Screening and Characterization of Aerobic Xylene-Degrading Bacteria from Gasoline Contaminated Soil Sites Around Gas Stations in Northern Jordan

Abstract

A B S T R A C T Xylene is frequently released into the environment from biomass. As a consequence of this, its bioaccumulation can cause adverse health effects in humans. The purpose of this study was to screen for aerobic xylene-degrading bacteria from gasoline contaminated soil sites located around gas stations in the city of Al-Mafraq, Jordan. The effects of some physicochemical factors were examined. The 10 g of soil sample were transferred to Stanier's mineral medium supplemented with 1% m-xylene and incubated at 30°C for 72 h. At least 4 aerobic m-xylene degrading isolates, designated as X1-X4 were identified using biochemical and molecular biology techniques. Isolates X1 and X2 were rod-shape Gram negative, oxidase and catalase positive bacteria. Isolate X3 was a rod-shape and Gram negative bacterium that was catalase positive and oxidase negative. Isolate X4 was a rod-shape, spore forming and Gram positive bacterium that was oxidase and catalase positive. Isolates X1, X2 and X4 showed high similarity to Pseudomonas aeruginosa, Pseudomonas stutzeri and Bacillus firmus, respectively, whereas X3 was a novel species of the genus Citrobacter, similar to Citrobacter amalonaticus. The growth rates of these isolates were slower at 2% m-xylene than at 1% m-xylene. The growth rate was less when the temperature was reduced from 30-25°C, whereas, at 45°C, the growth rate almost completely ceased. The growth rate was higher at pH 6.5 than at pH 5.5 or 8.5. The shortest generation times were found to be 8 h for Bacillus firmus, followed by 9 h for Pseudomonas stutzeri, 10 h for Citrobacter amalonaticus and 11 h for Pseudomonas aeruginosa under 1% m-xylene at 30°C and pH 6.8. In conclusion, we reported for the first time the isolation of four bacterial species with the ability to utilize m-xylene as a growth substrate.

Biofilm and Biosurfactant Mediated Aromatic Hydrocarbons Degradation by Marine Bacteria Isolated from Contaminated Marine Environments of Niger Delta

“…strain XYL8 and Bacillus cereus strain PYR9 using Bergey's Manual for Determinative Bacteriology by Holt et al [21]. These findings agree with the reports of Irshaid and Jacob [35], Wanjohi et al [36], Isiodu et al [32] and Fagbemi and Sanusi [37] that two -third of most petroleum hydrocarbon degraders are Gram negatives with one -third being Gram positives but contradict the finding of Kafilzadeh and Pour [16], who reported that more of Gram positive bacteria were isolated than Gram negative bacteria. A lot of rod -shaped bacteria have also been implicated in hydrocarbon degradation studies (Chikere et al [12], Irshaid and Jacob [35], Wanjohi et al [36], Isiodu et al [32] and Fagbemi and Sanusi [37]) and similar result was obtained in this study.…”

In vitro Degradation and Reduction of Aromatic Hydrocarbons by Marine Bacteria Isolated from Contaminated Marine Environments of Niger Delta

“…This contradiction might be due to the nature of the ecosystem as marine environment is generally characterized with lower temperatures unlike the terrestrial ecosystem with higher temperatures. The result in Table 4 showed that the drops in pH are probably because the degradation of the hydrocarbons by these bacteria resulted in the discharge of acidic substances and intermediates (organic acids and other metabolic products) which reduces the pH of the medium and is in agreement with the researches carried out by previous studies [16,25,31]. The result in Table 5 revealed that the degradation and utilization of these compounds resulted in increase in optical density (cell mass) of these bacteria and corroborates with the findings of John et al [18] and Akinbankole et al…”

“…Similar result was observed by Athar et al [30]. The result contradicts the report of Irshaid and Jacob [16] that the decrease in temperature from 30 -25°C led to decrease in growth rates of xylene degrading bacteria from gasoline contaminated soil sites while whereas the growth rates almost terminated at 45 °C,. This contradiction might be due to the nature of the ecosystem as marine environment is generally characterized with lower temperatures unlike the terrestrial ecosystem with higher temperatures.…”

“…The previous study reported that the growth rate of bacterial strains X1, X2, X3 and X4 under 1 % of m-xylene decreased as the temperature reduced from 30 -25 °C, whereas at 45 °C, the growth rate was practically ceased. The optimum growth rate of the strains was obtained at pH 6.5 but had fluctuating growth rate at pH 5.5 or 8.5 [16].…”

“…Also, among the biological factor, the kind of microorganisms, their genomes and their earlier contact to hydrocarbons affects the capacity with which the hydrocarbons could be degraded [15]. Several studies have reported that the growth rates of aromatic hydrocarbon degrading bacteria were affected by the concentration of xylene compounds, temperature, pH of the medium and other factors such as microbial number and nutrient availability [16]. The previous study reported that the growth rate of bacterial strains X1, X2, X3 and X4 under 1 % of m-xylene decreased as the temperature reduced from 30 -25 °C, whereas at 45 °C, the growth rate was practically ceased.…”