Biodegradation of volatile organic compounds by five fungal species

Three strategy rules of filamentous fungi in hydrocarbon remediation: an overview

Remediation of hydrocarbon contaminations requires much attention nowadays since it causes detrimental effects on land and even worse impacts on aquatic environments. Tools of bioremediation especially filamentous fungi permissible for cleaning up as much as conceivable, at least they turn into non-toxic residues with less consumed periods. Inorganic chemicals, CO2, H2O, and cell biomass are produced as a result of the breakdown and mineralization of petroleum hydrocarbon pollutants. This paper presents a detailed overview of three strategic rules of filamentous fungi in remediating the various aliphatic, and aromatic hydrocarbon compounds: utilizing carbons from hydrocarbons as sole energy, Co-metabolism manners (Enzymatic and Non-enzymatic theories), and Biosorption approaches. Upliftment in the degradation rate of complex hydrocarbon by the Filamentous Fungi in consortia scenario we can say, "Fungal Talk", which includes a variety of cellular mechanisms, including biosurfactant production, biomineralization, and precipitation, etc., This review not only displays its efficiency but showcases the field applications - cost-effective, reliable, eco-friendly, easy to culture as biomass, applicable in both land and any water bodies in operational environment cleanups. Nevertheless, the potentiality of fungi-human interaction has not been fully understood, henceforth further studies are highly endorsed with spore pathogenicity of the fungal species capable of high remediation rate, and the gene knockout study, if the specific peptides cause toxicity to any living matters via Genomics and Proteomics approaches, before application of any in situ or ex situ environments.

A novel integrated industrial-scale biological reactor for odor control in a sewage sludge composting facility: Performance, pollutant transformation, and bioaerosol emission mechanism

In order to remove multiple pollutants in the sewage sludge (SS) composting facility, a novel integrated industrial-scale biological reactor based on biological trickling filtration and fungal biological filtration (BTF-FBF) was developed. This study examined bioaerosol emission, odour removal, pollutant transformation mechanism, and project investment. At an inlet flow rate of 7200 m³/h, the average removal efficiencies of hydrogen sulfide (H₂S), ammonia (NH₃), and volatile organic compounds (VOCs) during the steady stage were 97.2 %, 98.9 %, and 92.2 %. The BTF-FBF separates microbial phases (bacteria and fungi) of different modules. BTF removed most hydrophilic compounds, while FBF removed hydrophobic ones. Moreover, the reactor could effectively remove pathogens or opportunistic pathogens bioaerosols, such as Escherichia coli (61.9%), Salmonella sp. (85%), and Aspergillus fumigatus (82.1%). The pollutant transformation mechanism of BTF-FBF was proposed. BTF-FBF annualized costs were 324,783 CNY/year at 15 years. In conclusion, BTF-FBF provides new insights into composting facility bioaerosol, odour, and pathogen emission control.

Removal of a complex VOC mixture by potted plants-effects on soil microorganisms

Microorganisms in the soil of potted plants are important for removal of volatile organic compounds (VOCs) from indoor air, but little is known about the subject. The aim of this study was therefore to obtain a better understanding of the effect of VOCs on the microbial community in potted plants. Hedera helix was exposed to gasoline vapors under dynamic chamber conditions for 21 days and three main parameters were investigated. These were (1) removal of the target compounds heptane, 3-methylhexane, benzene, toluene, ethylbenzene, m,p-xylene, and naphthalene from the gasoline mixture; (2) toluene mineralization; and (3) bacterial abundance and bacterial community structure. H. helix was able to reduce the concentration of the target compounds in the continuously emitted gasoline by 25-32%, except for naphthalene, which was too low in concentration. The soil microcosm of gasoline exposed plants had for an initial 66 h increased toluene mineralization rate compared to the soil microcosm in the soil of plants exposed to clean air. Bacterial abundance was decreased in response to gasoline exposure while bacterial community structure was changed. The change in bacterial community structure was, however, different between the two experiments indicating that several taxonomic units can degrade gasoline components. Especially the genera Rhodanobacter and Pseudonorcardia significantly increased in abundance in response to gasoline vapors. Bauldia, Devosia, and Bradyrhizobium, on the other hand, decreased.

Acidophilic microorganisms in remediation of contaminants present in extremely acidic conditions

Acidophiles are a group of microorganisms that thrive in acidic environments where pH level is far below the neutral value 7.0. They belong to a larger family called extremophiles, which is a group that thrives in various extreme environmental conditions which are normally inhospitable to other organisms. Several human activities such as mining, construction and other industrial processes release highly acidic effluents and wastes into the environment. Those acidic wastes and wastewaters contain different types of pollutants such as heavy metals, radioactive, and organic, whose have adverse effects on human being as well as on other living organisms. To protect the whole ecosystem, those pollutants containing effluents or wastes must be clean properly before releasing into environment. Physicochemical cleanup processes under extremely acidic conditions are not always successful due to high cost and release of toxic byproducts. While in case of biological methods, except acidophiles, no other microorganisms cannot survive in highly acidic conditions. Therefore, acidophiles can be a good choice for remediation of different types of contaminants present in acidic conditions. In this review article, various roles of acidophilic microorganisms responsible for removing heavy metals and radioactive pollutants from acidic environments were discussed. Bioremediation of various acidic organic pollutants by using acidophiles was also studied. Overall, this review could be helpful to extend our knowledge as well as to do further relevant novel studies in the field of acidic pollutants remediation by applying acidophilic microorganisms.

