Characterization of a novel bioemulsifier from Pseudomonas stutzeri.

This study describes a novel and efficient alasan-like bioemulsifier produced by Pseudomonas stutzeri NJtech 11-1, which was isolated from the Shengli Oilfield. The strain was found to produce a new and interesting emulsion stabilizer. The crude bioemulsifier showed super stability with 50% salinity and broad pH 3-10. The emulsion index (EI24) was increased to 100% after heating from 45 to 95 °C and the emulsion could be stable for at least 30 days. The yield of Ps-bioemulsifier (pure bioemulsifier) was 0.68 ± 0.05 mg mL-1. The Ps-bioemulsifier was composed of carbohydrates (80 ± 2.6%) and proteins (9.5 ± 0.5%). A low concentration (0.2 mg mL-1) of the Ps-bioemulsifier was obtained maximum emulsifying activity at pH 7.1 and its emulsifying activity strengthened by suitable salinity. Furthermore, Ps-bioemulsifier could also emulsify cyclohexane, hexadecane, kerosene, xylene hydrocarbons efficiently. Therefore, the Ps-bioemulsifier showed emulsifying characteristics which make it a good candidate for potential applications in bioremediation and microbial enhanced oil recovery.

Optimization of culture medium for anaerobic production of rhamnolipid by recombinant Pseudomonas stutzeri Rhl for microbial enhanced oil recovery.

UNLABELLED: Response surface methodology was employed to enhance the anaerobic production of rhamnolipid by recombinant Pseudomonas stutzeri Rhl. Glycerol is a promising carbon source used to anaerobically produce rhamnolipid. In a Plackett-Burman design, glycerol, KH2 PO4 and yeast extract were significant factors. The proposed optimized medium contained the following: 46·55 g l(-1) glycerol; 3 g l(-1) NaNO3 ; 5·25 g l(-1) K2 HPO4 ·3H2 O; 5·71 g l(-1) KH2 PO4 ; 0·40 g l(-1) MgSO4 ·7H2 O; 0·13 g l(-1) CaCl2 ; 1·0 g l(-1) KCl; 1·0 g l(-1) NaCl; and 2·69 g l(-1) yeast extract. Using this optimized medium, we obtained an anaerobic yield of rhamnolipid of 3·12 ± 0·11 g l(-1) with a 0·85-fold increase. Core flooding test results also revealed that Ps. stutzeri Rhl grown in an optimized medium enhanced the oil recovery efficiency by 15·7%, which was 6·6% higher than in the initial medium. Results suggested that the optimized medium is a promising nutrient source that could effectively mobilize oil by enhancing the in situ production of rhamnolipid. SIGNIFICANCE AND IMPACT OF THE STUDY: The ex situ application of rhamnolipid for microbial enhanced oil recovery (MEOR) is costly and complex in terms of rhamnolipid production, purification and transportation. Compared with ex situ applications, the in situ production of rhamnolipid in anaerobic oil reservoir is more advantageous for MEOR. This study is the first to report the anaerobic production optimization of rhamnolipid. Results showed that the optimized medium enhanced not only the anaerobic production of rhamnolipid but also crude oil recovery.

Antioxidative and antibacterial effects of seeds and fruit rind of nutraceutical plants belonging to the Fabaceae family.

In the present study, the seeds and fruit rind of six plants of the Fabaceae family were selected to evaluate their potential as antioxidant and antibacterial agents. The dried powders were individually extracted with various organic solvents by the cold percolation method, were evaluated for antibacterial activity and methanol extracts used for antioxidant activities. Total phenol, protein and sugar contents were also measured. Antioxidant activities were measured by DPPH free radical scavenging activity, superoxide anion radical scavenging activity and reducing capacity assessment. Antibacterial activity was measured by the agar well diffusion method against four Gram positive and four Gram negative bacteria. The methanol extract of the fruit rind of C. indica showed the maximum DPPH free radical scavenging activity, superoxide anion radical scavenging activity, a high reducing capacity assessment and also had the highest total phenol content. There was a direct correlation between the phenol content and the antioxidant activity. The antibacterial activity of all the extracts was more pronounced on Gram positive bacteria than on Gram negative bacteria. Thus, the fruit rind of C. indica showed the best antioxidant and antibacterial activities.

Enhanced crude oil biodegradation and rhamnolipid production by Pseudomonas stutzeri strain G11 in the presence of Tween-80 and Triton X-100.

In this study, the growth of sixty-one bacterial strains in crude oil were determined spectrophotometrically at 620 nm. Pseudomonas aeruginosa G1, Pseudomonas fluorescens G6, Pseudomonas stutzeri G11 and Pseudomonas putida G15 were chosen for the study based on the efficiency of crude oil utilisation. At 1% (v/v) crude oil concentration, P. stutzeri G11 strain degraded a maximum of 69%. The percentage of degradation by the P. stutzeri G11 strain decreased from 69% to 59% as the concentration of crude oil was increased from 1% (v/v) to 2.5% (v/v). Strain G11 was selected to determine the effects of surfactants (Tween-80 and TritonX-100) on the biodegradation of crude oil. While strain G11 showed 76% degradation at mineral salts medium (MSM) containing 1% (v/v) crude oil + 1% (v/v) TritonX-100, it showed 61% degradation at MSM containing 2.5% (v/v) crude oil + 2.5% (v/v) TritonX-100. Also, degradation rate of this strain was 96% in the presence of 1% (v/v) crude oil + 1% (v/v) Tween-80, while degradation rate was 48% in the presence of 25% (v/v) crude oil+ 2.5% (v/v) Tween-80. Additionally, we investigated the rhamnolipid production of P. stutzeri G11 strain both in crude oil and in crude oil + two different surfactants (TritonX-100 and Tween-80, separately). These results suggest that surfactants have improved both crude oil degradation and rhamnolipid production and the degradation rates have depended very much on the chemical structure of surfactants.

Pyridine-2,6-bis(thiocarboxylic acid) produced by Pseudomonas stutzeri KC reduces and precipitates selenium and tellurium oxyanions.

The siderophore of Pseudomonas stutzeri KC, pyridine-2,6-bis(thiocarboxylic acid) (pdtc), is shown to detoxify selenium and tellurium oxyanions in bacterial cultures. A mechanism for pdtc's detoxification of tellurite and selenite is proposed. The mechanism is based upon determination using mass spectrometry and energy-dispersive X-ray spectrometry of the chemical structures of compounds formed during initial reactions of tellurite and selenite with pdtc. Selenite and tellurite are reduced by pdtc or its hydrolysis product H(2)S, forming zero-valent pdtc selenides and pdtc tellurides that precipitate from solution. These insoluble compounds then hydrolyze, releasing nanometer-sized particles of elemental selenium or tellurium. Electron microscopy studies showed both extracellular precipitation and internal deposition of these metalloids by bacterial cells. The precipitates formed with synthetic pdtc were similar to those formed in pdtc-producing cultures of P. stutzeri KC. Culture filtrates of P. stutzeri KC containing pdtc were also active in removing selenite and precipitating elemental selenium and tellurium. The pdtc-producing wild-type strain KC conferred higher tolerance against selenite and tellurite toxicity than a pdtc-negative mutant strain, CTN1. These observations support the hypothesis that pdtc not only functions as a siderophore but also is involved in an initial line of defense against toxicity from various metals and metalloids.