The influence of surfactants on cell surface properties of Aeromonas hydrophila during diesel oil biodegradation

The biotechnological potential of Aeromonas: a bird's eye view

The genus Aeromonas comprises Gram-negative bacilli widely distributed in aquatic habitats that can also be found in the terrestrial environment and in close association with humans and animals. Aeromonas spp. are particularly versatile bacteria, with high genomic plasticity and notable capacity to adapt to different environments and extreme conditions. On account of being mostly associated with their pathogenic potential, research on the biotechnological potentialities of Aeromonas spp. is considerably scarce when compared to other bacterial groups. Nonetheless, studies over the years have been hinting at several interesting hidden potentialities in this bacterial group, especially with the recent advances in whole-genome sequencing, unveiling Aeromonas spp. as interesting candidates for the discovery of novel industrial biocatalysts, bioremediation strategies, and biopolyester production. In this context, the present study aims to provide an overview of the main biotechnological applications reported in the genus Aeromonas and provide new insights into the further exploration of these frequently overlooked, yet fascinating, bacteria.

Physiological changes in Rhodococcus ruber S103 immobilized on biobooms using low-cost media enhance stress tolerance and crude oil-degrading activity

For economic feasibility, sugarcane molasses (0.5%, w/v) containing K₂HPO₄ (0.26%, w/v) and mature coconut water, low value byproducts, were used in cultivation of Rhodococcus ruber S103 for inoculum production and immobilization, respectively. Physiological changes of S103 grown in low-cost media, including cell hydrophobicity, saturated/unsaturated ratio of cellular fatty acids and biofilm formation activity, enhanced stress tolerance and crude oil biodegradation in freshwater and even under high salinity (5%, w/v). Biobooms comprised of S103 immobilized on polyurethane foam (PUF) was achieved with high biomass content (10¹⁰ colony-forming units g^-1 PUF) via a scale-up process in a 5-L modified fluidized-bed bioreactor within 3 days. In a 500-L mesocosm, natural freshwater was spiked with crude oil (72 g or 667 mg g^-1 dry biobooms), and a simulated wave was applied. Biobooms could remove 100% of crude oil within only 3 days and simultaneously biodegraded 60% of the adsorbed oil after 7 days when compared to boom control with indigenous bacteria. In addition, biobooms had a long shelf-life (at least 100 days) with high biodegradation activity (85.2 ± 2.3%) after storage in 10% (w/v) skimmed milk at room temperature. This study demonstrates that the low-cost production of biobooms has potential for future commercial bioremediation.

The proliferation and colonization of functional bacteria on amorphous polyethylene terephthalate: Key role of ultraviolet irradiation and nonionic surfactant polysorbate 80 addition

Environmental pollution with plastics including polyethylene terephthalate (PET) has become a severe global problem, especially microplastic pollution, which is acknowledged as an emerging global pollutant. Biodegradation as a feasible and promising method has been studied, while colonization as the initiating step of the degradation process has seldom been studied. Here in this paper, we explored for the first time the key role of ultraviolet (UV) irradiation and nonionic surfactant polysorbate 80 (Tween-80, 0.2% V/V) in the proliferation and colonization of three functional bacteria (Pseudomonas putida, Pseudomonas sp. and Paracoccus sp.) on amorphous PET (APET). We found that 25 days of UV irradiation can trigger photolytic degradation process (appear the stretching vibration of associating carboxyl end group and the in-plane bending vibration of -OH) and introduce oxygen-containing functional groups on the surface of APET, even though the hydrophobicity of APET was scarcely changed. With regard to Tween-80, it can be utilized by these bacteria strains as carbon source to promote the proliferation, and it can also improve the cell surface hydrophobicity to stimulate the bacterial colonization during the first ten days of the experiment. When UV-irradiation and Tween-80 were provided together, the former factor can provide the target sites for functional bacteria to colonize, and the later factor can provide more candidates waiting to colonize by stimulating proliferation. As a result, an even better proliferation and colonization result can be achieved through the synergistic effect between the two factors. To some extent, the exposure between potential degrading bacteria and substrates to be degraded can be increased, which will create conditions for degrading. Generally, this research can provide certain theoretical basis and technical guidance for the remediation of plastic-polluted soil and the ocean.

Biodegradation of a Complex Phenolic Industrial Stream by Bacterial Strains Isolated from Industrial Wastewaters

Molecular and metabolomic tools were used to design and understand the biodegradation of phenolic compounds in real industrial streams. Bacterial species were isolated from an industrial wastewater treatment plant of a phenol production factory and identified using molecular techniques. Next, the biodegradation potential of the most promising strains was analyzed in the presence of a phenolic industrial by-product containing phenol, alfa-methylstyrene, acetophenone, 2-cumylphenol, and 4-cumylphenol. A bacterial consortium comprising Pseudomonas and Alcaligenes species was assessed for its ability to degrade phenolic compounds from the phenolic industrial stream (PS). The consortium adapted itself to the increasing levels of phenolic compounds, roughly up to 1750 ppm of PS; thus, becoming resistant to them. In addition, the consortium exhibited the ability to grow in the presence of PS in repeated batch mode processes. Results from untargeted metabolomic analysis of the culture medium in the presence of PS suggested that bacteria transformed the toxic phenolic compounds into less harmful molecules as a survival mechanism. Overall, the study demonstrates the usefulness of massive sequencing and metabolomic tools in constructing bacterial consortia that can efficiently biodegrade complex PS. Furthermore, it improves our understanding of their biodegradation capabilities.

