Bloom of the diatom, Biddulphia sp. and ecology of Pulicat lagoon, Southeast India in the aftermath of the 2015 north east monsoonal rainfall.

Pulicat lagoon in the south-east coast of India is recharged with the highest fresh water influx annually during north-east winter monsoon. An abrupt heavy rainfall in November-December 2015 was a flood calamity in the region that inundated the lagoon. We investigated the physico-chemical characteristics and palynological profile of the surface sediments from the lagoon at water depth between 0.5 and 2 m to understand the impact of the 2015 event. On the basis of a 'marine index', three zones were demarcated, the 'LC zone' (Araniar river-lagoon confluence, south), the 'LM zone' and the 'LL zone' (Kalangi river confluence, north) showing values of 4.55, 1.25 and 0.25, respectively, indicating the extent of tidal influence. The dissolved oxygen, pH and salinity ranged between 6.4 and 9.6 mg/L, 7.96-9.23 and average ~ 12.3 ppt at different sites, respectively. The highest salinity (31 and 31.8 ppt) was in the LC zone along with the highest dissolved inorganic nitrogen (DIN) concentrations (275-288 mmol/m3) too. The dissolved inorganic phosphates (DIP) ranged between 8.5 and 29.5 mmol/m3, which was relatively high. Sandy sediment, high sodium (Na+) and chloride (Cl-) ions too indicate the landward extension of seawater influx. Forsterite (Mg2SiO4) and beta-uranophane (Ca[(UO2)SiO3(OH)]2.(H2O) minerals show higher values with the dominance of olivine (MgFe)2SiO4) and quartz (SiO2) in this zone indicating magnitude of fresh water influx too through Araniar river. The highest calcium, magnesium and potassium ions were also observed in LC zone. Fe-rich goethite, calcite and aragonite were recorded at all sites but with dominance of illite in LL zone. Halite, an evaporite recorded from all sites shows inundation of the entire lagoon during flooding event. Results show a bloom of Biddulphia pulchella, B. biddulphiana and B. laevis in association with Cladophora in LC zone which serves as potential indicators of physico-chemical characteristics of the lagoon showing intense response to catastrophic events of floods due to above normal monsoon variability.

Isolation and characterization of Magnetospirillum from saline lagoon.

Magnetotactic bacteria (MTB) are aquatic prokaryotes that orient themselves to earth's magnetic field with the help of intracellular organelle magnetosomes. Although many species of MTB have been identified, the isolation of MTB is a challenging task due to the lack of systematic isolation procedure and/or commercial media. In this study, we are reporting the isolation of magnetotactic spirillum from the Pulicat lagoon, India using a systematic and selective procedure. Sampling site was chosen on the basis of physicochemical properties of the ecosystem and the catalysed reporter deposition fluorescence in situ hybridization (CARD-FISH) analysis of sediment samples. In the current study, a combination of techniques including 'capillary racetrack' Purification and gradient cultivation resulted in the isolation of magnetotactic spirilla from aquatic sediments. Based on the 16S rRNA gene sequence analysis, the strain was identified as Magnetospirillum and was designated as Magnetospirillum sp. VITRJS1. The genes responsible for magnetosome formation (mamA, B, E, F, K, M, O, P, Q, T) were successfully detected using PCR amplification. The presence of cbbM gene confirmed that the isolate is chemolithoautotroph and utilises reduced sulphur as an electron source. Furthermore, magnetosomes extracted from VITRJS1 found to be cubo-octahedral in shape and 45 nm in size. Our results indicate that the systematic procedure using sediment analysis, CARD-FISH, and a combination of isolation methods enables the selective and rapid isolation of MTB from aquatic sediment sample.