IIT Madras Identifies Unique Microbial Signature in Chennai Metro, Reveals New Insights into Urban Microbiology

Researchers at the Indian Institute of Technology Madras (IIT Madras) have identified a distinctive microbial signature across Chennai Metro trains and stations, revealing how urban environments develop characteristic communities of microorganisms. The study, published in the international scientific journal mSphere, identified nine bacterial species that were consistently prevalent in Chennai Metro samples but did not exhibit the same prevalence patterns in comparable public transport environments across 31 other cities.

The research represents one of India’s first comprehensive metagenomic investigations of microorganisms inhabiting public transport surfaces. By examining microbial DNA collected from frequently touched surfaces, the scientists documented the diversity of microorganisms present in Chennai’s urban transit environment and investigated the distribution of genes associated with antimicrobial resistance.

The study, titled Microbial Communities on Station and Train Surfaces in Chennai Metro: Insights into Urban Transit Microbiome, was published online on October 8, 2026, by the American Society for Microbiology.

Scientists Collect 96 Samples Across Chennai Metro

The research team collected 96 surface samples from 12 locations associated with Chennai Metro’s Blue and Green Lines during December 2021 and January 2022.

The samples were obtained from surfaces frequently touched by commuters, including handrails inside trains, station banisters, ticket-vending kiosks and ticket counters.

Researchers used sterile swabs to collect microbial material from selected portions of these surfaces. The samples were subsequently processed to extract microbial DNA for genetic analysis.

Of the 96 samples collected, 47 satisfied the initial quality requirements for sequencing. Following further assessment of sequencing depth, 41 samples were retained for the final analysis.

The scientists employed a technique known as shotgun metagenomic sequencing, which allows researchers to examine genetic material from entire microbial communities without first isolating and cultivating individual microorganisms in laboratories.

This approach enabled the researchers to investigate the composition and genetic characteristics of microbial communities present on Chennai Metro surfaces, including organisms that may be difficult to study through conventional laboratory cultivation.

Chennai Metro Reveals a Distinctive Urban Microbial Signature

The researchers discovered that Chennai Metro possesses a characteristic microbial profile that differs from those documented in several other urban transport systems around the world.

To establish these differences, the scientists compared their findings with microbial data collected through the international MetaSUB initiative, which investigates microorganisms inhabiting urban environments.

The comparison involved datasets from 31 other cities, allowing the researchers to identify patterns shared among urban environments and those particularly associated with Chennai.

The study identified nine bacterial species that were part of Chennai’s core microbial community but were not similarly prevalent in the other cities examined.

A core microbial community consists of microorganisms consistently detected across a substantial proportion of samples within a particular environment.

The identification of nine distinctive core species demonstrates that Chennai’s urban transport environment possesses a recognisable microbial signature, reflecting the influence of local environmental conditions and human activity.

The researchers also found that bacterial groups belonging to Actinobacteria, Alphaproteobacteria and Gammaproteobacteria accounted for important components of the microbial communities examined.

The findings contribute to the growing scientific understanding that cities can develop characteristic microbial environments influenced by factors such as climate, population density, human movement and the design of urban infrastructure.

Ticket-Vending Kiosks Show Highest Microbial Diversity

One of the notable findings was that the composition and diversity of microorganisms varied significantly depending on the type of surface examined.

Among the surfaces investigated, ticket-vending kiosks exhibited the highest microbial diversity.

The researchers also identified differences between microbial communities associated with station handrails, train handrails and ticket counters.

These variations demonstrate that public transport environments do not contain a uniform distribution of microorganisms. Instead, individual surfaces can support different microbial communities depending on their physical characteristics, patterns of human contact and surrounding environmental conditions.

The findings suggest that surface type is an important factor when investigating microbial distribution in densely used public spaces.

The study establishes that even within a single metropolitan transport network, different surfaces can possess substantially different microbial communities.

This information is relevant to the design of future investigations into microbial ecology, environmental hygiene and the distribution of microorganisms in urban infrastructure.

Researchers Detect Antimicrobial Resistance Genes

The IIT Madras study also examined the presence of genes associated with antimicrobial resistance, an important area of scientific research because of the increasing global challenge posed by drug-resistant microorganisms.

Antimicrobial resistance occurs when microorganisms develop or possess biological mechanisms that enable them to survive exposure to medicines intended to control or eliminate them.

The researchers identified antimicrobial resistance gene families associated with several categories of antibiotics, including rifamycins and sulfonamides, as well as genes associated with resistance to multiple antimicrobial agents.

Although these genes were generally present in relatively low abundance, more than 80% of the analysed samples contained at least one gene associated with antimicrobial resistance.

The finding provides information about the environmental distribution of resistance-related genetic material in public transport settings.

