Degradation of selected (bio-)surfactants by bacterial cultures monitored by calorimetric methods

The subjects of the article are investigations concerning the ability of both Rhodococcus opacus 1CP and mixed bacterial cultures to use selected surfactants as sole carbon and energy source. In a comparative manner the biosurfactants rhamnolipid, sophorolipid and trehalose tetraester, and the synthetic surfactant Tween 80 were examined. Particular emphasis was put on a combinatorial approach to determine quantitatively the degree of surfactant degradation by applying calorimetry, thermodynamic calculations and mass spectrometry, HPLC as well as determination of biomass. The pure bacterial strain R. opacus was only able to metabolize a part of the synthetic surfactant Tween 80, whereas the mixed bacterial cultures degraded all of the applied surfactants. Exclusive for the biosurfactant rhamnolipid a complete microbial degradation could be demonstrated. In the case of the other surfactants only primary degradation was observed.     

Effect of a synthetic surfactant on phenanthrene and n-eicosane utilization by two pure marine strains grown separately in batch cultures with or without sand particles

The effect of Tween 80, a nonionic surfactant, on the extent of biodegradation of phenanthrene by Sphingomonas sp. 2MPII and n-eicosane by Corynebacterium sp. 8 was investigated. This surfactant was beneficial only for phenanthrene biodegradation, where it increased the extent of degradation from 54 to 74%. It appears to be used as carbon source by Corynebacterium sp. 8 but the extent of biodegradation decreases from 43 to 20%. In sand-containing cultures, the phenanthrene sorption observed only in the presence of Tween reduced the biodegradation extent to 35%. On the other hand, for n-eicosane, which remains in the aqueous phase, the biodegradation extent was markedly enhanced to 74%.     

Temperature-dependent differences in community structure of bacteria involved in degradation of petroleum hydrocarbons under sulfate-reducing conditions

Aim: The aim of this study was to characterize the microbial community involved in anaerobic degradation of petroleum hydrocarbon under low‐ and moderate‐temperature conditions. Methods and Results: Sulfate‐reducing enrichment cultures growing on crude oil and p‐xylene were established at low and moderate temperatures. Bacterial community structures of the cultures were characterized by 16S rRNA gene‐based analysis and organisms responsible for degradation of p‐xylene were investigated by analysis of the bamA gene, involved in anaerobic degradation of aromatic compounds. The PCR‐denaturing gradient gel electrophoresis analysis indicated significant differences in microbial community structures among the cultures, depending on the temperatures of incubation. Difference depending on the temperatures was also observed in the cloning analysis of the bamA gene performed on the p‐xylene‐degrading enrichment cultures. Majority of clones detected in the culture of moderate temperature were related to Desulfosarcina ovata, whereas more diverse bamA gene sequences were obtained from the culture incubated at low temperature. Conclusions: Temperature‐dependent differences in microbial community were demonstrated by the analyses of two genes. It was suggested that sulfate‐reducing bacteria of phylogenetically different groups might be involved in the degradation of petroleum hydrocarbons in different temperature environments. Significance and Impact of the Study: This study is the first report of p‐xylene‐degrading sulfate‐reducing enrichment culture at low temperature. The results of the experiments at low temperature were distinctly different from those reported in previous studies performed at moderate temperatures.     

基于吐温-80下2株功能菌协同降解多环芳烃的特性研究

【目的】研究恶臭假单胞菌B6-2和克雷伯氏菌CW-D3T构建的混合功能菌对多环芳烃的协同修复效能,并探究非离子表面活性剂吐温-80对混菌降解多环芳烃的影响,以期为芳烃化合物的生物修复提供技术参考和理论依据。【方法】通过生长曲线及平板菌落计数法反映混菌生长情况及比例,从而评估混菌降解体系的可行性;通过高效液相色谱法探究各体系以及不同吐温-80浓度下混培体系对多环芳烃的降解效能;最后通过烷烃吸附法测定细胞表面疏水性,以探究吐温-80对混合功能菌降解多环芳烃的影响机制。【结果】等比例混合的2株菌共培养生长状态优于纯培体系,对混合多环芳烃(菲、荧蒽、芘)的降解率分别为33.4%、30.1%、28.6%(7 d),相较于菌CW-D3T,分别提高了1.31倍、1.46倍、1.42倍。混培体系中加入500 mg/L的吐温-80对菲、荧蒽、芘的降解率分别为47.7%、43.2%、38.8%(7 d),相较于对照组各提高了1.55倍、1.38倍、1.31倍,而更高浓度的吐温-80无明显促进作用或轻微抑制。添加吐温-80使菌CW-D3T和混菌的表面疏水性提高,而菌B6-2表面疏水性降低。结合细菌生长量分析...     