Phenotypic Characterization and Comparative Genomics of the Melanin-Producing Yeast Exophiala lecanii-corni Reveals a Distinct Stress Tolerance Profile and Reduced Ribosomal Genetic Content

The black yeast Exophiala lecanii-corni of the order Chaetothyriales is notable for its ability to produce abundant quantities of DHN-melanin. While many other Exophiala species are frequent causal agents of human infection, E. lecanii-corni CBS 102400 lacks the thermotolerance requirements that enable pathogenicity, making it appealing for use in targeted functional studies and biotechnological applications. Here, we report the stress tolerance characteristics of E. lecanii-corni, with an emphasis on the influence of melanin on its resistance to various forms of stress. We find that E. lecanii-corni has a distinct stress tolerance profile that includes variation in resistance to temperature, osmotic, and oxidative stress relative to the extremophilic and pathogenic black yeast Exophiala dermatitidis. Notably, the presence of melanin substantially impacts stress resistance in E. lecanii-corni, while this was not found to be the case in E. dermatitidis. The cellular context, therefore, influences the role of melanin in stress protection. In addition, we present a detailed analysis of the E. lecanii-corni genome, revealing key differences in functional genetic content relative to other ascomycetous species, including a significant decrease in abundance of genes encoding ribosomal proteins. In all, this study provides insight into how genetics and physiology may underlie stress tolerance and enhances understanding of the genetic diversity of black yeasts.

Biological-based methods for the removal of volatile organic compounds (VOCs) and heavy metals

The current scenario of increased population and industrial advancement leads to the spoliation of freshwater and tapper of the quality of water. These results decrease in freshwater bodies near all of the areas. Besides, organic and inorganic compounds discharged from different sources into the available natural water bodies are the cause of pollution. The occurrence of heavy metals in water and volatile organic compounds (VOCs) in the air is responsible for a vast range of negative impacts on the atmosphere and human health. Nonetheless, high uses of heavy metals for human purposes may alter the biochemical and geochemical equilibrium. The major air contaminants which are released into the surroundings known as VOCs are produced through different kinds of sources, such as petrochemical and pharmaceutical industries. VOCs are known to cause various health hazards. VOCs are a pivotal group of chemicals that evaporate readily at room temperature. To get over this problem, biofiltration technology has been evolved for the treatment of heavy metals using biological entities such as plants, algae, fungi, and bacteria. Biofiltration technology is a beneficial and sustainable method for the elimination of toxic pollutants from the aquatic environment. Various types of biological technologies ranging from biotrickling filters to biofilters have been developed and they are cost-effective, simple to fabricate, and easy to perform. A significant advantage of this process is the pollutant that is transformed into biodegradable trashes which can decompose within an average time period, thus yielding no secondary pollutants. The aim of this article is to scrutinize the role of biofiltration in the removal of heavy metals in wastewater and VOCs and also to analyze the recent bioremediation technologies and methods.

Effect of surfactants at natural and acidic pH on microbial activity and biodegradation of mixture of benzene and o-xylene

The aim of this work was to explore the effect of lowering pH and application of surfactants (Brij 35, Tween 20 and Saponin) in increasing bioavailability and biodegradability of benzene and o-xylene (BX) as two hydrophobic VOCs in a liquid mixture. All experiments were conducted at neutral and acidic pH to evaluate the effect of population change from bacteria to fungi on the BX biodegradation. The experiments demonstrated that acclimating wastewater inoculum at pH 4 increased the fungal to bacterial ratio. An increase of 11% for benzene and 22% for o-xylene was observed at pH 4 unamended-culture as compared to pH 7. Brij 35 was chosen as the optimum surfactant which was favorable for enhancing the bioavailability of BX at pH 4. Fitting the experimental data to pseudo first-order biodegradation kinetics model showed the BX were biodegraded faster in the presence of optimum surfactant at pH 7 than pH 4.

Evaluation of Immobilization of Selected Peat-Isolated Yeast Strains of the Species Candida albicans and Candida subhashii on the Surface of Artificial Support Materials Used for Biotrickling Filtration

The paper describes the process of n-butanol abatement by unicellular fungi, able to deplete n-butanol content in gas, by using n-butanol as source of carbon. Isolated and identified fungi species Candida albicans and Candida subhashii were subjected to a viability process via assimilation of carbon from hydrophilic and hydrophobic compounds. The isolates, which exhibited the ability to assimilate carbon, were immobilized on four different types of artificial support materials used for biotrickling filtration. Application of optical microscopy, flow cytometry and the tests employing propidium iodide and annexin V revealed viability of the fungi isolated on support materials’ surfaces at the average level of 95%. The proposed method of immobilization and its evaluation appeared to be effective, cheap and fast. Based on performed comparative analyses, it was shown that polyurethane foam and Bialecki rings (25 × 25) could be attractive support materials in biotrickling filtration.

