Hridip Kumar Sarma

Application of bioflocculating property of Pseudomonas aeruginosa strain IASST201 in treatment of oil-field formation water

A bioflocculating activity of 89.8% was depicted by an activated sludge‐borne bacteria Pseudomonas aeruginosa strain IASST201 with a yield of bioflocculant of 2.68 g L−1 obtained from production media broth after optimization of different parameters. The highest bioflocculation efficiency was found at the pre‐stationary phase of the bacterial growth period in the production media broth at 96th hour examined from a growth‐flocculation kinetics study. 85.67% of bioflocculation was observed in oil‐field formation water, with a separation of 68.7% of aliphatic hydrocarbon contents of the formation water after the application of the bacterial bioflocculant by entrapment mechanism with formation of flocs which was analyzed and examined comparatively through gas‐chromatography. Extensive removal of heavy metal contents of the oil‐field formation water due to bioflocculation was estimated by Atomic Absorption Spectrophotometer (AAS). The SEM and AFM studies declare the extracellular polymeric nature of the bioflocculant produced by this bacterium clumped within bacterial biofilm supported with FTIR study of the extracted bioflocculant.

Production of a non-cytotoxic bioflocculant by a bacterium utilizing a petroleum hydrocarbon source and its application in heavy metal removal

A bacterium isolated from the activated sludge of an oil refinery of Assam, India retained efficient bioflocculating activity through production of the bioflocculant when it was grown on a crude oil amended medium void of any other carbon source. The bioflocculating activity gained from the optimized medium broth was 86.2%, which could be enhanced up to 89.1% with the purified bioflocculant. During the course of the bioflocculant production, the bacterium utilized about 77% of the petroleum hydrocarbons after incubation for 168 h when the activity was found to be the highest. The bioflocculant was efficient in flocculating Ni2+, Zn2+, Cd2+, Cu2+ and Pb2+. The bioflocculant was characterized as a glycoprotein complex by biochemical tests, FT-IR, SEM-EDX and LC/MS analyses. The bioflocculant showed negligible cytotoxicity on testing with the L292 cell line indicating the tremendous possibility of its use in bioremediation.

Rhamnolipid Biosurfactant against Fusarium verticillioides to Control Stalk and Ear Rot Disease of Maize.

Antifungal activity of rhamnolipids (RLs) has been widely studied against many plant pathogenic fungi, but not against Fusarium verticillioides, a major pathogen of maize (Zea mays L.). F. verticillioides causes stalk and ear rot of maize or asymptomatically colonizes the plant and ears resulting in moderate to heavy crop loss throughout the world. F. verticillioides produces fumonisin mycotoxins, reported carcinogens, which makes the contaminated ears unsuitable for consumption. In this study, the RL produced using glucose as sole carbon source was characterized by FTIR and LCMS analyses and its antifungal activity against F. verticillioides was evaluated in vitro on maize stalks and seeds. Further, the effect of RL on the mycelia of F. verticillioides was investigated by scanning electron microscopy which revealed visible damage to the mycelial structure as compared to control samples. In planta, treatment of maize seeds with a RL concentration of 50 mg l-1 resulted in improved biomass and fruiting compared to those of healthy control plants and complete suppression of characteristic disease symptoms and colonization of maize by F. verticillioides. The study highlights the potential of RLs to be used for an effective biocontrol strategy against colonization of maize plant by F. verticillioides.

Characterization of a Novel Polymeric Bioflocculant Produced from Bacterial Utilization of n-Hexadecane and Its Application in Removal of Heavy Metals

A novel polymeric bioflocculant was produced by a bacterium utilizing degradation of n-hexadecane as the energy source. The bioflocculant was produced with a bioflocculating activity of 87.8%. The hydrocarbon degradation was confirmed by gas chromatography-mass spectrometry analysis and was further supported with contact angle measurements for the changes in hydrophobic nature of the culture medium. A specific aerobic degradation pathway followed by the bacterium during the bioflocculant production and hydrocarbon utilization process has been proposed. FT-IR, SEM-EDX, LC/MS, and 1H NMR measurements indicated the presence of carbohydrates and proteins as the major components of the bioflocculant. The bioflocculant was characterized for its carbohydrate monomer constituents and its practical applicability was established for removing the heavy metals (Ni2+, Zn2+, Cd2+, Cu2+, and Pb2+) from aqueous solutions at concentrations of 1–50 mg L-1. The highest activity of the bioflocculant was observed with Ni2+ with 79.29 ± 0.12% bioflocculation efficiency.

Population genetic assessment of extant populations of greater one-horned rhinoceros (Rhinoceros unicornis) in India

The greater one-horned rhino has a wide range of historical distribution across the northern Indian subcontinent and now being confined to restricted patches in India and Nepal. Development of effective conservation strategy for rhino requires a clear understanding of the extant and spatial distribution of genetic diversity. In the present study, we employed nine microsatellite markers to analyze 238 noninvasively sampled individual rhinos from five protected areas in India, in order to assess genetic diversity and population genetic structure in the wild. We observed a moderate to high level of genetic diversity with allelic richness (Ar) ranging from 2.589 (±0.88) to 3.635 (±0.93) and expected heterozygosity (He) ranging from 0.352 (±0.20) to 0.59 (±0.13) in the area. Significant level of genetic differentiation was observed between the Protected Areas of Assam and West Bengal, especially, Gorumara National Park showing a unique genetic signature (FST ≥ 0.25; p < 0.001, with all other protected areas). Given the degree of population genetic structure observed, prolonged separation of these protected areas is unwanted as this could lead to further loss of genetic diversity, consequently, affecting long-term viability of the species. The results presented here will be crucial in designing in situ conservation and management strategies of the species.