Bioremediation perspectives and progress in petroleum pollution in the marine environment: a review

The marine environment is often affected by petroleum hydrocarbon pollution due to industrial activities and petroleum accidents. This pollution has recalcitrant and persistent compounds that pose a high risk to the ecological system and human health. For this reason, the world claims to seek to clean up these pollutants. Bioremediation is an attractive approach for removing petroleum pollution. It is considered a low-cost and highly effective approach with fewer side effects compared to chemical and physical techniques. This depends on the metabolic capability of microorganisms involved in the degradation of hydrocarbons through enzymatic reactions. Bioremediation activities mostly depend on environmental conditions such as temperature, pH, salinity, pressure, and nutrition availability. Understanding the effects of environmental conditions on microbial hydrocarbon degraders and microbial interactions with hydrocarbon compounds could be assessed for the successful degradation of petroleum pollution. The current review provides a critical view of petroleum pollution in seawater, the bioavailability of petroleum compounds, the contribution of microorganisms in petroleum degradation, and the mechanisms of degradation under aerobic and anaerobic conditions. We consider different biodegradation approaches such as biostimulation, bioaugmentation, and phytoremediation.

Adaptation of phenol-degrading Pseudomonas putida KB3 to suboptimal growth condition: A focus on degradative rate, membrane properties and expression of xylE and cfaB genes

Detailed characterization of new Pseudomonas strains that degrade toxic pollutants is required and utterly necessary before their potential use in environmental microbiology and biotechnology applications. Therefore, phenol degradation by Pseudomonas putida KB3 under suboptimal temperatures, pH, and salinity was examined in this study. Parallelly, adaptive mechanisms of bacteria to stressful growth conditions concerning changes in cell membrane properties during phenol exposure as well as the expression level of genes encoding catechol 2,3-dioxygenase (xylE) and cyclopropane fatty acid synthase (cfaB) were determined. It was found that high salinity and the low temperature had the most significant effect on the growth of bacteria and the rate of phenol utilization. Degradation of phenol (300 mg L^-1) proceeded 12-fold and seven-fold longer at 10 °C and 5% NaCl compared to the optimal conditions. The ability of bacteria to degrade phenol was coupled with a relatively high activity of catechol 2,3-dioxygenase. The only factor that inhibited enzyme activity by approximately 80% compared to the control sample was salinity. Fatty acid methyl ester (FAMEs) profiling, membrane permeability measurements, and hydrophobicity tests indicated severe alterations in bacteria membrane properties during phenol degradation in suboptimal growth conditions. The highest values of pH, salinity, and temperature led to a decrease in membrane permeability. FAME analysis showed fatty acid saturation indices and cyclopropane fatty acid participation at high temperature and salinity. Genetic data showed that suboptimal growth conditions primarily resulted in down-regulation of xylE and cfaB gene expression.

Chemo-metrically formulated consortium with selectively screened bacterial strains for ameliorated biotransformation and detoxification of 1,4-dioxane

The biotransformation of 1,4-dioxane, a endrocrine disrupting chemical was achieved using different bacterial strains and their consortia. Three different bacterial isolates were screened on their ability to grow with 50 mg/L 1,4-dioxane in the basal mineral medium. Then the isolates were tested for its efficiency to biotransform 1000 mg/L 1,4-dioxane at varying period of time; 24-120 h. The isolates were distinguished by their morphological features and 16 S rRNA gene sequencing was done to evaluate the phylogenetic relationships. The isolates were identified as Bacillus marisflavi strain MGA, Aeromonas hydrophila strain AG and Shewanella putrefaciens strain AG. The degree of biotransformation was escalated by constructing a bacterial consortium using statistical tool; response-mixture matrix under the design of experiments. The fully grown bacterial strains were used as ingredients in different proportions to formulate the consortium. The biotransformation was analyzed for functional attenuation using spectroscopic techniques and reduction in 1,4-dioxane level was confirmed using mass spectrometry. The precise quantification of biotransformation using mass spectral profile revealed that the consortium removed 31%, 61% and 85% of 1000 mg/L 1,4-dioxane within 96, 120 and 144 h respectively. The activities of inducible laccase were elucidated during biotransformation of 1,4-dioxane. Bio-toxicity of treated and untreated 1,4-dioxane on brine shrimp; Artemia salina showed that the biotransformed products were less toxic. Therefore, this report would be first of its kind to report the biotransformation and detoxification of 1,4-dioxane by a statistically designed bacterial consortium.