However, the researchers emphasised an important scientific distinction: detecting microbial DNA or resistance genes on a surface does not necessarily establish that living disease-causing bacteria are present or that passengers face an immediate infection risk.

DNA-based investigations can detect genetic material from both living and non-viable microorganisms.

Consequently, the results should be interpreted as evidence of microbial and genetic diversity rather than direct evidence of disease transmission through Chennai Metro.

Understanding the Relationship Between Cities and Microorganisms

Urban environments contain complex communities of microorganisms associated with human activity, buildings, transport infrastructure, air, soil and water.

Public transport systems are particularly interesting environments for microbiological research because large numbers of people repeatedly interact with shared spaces.

Microorganisms can enter these environments through several pathways, including contact with human skin, airborne particles, environmental dust and surrounding outdoor ecosystems.

The composition of these microbial communities can vary between cities because of differences in climate, architecture, environmental conditions and patterns of human activity.

Chennai’s coastal location, warm temperatures and humid conditions provide an environmental setting distinct from many cities included in international microbiome studies.

The researchers’ findings contribute to understanding how such regional characteristics may influence urban microbial diversity, although the study does not establish the precise contribution of each environmental factor.

The identification of a distinctive Chennai Metro microbiome demonstrates that urban infrastructure can be studied as an ecological environment in which microorganisms reflect interactions between people and their surroundings.

Advanced Genetic Analysis Reveals Microbial Characteristics

Beyond identifying microorganisms present in the collected samples, the researchers investigated the genetic characteristics of microbial communities through advanced computational analysis.

The study reconstructed 47 high-quality metagenome-assembled genomes from the sequencing data.

Metagenome-assembled genomes are reconstructed collections of genetic sequences that allow scientists to investigate microorganisms without necessarily obtaining them as isolated laboratory cultures.

These reconstructions provided information about the genetic diversity and potential functional characteristics of microorganisms detected within the Chennai Metro environment.

The researchers also performed comparative genomic investigations to examine variations within microbial populations and identify characteristics associated with their adaptation to urban surroundings.

Such techniques are increasingly used in environmental microbiology to investigate the distribution, evolution and genetic capabilities of microorganisms inhabiting complex ecosystems.

The study demonstrates the application of modern DNA sequencing and computational analysis to public transport environments in India.

IIT Madras Contributes to International Urban Microbiome Research

The investigation was conducted by researchers associated with IIT Madras, including Vijaya Yuvaram Singh, Veerendra P. Gadekar, Srijith Sasikumar, R. M. Rajeeva Lokshanan, V. Senthamizhan, Bharath Prithiviraj, Himanshu Sinha and Karthik Raman.

The research involved expertise in biotechnology, computational biology, microbial genomics and data analysis.

The study also benefited from the cooperation of Chennai Metro Rail Limited, which facilitated access to stations and trains for sample collection.

International urban microbiome research has expanded considerably through initiatives such as MetaSUB, which collects and analyses microbial samples from cities around the world.

By contributing data from Chennai, the IIT Madras investigation addresses an important geographical gap in research on urban microbial communities.

The findings also provide a foundation for comparing microbial diversity across Indian cities and examining how environmental conditions influence microorganisms associated with public infrastructure.

Implications for Public Health Research and Urban Planning

The study provides baseline scientific information that can support future investigations into microbial ecology and antimicrobial resistance in Indian urban environments.

Understanding microbial communities on shared surfaces can help researchers identify patterns of microbial distribution and examine how these patterns change under different environmental conditions.

Long-term monitoring may also provide insights into seasonal variations, changes associated with passenger movement and the distribution of resistance-related genetic material.

However, the researchers acknowledged several limitations, including the relatively small number of samples retained for final analysis and the fact that the samples were collected during a limited period in December 2021 and January 2022.

The investigation therefore represents a snapshot of the microbial environment during the sampling period rather than a continuous assessment of present-day conditions.

The researchers also cautioned that DNA-based analysis cannot independently determine whether detected microorganisms are alive, capable of transmission or associated with clinical risk.

These limitations are important when interpreting the results and considering their relevance to public health.

A New Direction for Urban Microbiology Research in India

The IIT Madras investigation demonstrates how advanced genomic technologies can be applied to understand microorganisms inhabiting India’s rapidly expanding urban infrastructure.

By identifying distinctive bacterial communities, examining microbial differences between frequently touched surfaces and documenting antimicrobial resistance-related genes, the study contributes valuable scientific data to the field of urban microbiology.

The findings also expand India’s participation in international investigations examining how cities develop characteristic microbial ecosystems.

The discovery of nine distinctive core bacterial species in Chennai Metro highlights the scientific value of studying urban environments at the microscopic level, while establishing an important reference point for future research into microbial diversity, environmental monitoring and antimicrobial resistance across Indian cities.

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