Chapter 14 - Spatial variation of the microbial diversity in the mangrove dominated Sundarban Forest of India

Abstract

The deltaic Sundarbans, also known as the Sundarban Biosphere Reserve (SBR), consisting of mangrove ecosystems, are known for their rich taxonomic diversity of flora and fauna. The microbial community of Sundarbans provides multiple services to mankind starting from the production of bioactive substances to the maintenance of biogeochemical cycles. The Indian Sundarban is divided into three sectors depending on salinity, mainly the hyposaline region in the eastern and western parts of the deltaic complex and the central hypersaline sector. In all these sectors, the microbial community has not been studied in detail in terms of salinity and other environmental variables. The microbial community of deltaic Sundarban includes bacteria, fungi, cyanobacteria and phytoplankton in the ambient aquatic phase. A wide spectrum of bacterial strains are found in the detritus/litter of this complex environment and are thought to be associated with the benthic fauna/flora. These microbes vary depending on their niche specificity and form a heterogeneous association within the communities that directly affects the food web. Identified bacterium such as Bacillus spp., Brevibacterium spp., Clostridium spp., Corynebacterium spp. and Kurthia spp. are found to be proteolytic in nature, while Bacillus alvei, Kurthia bessoni and Brevibacterium spp. exhibit chitinolytic, ammonifying and pectinolytic properties, respectively. Analysis of estuarine water during 2017-18 confirms that the total coliform load varied from 620–1700 MPN/100 mL in Kakdwip (western Indian Sundarbans), 490–1300 MPN/100 mL in Canning (central Indian Sundarbans) and 170–600 MPN/100 mL in Bagmara (eastern Indian Sundarbans), respectively. The total coliforms recorded in the sediments of Kakdwip, Canning and Bagmara were 18.5–130 MPN/g, 9.5–90 MPN/g and 5–40 MPN/g, respectively. Industrial discharges from the port-cum-industrial complex of Haldia along with large number of mechanized and non-mechanized boats involved in fishing activities, make this region contaminated with different microbial population. The Canning zone has a high load of heterotrophs due to unorganized fishing, while in the region adjacent to Bangladesh and within the core zone of the mangrove forest (eastern Sundarbans), lowest microbial count is observed, which may be attributed to minimum anthropogenic activity in the region.