Contribution of bacterial biodiversity on the operational performance of a styrene biotrickling filter

Long-term operational stability of biotrickling filters (BTFs) degrading volatile organic compounds (VOCs) is dependent on both physicochemical as well as biological properties. Effects of increasingly stressful levels of air pollutants on the microbial structure of biofilms within BTFs are not well understood, especially for VOCs such as styrene. To investigate the relationship between biofilm biodiversity and operational stability, the temporal dynamics of a biofilm from a biotrickling filter subjected to stepwise increasing levels of air polluted with styrene was investigated using 16S rDNA pyrosequencing and PCR-denaturing gradient gel electrophoresis (PCR-DGGE). As styrene contaminant loads were increased, microbial community composition was distinctly altered and diversity was initially reduced in early stages but gradually stabilized and increased diversity in later stages, suggesting a recovery and acclimatization period within the microbial community during incremental exposure of the pollutant. Although temporary reductions in known styrene-degrading bacterial genera (Pseudomonas and Rhodococcus) occurred under increased styrene loads, stable BTF performance was maintained due to functional redundancy. New candidate genera for styrene degradation (Azoarcus, Dokdonella) were identified in conditions of high styrene loads, and may have supported the observed stable BTF performance throughout the experiment. Styrene inlet load was found to be important modulator of community composition and may have been partly responsible for the observed temporary reductions of Pseudomonas. Notable differences between dominant genera detected via pyrosequencing compared to species detected by PCR-DGGE suggests that simultaneous implementation of both techniques is valuable for fully characterizing dynamic microbial communities.

A combination of absorption and enzymatic biodegradation: phenol elimination from aqueous and organic phase

Peroxidase from Brassica rapa was immobilized as cross-linked enzyme aggregates (CLEAs) and used to treat air containing phenol as a model molecule of volatile organic compounds (VOCs). Prior to an enzymatic treatment, phenol was absorbed into an aqueous or organic phase (silicone oil) to reach concentrations ranging from 20 to 160 mg/L. The process was carried out by introducing a desired weighing of BRP-CLEAs into preparations and reaction was started by injecting H₂O₂ solution to the medium. Optimization of the reaction conditions in the organic solvent revealed an optimal contact time of 60 min, 60 mg/L of phenol concentration and 3 mM H₂O₂, leading to a maximum removal yield of 70% for 3.4 UI/mL of BRP-CLEAs. These results were compared to those obtained in an aqueous medium that showed 90% of degradation yield after 40 min in the following conditions, 90 mg/L of initial phenol amount, 2 mM of H₂O₂ and 2.5 UI/mL of BRP-CLEAs. Parameters of the Michaelis-Menten model, Km and Vmax, were also determined for the reaction in both phases. Phenol removal by BRP-CLEAs in silicone oil succeeded with 70% of conversion yield. It is promising regarding the transposition of such enzymatic process to hydrophobic VOCs.

Genomic and transcriptomic analysis of the toluene degrading black yeast Cladophialophora immunda

Cladophialophora immunda is an ascomycotal species belonging to the group of the black yeasts. These fungi have a thick and melanized cell wall and other physiological adaptations that allows them to cope with several extreme physical and chemical conditions. Member of the group can colonize some of the most extremophilic environments on Earth. Cladophialophora immunda together with a few other species of the order Chaetothyriales show a special association with hydrocarbon polluted environments. The finding that the fungus is able to completely mineralize toluene makes it an interesting candidate for bioremediation purposes. The present study is the first transcriptomic investigation of a fungus grown in presence of toluene as sole carbon and energy source. We could observe the activation of genes involved in toluene degradatation and several stress response mechanisms which allowed the fungus to survive the toluene exposure. The thorough comparative genomics analysis allowed us to identify several events of horizontal gene transfer between bacteria and Cladophialophora immunda and unveil toluene degradation steps that were previously reported in bacteria. The work presented here aims to give new insights into the ecology of Cladophialophora immunda and its adaptation strategies to hydrocarbon polluted environments.

Isolation and Characterization of Phenol-Degrading Psychrotolerant Yeasts

In this study, the potential of selected psychrotolerant yeast strains for phenol biodegradation was studied. From 39 strains isolated from soil and water samples from Rucianka peat bog, three psychrotolerant yeast strains, A011, B021, and L012, showed the ability to degrade phenol. The result shows that all three yeast strains could degrade phenol at 500 and 750 mg l-1 concentration, whereas strains A011 and L012 could degrade phenol at 1000 mg l-1 concentration. The time needed for degradation of each phenol concentration was no longer than 2 days. Strains A011, B021, and L012 were identified based on 26S rDNA and ITS sequence analysis as belonging to species Candida subhashii, Candida oregonensis, and Schizoblastosporion starkeyi-henricii, respectively.

Impact of VOC removal by activated carbon on biodegradation rates of diesel, Syntroleum and biodiesel in contaminated sand

The degradation of conventional diesel (D), synthetic diesel (Syntroleum), and pure fish biodiesel (B100) by indigenous microbes was investigated in laboratory microcosms containing contaminated sand. The fate of volatiles and the influence of volatilization on degradation rates were examined by placing activated carbon (AC) in microcosm headspaces to sorb volatiles. Three AC regimes were compared: no activated carbon (NAC), regular weekly AC change (RAC), and frequent AC change (FAC), where the frequency of activated carbon exchange declined from daily to weekly. Generally, the alternative fuels were biodegraded faster than diesel fuel. Hydrocarbon mineralization percentages for the different fuel types over 28days were between 23% (D) and 48% (B100) in the absence of activated carbon, decreased to 12% (D) - 37% (B100) with weekly AC exchange, and were further reduced to 9-22% for more frequent AC change. Sorption of volatiles to AC lowered their availability as a substrate for microbes, reducing respiration. Volatilization was negligible for the biodiesel. A mass balance for the carbon initially present as hydrocarbons in microcosms with activated carbon in the head space was on average 92% closed, with 45-70% remaining in the soil after 4weeks, 9-37% mineralized and up to 12% volatilized. Based on nutrient consumption, up to 29% of the contaminants were likely converted into biomass.

