Organic Matter and Anaerobic Cellulolytic Activity in Sediments of Ashtamudi Estuary, Kerala, India

Estuarine sediments are best suited for bioprospecting cellulose-degrading microorganisms because of continuous input of cellulosic carbon from rivers and terrestrial runoff, and such sediments act as a substrate for decomposition by microbes. Sediment samples were collected from thirteen stations of Ashtamudi estuary, a tropical Ramsar site during April 2016 and January 2017 and analyzed for environmental variables such as temperature, pH, electrical conductivity, oxidation-reduction potential, sulphate, total organic carbon (C org ), carbohydrate, protein, lipid and labile organic matter. Microcosm experiments were conducted in the sediment samples to compare native and substrate-induced cellulase enzyme activities in mesophilic and thermophilic conditions added with crystalline cellulose and cellobiose as substrates. Abundance of cellulolytic anaerobes in the roll tubes was higher with cellobiose (3.15 in April 2016 and 3.38 in January 2017) than crystalline cellulose (2.84 in April 2016 and 3.92 in January 2017). Substrate induced enzyme activity was more than native enzyme activity [0.0012 ± 0.0001–0.004 ± 0.002 (April 2016) and 0.004 ± 0.001–0.161 ± 0.002 mg glucose h − 1 (January 2017) in the sediment samples and cellulolytic activity was more pronounced in thermophilic conditions during April 2016. Redundancy Analysis indicated that salinity was the highest determining factor for explaining variations among bacterial abundance and activity during April 2016 and sediment lipid content during January 2017. The study reveals that estuarine sediments can act as a potential source of thermophilic cellulase enzyme producing bacteria, which needs to be further explored owing to their vast industrial applications.