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How rainwater hides mysterious microbes

Nandkumar M Kamat

These are some results from our biometeorological research which were brought to the notice of scientists of Panaji IMD observatory on World Meteorological Day, March 23, 2018 in my presentation on the invitation of the then station director Sahu.

Biometeorology and its microbial dimension is still a novelty in India. But we wish to inform the people that rainwater falling in Goa is teeming with microorganisms. After 11 years of research we have a very strong suspicion about the monsoon clouds being very special ephemeral, extreme, and complex microbial habitats.

My PhD research student from Varanasi UGC NET scholar Sheela Pal who is working on freshwater yeasts presented a paper in February this year at an international conference at Benares Hindu University on ‘Yeast in Southwest monsoon rainwater: Some ecological and biometeorological implications’. We were intrigued by the isolation of yeast in directly sampled local rainwater. Its DNA based molecular identification showed that it could be a wild, benign form of the human pathogen Candida tropicalis. We had seen scattered yeast cells in rainwater samples collected since 2007 and had ignored them as possible artefacts or contaminants. But once these started showing up consistently under most sterile conditions, we attempted to isolate them, purify, maintain and identify them. This is pioneer work in India and Asia.

There is a very ancient and popular belief that rainwater falling directly from overhead clouds is the purest form of water. But this has no scientific basis and the rainwater falling anywhere on this planet is a cocktail of soluble and insoluble matter, living and dead cells and it can never be considered as pure unless filtered and sterilised.

In one experiment we found upto seven percent insoluble material in local rainwater. A 2017 paper by Ramaswamy and colleagues had reported deposition of various ions from rainwater. They found per every square metre of surface per year we get eight grams of sodium, half gram ammonium, a gram of magnesium, five grams of calcium, 15 grams of chloride ions, two grams of nitrates, five grams of sulphates from the sea and three grams of sulphate ions from other sources. The microbial dimension is more serious.

During the monsoons, people report sickness after getting accidentally soaked in the rain. The culprit is rainwater. So what’s there in the rainfall which is harmful? After examining the rainwater samples collected directly within few minutes, we could get an idea of the non-biological components. Since the monsoon season in 2013, I developed a simple technique to collect the rainwater directly in a germ-free sterile container and avoid contact with surrounding air environment. This technique permits sampling of water through a sterile plastic funnel in a sterile plastic bottle. The sealed bottle is then opened on a laminar air flow bench and processed to make the slides for microscopy, and special sterile isolation media prepared by us is employed to grow any microorganisms.

During 2014, we presented a paper titled –‘Do Unique Stratospheric Life Forms Get A Piggy Back Ride Inside SW Monsoon Clouds To Leave Signatures In Locally Sampled Rainwater?’. When a copy was sent to expert in the field of cloud microbiology and biometeorology Brent Christner (now at University of Florida) he questioned what we meant by stratosphere since rainfall phenomena is troposhere bound. He had not seen the paper ‘Stratosphere microbes may hold clue to life on earth’ by astrophysicist Jayant Naralikar published by Nature on March 25, 2009. This work was supported by ISRO. We suspected some of the microbes in monsoon rainwater could be of stratospheric origin and thus in sensu Naralikar implying their extraterrestrial origin.

Clouds can be defined as atmospheric air masses in which water is condensed around particles in solid (ice crystals) or liquid form.

Biological matter is found in the atmosphere in the form of living or ‘dead’ organisms. Dimmick et al. (1979), Fuzzi et al (1997) and Sattler et al. (2001) suggested that cloud droplets may provide a medium in which airborne cells can divide. Because bacteria require water for their metabolism, they are supposed to be good cloud condensation nuclei. In a changing climate, one can furthermore suppose that even more bacteria find viable conditions in the atmosphere and, thus, may become more abundant in clouds andbe transported more widely. According to Brent (2012) microbes and their metabolic activities could affect meteorological processes in the atmosphere both by changing cloud chemistry.

In 2014 in our pioneer presentation, we had clearly mentioned that one doesn’t really need rocket science to sample and analyse rainwater directly and detect interesting inorganic and microbial components- the later probably getting a piggy back ride in the clouds whereas the former may be signature of atmospheric dust, volcanic ash, aeolian processes , air transportation exhaust. We had concluded that rainwater falling in Goa during SW monsoon can no more be treated as “pure’ but full of inorganic and some potentially dangerous and pathogenic microbial life forms. These may have wide implications in ecology, hydrology, biogeochemistry, plant and human diseases.

A statewide effort must be launched to collect and analyse rainwater samples periodically in sterile containers and build a cohesive spatiotemporal picture of microbial life forms raining in Goa. People must take care during the monsoon to avoid exposure to rainwater and take a bath immediately if one gets soaked.

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