Dominance of Gas-Eating, Biofilm-Forming Methylobacterium Species in the Evaporator Cores of Automobile Air-Conditioning Systems

Abstract

Microbial communities in the evaporator core (EC) of automobile air-conditioning systems have a large impact on indoor air quality, such as malodor and allergenicity. DNA-based microbial population analysis of the ECs collected from South Korea, China, the United States, India, and the United Arab Emirates revealed the extraordinary dominance of Methylobacterium species in EC biofilms. Mixed-volatile organic compound (VOC) utilization and biofilm-forming capabilities were evaluated to explain the dominance of Methylobacterium species in the ECs. The superior growth of all Methylobacterium species could be possible under mixed-VOC conditions. Interestingly, two lifestyle groups of Methylobacterium species could be categorized as the aggregator group, which sticks together but forms a small amount of biofilm, and the biofilm-forming group, which forms a large amount of biofilm, and their genomes along with phenotypic assays were analyzed. Pili are some of the major contributors to the aggregator lifestyle, and succinoglycan exopolysaccharide production may be responsible for the biofilm formation. However, the coexistence of these two lifestyle Methylobacterium groups enhanced their biofilm formation compared to that with each single culture. IMPORTANCE Air-conditioning systems (ACS) are indispensable for human daily life; however, microbial community analysis in automobile ACS has yet to be comprehensively investigated. A bacterial community analysis of 24 heat exchanger fins from five countries (South Korea, China, the United States, India, and the United Arab Emirates [UAE]) revealed that Methylobacterium species are some of the dominant bacteria in automobile ACS. Furthermore, we suggested that the predominance of Methylobacterium species in automobile ACS is due to the utilization of mixed volatile organic compounds and their great ability for aggregation and biofilm formation.

The Microbiome of Things: Appliances, Machines, and Devices Hosting Artificial Niche-Adapted Microbial Communities

“…Here, we describe the microbial profile of “things”, which, despite being in constant contact with humans or the human activity, do not necessarily share a microbiome characterized by human-associated microorganisms but, instead, represent microbial micro-niches with their own selective pressures and characteristic microbiomes. Here, we look briefly into the previous research on the natural microbiomes of “things”, and we use examples such as that of the photovoltaic panels [ 20 , 21 ], the car tank lid [ 22 ], or the microbiome of automobile air-conditioning systems [ 23 ]. The focus of the “Microbiome of Things” (MoT), the existence of which we propose here, is analogous to the “Internet of Things” (IoT) concept.…”

Comparative genomics of wild-type and laboratory-evolved biofilm-overproducing Deinococcus metallilatus strains

“…Interestingly, Deinococcus spp. are commonly detected in the evaporator cores of air-conditioning systems, although their proportion varies among samples from different countries [15]. For instance, four Deinococcus species ( Deinococcus aluminii , Deinococcus multiflagellatus , Deinococcus metallilatus and Deinococcus carri ) were isolated from automobile air-conditioning systems, and their biochemical activities and bacterial phenotypes were analysed [16–18].…”