Subhajit Das

Microbial Ecosystem in Sunderban Mangrove Forest Sediment, North-East Coast of Bay of Bengal, India

This is the first documentation of seasonal and spatial fluctuation of the culturable microbial population collected from different zones in the sediment of the Sunderban mangrove forest. The population of cellulose degrading bacteria, [mean value of CFU 6.189 ± 1.025 × 106 (g dry weight of sediment)−1] was found to be maximum during post monsoon in the deep forest region, whereas, the fungal population [mean value of CFU 3.424 ± 0.886 × 106 (g dry weight of sediment)−1] was found to be maximum during pre-monsoon in the rooted region. The abundances of microbes, in decreasing order, studied from different zones are nitrifying bacteria [mean value of CFU 1.125 ± 0.359 × 106 (g dry weight of sediment)−1], phosphorous solubilizing bacteria (PSB) [mean value of CFU 0.805 ± 0.322 × 106 (g dry weight of sediment)−1], free living nitrogen fixing bacteria [mean value of CFU 0.417 ± 0.120 × 106 (g dry weight of sediment)−1] and sulfur reducing bacteria (SRB) [mean value of CFU 0.356 ± 0.125 × 106 (g dry weight of sediment)−1]. The content of organic carbon in the soil decreased from the deep forest region to the rooted and unrooted region but a reverse profile was found for soil salinity and soil silicate concentration. The results from the present study indicate that the monsoon cycle has a pronounced effect on the microbially dominated biogeochemistry in the sediment and consequently on the ecology of the Sundarban mangrove forest.

A Report on the Micro-Phytoplankton Size Range,Biovolume, Biomass and Geometric Shape in the Post Aila (Severe Cyclone) Waters of Estuarine Sundarban-Bay of Bengal, India

A Report on the Micro-Phytoplankton Size Range, Biovolume, Biomass and Geometric Shape in the Post “Aila” (Severe Cyclone) Waters of Estuarine Sundarban-Bay of Bengal, India The Sundarban was rampaged by a severe tropical super cyclone designated as BOB 02 or more popularly as “Aila” on 25th May of 2009 and it changed the face of the deltaic region forever. The present study commenced on March, 2010 and continued till February of 2013 to capture the detailed effect of the physicochemical and meteorological parameters on the existing phytoplankton community. In order to predict the changes, if any, in metabolism of the microphytoplanktons, biovolume and biomass were selected as indices. The Hooghly estuary was chosen as the study site since it is the largest estuary of the River Ganges and should reflect the scenario better being a tropical well mixed estuary. The study revealed higher proportion of diatoms, dinoflagellates and Cyanophyceae than before.

Vertical Profile of Phosphatase Activity in the Sundarban Mangrove Forest, North East Coast of Bay of Bengal, India

Impact of phosphate solubilizing bacteria along with soil phosphatase activity on phosphorous cycle was found to be quiet interesting in the Sundarban mangrove ecosystem. Soil phosphatase activity showed a decreasing pattern with increase in depth [soil phosphatase activity (μg pnp produced g−1 dry wt of soil) = 906.85 – 5.6316 Depth (cm)] from the deep forest region of the Sundarban forest ecosystem. Soil salinity showed a very little effect on soil phosphatase activity whereas soil temperature and pH was found to show significant impact on the soil phosphatase activity. This ensured that the microbes associated with phosphate mineralization present in the Sundarban forest ecosystem are more tolerant to fluctuation in salinity than that of temperature and pH. A direct correlation was perceptible between the number of phosphate solubilizing bacteria and phosphatase activity in the soil during the study period from 2007 to 2012. Soil phosphate concentration was found to be directly governed by the soil phosphatase activity [The regression equation is: avg PO4−3-P (μg g−1 dry wt of soil) = 0.0311 + 0.000606 soil phosphatase activity (μg pnp produced g−1 dry wt of soil); R2 = 63.2%, p < 0.001, n = 62].

Influence of Microbial Composition on the Carbon Storage Capacity of the Mangrove Soil at the Land-ocean Boundary in the Sundarban Mangrove Ecosystem, India

ABSTRACT Spatiotemporal assessment of the mangrove soil of Indian Sundarban revealed that decomposition rate of the organic matter was significantly lower in the anoxic condition than that of the oxic condition. Higher degree of enzyme activity in the oxic soil than the anoxic condition suggested that slower biomineralization in anoxic condition would facilitate long-term storage of organic matter in that particular ecosystem. Microbial population of nitrifying bacteria, phosphate solubilizing bacteria, free-living N2 fixing bacteria, and cellulose degrading bacteria and fungi showed significant reduction in anoxic incubation than that in oxic incubation. In contrary, sulfate reducing bacteria showed higher population in anoxic incubation indicating their preference for anaerobic condition. Soil CO2 emission rate decreased with the increase in anoxicity and was largely dependent on the soil redox potential, organic carbon, and microbial population of the mangrove soil.

Microbial assay of N 2 fixation rate, a simple alternate for Acetylene Reduction Assay

Graphical abstract Comparison between ARA and Microbial bio-assay in terms of N2 fixation rate.

An ex situ and in vitro approach to delineate pennate diatom species with bioindicator potentials in a well mixed tropical estuarine ecosystem

An experiment was performed on selected pennate diatom species collected from the well mixed waters of the Hooghly Estuary with the aim of distinguishing the ones with qualities to be employed as monitors of their ecosystem. The Hooghly Estuary is enriched with domestic, sewage and agricultural effluents and coastal upwelling along with tide-mediated advective circulation from the mangrove forests ensure concomitant nutrient pool replenishment in this ecoregion. There have been several attempts to establish certain centric diatom species as bioindicators in various parts of the world owing to their better responsiveness to sudden shifts in stoichiometry but hardly any with pennate diatoms. Pennate diatoms are typical benthic mat formers in the intertidal regions, on submerged surfaces and thus bear greater feasibility to be employed as accurate pointers to long term deviations in their respective ecosystems, in spite of the greater sensitivity of the centric diatoms. The study was carried out in laboratory controlled environment to minimize the interference from other extrinsic factors compromising the outcome and also due to the fact that such studies to be performed in natural conditions require a decent financial support and time to conclusively arrive upon the objectives. From the present endeavour it was inferred that Nitzschia sigmoidea, Pleurosigma angulatum and Ulnaria oxyrhyncus (formerly Synedra ulna var. oxyrhyncus) stood a good chance of being recruited as bioindicators to eutrophic well mixed estuaries, similar to the one they had been sampled from.