Microbes in deionized and tap water: Implications for maintenance of laboratory water production system
Microbes, with their vast metabolic capabilities and great adaptability, occupy almost every conceivable ecological niche on Earth. Thus, could they survive in oligotrophic deionized (DI) water? Observations of white cauliflower-like lumps and black specks in salt solutions after months of storage in plastic bottles suggested a microbial origin for the "contaminants". Growth experiments was conducted to profile the microbial diversity of fresh DI water, produced on a just-in-time basis by a
... time basis by a filter cum ion exchange system with tap water as feed. Inoculation of DI water on R2A agar and a formulated colourless agar followed by multi-day aerobic incubation revealed the presence of a large variety of microbes with differing pigmentations, growth rates, colony sizes and morphologies. Additionally, greater abundance and diversity of microorganisms was recovered at 30 oC compared to 25 and 37 oC; most probably due to adaptation of microbes to tropical ambient water temperatures of 25 to 30 oC. Comparative experiments with tap water as inoculum recovered a significantly smaller number and diversity of microorganisms; thus, suggesting that monochloramine residual disinfectant in tap water was effective in inhibiting cell viability. In contrast, possible removal of monochloramine by adsorption onto ion exchange resins of the DI water production system might explain the observed greater diversity and abundance of viable microbes in DI water. More importantly, greater diversity and abundance of microbes from tap water were recovered on R2A agar compared to formulated colourless agar, which suggested that chelating compounds in R2A agar could have complexed monochloramine and reduced its toxicity towards microbes. Similar chelating compounds were unlikely to be present in the formulated colourless agar. Finally, keystone species secreting signaling molecules and metabolites could induce the growth of neighbouring cells embedded in the agar matrix. This explained the presence of large clear zones devoid of colonies where there was no keystone species. Additionally, close proximity of colonies on agar suggested that cooperative and neutral relationships guided by exchange of metabolite and signaling molecules might be more prevalent compared to antagonistic relationships in which inhibitory compounds were used. Collectively, this study confirmed the presence of microbes in fresh DI water and tap water. Propensity of microbes in forming biofilm on various surfaces suggested that intermittent flow in just-in-time DI water production provided opportunities for cell attachment and biofilm formation during water stagnation, and subsequent dislodgement and resuspension of cells upon water flow. Thus, regular maintenance and cleaning of the production system should help reduce DI water's microorganism load.