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Applied Microbiology and Biotechnology (v.58, #5)
Biosynthesis and biotechnological production of statins by filamentous fungi and application of these cholesterol-lowering drugs by M. Manzoni; M. Rollini (pp. 555-564).
Hypercholesterolemia is considered an important risk factor in coronary artery disease. Thus the possibility of controlling de novo synthesis of endogenous cholesterol, which is nearly two-thirds of total body cholesterol, represents an effective way of lowering plasma cholesterol levels. Statins, fungal secondary metabolites, selectively inhibit hydroxymethyl glutaryl-coenzyme A (HMG-CoA) reductase, the first enzyme in cholesterol biosynthesis. The mechanism involved in controlling plasma cholesterol levels is the reversible inhibition of HMG-CoA reductase by statins, related to the structural similarity of the acid form of the statins to HMG-CoA, the natural substrate of the enzymatic reaction. Currently there are five statins in clinical use. Lovastatin and pravastatin (mevastatin derived) are natural statins of fungal origin, while symvastatin is a semi-synthetic lovastatin derivative. Atorvastatin and fluvastatin are fully synthetic statins, derived from mevalonate and pyridine, respectively. In addition to the principal natural statins, several related compounds, monacolins and dihydromonacolins, isolated fungal intermediate metabolites, have also been characterized. All natural statins possess a common polyketide portion, a hydroxy-hexahydro naphthalene ring system, to which different side chains are linked. The biosynthetic pathway involved in statin production, starting from acetate units linked to each other in head-to-tail fashion to form polyketide chains, has been elucidated by both early biogenetic investigations and recent advances in gene studies. Natural statins can be obtained from different genera and species of filamentous fungi. Lovastatin is mainly produced by Aspergillus terreus strains, and mevastatin by Penicillium citrinum. Pravastatin can be obtained by the biotransformation of mevastatin by Streptomyces carbophilus and simvastatin by a semi-synthetic process, involving the chemical modification of the lovastatin side chain. The hypocholesterolemic effect of statins lies in the reduction of the very low-density lipoproteins (VLDL) and LDL involved in the translocation of cholesterol, and in the increase in the high-density lipoproteins (HDL), with a subsequent reduction of the LDL- to HDL-cholesterol ratio, the best predictor of atherogenic risk. The use of statins can lead to a reduction in coronary events related to hypercholesterolemia, but the relationship between benefit and risk, and any possible interaction with other drugs, must be taken into account.
The natural chlorine cycle – fitting the scattered pieces by G. Öberg (pp. 565-581).
Chlorine is one of the most abundant elements on the surface of the earth. Until recently, it was widely believed that all chlorinated organic compounds were xenobiotic, that chlorine does not participate in biological processes and that it is present in the environment only as chloride. However, over the years, research has revealed that chlorine takes part in a complex biogeochemical cycle, that it is one of the major elements of soil organic matter and that the amount of naturally formed organic chlorine present in the environment can be counted in tons per km2. Interestingly enough, some of the pieces of the chlorine puzzle have actually been known for decades, but the information has been scattered among a number of different disciplines with little or no exchange of information. The lack of communication appears to be due to the fact that the points of departure in the various fields have not corresponded; a number of paradoxes are actually revealed when the known pieces of the chlorine puzzle are fit together. It appears as if a number of generally agreed statements or tacit understandings have guided perceptions, and that these have obstructed the understanding of the chlorine-cycle as a whole. The present review enlightens four paradoxes that spring up when some persistent tacit understandings are viewed in the light of recent work as well as earlier findings in other areas. The paradoxes illuminated in this paper are that it is generally agreed that: (1) chlorinated organic compounds are xenobiotic even though more than 1,000 naturally produced chlorinated compounds have been identified; (2) only a few, rather specialised, organisms are able to convert chloride to organic chlorine even though it appears as if the ability among organisms to transform chloride to organic chlorine is more the rule than the exception; (3) all chlorinated organic compounds are persistent and toxic even though the vast majority of naturally produced organic chlorine is neither persistent nor toxic; (4) chlorine is mainly found in its ionic form in the environment even though organic chlorine is as abundant or even more abundant than chloride in soil. Furthermore, the contours of the terrestrial chlorine cycle are outlined and put in a concrete form by constructing a rough chlorine budget over a small forested catchment. Finally, possible ecological roles of the turnover of chlorine are discussed.
