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Applied Microbiology and Biotechnology (v.51, #2)
Compostable packaging materials – test methods and limit values for biodegradation by U. Pagga (pp. 125-133).
In order to classify packaging materials as capable of organic recovery according to the packaging regulation of the European Union, the intended materials must be tested for their compostability. An important prerequisite is the determination of biodegradability by standardized test methods. Details of the intended tests are not comprehensible without further knowledge of the problems of biodegradation testing. The test methods and the limit values used to evaluate the biodegradation results are presented and discussed against the background of established test methods and limit values for chemicals. Furthermore the problem of ecotoxicity tests in connection with compost quality is discussed and an overview of European test laboratories is given.
Microbial degradation of polyurethane, polyester polyurethanes and polyether polyurethanes by T. Nakajima-Kambe; Y. Shigeno-Akutsu; N. Nomura; F. Onuma; T. Nakahara (pp. 134-140).
Polyurethane (PUR) is a polymer derived from the condensation of polyisocyanate and polyol and it is widely used as a base material in various industries. PUR, in particular, polyester PUR, is known to be vulnerable to microbial attack. Recently, environmental pollution by plastic wastes has become a serious issue and polyester PUR had attracted attention because of its biodegradability. There are many reports on the degradation of polyester PUR by microorganisms, especially by fungi. Microbial degradation of polyester PUR is thought to be mainly due to the hydrolysis of ester bonds by esterases. Recently, polyester-PUR-degrading enzymes have been purified and their characteristics reported. Among them, a solid-polyester-PUR-degrading enzyme (PUR esterase) derived from Comamonas acidovorans TB-35 had unique characteristics. This enzyme has a hydrophobic PUR-surface-binding domain and a catalytic domain, and the surface-binding domain was considered as being essential for PUR degradation. This hydrophobic surface-binding domain is also observed in other solid-polyester-degrading enzymes such as poly(hydroxyalkanoate) (PHA) depolymerases. There was no significant homology between the amino acid sequence of PUR esterase and that of PHA depolymerases, except in the hydrophobic surface-binding region. Thus, PUR esterase and PHA depolymerase are probably different in terms of their evolutionary origin and it is possible that PUR esterases come to be classified as a new solid-polyester-degrading enzyme family.
Regulation and cloning of microbial chitinase genes by P. A. Felse; T. Panda (pp. 141-151).
A range of chitinase genes from microorganisms have been cloned and the potential uses of these genetically manipulated organisms are being investigated by various researchers. Fungi and yeast are better producers of chitinase than bacteria. Since fungi grow at a slower rate, there have been efforts to clone the fungal chitinase genes into fast-growing bacteria. This review gives a brief survey of recent progress in the regulation and cloning of microbial chitinase genes. Emphasis is placed on the post-translational modification and localization of the recombinant protein in the host. Various amino acid domains are present in this protein. The mode of catalytic activity of the recombinant protein in comparison to the wild-type protein is discussed in the available literature. The different mechanisms involved in the regulation of chitinase genes from various microorganisms is discussed by the researchers. The scope of future research and conclusions yet to be obtained in this particular area are also outlined in this review.
Pilot-scale production of butanol by Clostridium beijerinckii BA101 using a low-cost fermentation medium based on corn steep water by M. Parekh; J. Formanek; H. P. Blaschek (pp. 152-157).
To improve the economic competitiveness of the acetone/butanol/ethanol fermentation process, glucose/corn steep water (CSW) medium was used on a pilot scale for the production of solvents. The production of butanol by the Clostridium beijerinckii NCIMB 8052 parent strain and the solvent-hyperproducing BA101 mutant was compared. In a 20-l fermentation using 5% glucose/CSW medium, C. beijerinckii 8052 produced 8.5 g butanol/l and 5 g acetone/l, while C. beijerinckii BA101 produced 16 g butanol/l and 7.5 g acetone/l. Further studies were carried out on a larger scale using an optimized 6% glucose/CSW medium. In a 200-l pilot-scale fermentor, C. beijerinckii 8052 produced 12.7 g butanol/l and 6 g acetone/l following 96 h of fermentation. C. beijerinckii BA101 produced 17.8 g/l and 5.5 g/l butanol and acetone respectively, following 130 h of fermentation. These results represent a 40% increase in final butanol concentration by the C. beijerinckii BA101 mutant strain when compared to the 8052 parent strain. The total solvents (acetone, butanol, and ethanol) produced by C. beijerinckii NCIMB 8052 and BA101 in a 200-l fermentation were 19.2 g/l and 23.6 g/l respectively. This is the first report of pilot-scale butanol production by the solvent-hyperproducing C. beijerinckii BA101 mutant employing an inexpensive glucose/CSW medium.
