Temporal stability and niche partitioning of bacterial communities in paired residential sink P-traps

Sink P-traps harbor microbial communities derived from environmental and human sources, yet longitudinal studies examining their stability and assembly dynamics remain limited. Here, we present, to our knowledge, the longest continuous characterization of bacteria collected from residential sink P-traps, with daily sampling over two months (n = 61 days). Samples were collected from paired sinks in a shared bathroom to identify dominant taxa, quantify temporal stability, and determine how occupant usage patterns influence community assembly. Using full-length 16S rRNA gene sequencing, we identified 3,865 unique taxa, with both sinks dominated by common sink-associated genera, including Pseudomonas, Citrobacter, Klebsiella, and Arcobacter. Despite sharing identical plumbing, environmental conditions, and cleaning regimes, the two sinks maintained distinct communities (p < 0.001). Temporal stability analyses revealed notable differences: Sink A (male; hand washing, toothbrushing, shaving) exhibited deterministic dynamics with low variability (CV = 4.9%), significant temporal autocorrelation (p = 0.001), and predictable trajectories, with time explaining 49.9% of community variation. In contrast, Sink B (female; hand washing, toothbrushing, face washing, mouthwash use) displayed stochastic dynamics with high volatility (CV = 26.5%), no significant autocorrelation (p = 0.53), and minimal temporal predictability. Differential abundance analysis revealed that Sink B was enriched in anaerobes, biofilm-forming taxa, oral microbiome associates, and preservative-resistant and lipid-degrading bacteria, while Sink A harbored a more aerobic, skin-associated community. These findings demonstrate that individual usage patterns (particularly exposure to biocidal agents) can alter P-trap community structure and temporal dynamics, with implications for microbial community prediction in residential and healthcare settings. ImportanceSink drains are increasingly recognized as reservoirs for antimicrobial-resistant pathogens, yet we lack fundamental knowledge about what drives bacterial community dynamics in these environments. By sampling paired residential sink P-traps daily for two months, we show that individual-specific behaviors, such as using products with a biocidal effect, can alter community composition from a stable, predictable state to one characterized by stochastic fluctuations. The sink exposed to mouthwash and face wash harbored more anaerobes, biofilm formers, and oral bacteria, suggesting that repeated exposure promotes disturbance-tolerant taxa rather than reducing bacterial colonization. These results provide a baseline ecological framework for understanding P-trap microbiomes and suggest that predictive monitoring of sink-associated pathogens might be feasible in stable environments but more difficult when there is variable antimicrobial exposure -- a finding directly relevant to hospital infection control.