Station and train surface microbiomes of Mexico City’s metro (subway/underground)

Abstract

The metro is one of the more representative urban systems of Mexico City, and it transports approximately 4.5 million commuters every day. Large crowds promote the constant exchange of human and environmental microbes. In this study, we determined the bacterial diversity profile of the Mexico City subway by massive sequencing of the 16S rRNA gene. We identified a total of 50,197 operative taxonomic units (OTUs) and 1058 genera. The metro microbiome was dominated by the phylum Actinobacteria and by the genera Propionibacterium (15%) (P. acnes 13%), Corynebacterium (13%), Streptococcus (9%), and Staphylococcus (5%) (S. epidermidis; 4%), reflecting the microbe composition of normal human skin. The metro microbial sources were skin, dust, saliva, and vaginal, with no fecal contribution detected. A total of 420 bacterial genera were universal to the twelve metro lines tested, and they contributed to 99.10% of the abundance. The large OTUs number are probably reflecting the vast human influx, while selection from hosts and environments are constraining the genera diversity, shown by the OTUs to genus ratio. Finally, this study shows that the microbial composition of the Mexico City subway comes from a mixture of environmental and human sources and that commuters are exposed to normal human microbiota.