Fungal Volatiles Can Act as Carbon Sources and Semiochemicals to Mediate Interspecific Interactions Among Bark Beetle-Associated Fungal Symbionts

Mountain pine beetle (Dendroctonus ponderosae) has killed millions of hectares of pine forests in western North America. Beetle success is dependent upon a community of symbiotic fungi comprised of Grosmannia clavigera, Ophiostoma montium, and Leptographium longiclavatum. Factors regulating the dynamics of this community during pine infection are largely unknown. However, fungal volatile organic compounds (FVOCs) help shape fungal interactions in model and agricultural systems and thus may be important drivers of interactions among bark beetle-associated fungi. We investigated whether FVOCs can mediate interspecific interactions among mountain pine beetle's fungal symbionts by affecting fungal growth and reproduction. Headspace volatiles were collected and identified to determine species-specific volatile profiles. Interspecific effects of volatiles on fungal growth and conidia production were assessed by pairing physically-separated fungal cultures grown either on a carbon-poor or -rich substrate, inside a shared-headspace environment. Fungal VOC profiles differed by species and influenced the growth and/or conidia production of the other species. Further, our results showed that FVOCs can be used as carbon sources for fungi developing on carbon-poor substrates. This is the first report demonstrating that FVOCs can drive interactions among bark beetle fungal symbionts, and thus are important factors in beetle attack success.

Treatment of gaseous toluene in three biofilters inoculated with fungi/bacteria: Microbial analysis, performance and starvation response

Bacteria and fungi are often utilized for the biodegradation of organic pollutants. This study compared fungal and/or bacterial biofiltration in treating toluene under both steady and unsteady states. Fungal biofilter (F-BF) removed less toluene than both bacterial biofilters (B-BF) and fungal & bacterial biofilters (F&B-BF) (<20% vs >60% vs >90%). The mineralization ratio was also lower in F-BF-levels were 2/3 and 1/2 of those values obtained by the other biofilters. Microbial analysis showed that richer communities were present in B-BF and F&B-BF, and that the Hypocreales genus which Trichoderma viride belongs to was much better represented in F&B-BF. The F&B-BF also supported enhanced robustness after 15-day starvation episodes; 1 day later the performance recovered to 80% of the original removal level. The combination of bacteria and fungi makes biofiltration a good option for VOC treatment including better removal and performance stability versus individual biofilters (bacteria or fungi dominated).

Succession of microorganisms in a plate-type air treatment biofilter during filtration of various volatile compounds

Changes in the number and species diversity of cultivable microorganisms in a newly developed plate-type biofilter during filtration of various volatile pollutants were studied. The novelty of the investigation is the monitoring of microorganism succession in different parts of biofilter plates with original packing material consisting of birch fibre and needle-punched non-woven fabric. It was shown that the largest number of fungi and yeasts develop on the top and middle, while bacteria develop on the bottom and middle parts of plates. The number of microorganisms depends on the origin of the pollutant, the pH and temperature inside the biofilter and the moisture of the porous plates. The statistically significant correlation between the number of microorganisms and inlet concentration of acetone was estimated, while ammonia showed a negative influence on yeast distribution. Paecilomyces variotii, Rhodotorula mucilaginosa and Bacillus subtilis were the most common organisms found during filtration of all examined volatiles; however, some differences of microbial communities in different parts of the biofilter plates and filtrated volatile compounds were obtained.

Investigating bacterial populations in styrene-degrading biofilters by 16S rDNA tag pyrosequencing

Microbial biofilms are essential components in the elimination of pollutants within biofilters, yet still little is known regarding the complex relationships between microbial community structure and biodegradation function within these engineered ecosystems. To further explore this relationship, 16S rDNA tag pyrosequencing was applied to samples taken at four time points from a styrene-degrading biofilter undergoing variable operating conditions. Changes in microbial structure were observed between different stages of biofilter operation, and the level of styrene concentration was revealed to be a critical factor affecting these changes. Bacterial genera Azoarcus and Pseudomonas were among the dominant classified genera in the biofilter. Canonical correspondence analysis (CCA) and correlation analysis revealed that the genera Brevundimonas, Hydrogenophaga, and Achromobacter may play important roles in styrene degradation under increasing styrene concentrations. No significant correlations (P > 0.05) could be detected between biofilter operational/functional parameters and biodiversity measurements, although biological heterogeneity within biofilms and/or technical variability within pyrosequencing may have considerably affected these results. Percentages of selected bacterial taxonomic groups detected by fluorescence in situ hybridization (FISH) were compared to results from pyrosequencing in order to assess the effectiveness and limitations of each method for identifying each microbial taxon. Comparison of results revealed discrepancies between the two methods in the detected percentages of numerous taxonomic groups. Biases and technical limitations of both FISH and pyrosequencing, such as the binding of FISH probes to non-target microbial groups and lack of classification of sequences for defined taxonomic groups from pyrosequencing, may partially explain some differences between the two methods.

Temperature and moisture effect on spore emission in the fungal biofiltration of hydrophobic VOCs

The effect of temperature and moisture on the elimination capacity (EC), CO(2) production and spore emission by Fusarium solani was studied in biofilters packed with vermiculite and fed with n- pentane. Three temperatures (15, 25 and 35°C) were tested and the highest average EC (64 g m(-3) h(-1)) and lower emission of spores (2.0 × 10(3) CFU m(-3) air) were obtained at 25°C. The effect of moisture content of the packing material indicates that the highest EC (65 g m(-3) h(-1)) was obtained at 50 % moisture. However, lowest emission (1.3 × 10(3) CFU m(-3) air) was obtained at 80 % moisture. Furthermore, the results show that a slight decrease in spore emission was found with increasing moisture content. In all cases, the depletion of the nitrogen source in the biofilter induced the sporulation, a decay of the EC and increased spore emission.