Biotechnological applications and potential of wood-degrading mushrooms of the genus Pleurotus by R. Cohen; L. Persky; Y. Hadar (pp. 582-594).
The genus Pleurotus comprises a group of edible ligninolytic mushrooms with medicinal properties and important biotechnological and environmental applications. The cultivation of Pleurotus spp is an economically important food industry worldwide which has expanded in the past few years. P. ostreatus is the third most important cultivated mushroom for food purposes. Nutritionally, it has unique flavor and aromatic properties; and it is considered to be rich in protein, fiber, carbohydrates, vitamins and minerals. Pleurotus spp are promising as medicinal mushrooms, exhibiting hematological, antiviral, antitumor, antibiotic, antibacterial, hypocholesterolic and immunomodulation activities. The bioactive molecules isolated from the different fungi are polysaccharides. One of the most important aspects of Pleurotus spp is related to the use of their ligninolytic system for a variety of applications, such as the bioconversion of agricultural wastes into valuable products for animal feed and other food products and the use of their ligninolytic enzymes for the biodegradation of organopollutants, xenobiotics and industrial contaminants. In this Mini-Review, we describe the properties of Pleurotus spp in relation to their biotechnological applications and potential.
Diastereoselective synthesis of optically active (2R,5R)-hexanediol by J. Haberland; A. Kriegesmann; E. Wolfram; W. Hummel; A. Liese (pp. 595-599).
Diastereoselective reduction of diketones with Lactobacillus kefir DSM 20587 was examined. The reduction of both oxo-functions proceeded highly diastereoselectively. (2R,5R)-Hexanediol 3 was produced starting from (2,5)-hexanedione 1 in quantitative yields with enantiomeric excess >99% and diastereomeric excess >99%. The reaction conditions were optimized: maximum yield of (2R,5R)-hexanediol was reached at pH 6, 30°C and with equal amounts of substrate and cosubstrate. The applicability of the system in fed-batch experiments was demonstrated. The feed specific biomass concentration required to reach maximal yield and selectivity in fed-batch mode was determined.
Improvement of mass transfer characteristics and productivities of inclined tubular photobioreactors by installation of internal static mixers by C. Ugwu; J. Ogbonna; H. Tanaka (pp. 600-607).
The feasibility of improving mass transfer characteristics of inclined tubular photobioreactors by installation of static mixers was investigated. The mass transfer characteristics of the tubular photobioreactor varied depending on the type (shape) and the number of static mixers. The volumetric oxygen transfer coefficient (k La) and gas hold up of the photobioreactor with internal static mixers were significantly higher than those of the photobioreactor without static mixers. The k La and gas hold up increased with the number of static mixers but the mixing time became longer due to restricted liquid flow through the static mixers. By installing the static mixers, the liquid flow changed from plug flow to turbulent mixing so that cells were moved between the surface and bottom of the photobioreactor. In outdoor culture of Chlorella sorokiniana, the photobioreactor with static mixers gave higher biomass productivities irrespective of the standing biomass concentration and solar radiation. The effectiveness of the static mixers (average percentage increase in the productivities of the photobioreactor with static mixers over the productivities obtained without static mixers) was higher at higher standing biomass concentrations and on cloudy days (solar radiation below 6 MJ m–2 day–1).
Degradation of lignocellulose by extracellular enzymes produced by Thermomonospora fusca BD25 by M. Tuncer; A. Ball (pp. 608-611).
