In early April 2015, as wind-borne dust particles, remnants from a major dust storm in the Gulf region, made their way towards the Indian peninsula, a group of citizen scientists and researchers strategically fanned out and placed prepared Petri dishes at vantage points in the west Indian state of Maharashtra by the Arabian Sea.

The hill station of Lonavala, set in the Sahyadri mountain range, Pune city in the eastern edge of the Deccan Plateau, and the coastal city of Mumbai were under the group’s radar, as visibility dropped.

They repeated the exercise 40 days later on May 18, 2015, after the storm had blown over.

As the dust-laden air settled on the Petri dishes filled with a nutrient mix to support the growth of microorganisms (or culture media), a section of microorganisms that hitched a ride on the dust particles clung on to the growth media and thrived.

Basic laboratory tests run by researchers at the National Centre for Microbial Resource (NCMR) confirmed what the citizen scientists and researchers had suspected: that microbes travelled more than 2000 km across the Arabian Sea and dust storms did shake up and shape the microbial composition of the surrounding air, indicating the possible spread of specific microbial species during a dust storm event.

“We wanted to enhance our understanding of the status of dust-borne microorganisms that travelled from the Gulf countries and reached the Indian peninsula and also to ascertain if culturable populations could be detected after travelling more than 2000 km across the Arabian Sea,” lead author Yogesh S. Shouche at NCMR at National Centre for Cell Science (NCMR-NCCS), Pune, told this visiting Mongabay-India correspondent. The idea of profiling microbial species centred on the dust storm remnants evolved quite spontaneously with weather forecasts said the researchers.

The researchers documented a total of 92 species belonging to 32 bacterial genera and four fungal genera in a preliminary study published in November 2019, highlighting the high diversity of microorganisms in the air samples.

“Moreover, we sought to track changes in and compare the structure of microbial communities during and after the dust storm,” said Mayuresh Prabhune of Pune-based Center for Citizen Science (CCS), a voluntary organisation of citizens that works under the guidance of working and retired scientists from various research institutes. In Mumbai, Professor Durga Pawar and her students at the department of microbiology, Khalsa College, Mumbai aided in sample collection.

Microbial count recorded during dust storm day was distinctively high compared to that recorded post dust storm and these findings are consistent with other similar studies conducted across Iran, Egypt and the Mediterranean region, said Prabhune who helped orchestrate the collaboration of citizen scientists with institutional researchers.

The results also reveal species that can tolerate environmental stresses (such as high salinity and extreme temperatures) and species that are opportunistic and potential pathogens (that normally do not cause disease in healthy individuals but strike when the opportunity arises) were present in the samples.

“The presence of stress-tolerant, opportunistic and potential pathogens as marker microbial species in the samples collected during dust storm day, indicated the plausible spread of these organisms along with dust particles,” said Prabhune.

Microbes that thrive during dust storms could impact human health

Environmental microbiologist and study co-author Shrikant P. Pawar observed that microbial diversity was also more on the day of the dust storm (DSD) in contrast to post-dust storm day (PSD). “Members of 15 genera were specifically present on the storm day and 11 genera during PSD, indicating a shift in microbial communities in response to the dust storm,” Pawar of NCMR-NCCS said.

And as the dust fall occurred, the proportion of certain microorganisms, including certain human and animal pathogens, shot up, the researchers added.

Osmotolerant and halotolerant (salt-tolerant) bacterial genera, such as Psychrobacter and Exiguobacterium, were recorded specifically during DSD and the proportion of opportunistic pathogens including Staphylococcus and Enterobacter was high during DSD in comparison to PSD.  “Staphylococcus was present on both the days but their abundance was higher during the dust storm,” said Praveen Rahi, NCMR-NCCS scientist and study co-author.

Members of Bacillus, Arthrobacter, Staphylococcus, Kocuria, Streptomyces and Lysinibacillus were the most dominant on both PSD and DSD, representing 51 percent of the total observed microbial species, the study reported.

Rahi said despite limitations to the study, one thing is clear, that during dust storm the number of microbes that settle down is much, much higher compared to post dust storm.

“This could be because of the fact that the microorganisms settle on the fine particulate matter. The presence of bacteria and fungi on inhalable airborne fine particulate matter (PM 2.5) has implications for human health which is why long-term studies like these are necessary,” explained Rahi.

The study mapped a change in air quality on the two study days based on humidity, velocity and particulate matter (PM 2.5 and PM 10) data shared by the Indian Institute of Tropical Meteorology (IITM), Pune. Air quality dipped on the day of the dust storm while good air quality prevailed on the post-dust storm day.

“The PM 2.5/PM 10 ratios during PSD were below the threshold in all the three sites indicating good air quality. A marked increase was observed in PM 2.5/PM 10 ratios during DSD, suggesting depletion of air quality in the sites due to dust storm,” the study said.

A similar impact on air quality (particle matter concentration) has also been observed during dust storm events in Cairo, Egypt and Ahvaz, Iran, the study notes.

Researchers also underscored the link between geographic barriers and the spread of microorganisms, which explains the choice of three distinct study sites.

While the higher microbial count during dust storm day (DSD) was recorded at all sampling sites, a steady decrease in the microbial count was observed for the sampling sites. The highest count was recorded in Mumbai, followed by Lonavala and Pune.

“Oceanic bacterial species were more in Mumbai because of its proximity to the Arabian Sea. The Sahyadris shielded Lonavla from the spread of microbes while Pune being the farthest from the seashore among the three cities recorded a lower microbial count,” said Rahi.

The intensity of sandstorms is increasing across the world and India could witness an increase in the severity and frequency of dust storms and thunderstorms due to rising global temperatures, experts have said.

Read more: Dust storms may increase in India due to climate change.

Shouche said in the context of climatic changes and increasing extreme weather events, long-term and planned studies on microbial components in the air are warranted. Also crucial is the generation of baseline data to compare and contrast as events progress.

“The best thing would be to be in touch with the meteorology department and plan out systematic studies. We would like to see how the microbial species change with the progress of the dust storm and how long do they persist in the air after the dust storm has gone away,” Shouche said, adding the institute is in the process of designing more such studies.

According to Gufran Beigh of IITM-Pune, bioaerosols (tiny airborne particles that are biological in nature) are components of fine particulate matter and their profile as components of particulate matter should be mapped. “For example, the wind-mediated spread of influenza is just one aspect of studying bioaerosols as part of atmospheric sciences,” added Beigh.