Effect of surfactants and identification of metabolites on the biodegradation of fluoranthene by basidiomycetes fungal isolate Armillaria sp. F022

The effects of structure and concentration of surfactants on the biodegradation of fluoranthene, a three rings polycyclic aromatic hydrocarbon in the aqueous phase, as well as their effects on the biodegradation and enzyme activity were investigated. The toxicity ranking of studied surfactants is: non-ionic Tween 80 <anionic sodium dodecyl sulfate <cationic Tetradecyltrimethylammonium bromide. The maximum growth of Armillaria sp. F022 (>4,500 mg/L) was showed by Tween 80 (10 mg/L) culture, manifesting that the non-ionic surfactant present in the culture were beneficial to the fungal growth. Laccase showed the highest enzymes activity in all surfactants culture. Non-ionic Tween 80 showed a significant result for laccase activity (1,902 U/L) in the Armillaria sp. F022 culture. The increased enzymes cumulative activity may stem directly from the rising fluoranthene biodegradability as addition of appropriate surfactants. The biotransformation of fluoranthene was greatly improved by Tween 80, and totally fluoranthene degradation was obtained as Tween 80 was 10 mg/L. Two fluoranthene metabolites were isolated from the culture medium and analyzed by a thin layer chromatography, UV visible spectrometer and gas chromatography–mass spectrometry (GC–MS). The oxidation of fluoranthene is initiated by oxygenation at the C-2,3 positions resulting 9-fluorenone. At the end of experiment, one metabolite was detected in the culture extract and identified as phthalic acid. Evidently, Armillaria sp. F022 seems efficient, high effective and deserves further application on the enhanced bioremediation technologies for the treatment of fluoranthene-contaminated soil.     

Effects of modified carbon black nanoparticles on plant-microbe remediation of petroleum and heavy metal co-contaminated soils

Abstract

Little is known about the effect of modified carbon black nanoparticles (MNCB) on the availability of heavy metals and petroleum degradation in petroleum and heavy metals co-contaminated soils. The overall objective of this study was to investigate the simultaneous effect of MNCB on heavy metal immobilization and petroleum biodegradation in co-contaminated soil in plant and plant-microbe combined remediation. The results showed that the petroleum degradation increased by 50% in petroleum-Cd co-contaminated soil and 65% in petroleum-Ni co-contaminated soil in plant-microbe combined remediation, comparing with the plant remediation and the application of MNCB did not show significant improvement on petroleum degradation in both plant and plant-microbe combined remediation. MNCB could significantly reduce the availability of heavy metals in soil and the uptakes of Cd and Ni by Suaeda salsa by roughly 18 and 10% and improve the growth of plant by alleviating the growth inhibition caused by heavy metals. The application of Bacillus subtilis and Sphingobacterium multivorum (heavy metal tolerant bacteria) inhibited the biomass of Suaeda salsa by enhancing the petroleum degradation. It could be concluded that MNCB played a major role in immobilizing the heavy metals and bacteria dominated the petroleum degradation in petroleum-metal co-contaminated soil.     

