterial growth, viewed in high magnification in panel b where the scale bar is 10 μm

Fig. 3

The most abundant bacterial OTUs on kitchen coupons and bathroom tiles in the two sampling campaigns, as detected through amplicon sequencing of DNA and RNA

Fig. 4

Most abundant VOC ions from blanks, bathroom tiles, and kitchen coupons (“coup”) in sampling 1 (a) and sampling 2 (b). Letters A–J denote different samples

Fig. 5

Sum of VOCs, as measured with the PTR-TOF-MS, and microbial gene copies (sum of bacteria and fungi), as estimated with qPCR. “S1” corresponds to sampling period 1 and “S2” to sampling period 2

Fig. 6

Modeling results of source-specific contributions to indoor concentrations (C _{in, ss}) from the kitchen sink (left) and shower stall (right)

Fig. 7

Examples of clusters (a–c) found in the network constructed using LC-MS data collected from both indoor material samples and microbial cultures. Edges between nodes indicate structural similarity of compounds. Size of the nodes reflects number of spectra found for the same compound and is a measure of compound abundance. Numbers inside each node refer to ion parent mass. Red nodes represent compounds detected in both the culture and indoor material samples. Blue nodes represent compounds found only on microbial cultures. Green nodes represent compounds found only on material samples