Uptake and detoxification of diesel oil by a tropical soil Actinomycete Gordonia amicalis HS-11: Cellular responses and degradation perspectives

A tropical soil Actinomycete, Gordonia amicalis HS-11, has been previously demonstrated to degrade unsaturated and saturated hydrocarbons (squalene and n-hexadecane, respectively) in an effective manner. In present study, G. amicalis HS-11 degraded 92.85 ± 3.42% of the provided diesel oil [1% (v/v)] after 16 days of aerobic incubation. The effect of different culture conditions such as carbon source, nitrogen source, pH, temperature, and aeration on degradation was studied. During degradation, this Actinomycete synthesized surface active compounds (SACs) in an extracellular manner that brought about a reduction in surface tension from 69 ± 2.1 to 30 ± 1.1 mN m^-1 after 16 days. The morphology of cells grown on diesel was monitored by using a Field Emission Scanning Electron Microscope. Diesel-grown cells were longer and clumped with smooth surfaces, possibly due to the secretion of SACs. The interaction between the cells and diesel oil was studied by Confocal Laser Scanning Microscope. Some cells were adherent on small diesel droplets and others were present in the non-attached form thus confirming the emulsification ability of this organism. The fatty acid profiles of the organism grown on diesel oil for 48 h were different from those on Luria Bertani Broth. The genotoxicity and cytotoxicity of diesel oil before and after degradation were determined. Cytogenetic parameters such as mitotic index (MI); mitosis distribution and chromosomal aberration (type and frequency) were assessed. Oxidative stress was evaluated by measuring levels of catalase, superoxide dismutase and concentration of malondialdehyde. On the basis of these studies it was deduced that the degradation metabolites were relatively non-toxic.

Modification of the Bacterial Cell Wall—Is the Bioavailability Important in Creosote Biodegradation?

Creosote oil, widely used as a wood preservative, is a complex mixture of different polycyclic aromatic compounds. The soil contamination result in the presence of a specific microcosm. The presented study focuses on the most active strains involved in bioremediation of long-term creosote-contaminated soil. In three soil samples from different boreholes, two Sphingomonas maltophilia (S. maltophilia) and one Paenibacillus ulginis (P. ulginis) strain were isolated. The conducted experiments showed the differences and similarities between the bacteria strains capable of degrading creosote from the same contaminated area. Both S. maltophilia strains exhibit higher biodegradation efficiency (over 50% after 28 days) and greater increase in glutathione S-transferase activity than P. ulginis ODW 5.9. However, S. maltophilia ODW 3.7 and P. ulginis ODW 5.9 were different from the third of the tested strains. The growth of the former two on creosote resulted in an increase in cell adhesion to Congo red and in the total membrane permeability. Nevertheless, all three strains have shown a decrease in the permeability of the inner cell membrane. That suggests the complex relationship between the cell surface modifications and bioavailability of the creosote to microorganisms. The conducted research allowed us to broaden the current knowledge about the creosote bioremediation and the properties of microorganisms involved in the process.

Bacteria involved in biodegradation of creosote PAH - A case study of long-term contaminated industrial area

Polycyclic aromatic hydrocarbons (PAH) contained in creosote oil are particularly difficult to remove from the soil environment. Their hydrophobic character and low bioavailability to soil microorganisms affects their rate of biodegradation. This study was performed on samples of soil that were (for over forty years) subjected to contamination with creosote oil, and their metagenome and physicochemical properties were characterized. Moreover, the study was undertaken to evaluate the biodegradation of PAHs by autochthonous consortia as well as by selected bacteria strains isolated from long-term contaminated industrial soil. From among the isolated microorganisms, the most effective in biodegrading the contaminants were the strains Pseudomonas mendocina and Brevundimonas olei. They were able to degrade more than 60% of the total content of PAHs during a 28-day test. The biodegradation of these compounds using AT7 dispersant was enhanced only by Serratia marcescens strain. Moreover, the addition of AT7 improved the effectiveness of fluorene and acenaphthene biodegradation by Serratia marcescens 6-fold. Our results indicated that long-term contact with aromatic compounds induced the bacterial strains to use the PAHs as a source of carbon and energy. We observed that supplementation with surfactants does not increase the efficiency of hydrocarbon biodegradation.

Biodegradation of Petroleum Hydrocarbons by Bacillus subtilis BL-27, a Strain with Weak Hydrophobicity

The biodegradation of petroleum hydrocarbons has many potential applications and has attracted much attention recently. The hydrocarbon-degrading bacterium BL-27 was isolated from petroleum-polluted soil and was compounded with surfactants to improve biodegradation. Its 16S rDNA and rpoD gene sequences indicated that it was a strain of Bacillus subtilis. Strain BL-27 had extensive adaptability and degradability within a broad range of temperatures (25–50 °C), pH (4.0–10.0) and salinity (0–50 g/L NaCl). Under optimal conditions (45 °C, pH 7.0, 1% NaCl), the strain was able to degrade 65% of crude oil (0.3%, w/v) within 5 days using GC-MS analysis. Notably, strain BL-27 had weak cell surface hydrophobicity. The adherence rate of BL-27 to n-hexadecane was 29.6% with sucrose as carbon source and slightly increased to 33.5% with diesel oil (0.3%, w/v) as the sole carbon source, indicating that the cell surface of BL-27 is relatively hydrophilic. The strain was tolerant to SDS, Tween 80, surfactin, and rhamnolipids at a concentration of 500 mg/L. The cell surface hydrophobicity reduced more with the addition of surfactants, while the chemical dispersants, SDS (50–100 mg/L) and Tween 80 (200–500 mg/L), significantly increased the strain’s ability to biodegrade, reaching 75–80%. These results indicated that BL-27 has the potential to be used for the bioremediation of hydrocarbon pollutants and could have promising applications in the petrochemical industry.