A comparative assessment of biofiltration and activated sludge diffusion for odour abatement

The deodorization performance of a biofilter and an activated sludge diffusion (AS) system was comparatively evaluated in terms of removal efficiency (RE) and process stability at empty bed residence times (EBRT) ranging from 94 to 32s. Both bioreactors were fed with a synthetic odorous emission containing H(2)S, butanone and toluene at 23.6-43.3, 4.3-6.3 and 0.4-0.6 mg m(-3), respectively. While the outlet H(2)S concentration was always lower than 1.4 mg m(-3), the REs for butanone and toluene remained higher than 95% in both bioreactors regardless of the EBRT. The continuous supply of wastewater in the AS unit did not affect removal and appeared to be a requirement for efficient pollutant abatement. Despite the narrow carbon source spectrum treated, the AS system maintained a large bacterial diversity over time. Therefore, the results obtained confirmed the potential of AS systems as a robust and efficient biotechnology for odour treatment in WWTPs.

Photolysis of gaseous butyl acetate using built-in microwave discharge electrodeless lamps

This paper examined the photolysis of gaseous butyl acetate by built-in microwave discharge electrodeless lamps. Bromine and iodine lamps were used to investigate the effects of microwave input power, inlet concentration, gas residence time, and different filling materials on butyl acetate decomposition and energy yield. Water vapor and ammonia were utilized as additional chemicals to determine if they can improve removal efficiency. Built-in structure and external structure were also compared. When the gas flow velocity is 0.025 m/s, and the inlet concentration is 1.5 mg/m(3), the removal efficiency of butyl acetate can reach over 78%, which is the highest in this study. Additional water vapor and ammonia can hardly improve the degradation. To some extent, built-in MDELs are better than external MDELs. The results will help promote the study of microwave discharge electrodeless lamps and their effect on the degradation of gaseous pollutants. Maybe, as the research goes on, it could realize the span from laboratory scale to practical application, and will become an advanced technology for the gaseous pollutants control.

Mutual influence of soil basidiomycetes and white mustard plants on their enzymatic and catabolic activities

Liquid and volatile emanations in interactions of soil basidiomycetes with herbs affect fungal oxidoreductases and stress-related plant peroxidases (PO). In this study, gnotobiotic co-cultures between 6 non-pathogenic saprobes and 2 ectomycorrhizal basidiomycetes with the non-host plant white mustard were established on glucose-salt medium with the respective controls. Determined were oxidoreductase activities for culture fluids and plant tissues at initial fungal idiophase and degradation rates of Remazol-BBR and 5 PAHs. In culture fluids of Agaricus arvensis, A. porphyrizon, Lepista nebularis, Stropharia rugoso-annulata, and Hypholoma fasciculare (group-5), the laccase-deficient plant enabled activity increases in fungal laccase (by 2300-fold), in extracellular (fungal and?) plant-derived peroxidases (by 21-fold), and in the dissipation of phenanthrene and anthracene. Oxidative activities in roots rose by 46000-fold during adsorption of fungal laccases. Increases in the stress-related shoot-PO (by 4.1-fold) were exclusively elicited by group-5 saprobes and correlated with plant-phenolic-mediated formations of Mn(III) and increases in Remazol BBR bleaching. Agaricus bisporus and the ectomycorrhizal Hebeloma crustuliniforme and Suillus granulatus did not respond to plant emanations with elevated laccase activities but solubilized apparently root-surface PO. They failed to elicit stress-related activity increases of PO in white mustard shoot and prevented Mn(III) formation in several tissues. It is concluded that white mustard emanations promoted the catabolic performance of the plant-stress eliciting group-5 saprobes but not of A. bisporus and the ectomycorrhizal fungi with their low stress-inducing potential. The nature of the plant-released stimuli and the classes of fungus-released stress agents discussed must be determined in further studies.

Biofiltration of Air: A Review

In this paper we present a review of the existing air pollution control technologies (APCT), when used essentially for the elimination of volatile organic compounds (VOC). The biotechnologies referred to, bioscrubbers, biotrickling filters and biofilters, are also described. A more detailed review of biofiltration is proposed, presenting the most recent and latest developments achieved in the field of bioprocessing. In particular, the influence of the filter bed, the polluted air flowrates, the pollutants, the pressure drop, bed moisture content, temperature, nutrients, pH and the microorganisms are reviewed. Models of biofiltration are also presented.

Elimination of volatile organic compounds by biofiltration: a review

Volatile organic compounds (VOCs) are pollutants that are responsible for the formation of the tropospheric ozone, one of the precursors of smog. VOCs are emitted by various industries including chemical plants, pulp and paper mills, pharmaceuticals, cosmetics, electronics and agri-food industries. Some VOCs cause odor pollution while many of them are harmful to environment and human or animal health. For the removal of VOCs, biofiltration, a biological process, has proved to be reliable when properly operated. This process has therefore been widely applied in Europe and North America. The main advantages associated with the use of biofiltration are related to its set-up, maintenance, and operating costs which are usually lower than those related to other VOCs control technologies and because it is less harmful for the environment than conventional processes like incineration. In the present paper, the main parameters (type, moisture, pH, and temperature of filter bed, microbial population, nutrients concentrations, and VOCs' inlet load) to be controlled during the biofiltration are identified and described in detail. The main phenomena involved in biofiltration are also discussed. For improving the efficiency of VOC control biotechnology, new techniques are now proposed that include the use of membranes, biphasic reactors, UV photolysis, and many others.

