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Tiny but mighty: Newly-discovered diatom from Meghalaya’s cave puts the spotlight on these algae

Read time: 6 mins
26 Aug 2020
Tiny but mighty: Newly-discovered diatom from Meghalaya’s cave puts the spotlight on these algae

Diploneis mawsmaii, the new species of diatoms discovered [Image Credits: Dr Karthick Balasubramanian]

The Arabian folklore says that Ali Baba stumbled into a cave and found treasure. Back home, Dr Karthick Balasubramanian and his team of researchers, including Mr Chintan Bhatt, trekked to one and found life—in tiny glass bodies. Diatoms, as they are called, are single-celled organisms with tough silica shells. They use up almost 6.7 billion metric tons of silicon each year from oceans and other water bodies where they live. They also generate nearly one-fourth of the oxygen produced on Earth.

More than two hundred genera of diatoms are known to science, comprising about one lakh species. The endeavour of Mr Chintan Bhatt and other researchers from the Agharkar Research Institute (ARI), Pune, has added a new species to this list. In a recent study, published in the journal Phytotaxa, the researchers describe this new species of diatoms from the Mawsmai caves in Meghalaya. This first-ever study of cave diatoms was part of a biodiversity assessment project funded by the Department of Biotechnology’s (DBT). This project is part of DBT’s initiative to understand the biodiversity and sustainable livelihoods of the North East India region.

In recent years, many species of diatoms have been discovered in India, including an entire genus from the Western Ghats and two new species from Sikkim. The latest species discovered by Mr Bhatt and his team is named Diploneis mawsmaii after the Mawsmai caves of Cherrapunji, where it was found. It belongs to a large genus of diatoms found throughout the world that has nearly 900 records of described species. Members of this genus exist in a variety of habitats, mostly inhabiting saline water, but some are also found in freshwater.

D. mawsmaii stands out in its genus, with a conspicuously round area at its centre.

"We did not expect to find a member of the genus Diploneis from the cavern habitat with this rare feature," says Mr Bhatt, the lead author of the study. "This finding is surprising and is purely a result of our curiosity."

Treasure in the caves

The Mawsmai caves where the new diatoms were found [Image Credits: Dr Karthick Balasubramanian]

The Mawsmai caves of Meghalaya lie in the Indo-Burma Biodiversity Hotspot. The hotspot, spanning an area of almost two million square kilometres across Southeast Asia, has rich biodiversity and many endemic plants and animals. Still, only 5% of the natural habitat remains undisturbed by human activity.

"We wanted to explore and collect samples of diatoms from every possible potential habitat," says Mr Bhatt. They included the caves of Meghalaya in their field tour, choosing the Mawsmai cave due to its ease of access.

Of the 13,500 species of plant and animal species found in the region, more than half of them are found nowhere else in the world. D. mawsmaii, the researchers say, is one such species.

"This species is so far only known from the Mawsmai caves," says Dr Karthick Balasubramanian, a scientist at ARI, who has led other such studies on diatoms in the region. This uniqueness, in part, can be attributed to the caves themselves.

However, declaring a microbe as endemic is difficult owing to the general lack of studies on microbe diversity. Hence, they can only be called 'possibly endemic'—a term that indicates that this particular species is possibly rare, threatened, and in need of legal protection and conservation. While D. mawsmaii is now identified and labelled unique, the rest of the cave's microflora awaits discovery. "We may conclude our final study only when we explore an ample number of caves," says Dr Balasubramanian.

Caves are a world of their own. Lack of sunlight means that the organisms in the cave have to deal with different conditions of temperature and moisture than the outside world. This environment makes them evolve adaptations that consume less energy. Scientists have long regarded caves as 'natural laboratories', ideal for the observation of various evolutionary processes ranging from genetic to ecosystem levels.

"Cave habitats are peculiar, and the diatoms here are certainly exposed to varied environmental conditions often different than in the major aquatic habitats," says Mr Bhatt. "In many cases, the ecology of the particular area is responsible for the biology of the organism living in that particular area. So, caves are interesting habitats not only in the case of taxonomic studies but also in studies on the ecology and evolution of the diatoms," he adds.

Although rising, diatom discoveries are never easy

Unlike other species of animals or plants, there is a long "eureka!" moment for diatomists as identifying microbes on-site is impossible. After collection, the samples need to be taken to a facility that has good microscopes and access to diatom identification databases, which, in the case of D. mawsmaii, was a long distance away.

"The cave is a two-hour drive from Shillong and can be reached only by foot. We collected the samples there, and it was only when we got back to Pune that we were finally able to examine the samples. This process took us two months," explains Dr Balasubramanian. This delay in the joy of discovery, he rues, is often a deterrent for scientists.

Most studies on diatoms in India have been about their uses and biotechnological benefits, but not as a part of the ecosystem.

"We don't look at their role in our ecosystems. We don't study their diversity just for the sake of studying the diversity of life," says Dr Balasubramanian.

Based on his journey of studying diatoms for the past 15 years, he has published an essential field guide, describing over 180 species of diatoms commonly found in India.

One of the struggles diatomists often face, says Dr Balasubramanian, is the lack of resources in identifying and describing species.

"When you go to a place and see plants or animals that you haven't seen before, the first thing you do is consult a field guide about plants or animals common to that region. What do you do when such a guide doesn't exist? Many scientists then resort to 'force-fitting'—consulting a guide that describes species from regions like Europe or the Americas, and try to fit the new species into their descriptions."

Interestingly, diatom studies aren't new or even recent in India.

"The first algae to be studied and described in India were diatoms. In the 1850s, Prof Christian Ehrenberg, a German biologist, published an excellent volume called Mikrogeologie and described many new species of diatoms from India," says Dr Balasubramanian. After this initial burst of discovery over two centuries ago, however, it has been a mostly silent field.

The discovery of a tiny microbe, invisible to the naked eye, might seem insignificant. Still, their staggering global abundance is anything but microscopic. Besides, their presence in almost every habitat, including extreme climates like volcanoes and deep-sea, could help us understand the implications of climate change much better in many environments.

"What affects higher organisms, like plants or animals, also affects lower organisms. Hence, to understand the impacts of climate change, diatoms are excellent model organisms. There is a need for climate change studies featuring diatoms," he urges. 

This article has been run past the researchers, whose work is covered, to ensure accuracy.