Isolation, identification, and characterization of diesel-oil-degrading bacterial strains indigenous to Changqing oil field, China

In the present study, 12 indigenous diesel-oil-degrading bacteria were isolated from the petroleum-contaminated soils of the Changqing oil field (Xi'an, China). Measurement of the diesel-oil degradation rates of these strains by the gravimetric method revealed that they ranged from 42% to 66% within 2 weeks. The highest degradation rates were observed from strains CQ8-1 (66%), CQ8-2 (62.6%), and CQ11 (59%), which were identified as Bacillus thuringiensis, Ochrobactrum anthropi, and Bordetella bronchialis, respectively, based on their 16S rDNA sequences. Moreover, the physiological and biochemical properties of these three strains were analyzed by Gram staining, catalase, oxidase, and Voges-Proskauer tests. Transmission electron microscopy showed that all three strains were rod shaped with flagella. Gas chromatography and mass spectrometric analyses indicated that medium- and long-chain n-alkanes in diesel oil (C11-C29) were degraded to different degrees by B. thuringiensis, O. anthropi, and B. bronchialis, and the degradation rates gradually decreased as the carbon numbers increased. Overall, the results of this study indicate strains CQ8-1, CQ8-2, and CQ11 might be useful for environmentally friendly and cost-effective bioremediation of oil-contaminated soils.

Fast Biodegradation of Diesel Hydrocarbons at High Concentration by the Sophorolipid-Producing Yeast KP324968

In the last decades, biodegradation as an environmentally friendly approach has raised interest in connection with the removal of hydrocarbon pollutants. Its capacity for removing pollutants strongly depends on the type of living cell and environmental conditions. The degradative activity of a new sophorolipid-producing yeast, <i>Candida catenulata</i> KP324968, in the removal of high concentrations of diesel from effluents was statistically evaluated considering the initial pH, the agitation speed, and the initial diesel concentration. The optimal setting of the operational variables at an initial pH of 4.7, an agitation speed of 204 rpm, and an initial diesel concentration of 93.4 g L^–1 resulted in the highest total petroleum hydrocarbon removal efficiency: about 82.1% after 6 days (biodegradation rate: 0.378 g g_cell^–1 h^–1). During the cell growth phase, the emulsification index in the medium increased and reached its highest level at 64.6% after 48 h. Further tests indicated that the emulsification capacity was obtained by in situ production of two sophorolipid molecules with an m/z of 533 and 583. In summary, its effective diesel removal and high emulsification capacity makes <i>C. catenulata</i> KP324968 an attractive candidate yeast for the degradation of hydrocarbons from aqueous environments.

The Impact of Biosurfactants on Microbial Cell Properties Leading to Hydrocarbon Bioavailability Increase

The environment pollution with hydrophobic hydrocarbons is a serious problem that requires development of efficient strategies that would lead to bioremediation of contaminated areas. One of the common methods used for enhancement of biodegradation of pollutants is the addition of biosurfactants. Several mechanisms have been postulated as responsible for hydrocarbons bioavailability enhancement with biosurfactants. They include solubilization and desorption of pollutants as well as modification of bacteria cell surface properties. The presented review contains a wide discussion of these mechanisms in the context of alteration of bioremediation efficiency with biosurfactants. It brings new light to such a complex and important issue.

Advances in applications of rhamnolipids biosurfactant in environmental remediation: A review

The objective of this review is to provide a comprehensive overview of the advances in the applications of rhamnolipids biosurfactants in soil and ground water remediation for removal of petroleum hydrocarbon and heavy metal contaminants. The properties of rhamnolipids associated with the contaminant removal, that is, solubilization, emulsification, dispersion, foaming, wetting, complexation, and the ability to modify bacterial cell surface properties, were reviewed in the first place. Then current remediation technologies with integration of rhamnolipid were summarized, and the effects and mechanisms for rhamnolipid to facilitate contaminant removal for these technologies were discussed. Finally rhamnolipid-based methods for remediation of the sites co-contaminated by petroleum hydrocarbons and heavy metals were presented and discussed. The review is expected to enhance our understanding on environmental aspects of rhamnolipid and provide some important information to guide the extending use of this fascinating chemical in remediation applications.

Impact of potent bioremediation enhancing plant extracts on Raoultella ornithinolytica properties

Long-term contact of microorganisms with different compounds in the environment can cause significant changes in cell metabolism. Surfactants adsorption on cell surface or incorporation in the cell membrane, lead to their modification, which helps microorganisms adopt to the conditions of metabolic stress. The main objective of this study was to investigate the effects of three saponin-reach plant extracts from Hedera helix, Saponaria officinalis and Sapindus mucorossi on growth and adaptation of Raoultella ornithinolytica to high concentrations of these substances. For this purpose we investigated cell surface properties, membrane fatty acids and genetic changes of the microorganisms. The results revealed that prolonged exposure of the microorganisms to high concentrations of these surfactants can induce genetic changes of their genes. Moreover, the adaptation to contact with high concentrations of saponins was also associated with changes in composition of fatty acids responsible for the stabilisation of membrane structure and the increase in membrane permeability. The changes affected also the outer layer of cells. A significant increase (p < 0.05) in the cell surface hydrophobicity of tested strain was also observed. The cells after long-term contact with S. officinalis and S. mucorossi acquire properties that may be favourable in hydrophobic substances bioremediation.

