Scientists map the microbes behind a climate-regulating gas in India's busiest estuary — a first

Scientists Map the Microbes Behind a Climate-Regulating Gas in India's Busiest Estuary — A First

Article by Dibu Divakaran / Dr. Doniya Elze Mathew Department of Chemical Oceanography, Cochin University of Science and Technology (CUSAT), Kochi, Kerala, India E-mail: dibudk@gmail.com / doniyaelze@gmail.com

Why This Estuary Matters to the Global Sulfur Cycle

Every year, marine plants — from microscopic phytoplankton to seaweeds — produce vast quantities of a sulfur compound called dimethylsulfoniopropionate, or DMSP. When bacteria in the water and sediment break DMSP down, they release dimethylsulfide (DMS), a gas that drifts into the atmosphere and helps form clouds by seeding cloud condensation nuclei — making it one of the most climate-relevant gases produced by ocean life. Yet despite decades of research on this process in open-ocean and temperate waters, tropical estuaries have been largely overlooked. The Cochin Estuary (CE) in Kerala, southwest India, is one of the most biologically productive and heavily used coastal waterways in the country — fed by six major rivers, shaped by the monsoon, and bordered by industrial activity. A research team led by Dr. Dibu Divakaran and Dr. Doniya Elze Mathew, from the Department of Chemical Oceanography, Cochin University of Science and Technology (CUSAT), Kochi, India, set out to fill this knowledge gap by conducting the first-ever study of DMSP concentrations and the bacteria that degrade it along the entire length of the Cochin Estuary.

What the Team Measured, Collected, and Found

Between 2015 and 2018, the researchers sampled water and sediment at fifteen stations spread across the upper, middle, and lower sections of the estuary — covering three distinct seasons: pre-monsoon, monsoon, and post-monsoon. DMSP and DMS levels were measured using gas chromatography, and bacterial communities were cultured, counted, and identified using 16S rRNA gene sequencing. The picture that emerged was clear: the estuary's sediments, not the overlying water, are where most of the microbial action takes place. DMSP concentrations in the sediment were consistently higher than in the water column, and the sediment harboured roughly twice as many bacteria per gram as the water held per millilitre. The highest DMSP levels were recorded at station S7 in the middle estuary (Thevara) during the pre-monsoon season, when salinity and temperature were at their peak — conditions that strongly correlate with increased phytoplankton DMSP production. Four bacterial strains capable of growing on DMSP as their sole carbon source were isolated, all from sediment: two members of the γ-Proteobacteria group (Acinetobacter calcoaceticus and Acinetobacter beijerinckii) and two from the Firmicutes group (Bacillus cereus and Lysinibacillus fusiformis). Crucially, A. calcoaceticus was found to carry the dddP gene — a gene that codes for the enzyme directly responsible for splitting DMSP into DMS — confirming that active enzymatic release of the climate gas is occurring within this estuary's sediments.

What These Findings Mean for Science and Beyond

This study is the first to establish a baseline for DMSP dynamics and DMSP-degrading bacteria in the Cochin Estuary, and its findings carry significance well beyond Kerala. By confirming that estuarine sediments in tropical India serve as active sites for sulfur cycling — and by identifying the specific bacteria driving that process — the research fills a genuine blank in the global map of marine sulfur flux. The monsoon-driven swings in salinity and temperature were found to directly shape which bacteria thrive and how active they are, underscoring how sensitive this process is to seasonal and, by extension, longer-term climatic changes. The authors also highlight a practical dimension: bacteria like A. calcoaceticus and B. cereus, with their demonstrated ability to break down organosulfur compounds, could in the future be used in bioengineering applications to manage sulfur emissions or treat volatile sulfur pollutants in aquatic environments. The researchers call for follow-up studies using metagenomics and metatranscriptomics to map the full range of DMSP-degrading pathways operating in this estuary across more stations and seasons — work that will ultimately sharpen our ability to model how coastal ecosystems influence the atmosphere and, through it, the climate.

About the Study Divakaran D, Sujatha C.H, Mathew D.E. Dimethylsulfoniopropionate (DMSP) Degradation by Marine Bacteria along the Cochin Estuarine System. Open Biotechnol. J., 2026; 20: e18740707433988.

Read the published article here: https://bit.ly/4uFVLvF
 
The Open Biotechnology Journal

DOI: 10.2174/0118740707433988260408095129

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