Simultaneous hydrocarbon biodegradation and biosurfactant production by oilfield-selected bacteria.

AIMS: To study the bacterial diversity associated with hydrocarbon biodegradation potentiality and biosurfactant production of Tunisian oilfields bacteria. METHODS AND RESULTS: Eight Tunisian hydrocarbonoclastic oilfields bacteria have been isolated and selected for further characterization studies. Phylogenetic analysis revealed that three thermophilic strains belonged to the genera Geobacillus, Bacillus and Brevibacillus, and that five mesophilic strains belonged to the genera Pseudomonas, Lysinibacillus, Achromobacter and Halomonas. The bacterial strains were cultivated on crude oil as sole carbon and energy sources, in the presence of different NaCl concentrations (1, 5 and 10%, w/v), and at 37 or 55°C. The hydrocarbon biodegradation potential of each strain was quantified by GC-MS. Strain C450R, phylogenetically related to the species Pseudomonas aeruginosa, showed the maximum crude oil degradation potentiality. During the growth of strain C450R on crude oil (2%, v/v), the emulsifying activity (E24) and glycoside content increased and reached values of 77 and 1.33 g l(-1), respectively. In addition, the surface tension (ST) decreased from 68 to 35.1 mN m(-1), suggesting the production of a rhamnolipid biosurfactant. Crude biosurfactant had been partially purified and characterized. It showed interest stability against temperature and salinity increasing and important emulsifying activity against oils and hydrocarbons. CONCLUSIONS: The results of this study showed the presence of diverse aerobic bacteria in Tunisian oilfields including mesophilic, thermophilic and halotolerant strains with interesting aliphatic hydrocarbon degradation potentiality, mainly for the most biosurfactant produced strains. SIGNIFICANCE AND IMPACT OF THE STUDY: It may be suggested that the bacterial isolates are suitable candidates for practical field application for effective in situ bioremediation of hydrocarbon-contaminated sites.

Isolation and characterization of Halomonas sp. strain C2SS100, a hydrocarbon-degrading bacterium under hypersaline conditions.

AIMS: To isolate and characterize an efficient hydrocarbon-degrading bacterium under hypersaline conditions, from a Tunisian off-shore oil field. METHODS AND RESULTS: Production water collected from 'Sercina' petroleum reservoir, located near the Kerkennah island, Tunisia, was used for the screening of halotolerant or halophilic bacteria able to degrade crude oil. Bacterial strain C2SS100 was isolated after enrichment on crude oil, in the presence of 100 g l(-1) NaCl and at 37 degrees C. This strain was aerobic, Gram-negative, rod-shaped, motile, oxidase + and catalase +. Phenotypic characters and phylogenetic analysis based on the 16S rRNA gene of the isolate C2SS100 showed that it was related to members of the Halomonas genus. The degradation of several compounds present in crude oil was confirmed by GC-MS analysis. The use of refined petroleum products such as diesel fuel and lubricating oil as sole carbon source, under the same conditions of temperature and salinity, showed that significant amounts of these heterogenic compounds could be degraded. Strain C2SS100 was able to degrade hexadecane (C16). During growth on hexadecane, cells surface hydrophobicity and emulsifying activity increased indicating the production of biosurfactant by strain C2SS100. CONCLUSIONS: A halotolerant bacterial strain Halomonas sp. C2SS100 was isolated from production water of an oil field, after enrichment on crude oil. This strain is able to degrade hydrocarbons efficiently. The mode of hydrocarbon uptake is realized by the production of a biosurfactant which enhances the solubility of hydrocarbons and renders them more accessible for biodegradation. SIGNIFICANCE AND IMPACT OF THE STUDY: The biodegradation potential of the Halomonas sp. strain C2SS100 gives it an advantage for possibly application on bioremediation of water, hydrocarbon-contaminated sites under high-salinity level.

Involvement of microbial populations during the composting of olive mill wastewater sludge.

Olive mill waste water sludge obtained by the electro-Fenton oxidation of olive mill waste water was composted in a bench scale reactor. The evolution of microbial species within the composter was investigated using a respirometric test and by means of both cultivation-dependent and independent approaches (Polymerase Chain Reaction-Single Strand Conformation Polymorphism, PCR SSCP). During the period of high respiration rate (7-24 days), cultivation method showed that thermophilic bacteria as well as actinomycetes dominated over eumycetes. During the composting process, the PCR-SSCP method showed a higher diversity of the bacterial community than the eukaryotic one. After 60 days of composting, the compost exhibited a microbial stability and a clear absence of phytotoxicity.

Isolation of a cinnamic acid-metabolizing Clostridium glycolicum strain from oil mill wastewaters and emendation of the species description.

A strictly anaerobic, gram-positive, motile, sporulated bacterium, designated strain CIN5, was isolated from olive mill wastewaters after enrichment on cinnamic acid. The rod-shaped cells were slightly curved (0.4-1.1 x 2.0-15 microm) and occurred singly or in pairs. Strain CIN5 utilized a limited number of carbohydrates (glucose, fructose, maltose, sorbitol), grew optimally at 37 degrees C and at pH 7.3-7.5 and had a DNA G+C content of 29.1+/-0.3 mol%. Strain CIN5 was very closely related to Clostridium glycolicum DSM 1288T. Both strain CIN5 and the type strain of C. glycolicum transformed cinnamic acid to hydrocinnamic acid and a wide range of other cinnamic acid derivatives, including o-, m- and p-coumaric, o-, m- and p-methoxycinnamic, p-methylcinnamic, caffeic, ferulic and isoferulic acids, to their corresponding 3-phenylpropionic acids by reducing the double bond of the side chain. Glucose supplementation increased the rate of conversion markedly. The emendation of the description of C. glycolicum is proposed to include these new characteristics.

Metabolism of cinnamic acids by some Clostridiales and emendation of the descriptions of Clostridium aerotolerans, Clostridium celerecrescens and Clostridium xylanolyticum.

The ability of Clostridium aerotolerans DSM 5434T, Clostridium celerecrescens DSM 5628T, Clostridium methoxybenzovorans DSM 12182T, Clostridium stercorarium ATCC 35414T, Clostridium subterminale DSM 2636, Clostridium termitidis DSM 5398T, Clostridium thermolacticum DSM 2910T, Clostridium thermopalmarium DSM 5974T and Clostridium xylanolyticum DSM 6555T to metabolize cinnamic acid and various derivatives, with or without glucose supplementation, was examined. Only C aerotolerans DSM 5434T and C. xylanolyticum DSM 6555T, closely related species, transformed cinnamic acid to 3-phenylpropionic acid. Both species also reduced a wide range of cinnamic acid derivatives, including o-, m- and p-coumaric, o-, m- and p-methoxycinnamic, p-methylcinnamic, caffeic, ferulic, isoferulic and 3,4,5-trimethoxycinnamic acids to their corresponding 3-phenylpropionic acid derivatives. C. aerotolerans DSM 5434T, however, also decarboxylated p-coumaric acid into 4-vinylphenol, which was then reduced to 4-ethylphenol. C. celerecrescens was grouped with C. aerotolerans and C. xylanolyticum in subcluster XIVa of the Clostridiales. C. celerecrescens DSM 5628T only metabolized m- and p-methoxycinnamic and p-methylcinnamic acids to their corresponding 3-phenylpropionic acid derivatives, reducing the double bond in the C3 aliphatic side chain. Addition of glucose markedly increased the yield of the biotransformations by these three species. An emendation of the descriptions of C. aerotolerans, C. celerecrescens and C. xylanolyticum is proposed, based on these observations.