Alkyl Xylosides: Physico-Chemical Properties and Influence on Environmental Bacteria Cells

A group of four selected non-ionic surfactants based on carbohydrates, namely octyl d-xyloside (C8X), nonyl d-xyloside (C9X), decyl d-xyloside (C10X) and dodecyl d-xyloside (C12X), have been investigated to accomplish a better understanding of their physico-chemical properties as well as biological activities. The surface-active properties, such as critical micelle concentration (CMC), emulsion and foam stability, the impact of the compounds on cell surface hydrophobicity and cell membrane permeability together with their toxicity on the selected bacterial strains have been determined as well. The studied group of surfactants showed high surface-active properties allowing a decrease in the surface tension to values below 25 mN m-1 for dodecyl d-xyloside at the CMC. The investigated compounds did not have any toxic influence on two Pseudomonas bacterial strains at concentrations below 25 mg L-1. The studied long-chain alkyl xylosides influenced both the cell inner membrane permeability and the cell surface hydrophobicity. Furthermore, the alkyl chain length, as well as the surfactant concentration, had a significant impact on the modifications of the cell surface properties. The tested non-ionic surfactants exhibited strong surface-active properties accompanied by the significant influence on growth and properties of Pseudomonas bacteria cells.

Characteristics and proteomic analysis of pyrene degradation by Brevibacillus brevis in liquid medium

Polycyclic aromatic hydrocarbons (PAHs) are widely spread in various ecosystems and are of great concern due to their potential toxicity, mutagenicity and carcinogenicity. Bioremediation has been proposed as an effective approach to remove PAHs. In this study, the physiological responses and proteome of Brevibacillus brevis under exposure to pyrene, a four-ring compound from PAHs family, were investigated. The changes of cell viability of B. brevis were observed during the degradation of pyrene by means of flow cytometry. The results indicated that pyrene stimulated superoxide dismutase (SOD) activity from 93.9 to 100.6 U mg^-1 prot, whereas inhibited catalase (CAT) activity from 29.1 to 20.3 U mg^-1 prot. The main compositions of B. brevis changed during pyrene degradation, with the proportion of unsaturated fatty acids increased by 13.4%. In addition, we performed a proteomic approach (two-dimensional gel electrophoresis and MALDI-TOF/TOF-MS) in order to explore how B. brevis survived upon treatment with pyrene. It was showed that the expression of 13 proteins increased whereas 10 other decreased after pyrene-treatment. The differentially expressed proteins were identified and the results indicated that they were involved in multiple biological processes including energy metabolism, biosynthesis, transmembrane transport and oxidative stress. Overall, these findings offered a new insights into the cellular response strategy developed by B. brevis to overcome the pyrene stress.

Effects of rhamnolipids on microorganism characteristics and applications in composting: A review

Biosurfactant rhmnolipids have been applied in many fields, especially in environmental bioremediation. According to previous researches, many research groups have studied the influence of rhamnolipids on microorganism characteristics and/or its application in composting. In this review, the effects of rhamnolipids on the cell surface properties of microorganisms was discussed firstly, such as cell surface hydrophobicity (CSH), electrical, surface compounds, etc. Moreover, the deeper mechanisms were also discussed, such as the effects of rhamnolipids on the structural characteristics and functional characteristics of the cell membrane, and the effects of rhamnolipids on the related enzymes and genes. Additionally, the application of rhamnolipids in composting was discussed, which is an important way for pollutant biodegradation and resource reutilization. It is believed that rhamnolipids will play more and more important role in composting.

Saponaria officinalis L. extract: Surface active properties and impact on environmental bacterial strains

Plant-derived surfactants are characterised by low toxicity, high biodegradability and environmental compatibility. They therefore have many applications; for instance, they can be used in bioremediation to accelerate biodegradation processes, especially of hydrophobic pollutants. This paper analyses the properties of an extract from Saponaria officinalis L. containing saponins and its impact on bacterial strains isolated from soil, as well as its potential for application in hydrocarbon bioremediation. The tested extract from Saponaria officinalis L. contains gypsogenin, hederagenin, hydroxyhederagenin and quillaic acid aglycone structures and demonstrates good emulsification properties. Contact with the extract led to modification of bacterial cell surface properties. A decrease in cell surface hydrophobicity and an increase in membrane permeability were recorded in the experiments. An increase of up to 63% in diesel oil biodegradation was also recorded for Pseudomonas putida DA1 on addition of 1gL^-1 of saponins from Saponaria officinalis L. Saponaria extract showed no toxic impact on the tested environmental bacterial strains at the concentration used in the biodegradation process.

Influence of saponins on the biodegradation of halogenated phenols

Biotransformation of aromatic compounds is a challenge due to their low aqueous solubility and sorptive losses. The main obstacle in this process is binding of organic pollutants to the microbial cell surface. To overcome these, we applied saponins from plant extract to the microbial culture, to increase pollutants solubility and enhance diffusive massive transfer. This study investigated the efficiency of Quillaja saponaria and Sapindus mukorossi saponins-rich extracts on biodegradation of halogenated phenols by Raoultella planticola WS2 and Pseudomonas sp. OS2, as an effect of cell surface modification of tested strains. Both strains display changes in inner membrane permeability and cell surface hydrophobicity in the presence of saponins during the process of halogenated phenols biotransformation. This allows them to more efficient pollutants removal from the environment. However, only in case of the Pseudomonas sp. OS2 the addition of surfactants to the culture improved effectiveness of bromo-, chloro- and fluorophenols biodegradation. Also introduction of surfactant allowed higher biodegradability of halogenated phenols and can shorten the process. Therefore this suggests that usage of plant saponins can indicate more successful halogenated phenols biodegradation for selected strains.