Isolation and characterization of a nitrile hydrolysing acidotolerant black yeast-Exophiala oligosperma R1

Different nitriles were used as sole sources of nitrogen in a series of enrichments under acidic conditions to isolate acidotolerant nitriles hydrolysing microorganisms. From an enrichment in Na-citrate-phosphate buffer at pH 4 with glucose as carbon source and phenylacetonitrile as sole source of nitrogen, a black yeast (strain R1) was obtained which was identified by subsequent 18S rRNA gene sequencing as Exophiala oligosperma. The growth conditions of the organism were optimized for the production of cell material and the induction of the nitrile converting activity. Resting cell experiments demonstrated that phenylacetonitrile was converted via phenylacetic acid and 2-hydroxyphenylacetic acid. The organism could grow at pH 4 with phenylacetonitrile as sole source of carbon, nitrogen, and energy. The nitriles hydrolysing activity was also detected in cell-free extracts and indications for a nitrilase activity were found. The cell-free extracts converted, in addition to phenylacetonitrile, also different substituted phenylacetonitriles. Whole cells of E. oligosperma R1 converted phenylacetonitrile with almost the same reaction rates in the pH range from pH 1.5-pH 9.

Degradation of ethanol plant by-products by Exophiala lecanii-corni and Saccharomyces cerevisiae in batch studies

By-product emissions from ethanol production facilities have become a public health concern. Many of these by-products are classified as hazardous air pollutants by the USEPA and current treatment methods, mainly thermal-oxidation, for these compounds are costly, energy intensive, and may produce other undesirable by-products. Degradation of these by-products by the fungi Exophiala lecanii-corni and Saccharomyces cerevisiae was explored. Ethanol plant by-products, focused on in this study, included formaldehyde, acetaldehyde, ethanol, methanol, glycerol, acetic acid, and lactic acid. Initial batch studies were conducted to determine degradation rates and whether the contaminants would be toxic to the fungi. These batch studies demonstrated that E. lecanii-corni and S. cerevisiae are able to utilize all but methanol and formaldehyde as sole carbon and energy sources for growth; however, both contaminants were utilized as secondary metabolites by cultures initially fed either ethanol or acetic acid. Growth studies also were conducted using two contaminants simultaneously to determine if the presence of one contaminant inhibited the degradation of another. Growth and contaminant utilization was observed in cultures fed two contaminants simultaneously.

Quantification of homogentisate-1,2-dioxygenase expression in a fungus degrading ethylbenzene

A quantitative real time reverse transcription polymerase chain reaction (qRT-PCR) assay was utilized to quantify the expression of ElHDO in the fungus Exophiala lecanii-corni during the biodegradation of ethylbenzene and other volatile organic pollutants. The assay was applied to measure the impact of pollutant mixtures on ElHDO expression relative to that of a housekeeping gene (18S rRNA). Three compounds were tested in mixtures with ethylbenzene: methyl propyl ketone, phenylacetate and o-xylene. These chemicals repressed, induced, or had no effect on ethylbenzene degradation, respectively. The results demonstrate that the gene target expression value (T(N)) is a useful parameter for evaluating the effect of pollutant mixtures on gene expression. T(N) was found to reflect macroscopic changes in ethylbenzene utilization rates although these two parameters were not related in a linear fashion for all compounds. The assay was log-linear over 5 orders of magnitude of RNA concentration and reproducible between samples (the largest T(N) standard deviation was 20%). The comparative qRT-PCR assay used in this research represents a viable alternative to absolute quantification methods to monitor in situ fungal gene expression in natural and engineered environmental systems.

Growth of Phanerochaete chrysosporium on diesel fuel hydrocarbons at neutral pH

Generally, the white-rot fungus Phanerochaete chrysosporium performs its biodegradative activities in liquid culture while growing on easily utilized carbon sources such as malt- or potato-extract. However, less is known about the potential of this organism to grow directly on environmental pollutants without regard to special conditions. Growth of P. chrysosporium on a middle fraction (MF) of diesel fuel at neutral pH in mineral medium under non-ligninolytic conditions was explored. After 14 d, the GC-analyzable n-alkanes of 1000 mg l(-1)MF were reduced to background, with most biodegradation occurring by day 7 when quantified relative to the biodegradation of the internal fuel biodegradation marker, pristane. Investigations with n-hexadecane and unmodified diesel fuel further confirmed these biodegradation results. Biomass production was monitored and indicated that fungal biomass was more than 10 times less than positive controls (potato dextrose broth, PDB) but that biomass increased relative to negative controls. When P. chrysosporium was incubated with diesel fuel and PDB, fuel biodegradation was delayed for at least 4d and inhibited overall through 14 d. Experiments with P. chrysosporium growing on n-hexadecane in the presence of 1 mM 1-aminobenzotriazole (ABT), an inhibitor of the cytochrome P-450 enzyme system, resulted in inhibition of biomass production relative to positive controls implicating the utilization of this enzyme system in n-alkane metabolism. Finally, when P. chrysosporium was incubated in a non-aqueous phase liquid (NAPL) mixture of polycyclic aromatic hydrocarbons (PAHs) and MF, n-alkanes and phenanthrene were degraded in 2 weeks while anthracene, chrysene and benzo[a]pyrene were not.

Fungi growing on aromatic hydrocarbons: biotechnology's unexpected encounter with biohazard?

