Dipa Biswas

Survey of petroleum-degrading bacteria in coastal waters of Sunderban Biosphere Reserve

A survey of petroleum-degrading bacteria was carried out in the Indian part of deltaic Sunderbans to evaluate the distribution of the naturally occurring petroleum-degrading aerobic bacteria. Bacteriological analysis of surface water samples collected from five different locations in the Hooghly–Matla river mouth showed that, depending on the location, 0.08–2.0% of the heterotrophic bacteria culturable in marine agar medium could degrade crude petroleum hydrocarbons as the sole source of carbon. In the entire study area, the number of heterotrophic bacteria ranged from 1 × 103 to 3.8 × 105 c.f.u/ml, amongst which 2.7 × 101 to 6 × 103 c.f.u/ml were petroleum degraders. There was a maximum number of petroleum-degrading bacteria in the waters of Haldia Port and its surrounding areas, where the water is highly polluted by hydrocarbon discharges from a nearby oil refinery and from the ships docking at the port. Among the isolates, identified on the basis of their Gram reaction, morphological and biochemical tests including the use of API20E strips, Pseudomonas, Mycobacterium, Klebsiella, Acinetobacter, Micrococcus, and Nocardia were the most common petroleum degraders. Other heterotrophic bacteria included several species of Escherichia, Klebsiella, non-oil-degrading Pseudomonas, Vibrio, Streptococcus, Staphylococcus and Bacillus. Following preliminary selection, five strains, showing best growth in medium with oil fraction as sole carbon source, were chosen for estimation of the efficiency of crude oil biodegradation. The selected strains belonged to Pseudomonas (two strains), Mycobacterium (two strains), and Nocardia (one strain). These strains degraded 47–78% of Arab-Mix crude oil over a period of 20 days. The best oil-degrading isolate, a strain of Pseudomonas aeruginosa, (BBW1), was found to degrade and multiply more rapidly in crude oil than the rest. BBW1 showed profuse growth in Bushnell Haas medium containing crude oil (as sole source of carbon) at high concentrations ranging from 0.2 to 20% (v/v), with optimum at 10%. As much as 75% of the oil was degraded within 72 h of incubation with the bacteria. Physicochemical analysis showed considerable decrease in initial boiling point and carbon residue of the degraded oil. The ability to degrade crude oil was found to be associated with a single 70-kb plasmid, pBN70. Resistance to the metals Mn2+ (50 mM), Mg2+ (200 mM), Zn2+ (6 mM), Ni2+ (10 mM) and antibiotics like ampicillin (10 μg/ml), cephalexin (30 μg/ml), nitrofurantoin (300 μg/ml) and penicillin (10 U/ml) were plasmid-mediated.

Assessment of synergistic antibacterial activity of combined biosurfactants revealed by bacterial cell envelop damage

Besides potential surface activity and some beneficial physical properties, biosurfactants express antibacterial activity. Bacterial cell membrane disrupting ability of rhamnolipid produced by Pseudomonas aeruginosa C2 and a lipopeptide type biosurfactant, BS15 produced by Bacillus stratosphericus A15 was examined against Staphylococcus aureus ATCC 25923 and Escherichia coli K8813. Broth dilution technique was followed to examine minimum inhibitory concentration (MIC) of both the biosurfactants. The combined effect of rhamnolipid and BS15 against S. aureus and E. coli showed synergistic activity by expressing fractional inhibitory concentration (FIC) index of 0.43 and 0.5. Survival curve of both the bacteria showed bactericidal activity after treating with biosurfactants at their MIC obtained from FIC index study as it killed >90% of initial population. The lesser value of MIC than minimum bactericidal concentration (MBC) of the biosurfactants also supported their bactericidal activity against both the bacteria. Membrane permeability against both the bacteria was supported by amplifying protein release, increasing of cell surface hydrophobicity, withholding capacity of crystal violet dye and leakage of intracellular materials. Finally cell membrane disruption was confirmed by scanning electron microscopy (SEM). All these experiments expressed synergism and effective bactericidal activity of the combination of rhamnolipid and BS15 by enhancing the bacterial cell membrane permeability. Such effect of the combination of rhamnolipid and BS15 could make them promising alternatives to traditional antibiotic in near future.