Nonionic surfactants induced changes in cell characteristics and phenanthrene degradation ability of Sphingomonas sp. GY2B

Surfactant-mediated bioremediation has been widely applied in decontaminating PAH-polluted sites. However, the impacts of surfactants on the biodegradation of PAHs have been controversial in the past years. To gain a clear insight into the influencing mechanisms, three nonionic surfactants (Tween80, TritonX-100 and Brij30) were selected to systematically investigate their effects on cell surface properties (membrane permeability, functional groups and elements), cell vitality as well as subsequent phenanthrene degradation ability of Sphingomonas sp. GY2B. Results showed that biodegradation of phenanthrene was stimulated by Tween80, slightly inhibited by TritonX-100 and severely inhibited by Brij30, respectively. Positive effect of Tween80 may arise from its role as the additional carbon source for GY2B to increase bacterial growth and activity, as demonstrated by the increasing viable cells in Tween80 amended degradation systems determined by flow cytometry. Although TritonX-100 could inhibit bacterial growth and disrupt cell membrane, its adverse impacts on microbial cells were weaker than Brij30, which may result in its weaker inhibitive extent. Results from this study can provide a rational basis on selecting surfactants for enhancing bioremediation of PAHs.

Effect of natural and synthetic surfactants on crude oil biodegradation by indigenous strains

Hydrocarbon pollution is a worldwide problem. In this study, five surfactants containing SDS, LAS, Brij 30, Tween 80 and biosurfactant were used to evaluate their effect on crude oil biodegradation. Hydrocarbon degrading bacteria were isolated from oil production water. The biosurfactant used was a kind of cyclic lipopeptide produced by Bacillus subtilis strain WU-3. Solubilization test showed all the surfactants could apparently increase the water solubility of crude oil. The microbial adhesion to the hydrocarbon (MATH) test showed surfactants could change cell surface hydrophobicity (CSH) of microbiota, depending on their species and concentrations. Microcalorimetric experiments revealed these surfactants exhibited toxicity to microorganisms at high concentrations (above 1 CMC), except for SDS which showed low antibacterial activity. Surfactant supplementation (about 0.1 and 0.2 CMC) could improve degradation rate of crude oil slightly, while high surfactant concentration (above 1 CMC) may decrease the degradation rate from 50.5% to 28.9%. Those findings of this work could provide guidance for the application of surfactants in bioremediation of oil pollution.

Saponin-enhanced biomass accumulation and demulsification capability of the demulsifying bacteria Alcaligenes sp. S-XJ-1

Saponin significantly enhanced biomass accumulation and demulsification capability of the demulsifying bacteria.

Effects of Two Surfactants and Beta-Cyclodextrin on Beta-Cypermethrin Degradation by Bacillus licheniformis B-1

The biodegradation efficiency of beta-cypermethrin (β-CY) is low especially at high concentrations mainly due to poor contact between this hydrophobic pesticide and microbial cells. In this study, the effects of two biodegradable surfactants (Tween-80 and Brij-35) and β-cyclodextrin (β-CD) on the growth and cell surface hydrophobicity (CSH) of Bacillus licheniformis B-1 were studied. Furthermore, their effects on the solubility, biosorption, and degradation of β-CY were investigated. The results showed that Tween-80 could slightly promote the growth of the strain while Brij-35 and β-CD exhibited little effect on its growth. The CSH of strain B-1 and the solubility of β-CY were obviously changed by using Tween-80 and Brij-35. The surfactants and β-CD could enhance β-CY biosorption and degradation by the strain, and the highest degradation was obtained in the presence of Brij-35. When the surfactant or β-CD concentration was 2.4 g/L, the degradation rate of β-CY in Brij-35, Tween-80, and β-CD treatments was 89.4%, 50.5%, and 48.1%, respectively. The half-life of β-CY by using Brij-35 was shortened by 69.1 h. Beta-CY content in the soil with both strain B-1 and Brij-35 decreased from 22.29 mg/kg to 4.41 mg/kg after incubation for 22 d. This work can provide a promising approach for the efficient degradation of pyrethroid pesticides by microorganisms.

Biosorption and biodegradation of pyrene by Brevibacillus brevis and cellular responses to pyrene treatment

Biodegradation has been proposed as an effective approach to remove pyrene, however, the information regarding cellular responses to pyrene treatment is limited thus far. In this study, the biodegradation and biosorption of pyrene by Brevibacillus brevis, along with cellular responses caused by pollutant were investigated by means of flow cytometry assay and scanning electron microscopy. The experimental results showed that pyrene was initially adsorbed by B. brevis and subsequently transported and intracellularly degraded. During this process, pyrene removal was primarily dependent on biodegradation. Cell invagination and cell surface corrugation occurred due to pyrene exposure. Nevertheless, cell regrowth after 96h treatment was observed, and the proportion of necrotic cell was only 2.8% after pyrene exposure for 120h, confirming that B. brevis could utilize pyrene as a sole carbon source for growth. The removal and biodegradation amount of pyrene (1mg/L) at 168h were 0.75 and 0.69mg/L, respectively, and the biosorption amount by inactivated cells was 0.41mg/L at this time.

