Effects of monorhamnolipid and Tween 80 on the degradation of phenol by Candida tropicalis

The effects of the biosurfactant monorhamnolipid (monoRL) and the chemical surfactant Tween 80 on the degradation of phenol by Candida tropicalis CICC 1463 were studied. Both surfactants impeded the decay in cell concentrations at the beginning of the fermentation and enhanced the cell growth thereafter. They also increased the degradation efficiencies of 500 mg/L phenol from 86.9% in control to above 99.0% for all test concentrations within 30 h. The monoRL could also be degraded by the C. tropicalis. These results indicate that the surfactants could diminish the toxicity of phenol to the yeast, increase cell growth and improve phenol removal. The monoRL is better than Tween 80 because of biodegradability.     

Biosurfactants,an help in the biodegradation of hexadecane? The case of <Emphasis Type="Italic">Rhodococcus</Emphasis> and <Emphasis Type="Italic">Pseudomonas</Emphasis> strains

The roles of the extracellular biosurfactants produced by two bacterial strains, Pseudomonas aeruginosa GL1 and Rhodococcus equi Ou2, in hexadecane uptake and biodegradation were compared. For this purpose, cell hydrophobicity and production of glycolipidic biosurfactants were evaluated during bacterial growth on hexadecane, as well the effects of these biosurfactants on culture supernatants properties i.e., surface and interfacial tensions, and emulsification and pseudosolubilization capacities. The results showed that the role of biosurfactants was different in these two strains and was directly related to the hydrophobicity of the bacterial cells concerned. Extracellular biosurfactants produced by strain R. equi Ou2 had only a minor role in hexadecane degradation. Direct interfacial accession appeared to be the main mechanism for hexadecane uptake by the hydrophobic cells of strain R. equi Ou2. On the contrary, the biosurfactants produced by P. aeruginosa GL1 were required for growth on hexadecane, and their pseudosolubilization capacity rather than their emulsification capacity was involved in substrate degradation, allowing uptake from hexadecane micelles by the hydrophilic cells of this bacterium. The roles of biosurfactants thus differ widely among bacteria degrading hydrophobic compounds. J.-P. Vandecasteele—in retirement     

Anaerobic biodegradation of phenol by <Emphasis Type="Italic">Candida albicans</Emphasis> PDY-07 in the presence of 4-chlorophenol

Biodegradation of phenol and 4-chlorophenol (4-cp) using pure culture of Candida albicans PDY-07 under anaerobic condition was studied. The results showed that the strain could completely degrade up to 1,800 mg/l phenol within 68 h. The capacity of the strain to degrade phenol was higher than that to degrade 4-cp. In the dual-substrate system, 4-cp intensely inhibited phenol biodegradation. Comparatively, low-concentration phenol from 25 to 150 mg/l supplied a carbon and energy source for Candida albicans PDY-07 in the early phase of biodegradation and accelerated the assimilation of 4-cp, which resulted in that 50 mg/l 4-cp was degraded within less time than that without phenol. While the biodegradation of 50 mg/l 4-cp was inhibited in the presence of 200 mg/l phenol. In addition, the intrinsic kinetics of cell growth and substrate degradation were investigated with phenol and 4-cp as single and dual substrates in batch cultures. The results demonstrated that the models adequately described the dynamic behaviors of biodegradation by Candida albicans PDY-07.     

Assessing the correlation between anaerobic toluene degradation activity and <Emphasis Type="Italic">bssA</Emphasis> concentrations in hydrocarbon-contaminated aquifer material

The assessment of biodegradation activity in contaminated aquifers is critical to demonstrate the performance of bioremediation and natural attenuation and to parameterize models of contaminant plume dynamics. Real time quantitative PCR (qPCR) was used to target the catabolic bssA gene (coding for benzylsuccinate synthase) and a 16S rDNA phylogenetic gene (for total Bacteria) as potential biomarkers to infer on anaerobic toluene degradation rates. A significant correlation (P = 0.0003) was found over a wide range of initial toluene concentrations (1–100 mg/l) between toluene degradation rates and bssA concentrations in anaerobic microcosms prepared with aquifer material from a hydrocarbon contaminated site. In contrast, the correlation between toluene degradation activity and total Bacteria concentrations was not significant (P = 0.1125). This suggests that qPCR targeting of functional genes might offer a simple approach to estimate in situ biodegradation activity, which would enhance site investigation and modeling of natural attenuation at hydrocarbon-contaminated sites.     