The biodegradation of aromatic hydrocarbons by fungi has traditionally been considered to be of a cometabolic nature. Recently, however, an increasing number of fungi isolated from air biofilters exposed to hydrocarbon-polluted gas streams have been shown to assimilate volatile aromatic hydrocarbons as the sole source of carbon and energy. The biosystematics, ecology, and metabolism of such fungi are reviewed here, based in part on re-evaluation of a collection of published hydrocarbon-degrading isolates obtained from authors around the world. Incorrect or outdated identifications in original publications are corrected by ribosomal DNA sequence analysis. The data show that many volatile-hydrocarbon-degrading strains are closely related to, or in some cases clearly conspecific with, the very restricted number of human-pathogenic fungal species causing severe mycoses, especially neurological infections, in immunocompetent individuals. Neurochemistry features a distinctive array of phenolic and aliphatic compounds that are related to molecules involved in the metabolism of aromatic hydrocarbons. Hence, there may be physiological connections between hydrocarbon assimilation and certain patterns of mammalian infection.

Influence of three species of arbuscular mycorrhizal fungi on the persistence of aromatic hydrocarbons in contaminated substrates

Aromatic hydrocarbons are pollutants which have mutagenic and carcinogenic properties as well as relatively high hydrosolubility. Their presence in soils makes techniques such as bioremediation an important topic for research. In this work, the effect of arbuscular mycorrhiza (AM) on the persistence of benzene, toluene, ethylbenzene and xylene (BTEX) in artificially contaminated substrates was evaluated. Leek plants were grown with three AM fungal species using a specially designed mesocosm system, in which internal air and substrate samples were analyzed by gas chromatography for BTEX content. Strong reductions in the BTEX concentration in substrates were generally observed in the presence of mycorrhizal plants. Residual BTEX content ranged between nearly total disappearance (<2%) and 40% of the original concentration, whereas there was a high persistence of hydrocarbons in the samples of substrate alone or with non-mycorrhizal plants. These results provide first evidence for an influence of AM activity in reducing pollution of substrates by aromatic hydrocarbons.

Correlation of biological activity and reactor performance in biofiltration of toluene with the fungus Paecilomyces variotii CBS115145

A biofiltration system inoculated with the mold Paecilomyces variotii CBS115145 showed a toluene elimination capacity (EC) of around 250 g/m3 of biofilter/h, which was higher than the values usually reported for bacteria. P. variotii assimilated m- and p-cresols but not the o isomer. Initial toluene hydroxylation occurred both on the methyl group and through the p-cresol pathway. These results were corroborated by detecting benzyl alcohol, benzaldehyde, and p-cresol as volatile intermediates. In liquid cultures with toluene as a substrate, the activity of toluene oxygenase (TO) was 5.6 nmol of O2/min/mg of biomass, and that of benzyl alcohol dehydrogenase was 16.2 nmol of NADH/min/mg of protein. Toluene biodegradation determined from the TO activity in the biofilter depended on the biomass distribution and the substrate concentration. The specific enzymatic activity decreased from 6.3 to 1.9 nmol of O2/min/mg of biomass along the reactor. Good agreement was found between the EC calculated from the TO activity and the EC measured on the biofilter. The results were confirmed by short-time biofiltration experiments. Average EC measured in different biofiltration experiments and EC calculated from the TO activity showed a linear relation, suggesting that in the biofilters, EC was limited by biological reaction. As the enzymatic activities of P. variotii were similar to those reported for bacteria, the high performance of the fungal biofilters can possibly be explained by the increased transfer of the hydrophobic compounds, including oxygen, from the gas phase to the mycelia, overcoming the transfer problems associated with the flat bacterial biofilms.

Biodegradation of phenol and phenol-related compounds by psychrophilic and cold-tolerant alpine yeasts

We characterized 32 cold-adapted, psychrophilic and cold-tolerant, yeast strains isolated from alpine habitats with regard to their taxonomy, growth temperature profile, and ability to degrade phenol and 18 phenol-related mono-aromatic compounds at 10 degrees C. Twenty of the strains were identified by sequencing of the ribosomal ITS region as seven species of the basidiomycota: Cryptococcus terreus (three strains), Cryptococcus terricola (one strain), Rhodosporidium lusitaniae (two strains), Rhodotorula creatinivora (10 strains), Rhodotorula ingeniosa (one strain), Mastigobasidium intermedium (one strain), and Sporobolomyces roseus (two strains). Twelve strains sharing closely related ITS sequences could not be identified to the species level; according to their ITS sequence they are included in the Microbotryomycetidae. These 12 strains were psychrophilic (no growth at temperatures above 20 degrees C); one-third of these strains did not grow above 15 degrees C. None of the 32 strains utilized any of the highly volatile mono-aromatic compounds (benzene, toluene, ethylbenzene, nitrobenzene, o-xylene, m-xylene, and p-xylene) as the sole carbon source. Non/low volatile aromatic compounds were degraded in the following order: phenol>hydroquinone>resorcinol>benzoate>catechol>salicylate>>p-cresol>m-cresol. o-Cresol, guaiacol, p-nitrophenol, or p-nitrotoluene were not utilized for growth. R. creatinivora strains degraded up to seven compounds, whereas C. terricola and S. roseus strains degraded only two compounds. The toxicity of the compounds was determined via growth inhibition in the presence of toxicants and nutrients at 10 degrees C. R. creatinivora strains were characterized by higher IC50 values than other species, S. roseus was the most sensitive species. The most toxic compounds were the xylene isomers, ethylbenzene, p-nitrophenol, and m-cresol. There was a relation between the chemical structure of the compounds and their toxicity, whereas a relation between the toxicity of the compounds and the ability of the yeasts strains to utilize these compounds for growth was only detected in some cases.