Impact of Alkyl Polyglucosides Surfactant Lutensol GD 70 on Modification of Bacterial Cell Surface Properties

Alkyl polyglucosides, due to their low toxicity and environmental compatibility, could be used in biodegradation of hydrophobic compounds. In this study, the influence of Lutensol GD 70 on the cell hydrophobicity and zeta potential was measured. The particle size distribution and surfactant biodegradation were also investigated. Microbacterium sp. strain E19, Pseudomonas stutzeri strain 9, and the same strain cultivated in stress conditions were used in studies. Adding surfactant to the diesel oil system resulted in an increase of the cell surface hydrophobicity and the formation of cell aggregates (a high polydispersity index). The correlation between cell hydrophobicity and zeta potential in examined samples was not found. The results showed a significant influence of Lutensol GD 70 on the changes in cell surface properties. Moreover, a high biodegradation of a surfactant (over 50 %) by tested strains was observed. The biodegradation of Lutensol GD 70 depends on the length of both polar and nonpolar chains. A long-term contact with diesel oil of stressed strain modifies not only cell surface properties but also its ability to a surfactant biodegradation.

Petroleum hydrocarbon degrading bacteria associated with chitosan as effective particle-stabilizers for oil emulsification

Bacteria act as an effective oil emulsifier with chitosan in sea water, together with its dramatically enhanced biodegradation.

Practical considerations and challenges involved in surfactant enhanced bioremediation of oil

Surfactant enhanced bioremediation (SEB) of oil is an approach adopted to overcome the bioavailability constraints encountered in biotransformation of nonaqueous phase liquid (NAPL) pollutants. Fuel oils contain n-alkanes and other aliphatic hydrocarbons, monoaromatics, and polynuclear aromatic hydrocarbons (PAHs). Although hydrocarbon degrading cultures are abundant in nature, complete biodegradation of oil is rarely achieved even under favorable environmental conditions due to the structural complexity of oil and culture specificities. Moreover, the interaction among cultures in a consortium, substrate interaction effects during the degradation and ability of specific cultures to alter the bioavailability of oil invariably affect the process. Although SEB has the potential to increase the degradation rate of oil and its constituents, there are numerous challenges in the successful application of this technology. Success is dependent on the choice of appropriate surfactant type and dose since the surfactant-hydrocarbon-microorganism interaction may be unique to each scenario. Surfactants not only enhance the uptake of constituents through micellar solubilization and emulsification but can also alter microbial cell surface characteristics. Moreover, hydrocarbons partitioned in micelles may not be readily bioavailable depending on the microorganism-surfactant interactions. Surfactant toxicity and inherent biodegradability of surfactants may pose additional challenges as discussed in this review.

Degradation of norgestrel by bacteria from activated sludge: comparison to progesterone

Natural and synthetic progestagens in the environment have become a concern due to their adverse effects on aquatic organisms. Laboratory studies were performed to investigate aerobic biodegradation of norgestrel by bacteria from activated sludge in comparison with progesterone, and to identify their degradation products and biotransformation pathways. The degradation of norgestrel followed first order reaction kinetics (T1/2 = 12.5 d), while progesterone followed zero order reaction kinetics (T1/2 = 4.3 h). Four and eight degradation products were identified for norgestrel and progesterone, respectively. Six norgestrel-degrading bacterial strains (Enterobacter ludwigii, Aeromonas hydrophila subsp. dhakensis, Pseudomonas monteilii, Comamonas testosteroni, Exiguobacterium acetylicum, and Chryseobacterium indologenes) and one progesterone-degrading bacterial strain (Comamonas testosteroni) were successfully isolated from the enrichment culture inoculated with aerobic activated sludge. To our best knowledge, this is the first report on the biodegradation products and degrading bacteria for norgestrel under aerobic conditions.

Biodegradation of alkyl derivatives of aromatic hydrocarbons and cell surface properties of a strain of Pseudomonas stutzeri

Pseudomonas stutzeri strain 9 was isolated from petroleum-contaminated soil. The main purpose of this study was to investigate how the long-term contact of this strain with diesel oil influences its surface and biodegradation properties. The experiments showed that the tested strain was able to degrade aromatic alkyl derivatives (butylbenzene, sec-butylbenzene, tert-butylbenzene and isobutylbenzene) and that the storage conditions had an influence on the cell surface properties. Also greater agglomeration of the cells was observed in the scanning electron microscope (SEM) micrographs and confirmed in particle size distribution results. The results also indicated that the addition of rhamnolipids to the hydrocarbons led to modification of the surface properties of P. stutzeri strain 9, which could be observed in the zeta potential and hydrophobicity values.