Biodegradation of Kerosene by Aspergillus flavus Using Statistical Experimental Designs

The ability of different local fungal isolates to degrade kerosene in liquid medium was studied. The results showed that the percent of kerosene degradation varied among the different tested fungi and that 60–96% of kerosene was degraded after 7 days in the presence of 0.2% (v/v) of Tween 80. The absence of the surfactant led to about 28.34% decrease of biodegradation. The degradation of 2% (v/v) of kerosene by the most efficient fungus (Aspergillus flavus) was significantly influenced by the incubation period and the composition of culture medium. Statistical experimental designs were used to optimize the process of kerosene degradation by the fungus. Under optimized medium compositions and culture conditions, A. flavus degraded kerosene (100%) after 111.3 h of incubation. Optimal conditions obtained in this work provided a solid foundation for further use of A. flavus in treatment of kerosene-polluted soil. The optimized conditions were applied to bioremediate 2.5% (v/w) kerosene-polluted soil by A. flavus, and the fungus efficiently degraded kerosene after 35 days of incubation.     

Enhancement of solubilization and biodegradation of petroleum by biosurfactant from Rhodococcus erythropolis HX-2

Abstract

The demand to repair areas contaminated with hydrocarbon products has led to the development of new technologies for the treatment of contaminants in an unconventional method, that is, no physical or chemical methods are used. Biosurfactants are amphiphilic biomolecules produced by microorganisms that can be used in environments contaminated by petroleum products due to their unexceptionable tensile properties. Petroleum degrading strain Rhodococcus erythropolis HX-2 was found to be an effective producer of biosurfactants. The resulting biosurfactant (named NK) exhibits high physicochemical properties in terms of surface activity. It is capable of reducing surface tension from 54.99 to 28.89?mN/m and critical micelle concentration (CMC) is 100?mg/L. NK was found to be a substitute for chemically synthesized surfactants because of its higher solubilization efficiency for petroleum and polycyclic aromatic hydrocarbons, superior to SDS, Tween 80, Triton X-100 and Rhamnolipid (a wide used biosurfactant). In addition, it exhibits favorable emulsion stability over a wide range of pH (3–10), temperature (20–100?°C) and salinity ranges (5–20?g/L). It was found that the addition of biosurfactant can improve the efficiency of petroleum degradation, therefore it has potential applications in bioremediation.

• Highlights

• Rhodococcus erythropolis HX-2 is an effective petroleum degrading strain.

• HX-2 is a potential source of biosurfactant production.

• The biosurfactant NK reduces surface tension and exhibits high emulsification activity.

• The biosurfactant NK is effective over a wide range of temperatures, pH and salinity.

• The biosurfactant NK shows high solubilization efficiency for petroleum as well as polycyclic aromatic hydrocarbons.

     

Fluorene biodegradation and identification of transformation products by white-rot fungus Armillaria sp. F022

A diverse surfactant, including the nonionic Tween 80 and Brij 30, the anionic sodium dodecyl sulphate, the cationic surfactant Tetradecyltrimethylammonium bromide, and biosurfactant Rhamnolipid were investigated under fluorine-enriched medium by Armilaria sp. F022. The cultures were performed at 25 °C in malt extract medium containing 1 % of surfactant and 5 mg/L of fluorene. The results showed among the tested surfactants, Tween-80 harvested the highest cell density and obtained the maximum specific growth rate. This due Tween-80 provide a suitable carbon source for fungi. Fluorane was also successfully eliminated (>95 %) from the cultures within 30 days in all flasks. During the experiment, laccase production was the highest among other enzymes and Armillaria sp. F022-enriched culture containing Non-ionic Tween 80 showed a significant result for laccase activity (1,945 U/L). The increased enzyme activity was resulted by the increased biodegradation activity as results of the addition of suitable surfactants. The biotransformation of fluorene was accelerated by Tween 80 at the concentration level of 10 mg/L. Fluorene was initially oxidized at C-2,3 positions resulting 9-fluorenone. Through oxidative decarboxylation, 9-fluorenone subjected to meta-cleavage to form salicylic acid. One metabolite detected in the end of experiment, was identified as catechol. Armillaria sp. F022 evidently posses efficient, high effective degrader and potential for further application on the enhanced bioremediation technologies for treating fluorene-contaminated soil.     