Towards a better production of bacterial exopolysaccharides by controlling genetic as well as physico-chemical parameters

Bacterial extracellular polymeric substances, which are basically bacterial metabolites, have currently become a subject of great concern of modern day microbiologists and biotechnologists. Among these metabolites, bacterial exopolysaccharides or EPS, in particular, have gained a significant importance. EPS are formed by the bacteria in their late exponential or stationary phase of growth under special situations for specific purposes. They take part in the formation of bacterial biofilms. There is a great diversity in the types of EPS. Strikingly enough, a same species of bacterium can produce different types of EPS under different situations. The importance of EPS is largely because of their different applications in various industries. Now that the bacterial EPS has got the potentiality to become an upcoming tool in various futuristic applications of human benefit, the focus currently develops towards how better they can be produced in the laboratory by promoting the favorable factors for their production. While studying with different EPS forming bacteria, both the intrinsic factors like genetic configuration of the bacteria and the extrinsic factors like culture conditions under the influence of different physico-chemical parameters in order to maximize the EPS production have been taken into consideration. Both the factors have proved their worth. Hence, towards a better outcome for EPS production, it is indicated that a genetic manipulation of the bacteria should be synchronized with a proper selection of its culture condition by controlling different physico-chemical parameters.

High pressure hydrocracking of vacuum gas oil to middle distillates

Abstract Hydrocracking of heavier petroleum fractions into lighter ones is of increasing importance today to meet the huge demand, particularly for gasoline and middle distillates. Much work on hydrocracking of a gas oil range feed stock to mainly gasoline using modified zeolite catalyst-base exchanged with metals (namely Ni, Pd, Mo, etc.) has been reported. In India, however, present demand is for a maximum amount of middle distillate. The present investigation was therefore aimed to maximize the yield of middle distillate (140–270°C boiling range) by hydrocracking a vacuum gas oil (365–450°C boiling range) fraction from an Indian Refinery at high hydrogen pressure and temperature. A zeolite catalyst-base exchanged with 4.5% Ni was chosen for the reaction. A high pressure batch reactor with a rocking arrangement was used for the study. No pretreatment of the feed stock for sulphur removal applied as the total sulphur in the feed was less than 2%. The process variables studied for the maximum yield of the middle distillate were temperature 300–450°C, pressure 100–200 bar and residence period 1–3 h at the feed to catalyst ratio of 9.3 (wt/wt). The optimum conditions for the maximum yield of 36% middle distillate of the product were: temperature 400°C, pressure 34.5 bar (initially) and residence period 2 h. A carbon balance of 90–92% was found for each run.

Synthesis and characterization of a sol-gel-derived zeolite prototype as a prospective hydrocracking catalyst

This paper deals with the preparation and evaluation of a zeolite prototype developed from an aluminosilicate precursor for its possible application as a hydrocracking catalyst. Aluminium nitrate and tetraethyl orthosilicate at definite proportions were the primary reagents for the gel synthesis. Nickel loading and stipulated post-synthesis treatment of the material are also addressed in this paper. The characteristics of the calcined aluminosilicate gel were estimated using X-ray diffraction (XRD), scanning electron microscope (SEM) study with energy dispersive spectroscopy (EDS), differential thermal analysis (DTA) with thermogravimetry (TG) and Fourier-transformed infrared spectroscopy (FTIR) at different temperatures. A preliminary laboratory-scale investigation of hydrocracking performance of this zeolite prototype was also conducted.

Green Techniques in Gas Chromatography

Gas chromatography (GC) is one of the most important analytical techniques among the various chromatographic processes currently in use. To widen it’s applicability and acceptability analysts are now concentrating to develop green GC, replacing conventional GC. The appreciating feature of green GC is it’s environment-friendliness by the way of reducing/eliminating the amount of solvents required for sample preparation and amount of waste generation or emission of volatile products. Reduction in chromatographic runtime and the possibilities of integrating GC with other efficient analytical tools are the other advantages of green GC which make it a highly efficient, sensitive and fast method of analysis in chemical science. This chapter highlights the different aspects of gas chromatography in the light of green techniques starting from sample preparation to the selection of mobile phase as well as chromatographic columns to be adopted. Coupling other analytical tools with GC to focus the versatility and high accuracy of analysis with dual system of separation and detection is also discussed.

Study of the Potential of Two Isolated Microorganisms to Degrade Various Petroleum Fractions

Biodegradation of petroleum by the microorganisms in polluted site has been gaining attention from the environment clean-up point of view. Two isolated organisms Acinetobacter junii CTA3 and Pseudomonas aeruginosa OCD1 were tested for their petroleum degrading ability in liquid Bushnell-Hass broth. Both the organisms degraded higher boiling petroleum fractions more efficiently. The strain OCD1 showed better degrading ability than the strain CTA3. The highest degradation of 47% and 57% was obtained with diesel after 20 days of incubation by the organism CTA3 and OCD1 respectively. Also it was observed that, most of the oils were degraded in first 10 days of incubation for both the isolates.