Degradation products from the addition of extracellular enzymes from Thermomonospora fusca BD25 to ball-milled wheat straw, oat spelt xylan and solubilised kraft pulps were characterised by HPLC and TLC. Overall, a high percentage hydrolysis of oat spelt xylan (28.9%) occurred after 26 h incubation. However, the rates of hydrolysis of ball-milled wheat straw and kraft pulp were approximately 4–6-fold less than xylan hydrolysis, although the total percentage hydrolysis of available substrate was similar (22.2% and 25.9% respectively). Incubation of kraft pulp and ball-milled wheat straw by crude extracellular enzymes of T. fusca BD25 resulted in the detection of aromatic compounds at concentrations of 0.6 µg ml–1 and 8.7 µg ml–1, respectively. Hydrolysis of oat spelt xylan by T. fusca BD25 extracellular enzymes yielded a mixture of xylose, xylotriose and putative substituted-xylotriose, while the products of ball-milled wheat straw hydrolysis were xylose, glucose and a small oligomer present in the digest. The results highlight the ability of culture supernatant from T. fusca to release both simple sugars and aromatic compounds from lignocellulosic substrates and suggest a role for this organism in the biobleaching of pulp.
A molybdenum-containing dehydrogenase catalyzing an unusual 2-hydroxylation of nicotinic acid by T. Schräder; B. Thiemer; J. Andreesen (pp. 612-617).
An enzyme of Ralstonia/Burkholderia strain DSM 6920 catalyzing the initial hydroxylation of 6-methylnicotinic acid at position 2 was purified to apparent homogeneity. It also catalyzed the unusual conversion of nicotinic acid to 2-hydroxynicotinic acid and was therefore designated as nicotinic acid dehydrogenase (NDH). Native NDH had a molecular mass of 280 kDa and was composed of subunits of 75, 30 and 16 kDa. It contained molybdenum, iron, acid-labile sulfur and FAD in a ratio of 1.6:7.3:8.0:0.6 mol–1 of native enzyme. The molybdenum cofactor was characterized as molybdopterin cytosine dinucleotide. Zinc was identified as an additional metal ion in a molar ratio of 1.8 mol mol–1 of native enzyme. Purified NDH exhibited a maximal specific activity of 22.6 µmol nitro blue tetrazoliumchloride reduced min–1 mg–1 of protein, using nicotinic acid as electron donor. The apparent K m value for nicotinic acid was determined to be 154 µM. Pyridine-3,5-dicarboxylic acid and quinoline-3-carboxylic acid were further substrates, but exhibited significantly different activity pH optima. Several artificial electron acceptors were reduced by NDH, but no activity was detected with NAD or O2. NDH was inactivated upon incubation with cyanide, but no loss of activity was obtained in the presence of arsenite.
Disruption of the uptake hydrogenase gene, but not of the bidirectional hydrogenase gene, leads to enhanced photobiological hydrogen production by the nitrogen-fixing cyanobacterium Anabaena sp. PCC 7120 by H. Masukawa; M. Mochimaru; H. Sakurai (pp. 618-624).
In order to determine the effects of the deletion of hydrogenase genes on nitrogenase-based photobiological H2 productivity by heterocystous N2-fixing cyanobacteria, we have constructed three hydrogenase mutants from Anabaena sp. PCC 7120: hupL – (deficient in the uptake hydrogenase), hoxH – (deficient in the bidirectional hydrogenase), and hupL –/hoxH – (deficient in both genes). The hupL – mutant produced H2 at a rate four to seven times that of the wild-type under optimal conditions. The hoxH – mutant produced significantly lower amounts of H2 and had slightly lower nitrogenase activity than wild-type. H2 production by the hupL –/hoxH – mutant was slightly lower than, but almost equal to, that of the hupL – mutant. The efficiency of light energy conversion to H2 by the hupL – mutant at its highest H2 production stage was 1.2% at an actinic visible light intensity of 10 W/m2 (PAR) under argon atmosphere. These results indicate that deletion of the hupL gene could be employed as a source for further improvement of H2 production in a nitrogenase-based photobiological H2 production system.
