Sami Mnif

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

Aims:u2002 To isolate and characterize an efficient hydrocarbon‐degrading bacterium under hypersaline conditions, from a Tunisian off‐shore oil field.

Simultaneous hydrocarbon biodegradation and biosurfactant production by oilfield-selected bacteria

Aims:u2002 To study the bacterial diversity associated with hydrocarbon biodegradation potentiality and biosurfactant production of Tunisian oilfields bacteria.

Isolation and characterization of Klebsiella oxytoca strain degrading crude oil from a Tunisian off-shore oil field

A facultatively anaerobic, Gram‐negative, mesophilic, moderately halotolerant, non‐motile, and non‐sporulated bacterium, designated strain BSC5 was isolated from an off‐shore “Sercina” oil field, located near the Kerkennah island, Tunisia. Yeast extract was not required for growth. Phenotypic characteristics and phylogenetic analysis of the 16S rRNA gene sequence of strain BSC5 revealed that it was related to members of the genus Klebsiella, being most closely related to the type strain of K. oxytoca (99% sequence similarity). Strain BSC5 was capable of using aerobically the crude oil as substrate growth. The growth of strain BSC5 on crude oil was followed by measuring the OD600 nm and by enumeration of viable cells at different cultures time. GC‐MS analysis showed that strain BSC5 was capable of degrading a wide range of aliphatic hydrocarbons from C13 to C30. The biodegradation rate for n ‐alkanes reached 44% and 75%, after 20 and 45 days of incubation, respectively. Addition of the synthetic surfactant, Tween 80, accelerated the crude oil degradation. The biodegradation rate for n ‐alkanes reached 61% and 98%, after 20 and 45 days of incubation, respectively. Moreover, three aromatic compounds, p ‐hydroxybenzoate, protocatechuate and gentisate, were metabolized completely by strain BSC5 after 24 h, under aerobic conditions. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Characterization of the microbial diversity in production waters of mesothermic and geothermic Tunisian oilfields

The microbial diversity of production waters of five Tunisian oilfields was investigated using Single Strand Conformation Polymorphism (SSCP) technique followed by cloning‐sequencing. Dynamics of bacterial populations in production waters collected from four wellheads were also evaluated. For all production water samples collected, DNA from Archaea and Eucarya was not sufficiently abundant to permit detection rRNA genes from these groups by PCR‐SSCP. In contrast, the bacterial rRNA genes were detected in all samples, except for samples from DOULEB12 and RAMOURA wells. SSCP profiles attested that two of the studied geothermic wells (ASHTART47 and ASHTART48) had shown a clear change over time, whereas a stable diversity was found with the mesophilic DOULEB well (DL3). PCR amplification of rRNA genes was unsuccessful with samples from DOULEB (DL12) at all three sampling time. The bacterial diversity present in production waters collected from pipelines of SERCINA and LITAYEM oilfields was high, while production waters collected from wellheads (ASHTART and DOULEB) exhibited lower diversity. The partial study of the biodiversity showed a dominance of uncultured bacteria and Pseudomonas genus (class of the Gammaproteobacteria) in three of the studied oilfields (ASHTART47, ASHTART48 and DOULEB3). However, for LITAYEM oilfield, a significant dominance of 5 phyla (Proteobacteria, Thermotogae, Firmicutes, Synergistetes, Bacteroidetes) was shown. Our study gives a real picture of the microbiology of some Tunisian oilfield production waters and shows that some of the sequenced bacterial clones have a great similarity to previous sequenced clones described from other oilfields all over the world, indicating that these ecosystems harbour specific microbial communities. These findings can be considered as an indirect indication of the indigenous origin of these clones.

Strategy for improving extracellular lipolytic activities by a novel thermotolerant Staphylococcus sp. strain

BackgroundExtracellular bacterial lipases received much attention for their substrate specificity and their ability to function under extreme environments (pH, temperature...). Many staphylococci produced lipases which were released into the culture medium. Reports of extracellular thermostable lipases from Staphylococcus sp. and active in alkaline conditions are not previously described.ResultsThis study focused on novel strategies to increase extracellular lipolytic enzyme production by a novel Staphylococcus sp. strain ESW. The microorganism needed neutral or alkaline pH values between 7.0 and 12.0 for growth. For pH values outside this range, cell growth seemed to be significantly inhibited. Staphylococcus sp. culture was able to grow within a wide temperature range (from 30 to 55°C). The presence of oils in the culture medium leaded to improvements in cells growth and lipolytic enzyme activity. On the other hand, although chemical surfactants leaded to an almost complete inhibition of growth and lipolytic enzyme production, their addition along the culture could affect the location of the enzyme. In addition, our results showed that this novel Staphylococcus sp. strain produced biosurfactants simultaneously with lipolytic activity, when soapstock (The main co-product of the vegetable oil refining industry), was used as the sole carbon source.ConclusionA simultaneous biosurfactant and extracellular lipolytic enzymes produced bacterial strain with potential application in soap stock treatment

Bioremediation of Petroleum Contaminated Water and Soils in Tunisia

The petrochemical industry generates series of liquid and solid wastes containing large amounts of priority pollutants during the petroleum-refining process. These residues must be treated through depuration processes. The bioremediation process, presenting countless advantages in relation to other processes employed, is an evolving method for the removal and the transformation of many environmental pollutants including those produced by the petroleum industry. In a first step, a continuously stirred tank bioreactor (CSTR) was used to optimize feasible and reliable bioprocess system for successful bioremediation of industrial effluent and to develop an efficient microbial consortium for the degradation of petroleum hydrocarbons. After an experimental period of 175 days, the process was shown to be highly efficient in decontaminating the wastewater. The performance of the bio augmented reactor was demonstrated by the reduction of COD rates up to 95%. Six microbial isolates from the CSTR were characterized and species identification was confirmed by sequencing the 16 S rRNA genes. Besides, the treated wastewater could be considered as non toxic according to the micro-toxicity test. In a second step, bioremediation of a refinery soil containing hydrocarbons climate was investigated. The objective of this study was to assess the ability of bioremediation technique in the presence of the acclimatized consortium to reduce the total petroleum hydrocarbon (TPH) content in the contaminated soil. Results clearly demonstrated that an enhanced bioremediation was carried when the acclimatized bacterial consortium was added to the hydrocarbons contaminated soil. The proposed bioremediation technology has proved significantly higher hydrocarbons removal efficiencies. TPH analysis showed that 50% of the hydrocarbons were eliminated during the first 15 days of bio remediation. TPH removal reached 96% at the end of the treatment. Further, GC/MS profile has proved that the acclimatized bacterial consortium could effectively remove the medium- and long-chain alkanes in the contaminated soil such as the alkanes were undetectable after a 30-day of incubation period. In a third step, a Halomonas sp. strain C2SS100 had been isolated and characterized from Sercina petroleum reservoir. The strain had shown potential hydrocarbon degradation under halophilic condition (100 g 1−1 NaCl). During growth on n-Hexadecane (C16), C2SS100 produced biosurfactant that could solubilise phenanthrene, a three-ring aromatic hydrocarbon. The halophilic character of this bacterium could add further advantages for its use in marine and saline environments-oil bioremediation.