Kinetic Modelling and Half-Life Study on Bioremediation of Soil Co-Contaminated with Lubricating Motor Oil and Lead Using Different Bioremediation Strategies

The focus of this study was to investigate the effect of nutrient supplement (urea fertilizer) and microbial species augmentation (mixed culture of Aeromonas, Micrococcus, and Serratia sp.) on biodegradation of lubricating motor oil (LMO) and lead uptake by the autochthonous microorganism in LMO and lead-impacted soil were investigated. The potential inhibitory effects of lead on hydrocarbon utilization were investigated over a wide range of lead concentrations (25–200 mg/kg) owing to the complex co-contamination problem frequently encountered in most sites. Under aerobic conditions, total petroleum hydrocarbons (TPH) removal was 45.3% in the natural attenuation microcosm while a maximum of 72% and 68.2% TPH removal was obtained in biostimulation and bioaugmentation microcosms, respectively. Lead addition, as lead nitrate, to soil samples reduced the number of hydrocarbon degraders in all samples by a wide range (11–52%) depending on concentration and similarly, the metabolic activities were affected as observed in mineralization of LMO (3–60%) in soils amended with various lead concentrations. Moreover, the uptake of lead by the autochthonous microorganisms in the soil reduced with increase in the initial lead concentration. First-order kinetics described the biodegradation of LMO very well. The biodegradation rate constants were 0.015, 0.033, and 0.030 day^?1 for LMO degradation in natural attenuation, biostimulation and bioaugmentation treatment microcosms, respectively. The presence of varying initial lead concentration reduced the biodegradation rate constant of LMO degradation in the biostimulation treatment microcosm. Half-life times were 46.2, 21, and 23 days for LMO degradation in natural attenuation, biostimulation and bioaugmentation treatment microcosms, respectively. The half-life time in the biostimulation treatment microcosm was increased with a range between 10.7 and 39.2 days by the presence of different initial lead concentration. The results have promising potential for effective remediation of soils co-contaminated with hydrocarbons and heavy metals.     

Responses and roles of roots,microbes, and degrading genes in rhizosphere during phytoremediation of petroleum hydrocarbons contaminated soil

Abstract

Rhizodegradation performed by plant roots and the associated bacteria is one of the major mechanisms that contribute to removal of petroleum hydrocarbons (PHCs) during phytoremediation. In this study, the pot-culture experiment using wild ornamental Hylotelephium spectabile (Boreau) H. Ohba was designed to explore responses and roles of roots, microbes, and degrading genes in the rhizodegradation process. Results showed that PHCs degradation rate by phytoremediation was up to 37.6–53.3% while phytoaccumulation accounted for a low proportion, just at 0.3–13.3%. A total of 37 phyla were classified through the high throughput sequencing, among which Proteobacteria, Actinobacteria, and Acidobacteria were the three most dominant phyla, accounting for >60% of the phylum frequency. The selective enrichment of PHC degraders with high salt-tolerance, including Alcanivorax and Bacteroidetes, was induced. Generally, relative abundance of the PHC degrading genes increased significantly with an increase in PHCs concentrations, and the gene copy number in the phytoremediation group was 1.46–14.44 times as much as that in the unplanted controls. Overall, the presence of PHCs and plant roots showed a stimulating effect on the development of specific degraders containing PHC degrading genes, and correspondingly, a biodegradation-beneficial community structure had been constructed to contribute to PHCs degradation in the rhizosphere.     

Cometabolic degradation of chloroallyl alcohols in batch and continuous cultures

The biodegradation of chloroallyl alcohols by pure and mixed bacterial cultures was investigated. Only 2-chloroallyl alcohol and cis- and trans-3-chloroallyl alcohol served as growth substrate for pure cultures. The other chloroallyl alcohols could be cometabolically degraded during growth on 2-chloroallyl alcohol. Cometabolic degradation of trichloroallyl alcohol, which was the most recalcitrant congener, by a Pseudomonas strain isolated on 2-chloroallyl alcohol resulted in 60% dechlorination. Efficient degradation of a mixture of chloroallyl alcohols in continuous culture could only be achieved in the presence of a satellite population. The mixed culture degraded 99% of the total chloroallyl alcohols added with 71% chloride release. The culture contained strains with a new catabolic potential. The results indicate the importance of mixed cultures and genetic adaptation for efficient chloroallyl alcohol removal.     