Development of molecular tools for the mulundocandin producer Aspergillus sydowii: DNA-mediated transformation and reporter gene expression by E. Schmitt; B. Eilinghoff; R. Olliger; H. Decker; U. Kück (pp. 625-631).
The echinocandin-type antimycotic mulundocandin and its derivatives are produced by the filamentous fungus Aspergillus sydowii (strain FH2551). These agents have been considered as a potential drug to treat immunocompromised patients who suffer from severe opportunistic fungal infections. In order to generate strains with a modified mulundocandin biosynthesis, we developed molecular tools for genetic engineering of A. sydowii as an alternative to conventional strain improvement procedures. For our experiments, we used strain FH2551, which was discriminated from other Aspergillus strains by determining the sequence of the two internal transcribed spacers (ITS1 and ITS2) of the rDNA locus. In addition, the electrophoretic karyotype of A. sydowii was established using pulsed-field gel electrophoresis (PFGE), leading to a calculated genomic size of about 40 Mb. For gene mapping, chromosomes were subjected to PFGE either unrestricted or after incubation with rare cutting enzymes and probed with heterologous genes. Using the bacterial hygromycin B phosphotransferase gene as a selectable marker for transformation of A. sydowii, we generated transformants with single and multiple copies of plasmid DNA. Subsequently, the heterologous lacZ and gfp genes were efficiently transferred and expressed in A. sydowii. The majority of lacZ-transformants showed more than 6 pkat β-galactosidase activity/mg protein, while the control strains had no significant background activity. Fluorescence microscopy of gfp-transformants demonstrated that the green-fluorescent protein is present in a stable and active form in the cytoplasm of vegetative hyphae and conidiospores.
Characterization of a partial duplication of the aflatoxin gene cluster in Aspergillus parasiticus ATCC 56775 by P.-K. Chang; J. Yu (pp. 632-636).
A partial duplication of the complete aflatoxin gene cluster containing homologues of aflR-aflJ-adhA-estA-norA-ver1 and omtB was identified from Aspergillus parasiticus ATCC 56775. The genes, verA-avnA-verB-avfA, between ver1 and omtB in the complete gene cluster, however, were not found. One-hybrid assays showed that the duplicated aflR gene (aflR2) encoded a protein that could activate transcription just as that encoded by aflR1, the aflR gene in the complete gene cluster. Two-hybrid assays showed that AFLR2 also interacted with a putative coactivator, AFLJ1, at comparable levels to AFLR1. Deletion of aflR1 resulted in the loss of production of aflatoxin precursors, which suggested that aflR2 could not completely replace the function of aflR1. Point mutations found in adhA2, pre-termination in ver1B and norA2, and a large deletion in omtB2 probably render these duplicated genes to become nonfunctional. A close examination of the history of isolates reported to have a partial duplication suggested that duplication of the aflatoxin cluster is not a prevalent event.
Spacer-elongated cell wall fusion proteins improve cell surface expression in the yeast Saccharomyces cerevisiae by F. Breinig; M. Schmitt (pp. 637-644).
Fusion proteins for cell surface expression in the yeast Saccharomyces cerevisiae were constructed that consisted of the N-terminal leader sequence of Kre1p, followed by the nine amino acid viral epitope hemagglutinin (HA), and the carboxyterminal anchoring domain of either Cwp2p or Flo1p. All fusions were constitutively expressed under transcriptional control of the phosphoglycerate kinase promoter and immunofluorescence analysis indicated that in each construct the HA peptide was correctly anchored to the outer yeast cell surface. Successful solubilization of the cell wall fusions by laminarinase treatment indicated that the fusions are covalently linked to cell wall β-1,3-D-glucans in vivo. FACS analyses further demonstrated that 70% of the yeast cell population expressed the corresponding cell wall fusion. Neither the number of positive cells within the population nor the distribution of the fusion at the single-cell level were negatively affected by replacing the "heterologous" Kre1p leader by the "native" Cwp2p leader. Insertion of a 350 amino acid Ser/Thr-rich spacer sequence into the fusions led to a dramatic increase in HA peptide accessibility on the yeast cell surface. Our data show that FACS analyses represent a valuable means for investigating cell surface expression, and indicate that artificial-spacer-elongated cell wall fusions might raise novel possibilities for cell surface expression of heterologous proteins in yeast.