First Report of Fusarium verticillioides Causing Stalk Rot of Maize in Assam, India

Maize (Zea mays L.) is cultivated in 8.6 million ha in India with a total production of 22.67 million tonnes and avg. yield of 27.52 tonnes/ha in 2014 (http://faostat3.fao.org/download/Q/QC/E). In September 2012, symptoms of Fusarium stalk rot were observed on maize cultivar PAC 740 (Advanta Ltd., Hyderabad, India) grown in a field in Tinsukia, Assam, northeast India (27.5° N; 95.37° E; elev. 116 m). Symptomatic plants were collected for study. External symptoms included softening and reddish coloration of the stalks near the first three internodes from the bottom. Internally, the pith appeared to be soft, disintegrating, and light brown to reddish. Lodging was observed in two plants out of a total of seven exhibiting visible external symptoms. The leaves and stalks of the lodged plants were dry and tan. Small pieces of infected stems were surface sterilized in a 5% aqueous solution of NaClO for 1 min, rinsed 3 times with sterile distilled water and dried in a laminar air flow cabinet. Then, 1 to 2 pieces per plate were transferred to potato dextrose agar (PDA) media supplemented with 0.5 g/liter ampicillin and incubated at 25°C for 5 to 7 days. The isolates were single-spore subcultured on PDA and incubated at 25°C for two weeks (Leslie and Summerell 2006). The mycelia were initially white and gradually developed a blackish pigmentation; the microconidia were single-celled, oval to club-shaped, 4.4 to 11.55 × 1.1 to 3.3 μm (avg. 6.6 × 1.65 μm) arranged in catenation from monophialides. The morphological characteristics were consistent with those of Fusarium verticillioides (Sacc.) Nirenberg (Leslie and Summerell 2006). After microscopic confirmation, the ITS1-5.8S-ITS2 regions of the rDNA were amplified using the primers ITS1 and ITS4 (White et al. 1990) and sequenced (GenBank Accession No. KF031434). The sequence was compared with those deposited in GenBank and the isolate showed 99% similarity with Gibberella moniliformis strain SA3 (EU151482) (Visentin et al. 2009). Pathogenicity tests were conducted on maize plants grown in 25 × 28-cm (diameter × height) pots filled with 4 kg sterilized soil. Five 75day-old PAC 740 plants were injected with 2 ml microconidial suspension (10conidia/ml) at the second internodes above the soil line (Munkvold et al. 1997) and incubated in a controlled environment chamber at 25°C and 80 to 85% humidity with a 14-h photoperiod. Conidial suspension was harvested from a 10-day-old culture in potato dextrose broth. Ten to 12 days post inoculation (dpi), inoculated plants developed characteristic external symptoms, like softening of the stalks followed by lodging at 21 to 22 dpi, similar to those observed on naturally infected maize plants in the field. The plants were removed from the pots and the pathogen was reisolated from split stalks and identified by morphological characteristics as F. verticillioides. Research on maize cultivation is still fragmentary in Assam with few districts actively involved in cultivation, but due to high commercial value, maize cultivation is gaining wider interest in the area. Considering the impact of stalk rot on maize yields, further research is needed to develop and implement measures for disease control. To our knowledge, this is the first report of F. verticillioides causing stalk rot of Z. mays in Assam or the northeastern India.

Phylogeny and evolutionary genetics of Frankia strains based on 16S rRNA and nifD-K gene sequences.

16S rRNA and nifD–nifK sequences were used to study the molecular phylogeny and evolutionary genetics of Frankia strains isolated from Hippöphae salicifolia D. Don growing at different altitudes (ecologically classified as riverside and hillside isolates) of the Eastern Himalayan region of North Sikkim, India. Genetic information for the small subunit rRNA (16S rRNA) revealed that the riverside Frankia isolates markedly differed from the hillside isolates suggesting that the riverside isolates are genetically compact. Further, for enhanced resolutions, the partial sequence of nifD (3′ end), nifK (5′ end) and nifD–K IGS region have been investigated. The sequences obtained, failed to separate riverside isolates and hillside isolates, thus suggesting a possible role of genetic transfer events either from hillside to riverside or vice versa. The evolutionary genetic analyses using evogenomic extrapolations of gene sequence data obtained from 16S rRNA and nifD–K provided differing equations with the pace of evolution being more appropriately, intermediate. Values of recombination frequency (R), nucleotide diversity per site (Pi), and DNA divergence estimates supported the existence of an intermixed zone where spatial isolations occurred in sync with the temporal estimates. J. Basic Microbiol. 2015, 54, 1–9