Aerobic Biotransformation of Gasoline Aromatics in MultiComponent Mixtures

The primary objective of this study was to evaluate the impact of substrate interactions on the biotransformation rates and mineralization potentials of gasoline monoaromatics and methyl tert-butyl ether (MTBE), compounds that commonly co-exist in groundwater contaminant plumes. A mixed culture was derived from gasoline-contaminated aquifer material using toluene as the enrichment substrate. Two pure cultures, Rhodococcus sp. RR1 and RR2, were isolated from the mixed culture. The three toluene-grown cultures were shown to biotransform all of the six BTEX compounds (benzene, toluene, ethylbenzene, o-xylene, m-xylene, and p-xylene), both individually and in mixtures, over a broad range of concentrations. The mixed culture was shown to degrade all of the BTEX compounds to ¹⁴CO₂, while the two isolates mineralized BTE(m-/p-)X, but biotransformed o-xylene without production of carbon dioxide. Studies to evaluate substrate interactions caused by the concurrent presence of multiple BTEX compounds during their biodegradation revealed a number of patterns,including competitive inhibition and cometabolism. Ethylbenzene was shown to significantly inhibit BTX degradation in mixtures. MTBE was not biodegraded by any of the three toluene-grown cultures over a range of MTBE concentrations. Furthermore, the presence of MTBE at concentrations of 2 to 100?mg/L had no effect on BTEX biotransformation rates.     

Biodegradation of BTEX at high salinity by an enrichment culture from hypersaline sediments of Rozel Point at Great Salt Lake

Aims: The primary goal of this research was to assess the biodegradation of benzene, toluene, ethylbenzene and xylenes in sediment from Great Salt Lake, near Rozel Point, UT. Methods and Results: An enrichment culture that degraded benzene or toluene as the sole carbon source at high salinity was developed from a sediment sample obtained from Rozel Point. The enrichment degraded benzene or toluene within 1, 2 and 5 weeks in the presence of 14%, 23% and 29% NaCl respectively. PCR studies using degenerate primers revealed that degradation occurred primarily via catechol and the meta‐cleavage pathway. Molecular analysis showed that the Gammaproteobacteria were the dominant members of the enrichment and that shifts in community composition occurred during benzene metabolism. Conclusions: This study demonstrated that micro‐organisms at Rozel Point have the ability to degrade hydrocarbons over a broad range of salinities (1–5 mol l^?1 NaCl) and that the members of the Gammaproteobacteria class play an important role in the degradation process. Significance and Impact of the Study: These results are significant as little is known about the fate of petroleum seeps at Rozel Point. Also, the identity of microbes and the key enzymes involved in the degradation steps are important for understanding natural attenuation potential of hydrocarbons.     

一株耐碱高效长链烷烃降解菌C24MT1的筛选及其降解特性

【背景】石油被称为“液体黄金”,人类的工业生产活动在利用其创造巨大社会价值的同时,也对自然环境造成了严重的污染。微生物修复技术是现阶段治理石油类污染有效的手段之一,具有经济、高效、无二次污染等优点。【目的】从受石油污染的土壤中分离高效降解长链烷烃正二十四烷的菌株,探究其降解特性及在微生物修复中的应用前景。【方法】通过形态学及16S rRNA基因测序进行菌株鉴定,采用气相色谱法检测菌株对正二十四烷的降解效果,并结合气相色谱-质谱(gas chromatography-mass spectrometer, GC-MS)分析降解中间产物以推测其潜在代谢途径。【结果】筛选到一株可高效降解正二十四烷的菌株C24MT1,经鉴定为不动杆菌属(Acinetobacter)。该菌株最适降解条件为30 °C、pH 9.0、盐度2 g/L,该条件下生长7 d对9 g/L正二十四烷的降解率高达86.63%;与此同时,菌株在强碱性环境(pH 11.0)中生长良好(OD₆₀₀为0.39)并保持较高烷烃降解率(75.38%),对极端环境具备较强的耐受能力;对降解中间产物进行分析,推断菌株代谢长链烷烃正二十四烷的途径可能包括末端氧化及次末端氧化。【结论】不动杆菌C24MT1具有良好的环境适应能力及烷烃降解能力,在后续微生物菌剂开发和石油类污染土壤的环境修复领域具有巨大的应用前景。本研究可为盐碱地区高浓度石油类污染土壤的修复提供优良菌种,并进一步丰富石油烃类生物降解的菌种资源库。     