Construction of a flocculent Saccharomyces cerevisiae strain secreting high levels of Aspergillus niger β-galactosidase by L. Domingues; J. Teixeira; M. Penttilä; N. Lima (pp. 645-650).
A flocculent Saccharomyces cerevisiae strain secreting Aspergillus niger β-galactosidase activity was constructed by transforming S. cerevisiae NCYC869-A3 strain with plasmid pVK1.1 harboring the A. niger β-galactosidase gene, lacA, under the control of the ADH1 promoter and terminator. Compared to other recombinant S. cerevisiae strains, this recombinant yeast has higher levels of extracellular β-galactosidase activity. In shake-flask cultures, the β-galactosidase activity detected in the supernatant was 20 times higher than that obtained with previously constructed strains (Domingues et al. 2000a). In bioreactor culture, with cheese-whey permeate as substrate, a yield of 878.0 nkat/gsubstrate was obtained. The recombinant strain is an attractive alternative to other fungal β-galactosidase production systems as the enzyme is produced in a rather pure form. Moreover, the use of flocculating yeast cells allows for enzyme production with high productivity in continuous fermentation systems with facilitated downstream processing.
Pitting corrosion inhibition of aluminum 2024 by Bacillus biofilms secreting polyaspartate or γ-polyglutamate by D. Örnek; A. Jayaraman; B. Syrett; C.-H. Hsu; F. Mansfeld; T. Wood (pp. 651-657).
Pitting corrosion of aluminum 2024 in Luria Bertani medium was reduced by the secretion of anionic peptides by engineered and natural Bacillus biofilms and was studied in continuous reactors using electrochemical impedance spectroscopy. Compared to sterile controls, pitting was reduced dramatically by the presence of the biofilms. The secretion of a 20 amino acid polyaspartate peptide by an engineered Bacillus subtilis WB600/pBE92-Asp biofilm slightly reduced the corrosion rate of the passive aluminum alloy at pH 6.5; however, the secretion of γ-polyglutamate by a Bacillus licheniformis biofilm reduced the corrosion rate by 90% (compared to the B. subtilis WB600/pBE92 biofilm which did not secrete polyaspartate or γ-polyglutamate). The corrosion potential (E corr) of aluminum 2024 was increased by about 0.15–0.44 V due to the formation of B. subtilis and B. licheniformis biofilms as compared to sterile controls. The increase of E corr and the observed prevention of pitting indicate that the pitting potential (E pit) had increased. This result and the further decrease of corrosion rates for the passive aluminum alloy suggest that the rate of the anodic metal dissolution reaction was reduced by an inhibitor produced by the biofilms. Purified γ-polyglutamate also decreased the corrosion rates of aluminum 2024.
Description of a cellulose-binding domain and a linker sequence from Aspergillus fungi by M. Quentin; M. Ebbelaar; J. Derksen; C. Mariani; H. van der Valk (pp. 658-662).
A family I cellulose-binding domain (CBD) and a serine- and threonine-rich linker peptide were cloned from the fungi Aspergillus japonicus and Aspergillus aculeatus. A glutathione S-transferase (GST) fusion protein comprising GST and a peptide linker with the CBD fused to its C-terminus, was expressed in Escherichia coli. The renatured GST-CBD recovered from inclusion bodies had a molecular mass of 36.5 kDa which agrees with the 29 kDa of the GST plus the calculated 7.5 kDa of the linker with the CBD. The isolated GST-CBD protein adsorbed to both bacterial microcrystalline cellulose and carboxymethyl cellulose. Deletion of the linker peptide caused a decrease in cellulose adsorbance and a higher sensitivity to protease digestion.
Isolation and characterization of a new succinic acid-producing bacterium, Mannheimia succiniciproducens MBEL55E, from bovine rumen by P. Lee; S. Lee; S. Hong; H. Chang (pp. 663-668).