Ethanol production from hexoses, pentoses, and dilute-acid hydrolyzate by

Consumption of hexoses and pentoses and production of ethanol by Mucor indicus were investigated in both synthetic media and dilute-acid hydrolyzates. The fungus was able to grow in a poor medium containing only carbon, nitrogen, phosphate, potassium, and magnesium sources. However, the cultivation took more than a week and the ethanol yield was only 0.2 gg(-1). Enrichment of the medium by addition of trace metals, particularly zinc and yeast extract, improved the growth rate and yield, such that the cultivation was completed in less than 24 h and the ethanol and biomass yields were increased to 0.40 and 0.20 gg(-1), respectively. The fungus was able to assimilate glucose, galactose, mannose, and xylose, and produced ethanol with yields of 0.40, 0.34, 0.39, and 0.18 gg(-1), respectively. However, arabinose was poorly consumed and no formation of ethanol was detected. Glycerol was the major by-product in the cultivation on the hexoses, while formation of glycerol and xylitol were detected in the cultivation of the fungus on xylose. The fungus was able to take up the sugars present in dilute-acid hydrolyzate as well as the inhibitors, acetic acid, furfural, and hydroxymethyl furfural. M. indicus was able to grow under anaerobic conditions when glucose was the sole carbon source, but not on xylose or the hydrolyzate. The yield of ethanol in anaerobic cultivation on glucose was 0.46 g g(-1).

Identification of a homogentisate-1,2-dioxygenase gene in the fungus Exophiala lecanii-corni: analysis and implications

Exophiala lecanii-corni is a dimorphic fungus capable of degrading several volatile organic compounds (VOCs) including ethylbenzene, which has been classified as a hazardous air pollutant by the Environmental Protection Agency. In contrast to bacterial species, little is known about the mechanisms of fungal degradation of VOCs. The results described herein suggest a potential pathway for ethylbenzene degradation in E. lecanii-corni via styrene, phenylacetate and homogentisate. Consistent with this proposed pathway, a full-length homogentisate-1,2-dioxygenase gene (ElHDO) has been identified, cloned and sequenced. The nucleotide sequence of ElHDO consists of a 1,452-bp open reading frame encoding a protein with 484 amino acids. The expression of the gene product increases when grown on ethylbenzene, further suggesting that it could be involved in ethylbenzene degradation and may be responsible for the aromatic ring cleavage reaction. In addition, a 907-bp fragment isolated upstream from this gene shares 78% sequence identity at the amino acid level with the amino acid sequences of two fungal phenylacetate hydroxylase genes. This observation suggests that the genes responsible for ethylbenzene degradation may be clustered. This research constitutes the first step towards a better understanding of ethylbenzene degradation in E. lecanii-corni.

Characterization of two polyketide synthase genes in Exophiala lecanii-corni, a melanized fungus with bioremediation potential

Exophiala lecanii-corni has significant bioremediation potential because it can degrade a wide range of volatile organic compounds. In order to identify sites for the insertion of genes that might enhance this potential, a genetic analysis of E. lecanii-corni was undertaken. Two polyketide synthase genes, ElPKS1 and ElPKS2, have now been discovered by a PCR-based strategy. ElPKS1 was isolated by a marker rescue technique. The nucleotide sequence of ElPKS1 consists of a 6576-bp open reading frame encoding a protein with 2192 amino acids, which was interrupted by a 60-bp intron near the 5' end and a 54-bp intron near the 3' end. Sequence analysis, results from disruption experiments, and physiological tests showed that ElPKS1 encoded a polyketide synthase required for melanin biosynthesis. Since ElPKS1 is non-essential, it is a desirable bioengineering target site for the insertion of native and foreign genes. The successful expression of these genes could enhance the bioremediation capability of the organism. ElPKS2 was cloned by colony hybridization screening of a partial genomic library with an ElPKS2 PCR product. ElPKS2 had a 6465-bp open reading frame that encoded 2155 amino acids and had introns of 56, 67, 54, and 71 bp. Although sequence analysis of the derived protein of ElPKS2 confirmed the polyketide synthase nature of its protein product, the function of that product remains unclear.

Fungal biocatalysts in the biofiltration of VOC-polluted air

Gas-phase biofilters used for the treatment of waste gases were originally packed with compost or other natural filter beds containing indigenous microorganisms. Over the past decade much effort has been made to develop new carrier materials, more performant biocatalysts and new types of bioreactors. Elimination capacities reached nowadays are 5 to 10 times higher than those originally reported with conventional compost biofilters. With the recently developed inert filter beds, inoculation is a prerequisite for successful start-up and operation. Either non-defined mixed cultures or pure bacterial cultures have originally been used. The search for efficient fungal biocatalysts started only a few years ago, mainly for the biofiltration of waste gases containing hydrophobic compounds, such as styrene, alpha-pinene, benzene, or alkylbenzenes. In this review, recently isolated new fungal strains able to degrade alkylbenzenes and other related volatile organic pollutants are described, as well as their major characteristics and their use as biocatalysts in gas-phase biofilters for air pollution control. In biofiltration, the most extensively studied organism belongs to the genus Exophiala, although strains of Scedosporium, Paecilomyces, Cladosporium, Cladophialophora, and white-rot fungi are all potential candidates for use in biofilters. Encouraging results were obtained in most of the cases in which some of those organisms were present in gas-phase biofilters. They allow reaching high elimination capacities and are resistant to low pH values and to reduce moisture content.