Development of a method for the application of solid-phase microextraction to monitor biodegradation of volatile hydrocarbons during bacterial growth on crude oil

A quantitative solid-phase microextraction, gas chromatography, flame ionization detector (SPME-GC-FID) method for low-molecular-weight hydrocarbons from crude oil was developed and applied to live biodegradation samples. Repeated sampling was achieved through headspace extractions at 30°C for 45 min from flasks sealed with Teflon Mininert. Quantification without detailed knowledge of oil–water–air partition coefficients required the preparation of standard curves. An inverse relationship between retention time and mass accumulated on the SPME fibre was noted. Hydrocarbons from C₅ to C₁₆ were dated and those up to C₁₁ were quantified. Total volatiles were quantified using six calibration curves. Biodegradation of volatile hydrocarbons during growth on crude oil was faster and more complete with a mixed culture than pure isolates derived therefrom. The mixed culture degraded 55% of the compounds by weight in 4 days versus 30–35% by pure cultures of Pseudomonas aeruginosa, Rhodococcus globerulus or a co-culture of the two. The initial degradation rate was threefold higher for the mixed culture, reaching 45% degradation after 48 h. For the mixed culture, the degradation rate of individual alkanes was proportional to the initial concentration, decreasing from hexane to undecane. P. fluorescens was unable to degrade any of the low-molecular-weight hydrocarbons and methylcyclohexane was recalcitrant in all cases. Overall, the method was found to be reliable and cost-effective. Journal of Industrial Microbiology & Biotechnology (2000) 25, 155–162. Received 04 March 2000/ Accepted in revised form 25 June 2000     

Effects of biosurfactants produced by Candida antarctica on the biodegradation of petroleum compounds

The effects of biosurfactants on the biodegradation of petroleum compounds were investigated. Candida antarctica T-34 could produce extracellular biosurfactant mannosylerythritol lipids (MELs) when it was cultured in vegetable oil. In addition, in our previous study, it was found that this strain could also produce a new type of biosurfactant while it grew on n-undecane (C₁₁H₂₄), and the biosurfactant was named as BS-UC. In flask culture of Candida antarctica, the addition of BS-UC could improve the biodegradation rate of some n-alkanes (e.g. 90.2% for n-decane, 90.2% for n-undecane, 89.0% for dodecane), a mixture of n-alkanes (82.3%) and kerosene (72.5%). By comparing the effects of the biosurfactants BS-UC and MEL and chemical surfactants on the biodegradation of crude oil, it was found that biosurfactants could be used to enhance the degradation of petroleum compounds instead of chemical surfactants. In a laboratory scale immobilized bioreactor, the addition of biosurfactant improved not only the emulsification of kerosene in simulated wastewater but also its biodegradation rate. The highest degradation rate of kerosene by addition of MEL and BS-UC reached 87 and 90% at 15 h, respectively. The results showed that the biosurfactant BS-UC was highly promising for work on biodegradation of hydrophobic contaminants.     