A novel succinic acid-producing bacterium was isolated from bovine rumen. The bacterium is a non-motile, non-spore-forming, mesophilic and capnophilic gram-negative rod or coccobacillus. Phylogenetic analysis based on the 16S rRNA sequence and physiological analysis indicated that the strain belongs to the recently reclassified genus Mannheimia as a novel species, and has been named Mannheimia succiniciproducens MBEL55E. Under 100% CO2 conditions, it grows well in the pH range of 6.0–7.5 and produces succinic acid, acetic acid and formic acid at a constant ratio of 2:1:1. When M. succiniciproducens MBEL55E was cultured anaerobically in medium containing 20 g l–1 glucose as carbon source, 13.5 g l–1 of succinic acid was produced.
Effects of high and fluctuating pressure on microbial abundance and activity in a water hydraulic system by S. Soini; K. Koskinen; M. Vilenius; J. Puhakka (pp. 669-674).
The effects of high and fluctuating pressure up to 220 bar on microbial growth and activity were determined in a pilot-scale water hydraulic system. An increase in the pipeline pressure from 70 to 220 bar decreased the total and the viable cell number in the pressure medium from 2.2(±0.5)×105 to 4.9(±1.5)×104 cells/ml and from 5.7(±2.8)×104 to 1.3(±0.7)×104 cfu/ml, respectively. Microbial attachment in the non-pressurised tank of the hydraulic system increased with increasing pipeline pressure [from 1.0(±0.3) to 3.8(±2.7)×105 cells/cm2 on stainless steel]. The phosphatase, aminopeptidase and β-glucosidase activities in the pressurised medium were between 0.02 and 1.4 µmol/lh (V max) and decreased in response to increasing pipeline pressure. The α-glucosidase activity was detected only at 70 bar and the glucuronidase activity only occasionally. Based on principal component and cluster analyses, both the pressure applied and the original filling water quality affected ubstrate utilisation patterns. This study demonstrated the capability of freshwater bacteria to tolerate high and fluctuating pressure in a technical water system. Microbial survival was due to attachment and growth on the surfaces of the non-pressurised components and the nutrient flux released by cell lysis in the pressurised components. In summary, high pressures in water hydraulic systems do not prevent potential microbiologically related operational problems.
Autotrophic synthesis of polyhydroxyalkanoates by the bacteria Ralstonia eutropha in the presence of carbon monoxide by T. Volova; G. Kalacheva; O. Altukhova (pp. 675-678).
It has been found that the carbon monoxide (CO)-resistant strain of the hydrogen bacteria Ralstonia eutropha B5786 is able to synthesise polyhydroxyalkanoates (PHAs) in the presence of CO under autotrophic conditions. This strain, grown on model gas mixtures containing 5–25% CO (v/v), accumulates up to 70–75% (of absolutely dry matter) PHA, without significant variation in the yield coefficient on hydrogen. No suppression of the activities of the key enzymes of PHA synthesis (β-ketothiolase, acetoacetyl-CoA-reductase, butyrate dehydrogenase and poly-3-hydroxybutyrate synthase) was recorded. The PHA synthesised is a co-polymer containing mostly β-hydroxybutyrate (more than 99 mol%) with trace amounts of β-hydroxyvalerate. The investigated properties of the polymer (molecular weight, crystallinity, temperature characteristics) do not differ from those of the polymer synthesised on electrolytic hydrogen.
Degradation of aniline by newly isolated, extremely aniline-tolerant Delftia sp. AN3 by Z. Liu; H. Yang; Z. Huang; P. Zhou; S.-J. Liu (pp. 679-682).