Alteration in cell surface properties of <Emphasis Type="Italic">Burkholderia</Emphasis> 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 Rhamnolipid (Biosurfactant) Structure on Solubilization and Biodegradation of n-Alkanes

A study to quantify the effect of rhamnolipid biosurfactant structure on the degradation of alkanes by a variety of Pseudomonas isolates was conducted. Two dirhamnolipids were studied, a methyl ester form (dR-Me) and an acid form (dR-A). These rhamnolipids have different properties with respect to interfacial tension, solubility, and charge. For example, the interfacial tension between hexadecane and water was decreased to <0.1 dyne/cm by the dR-Me but was only decreased to 5 dyne/cm by the dR-A. Solubilization and biodegradation of two alkanes in different physical states, liquid and solid, were determined at dirhamnolipid concentrations ranging from 0.01 to 0.1 mM (7 to 70 mg/liter). The dR-Me markedly enhanced hexadecane (liquid) and octadecane (solid) degradation by seven different Pseudomonas strains. For an eighth strain tested, which exhibited extremely high cell surface hydrophobicity, hexadecane degradation was enhanced but octadecane degradation was inhibited. The dR-A also enhanced hexadecane degradation by all degraders but did so more modestly than the dR-Me. For octadecane, the dR-A only enhanced degradation by strains with low cell surface hydrophobicity.     

Effect of rhamnolipid on biodegradation of hydrocarbons in non-aqueous-phase liquid (NAPL)

Aliphatic and aromatic hydrocarbons are environmental pollutants of serious concern. Their bioavailability is the major limiting factor that makes the bioremediation process slow. Therefore, the present study focuses on biodegradation of non-aqueous-phase liquids (NAPL) by a halophilic consortium (Pseudomonas aeruginosa and Escherichia fergusonii) in presence of rhamnolipid as well as a rhamnolipid-producing Pseudomonas aeruginosa AMB AS7. The study was performed in microcosms, and the residual hydrocarbons after degradation were estimated by gas chromatography. It was found that the degradation of hydrocarbons in NAPL was more in presence of rhamnolipid in comparison with their biotic controls. However, among NAPL, the degradation of phenanthrene (37.5%) and octadecane (47.8%) was found to be more by co-culture of halophilic consortium and rhamnolipid-producing P. aeruginosa AMB AS7. Denaturing gradient gel electrophoresis was performed to determine the viability of different bacterial strains (halophilic and rhamnolipid-producing bacterial strain). Besides, the results also revealed that during NAPL degradation, the cell surface hydrophobicity (CSH) of halophilic consortium increased from 9.12% to 69.55% when added with 100 mg/L of rhamnolipid, whereas CSH of rhamnolipid-producing P. aeruginosa AMB AS7 was constant at 31.9%, even though it produced about 271.8 mg/L of rhamnolipid.     

Relationships of respiratory quotient to microbial biomass and hydrocarbon contaminant degradation during soil bioremediation

