Halomona Case Study

It is important to isolate the bacteria having a high capacity to degrade hydrocarbon contamination to perform the bioremediation methods in contaminated areas (20). In the current study, a bacterium strain MS1 with high capacity responsible for crude oil degradation was isolated from surface sediment of Kish Island and identified as Halomonas sp. The genus Halomonas, which was initially suggested by Vreeland (21) and includes more than 20 species, are among the largest moderate halophilic bacterial groups with biodegradation potential of hydrocarbon pollutants (22,23).

In this study, the optimum culture condition for crude oil biodegradation by MS1 determined by Taguchi method indicated that the use of statistical experimental design techniques

The best biodegradation efficiency was achieved at temperature 30ºC. Temperature palys an important role in biodegradation by affecting the physical and chemical peroperties of the oil, rate of hydrocarbon metabolism by microorganism and composition of the microbial community (10). Aghamiri (10) and Lin (25) have been reported optimum temperature for biodegradation of crude oil and naphthalene as 30ºC. Das & Chandran (26) reported that highest degradation rates of petroleum that generally occure in the range 30-40ºC in soil environment, 20-30ºC in some freshwater environments and 15-20ºC in marine environments. Although biodegradation of hydrocarbons can happen in a wide range of temperatures, biodegradation rate generally decreases with decreasing temperature (26). So in this study, the lowest rate of biodegradation was observed at lowest temperature. This is due to the fact that at low temperatures, the viscosity of the oil is increased while the volatilization of toxic short-chain alkanes is reduced, and its water solubility is decreased, thereby delaying the onset of biodegradation

That means that there was a small lag phase. As the initial crude oil concentration increased to 20 and 40 ml/L the lag phase raised. In fact, it was found that the lag phase was increased when the initial crude oil concentration was higher due to the slower cell adaptation. This shows that the toxicity of crude oil inhibited MS1 strain at high concentrations (19, 33). Varius types of kinetic substrate consumption and inhibition models have been used to explain the dynamics of microbial growth on different compounds for example Phenol, Toluene, Benzene and p-cresol (16, 32, 34). To predict the kinetics of microbial at substrate adaptation conditions, an effort was made to fit the kinetic rate data to proper kinetic models. In these models, Value of Ks the affinity of microbes to substrate and Ki values indicate the sensitiveness of the culture to substrate inhibition. Larger Ki value means that the culture is less sensitive to substrate inhibition (16,35). From the Table 6, the best fit was achieved using Tessier and Haldane respectively. The models of Teissier and Haldane may be proposed as the kinetic models to describe the batch crude oil degradation behavior of