A bacterial strain, AN3, which was able to use aniline or acetanilide as sole carbon, nitrogen and energy sources was isolated from activated sludge and identified as Delftia sp. AN3. This strain was capable of growing on concentrations of aniline up to 53.8 mM (5000 mg/l). Substituted anilines such as N-methylaniline, N,N-dimethylaniline, 2-methylaniline, 4-methylaniline, 2-chloroaniline, 3-chloroaniline, o-aminoaniline, m-aminoaniline, p-aminoaniline, and sulfanilic acid did not support the growth of strain AN3. The optimal temperature and pH for growth and degradation of aniline were 30 °C and 7.0, respectively. The activities of aniline dioxygenase, catechol 2,3-dioxygenase and other enzymes involved in aniline degradation were determined, and results indicated that all of them were inducible. The K m and V max of aniline dioxygenase were 0.29 mM and 0.043 mmol/mg protein/min, respectively. The K m and V max of catechol 2, 3-dioxygenase for catechol were 0.016 mM and 0.015 mmol/mg protein/min, respectively. Based on the results obtained, a pathway for the degradation of aniline by Delftia sp. AN3 was proposed. The importance of the strain to the operation of municipal wastewater treatment plants is discussed.
Responses of Mycobacterium sp. LB501T to the low bioavailability of solid anthracene
by L. Wick; A. Ruiz de Munain; D. Springael; H. Harms (pp. 683-683).
Biodegradation of volatile organic compounds by five fungal species by B. Qi; W. Moe; K. Kinney (pp. 684-689).
Five fungal species, Cladosporium resinae (ATCC 34066), Cladosporium sphaerospermum (ATCC 200384), Exophiala lecanii-corni (CBS 102400), Mucor rouxii (ATCC 44260), and Phanerochaete chrysosporium (ATCC 24725), were tested for their ability to degrade nine compounds commonly found in industrial off-gas emissions. Fungal cultures inoculated on ceramic support media were provided with volatile organic compounds (VOCs) via the vapor phase as their sole carbon and energy sources. Compounds tested included aromatic hydrocarbons (benzene, ethylbenzene, toluene, and styrene), ketones (methyl ethyl ketone, methyl isobutyl ketone, and methyl propyl ketone), and organic acids (n-butyl acetate, ethyl 3-ethoxypropionate). Experiments were conducted using three pH values ranging from 3.5 to 6.5. Fungal ability to degrade each VOC was determined by observing the presence or absence of visible growth on the ceramic support medium during a 30-day test period. Results indicate that E. lecanii-corni and C. sphaerospermum can readily utilize each of the nine VOCs as a sole carbon and energy source. P. chrysosporium was able to degrade all VOCs tested except for styrene under the conditions imposed. C. resinae was able to degrade both organic acids, all of the ketones, and some of the aromatic compounds (ethylbenzene and toluene); however, it was not able to grow utilizing benzene or styrene under the conditions tested. With the VOCs tested, M. rouxii produced visible growth only when supplied with n-butyl acetate or ethyl 3-ethoxypropionate. Maximum growth for most fungi was observed at a pH of approximately 5.0. The experimental protocol utilized in these studies is a useful tool for assessing the ability of different fungal species to degrade gas-phase VOCs under conditions expected in a biofilter application.
Dynamic bioreactor operation: effects of packing material and mite predation on toluene removal from off-gas by J. Woertz; W. van Heiningen; M. van Eekert; N. Kraakman; K. Kinney; J. van Groenestijn (pp. 690-694).
Recent studies have focused on using vapor-phase bioreactors for the treatment of volatile organic compounds from contaminated air streams. Although high removal capacities have been achieved in many studies, long-term operation is often unstable at high pollutant loadings due to biomass accumulation and drying of the packing medium. In this study, three bench-scale bioreactors were operated to determine the effect of packing material and fungal predation on toluene removal efficiency and pressure drop. Toluene elimination capacities (mass toluene removed per unit packing per unit time) above 100 g m–3 h–1 were obtained in the fungal bioreactors packed with light-weight, artificial medium, and submersion of the packing in mineral medium once per week was found to provide sufficient moisture and nutrients to the biofilm. The use of mites as fungal predators improved performance by increasing the overall mineralization of toluene to CO2, and by dislodging biomass along the bioreactor.