This work focused on monitoring respiratory quotient, RQ (defined as a ratio of CO₂ production to O₂ uptake rates), microbial growth and residual hydrocarbon concentration during bioremediation experiments performed on laboratory soil microcosms. The aim of the study was to determine if the time course biodegradation profile of the contaminant can be related to the RQ evolution and to investigate the effect of the water content on RQ measurements. A natural soil was artificially contaminated with hexadecane and adjusted with inorganic nutrients to stimulate biodegradation. Microbial growth, CO₂ production, O₂ uptake and residual hexadecane were periodically monitored at different soil water contents ranging from 0.15 to 0.35 g water g⁻¹ of dry soil. Results showed that microbial activity and contaminant degradation were strongly dependent on soil water content. Maximal growth and hexadecane depletion were obtained at a water content of 0.20 g water g⁻¹ of dry soil, which corresponded to 46.6% of the water holding capacity. Hexadecane degradation was considerably reduced with increasing soil water content. RQ values fluctuated as a function of the hexadecane biodegradation phases. The lowest RQs corresponded to the highest hexadecane depletion and microbial growth. The water content variation did not significantly affect the shape of the RQ evolution curves as a function of time. It only modified the magnitude of RQ values. This study indicates that additional biological and chemical analyses are needed to support RQ data when monitoring contaminant degradation to have an accurate understanding of all the biotic processes, which may occur simultaneously.     

Degradation of polycyclic aromatic hydrocarbons and long chain alkanes at 6070 °C by Thermus and Bacillus spp

Although polycyclic aromatic hydrocarbons (PAH) and alkanesare biodegradable at ambient temperature, in some cases low bioavailabilities are thereason for slow biodegradation. Considerably higher mass transfer rates and PAH solubilities and hence bioavailabilities can be obtained at higher temperatures. Mixed and pure cultures of aerobic, extreme thermophilic microorganisms (Bacillus spp., Thermus sp.) were used to degrade PAH compounds and PAH/alkane mixtures at 65 °C. The microorganismsused grew on hydrocarbons as sole carbon and energy source. Optimal growthtemperatures were in the range of 60–70 °C at pH values of 6–7. The conversion of PAH with 3–5 rings (acenaphthene, fluoranthene, pyrene, benzo[e]pyrene) was demonstrated. Efficient PAH biodegradation required a second, degradable liquid phase. Thermus brockii Hamburg metabolized up to 40 mg (l h)^-1 pyrene and 1000 mg(1 h)^-1 hexadecane at 70 °C. Specific growth rates of 0.43 h^-1 were measured for this strain with hexadecane/pyrene mixtures as the sole carbon and energy source in a 2-liter stirred bioreactor. About 0.7 g cell dry weight were formed from 1 g hydrocarbon. The experiments demonstrate the feasibility and efficiency of extreme thermophilic PAH and alkane biodegradation.     

Isolation of Brazilian marine fungi capable of growing on DDD pesticide

The fungi Aspergillus sydowii Ce15, Aspergillus sydowii Ce19, Aspergillus sydowii Gc12, Bionectria sp. Ce5, Penicillium miczynskii Gc5, Penicillium raistrickii Ce16 and Trichoderma sp. Gc1, isolated from marine sponges Geodia corticostylifera and Chelonaplysylla erecta, were evaluated for their ability to grow in the presence of DDD pesticide. Increasing concentrations of DDD pesticide, i.e., 5.0 mg (1.56 × 10⁻¹² mmol), 10.0 mg (3.12 × 10⁻² mmol) and 15.0 mg (4.68 × 10⁻² mmol) in solid and liquid culture media were tested. The fungi Trichoderma sp. Gc1 and Penicillium miczynskii Gc5 were able to grow in the presence of up to 15.0 mg of DDD, suggesting their potential for biodegradation. A 100% degradation of DDD was attained in liquid culture medium when Trichoderma sp. Gc1 was previously cultivated for 5 days and supplemented with 5.0 mg of DDD in the presence of hydrogen peroxide. However, the quantitative analysis showed that DDD was accumulated on mycelium and biodegradation level reached a maximum value of 58% after 14 days.     