Biodegradation of selected UV-irradiated and non-irradiated polycyclic aromatic hydrocarbons (PAHs)

Biodegradation of UV-irradiated anthracene, pyrene,benz[a]anthracene,and dibenz[a,h]anthracene was comparedto that of the non-irradiated samples, individuallyand in synthetic mixtures with enrichment cultures.Combined treatment was repeated for individual anthraceneand for the PAH mixture with Sphingomonas sp.strain EPA 505 and Sphingomonas yanoikuyae.Enrichment culture studies were performed on the PAHmixtures in the presence of the main photoproduct ofanthracene, pure 9,10-anthracenedione. Photochemicallypretreated creosote solutions were also subjected tobiodegradation and the results were compared tothose of the non-irradiated solutions. The primaryinterest was on 16 polycyclic aromatic hydrocarbons(PAHs) listed as priority pollutants by European Union(EU) and the United States Environmental ProtectionAgency (USEPA). Irradiation accelerated thebiodegradation onset for anthracene, pyrene, andbenz[a]anthracene when they were treatedindividually. The biodegradation of irradiatedpyrene started with no lag phase andwas complete by 122 h whereas biodegradation of thenon-irradiated sample had a lag of 280 h andresulted in complete degradation by 720 h. Biodegradation ofPAHs was accelerated in synthetic mixtures, especiallyin the presence of pure 9,10-anthracenedione.In general, irradiation had no effect on the biodegradation of PAHsincubated in synthetic mixtures or with pure cultures. Undercurrent experimental conditions, the UV-irradiation invariablyreduced the biodegradation of PAHs in creosote. Based onthe results of the present and previous photochemical-biologicalstudies of PAHs, the influence of the photochemical pretreatmenton the biodegradation is highly dependent on the compoundsbeing treated and other process parameters.     

Influence of nonionic surfactants and hydroxypropyl-β-cyclodextrin on the biodegradation of nitrobenzene

This paper investigates the effect of two nonionic surfactants (Tween 80 and Triton X-100) and hydroxypropyl--cyclodextrin (HP--CD) on the biodegradation of nitrobenzene (NB) by Acinetobacter sp. in liquid cultures at different dosages as well as the fate of both surfactants. When the initial concentration of NB was about 400 mg/l, neither Tween 80 nor HP--CD had any effect on the degradation of NB. However, Triton X-100 retarded the full removal of NB and the bacterial growth entering the stationary phase. While the initial concentration of NB was increased to about 850 mg/l, they all significantly enhanced the extent and rate of biodegradation if they were added at concentrations above 2000 mg/l. HP--CD could not be utilized by Acinetobacter sp. as the sole carbon source whereas both surfactants could, but no surfactant depletion was observed during the biodegradation of NB. So the rapid bacterial growth observed in the presence of each additive should be attributed to the rapid metabolism of NB. Both surfactants would promote the degradation of NB more than HP--CD would do if their dosages were increased properly.     

Use of Rice Husk as Bulking Agent in Bioremediation of Automobile Gas Oil Impinged Agricultural Soil

Evaluation of rice husk (RH) as bulking agent in bioremediation of automobile gas oil (AGO) hydrocarbon polluted agricultural soil using renewal by enhanced natural attenuation (RENA) as control was the subject of the present investigation. The effect of different parameters such as total petroleum hydrocarbon (TPH), dehydrogenase activity (DHA), optical density and pH on bioremediation performance were evaluated. The studied parameters such as microbial dynamics, percentage degradation and DHA were found to be higher in RH-amended system and differed significantly with control at P < 0.05. RH resulted in high removal efficiency of 97.85 ± 0.93% under a two-month incubation period, while RENA had lesser removal efficiency of 53.15 ± 3.81%. Overall hydrocarbon biodegradation proceeded very slowly in the RENA particularly from week 0 to 4. Experimental data perfectly fitted into the first-order kinetic and generated high r² values (0.945), first-order degradation constant (0.47 day^?1), and shorter degradation half-life (1.50 d)—t_1/2 = Ln2/K and Ln2 numerically equals to 0.693 and hence written as 0.693/K. Micrococcus luteus and Rhizopus arrhizus were isolated in the present study, which displayed extreme AGO hydrocarbon biodegradative abilities. The use of RH in hydrocarbon-polluted soil significantly increased biodegradation rate and resulted in effective AGO cleanup within 2 months period. Therefore, RH provides an alternative source of bioremediation material in field application for abundant petroleum hydrocarbon soil pollution.