The influence of rhamnolipids on aliphatic fractions of diesel oil biodegradation by microorganism combinations

Twelve different bacteria-yeast combinations were tested for determination of their ability to biodegrade diesel oil. The cell surface properties of the bacterial and yeast strains were correlated with the type of carbon source used in the experiments. The highest biodegradation of diesel oil after 7 days was obtained for the following combinations: Aeromonas hydrophila MR4-Yarrowia lipolytica EH 56 (87 %) and Xantomonas maltophila MRP7-Candida maltosa EH15 (90 %). Degradation performances of 10 of 12 combinations were enhanced by the presence of rhamnolipids. The highest increases were observed for A. hydrophila MR4-C. maltosa EH15 (from 34 to 67 %), A. hydrophila MR4-C. maltosa EH60 (from 47 to 76 %) and for Pseudomonas stutzeri MR7-C. maltosa EH60 (from 29 to 79 %). The addition of rhamnolipids to the system reduces the removal time of diesel oil from the contaminated water and changes the microbial adhesion to hydrocarbons. Modification of the cell surface of the tested strain during biodegradation is a very important factor determining the removal of hydrophobic compounds.

Diesel oil removal by immobilized Pseudoxanthomonas sp. RN402

Pseudoxanthomonas sp. RN402 was capable of degrading diesel, crude oil, n-tetradecane and n-hexadecane. The RN402 cells were immobilized on the surface of high-density polyethylene plastic pellets at a maximum cell density of 10(8) most probable number (MPN) g(-1) of plastic pellets. The immobilized cells not only showed a higher efficacy of diesel oil removal than free cells but could also degrade higher concentrations of diesel oil. The rate of diesel oil removal by immobilized RN402 cells in liquid culture was 1,050 mg l(-1) day(-1). Moreover, the immobilized cells could maintain high efficacy and viability throughout 70 cycles of bioremedial treatment of diesel-contaminated water. The stability of diesel oil degradation in the immobilized cells resulted from the ability of living RN402 cells to attach to material surfaces by biofilm formation, as was shown by CLSM imaging. These characteristics of the immobilized RN402 cells, including high degradative efficacy, stability and flotation, make them suitable for the purpose of continuous wastewater bioremediation.

Cell surface properties of Pseudomonas stutzeri in the process of diesel oil biodegradation

Pseudomonas stutzeri, isolated from crude oil-contaminated soil, was used to degrade diesel oil. Of three surfactants, 120 mg rhamnolipids 1(-1) significantly increased degradation of diesel oil giving 88% loss after 14 days compared to 54% loss without the surfactant. The system with rhamnolipids was characterised by relatively high particle homogeneity. However, the addition of saponins to diesel oil caused the cells to aggregate (the polydispersity index: 0.542) and the biodegradation of diesel oil was only 46%. The cell yield was 0.22 g l(-1).

Alteration in cell surface properties of Burkholderia spp. during surfactant-aided biodegradation of petroleum hydrocarbons

Chemical surfactants may impact microbial cell surface properties, i.e., cell surface hydrophobicity (CSH) and cell surface charge, and may thus affect the uptake of components from non-aqueous phase liquids (NAPLs). This work explored the impact of Triton X-100, Igepal CA 630, and Tween 80 (at twice the critical micelle concentration, CMC) on the cell surface characteristics of Burkholderia cultures, Burkholderia cepacia (ES1, aliphatic degrader) and Burkholderia multivorans (NG1, aromatic degrader), when grown on a six-component model NAPL. In the presence of Triton X-100, NAPL biodegradation was enhanced from 21% to 60% in B. cepacia and from 18% to 53% in B. multivorans. CSH based on water contact angle (50-52°) was in the same range for both strains while zeta potential at neutral pH was -38 and -31 mV for B. cepacia and B. multivorans, respectively. In the presence of Triton X-100, their CSH increased to greater than 75° and the zeta potential decreased. This induced a change in the mode of uptake and initiated aliphatic hydrocarbon degradation by B. multivorans and increased the rate of aliphatic hydrocarbon degradation in B. cepacia. Igepal CA 630 and Tween 80 also altered the cell surface properties. For B. cepacia grown in the presence of Triton X-100 at two and five times its CMC, CSH increased significantly in the log growth phase. Growth in the presence of the chemical surfactants also affected the abundance of chemical functional groups on the cell surface. Cell surface changes had maximum impact on NAPL degradation in the presence of emulsifying surfactants, Triton X-100 and Igepal CA630.

Effect of monorhamnolipid on the degradation of n-hexadecane by Candida tropicalis and the association with cell surface properties

The effect of monorhamnolipid (monoRL) on the degradation of n-hexadecane by Candida tropicalis was investigated in this study. The concentration of hexadecane, cell growth, cell surface hydrophobicity (CSH), cell surface zeta potential (CSZP), and FT-IR spectra of cellular envelope were tested to determine the mechanisms. MonoRL at the initial concentrations of 11.4, 19, and 38 mg/l improved the degradation of hexadecane, and 19 mg/l was the best concentration. However, 114 mg/l monoRL suppressed the biodegradation probably because of the reduced bioavailability of hexadecane caused by the micelles. The presence of monoRL changed the cell surface properties, which was demonstrated by the increased CSH, the increased CSZP, and the changed FT-IR spectra of cellular envelope at 680 and 620 cm(-1). The changes of cell surface properties may be a reason for the enhanced biodegradation of hexadecane by the yeast. The results indicate the potential application of monoRL in the bioremediation of hydrocarbons.