Partition of hexadecane to the cell surface of Candida tropicalis: Mechanism for the transport of water-insoluble substrates

The partition of hexadecane to the cell surface of Candida tropicalis was measured by incubating heat-inactivated cells with hexadecane-1-¹⁴C on a gyratory shaker. The free hexadecane was separated by centrifuging the cells through a 15% sucrose solution, and the partitioned hexadecane was quantified by scintillation spectrometry of the samples from the resulting cell sediment. Heat-inactivated cells did not take up hexadecane as determined by a membrane filtration technique involving organic solvent washing. The partitioning was a time-dependent process. The velocity increased by increasing the shake rate of te shaker. At 360 rpm and with baffled flasks, saturation of the cell surface with hexadecane was obtained after a 20 min incubation period. The amount of hexadecane partitioned depended on the initial hexadecane-to-cell concentration ratio. At a ratio of 5 μmol/mg cell protein the highest amount of hexadecane partitioned was measured at 2100 μmol/mg cell protein. At ratios higher than 6 μmol/mg cell protein the cells were no longer sedimentable by centrifugation. The partition of hexadecane to the cell surface was affected by removing the surface layer of the cell wall by Pronase treatment and by using detergents in the partition assay. Pronase treatment lowered the amount of hexadecane partitioned as a consequence of the removal of the lipophilic layer of the cell surface. Detergents influence the partition coefficient and also lowered the amount of hexadecane partitioning to the cell surface. At a low shaking intensity (280 rpm, unbaffled flasks), after Pronase treatment, and in the presence of detergents he uptake of hexadecane by the cells was limited by the partitioning.     

Biodegradation of phenol and <Emphasis Type="Italic">m</Emphasis>-cresol by <Emphasis Type="Italic">Candida albicans</Emphasis> PDY-07 under anaerobic condition

Strain Candida albicans PDY-07 was used to study the anaerobic biodegradation of phenol and m-cresol as single and dual substrates in batch cultures. The strain had a higher potential to degrade phenol than m-cresol. The cell growth kinetics of batch cultures with various initial m-cresol concentrations was investigated, and the Haldane kinetic model adequately described the dynamic behavior of cell growth on m-cresol. When cells grew on the mixture of phenol and m-cresol, substrate interactions were observed. Phenol inhibited the utilization of m-cresol; on the other hand, m-cresol also inhibited the degradation of phenol. However, the presence of low-concentration phenol enhanced m-cresol biodegradation; 100 mg/l m-cresol could be completely degraded within a shorter period of time than m-cresol alone in the presence of 150–300 mg/l phenol. The maximum m-cresol biodegradation rate was obtained at the existence of 200 mg/l phenol. Phenol was preferably utilized by the strain as a carbon and energy source. In addition, a sum kinetics model was used to describe the cell growth behavior in binary mixture of phenol and m-cresol, and the interaction parameters were determined. The model adequately predicted the growth kinetics and the interaction between the substrates.     

Hydrolyzed polyacrylamide biotransformation in an up-flow anaerobic sludge blanket reactor system: key enzymes,functional microorganisms,and biodegradation mechanisms

Hydrolyzed polyacrylamide (HPAM) biotransformation in an up-flow anaerobic sludge blanket reactor including biodegradation performances, biodegradation mechanisms, key enzymes, and functional microorganisms was explored. Response surface methodology was applied to further improve HPAM degradation. The predicted degradation ratios of HPAM and COD_Cr were 46.2% and 83.4% under the optimal conditions. HPAM biodegradation ratio and total organic carbon removal ratio reached 40.5% and 38.9%. Total nitrogen concentration was dramatically decreased with the increasing fermentation time during the fermentation, while low ammonia nitrogen (NH₄⁺–N) and nitrite nitrogen (NO₂⁻–N) were generated. NH₄⁺–N and NO₂⁻–N increased slightly on the whole. Enzyme activity change was correlated with HPAM biodegradation. Dehydrogenase activity had a decline of 21.3–41.0%, and the minimum value occurred at 300 mg/L of HPAM. Urease activity was varied from 28.7 to 78.7% and the maximal inhibition ratio occurred at 200 mg/L of HPAM. Mechanisms for the biodegradation of HPAM were also explored by FT-IR, HPLC, and SEM. The results indicated that long-chain HPAM was broken into micromolecule compounds and the amide groups of HPAM were transformed into carboxyl groups. Based on the sequencing results on an Illumina MiSeq platform, Proteobacterias, Bacteroidetes, and Chloroflexi were turned out to be the critical microorganisms involved in HPAM degradation. This work lays a basis for HPAM-containing wastewater treatment and offers a support for water saving and emission reduction. It is of great significance to the sustainable development of oilfield.

     

Relation between Candida maltosa Hydrophobicity and Hydrocarbon Biodegradation

Summary The growth of Candida maltosa on hydrocarbons (dodecane and hexadecane) was influenced by adding various natural and synthetic surfactants. Microbial adhesion to the hydrocarbon was used to measure the surface cell hydrophobicity of the yeast, which in the presence of a synthetic surfactant correlated with the degree of hydrocarbon biodegradation. Non-ionic surfactants caused the highest degree of hydrocarbon biodegradation corresponding the lowest hydrophobicity. A different correlation was observed with natural surfactants, of which saponin was the most effective for hydrocarbon biodegradation, though the concentration of this surfactant had no influence on surface cell hydrophobicity.     

Isolation and complete genome sequence of Halorientalis hydrocarbonoclasticus sp. nov., a hydrocarbon-degrading haloarchaeon

Bioremediation in hypersaline environments is particularly challenging since the microbes that tolerate such harsh environments and degrade pollutants are quite scarce. Haloarchaea, however, due to their inherent ability to grow at high salt concentrations, hold great promise for remediating the contaminated hypersaline sites. This study aimed to isolate and characterize novel haloarchaeal strains with potentials in hydrocarbon degradation. A haloarchaeal strain IM1011 was isolated from Changlu Tanggu saltern near Da Gang Oilfield in Tianjin (China) by enrichment culture in hypersaline medium containing hexadecane. It could degrade 57 ± 5.2% hexadecane (5 g/L) in the presence of 3.6 M NaCl at 37 °C within 24 days. To get further insights into the mechanisms of petroleum hydrocarbon degradation in haloarchaea, complete genome (3,778,989 bp) of IM1011 was sequenced. Phylogenetic analysis of 16S rRNA gene, RNA polymerase beta-subunit (rpoB’) gene and of the complete genome suggested IM1011 to be a new species in Halorientalis genus, and the name Halorientalis hydrocarbonoclasticus sp. nov., is proposed. Notably, with insights from the IM1011 genome sequence, the involvement of diverse alkane hydroxylase enzymes and an intact β-oxidation pathway in hexadecane biodegradation was predicted. This is the first hexadecane-degrading strain from Halorientalis genus, of which the genome sequence information would be helpful for further dissecting the hydrocarbon degradation by haloarchaea and for their application in bioremediation of oil-polluted hypersaline environments.

     

Surfactant aided biodegradation of pyrene using immobilized cells of Mycobacterium frederiksbergense

Low aqueous phase solubility is the major limiting factor in successful biodegradation of pyrene and other polycyclic aromatic hydrocarbons (PAH), which can, however, be overcome by using a suitable surfactant. Biodegradation of pyrene by immobilized cells of Mycobacterium frederiksbergense in presence of non-ionic surfactant Tween 80 was evaluated. For cell immobilization, beads were prepared using calcium alginate as the immobilizing material based on immobilized cell viability and mechanical stability of the beads. Complete degradation of pyrene was achieved employing the immobilized cells in batch shake flask experiments for all four different initial concentrations of the PAH at 100 mg l⁻¹, 200 mg l⁻¹, 400 mg l⁻¹ and 1000 mg l⁻¹. The experimental results of biodegradation of pyrene at very high initial concentration of 1000 mg l⁻¹ using the cell immobilized beads was further investigated in a 3 l fermentor operated at controlled conditions of 150 rpm, 28 °C, pH 7 and 1.5 l min⁻¹ aeration. The results confirmed complete degradation of the PAH with a very higher degradation rate of 250 mg l⁻¹ d⁻¹, which is so far the highest value reported for pyrene biodegradation.     

Hydrophobicity of bacteria Zymomonas mobilis under varied environmental conditions

Changes in the cell surface hydrophobicity (CSH) of bacteria Zymomonas mobilis 113S were examined in response to varied environmental conditions (temperature and phase of growth, concentration or type of carbon source, the presence of amphiphilic compounds). The values of CSH were elevated with a decreased growth rate over the time of cultivation up to 20–22% at the stationary phase. CSH values increased proportionally with the growth of cultivation temperature and concentration of carbon source (glucose or sucrose) or amphiphilic compound (aliphatic alcohols, Tween80) in the medium. Replacement of sucrose by glucose and the presence of Tween20 in the growth medium resulted in reduced values of CSH. An inverse relationship was detected between the number of attached cells to the hydrophilic glass surfaces and the CSH values of Z. mobilis whereas direct linear relationship was observed for hydrophobic surfaces. Permeation rates of the fluorescent probe (NPN) into the cells were directly proportional to the concentration of extracellular protein in the medium and to the values of CSH indicating the impaired barrier function for more hydrophobic cells. The multiple correlation between the CSH values and absorption indices of FT-IR spectra at the fingerprint region (866–1088 cm⁻¹) suggests the possible contribution of carbohydrates and/or lipopolysaccharides in observed changes of Z. mobilis hydrophobicity.     

Identification and Kinetic Characteristics of an Indigenous Diesel-degrading Gordonia alkanivorans Strain

Summary An indigenous strain Gordonia alkanivorans CC-JG39 was isolated from oil-contaminated sludge of a local gas station located in central Taiwan. The bacterial isolate was able to grow on diesel-containing Bushnell–Haas medium and also tolerate various chemical additives frequently used in petroleum products (e.g. BETX, methyl-tert-butyl ether, and naphthalene). Kinetics of diesel-limited cell growth and biodegradation of diesel followed a Monod-type model. The kinetic constants for cell growth (μ_max and K_S,G) were 0.158 h⁻¹ and 3196 mg/l, respectively, while those for biodegradation of diesel (v_{max, diesel} and K_S,D) were 3.59 mg/h/mg cell and 2874 mg/l, respectively. G. alkanivorans CC-JG39 produced extracellular surface-active material, leading to a low surface tension of nearly 33 mN/m. The CC-JG39 strain also possessed the ability to float towards the oil/water interface. These features might play some roles in enhancing the mass transfer efficiency between oil substrate and the bacterial cells. Therefore, G. alkanivorans CC-JG39 may have potential applications in bioremediation of oil pollution sites.     

Cell hydrophobicity of <Emphasis Type="Italic">Pseudomonas</Emphasis> spp. and <Emphasis Type="Italic">Bacillus</Emphasis> spp. bacteria and hydrocarbon biodegradation in the presence of Quillaya saponin

Biodegradation and hydrophobicity of Pseudomonas spp. and Bacillus spp. strains were tested at different concentrations of the biosurfactant Quillaya saponin. A model mixture of hydrocarbon (dodecane and hexadecane) was used for estimating the influence of surfactants on biodegradation. The bacterial adhesion to hydrocarbon method for determination of bacterial cell surface hydrophobicity was exploited. Among the tested bacterial strains the higher hydrophobicity was noticed for Pseudomonas aeruginosa TK. The hydrophobicity of this strain was 84%. The highest hydrocarbon biodegradation was observed for P. aeruginosa TK (49%) and Bacillus subtilis (35%) strains after 7 days of experiments. Generally the addition of Quillaya saponin increased hydrocarbon biodegradation remarkably. The optimal concentration proved to be 80 mg l⁻¹. The degree of hydrocarbon biodegradation was 75% for P. aeruginosa TK after the addition of saponin. However the most significant increase in biodegradation after addition of Quillaya saponin was in the case of P. aeruginosa 25 and Pseudomonas putida (the increase of biodegradation from 21 to 52% and from 31 to 66%, respectively). It is worth mentioning that decrease of hydrophobicity is correlated with the best biodegradation by P. aeruginosa strain. For the remaining strains, no significant hydrophobicity changes in relation to the system without surfactant were noticed.