Biotransformation of citronellol by the basidiomycete Cystoderma carcharias in an aerated-membrane bioreactor by J. Onken; R. G. Berger (pp. 158-163).
The basidiomycete Cystoderma carcharias transformed citronellol into 3,7-dimethyl-1,6,7-octanetriol as the main product. 3,7-Dimethyl-6,7-epoxy-1-octanol was identified as important intermediary product of the biotransformation, and the allylic diols 2,6-dimethyl-2-octene-1,8-diol, 3,7-dimethyl-5-octene-1,7-diol and 3,7-dimethyl-7-octene-1,6-diol were found to be minor products. Microbial formation of rose oxide, a flavour-impact component, was observed for the first time. The formation of the main products was inhibited by 70% after addition of 0.1 mmol l−1 cytochrome monooxygenase inhibitors. Formation of 3,7-dimethyl-1,6,7-octanetriol was effective in a bioreactor with aeration over a coil of a hydrophobic microporous polypropene capillary membrane. Production rates of up to 150 mg l−1 day−1 were reached and led to a product concentration of 866 mg l−1 (conversion rate: 52%). The total loss of the added volatile substrate via the exhaust air was 4.5% when this aeration method was used.
Optimization of agitation and aeration conditions for maximum virginiamycin production by S. Shioya; M. Morikawa; Y. Kajihara; H. Shimizu (pp. 164-169).
To maximize the productivity of virginiamycin, which is a commercially important antibiotic as an animal feed additive, an empirical approach was employed in the batch culture of Streptomyces virginiae. Here, the effects of dissolved oxygen (DO) concentration and agitation speed on the maximum cell concentration at the production phase, as well as on the productivity of virginiamycin, were investigated. To maintain the DO concentration in the fermentor at a certain level, either the agitation speed or the inlet oxygen concentration of the supply gas was manipulated. It was found that increasing the agitation speed had a positive effect on the antibiotic productivity independent of the DO concentration. The optimum DO concentration, agitation speed and addition of an autoregulator, virginiae butanolide C (VB-C), were determined to maximize virginiamycin productivity. The optimal strategy was to start the cultivation at 450 rpm and to continue until the DO concentration reached 80%. After reaching 80%, the DO concentration was maintained at this level by changing the agitation speed, up to a maximum of 800 rpm. The addition of an optimal amount of the autoregulator VB-C in an experiment resulted in the maximal production of virginiamycin M (399 mg/l), which was about 1.8-fold those obtained previously.
The amylopullulanase of Bacillus sp. DSM 405 by J. M. Brunswick; C. T. Kelly; W. M. Fogarty (pp. 170-175).
The amylopullulanse produced by Bacillus sp. DSM 405 was purified to homogeneity. It exhibited dual activity, cleaving the α1-4 bonds in starch, releasing a range of malto-oligosaccharides, and also cleaving the α1-6 bonds in pullulan, releasing maltotriose as the sole end-product. The enzyme was a glycoprotein and had a relative molecular mass of 126 000 and an isoelectric point of 4.3. While the enzyme was optimally active on starch at pH 6.5 and at pH 6.0 on pullulan, activity on both substrates was maximal at 70 °C. Kinetic analyses of the enzyme in a system that contained both starch and pullulan as two competing substrates demonstrated the dual specificity of the enzyme. Chemical modification of the carboxyl groups within the active centre of the protein showed that one active site was responsible for hydrolysis of the α1-4 and α1-6 bonds in starch and pullulan respectively. This is the first comprehensive investigation of an amylopullulanse produced by an aerobic bacterium, showing a single active site responsible for both activities.
N -glycosylation is involved in the sensitivity of Saccharomyces cerevisiae to HM-1 killer toxin secreted from Hansenula mrakii IFO 0895 by T. Kimura; T. Komiyama; Y. Furuichi; Y. Iimura; S. Karita; K. Sakka; K. Ohmiya (pp. 176-184).
Saccharomyces cerevisiae rhk mutants were previously shown to have a phenotype that is resistant to HM-1 killer toxin secreted from Hansenula mrakii IFO 0895. The RHK1/ALG3 gene encodes a mannosyltransferase that is involved in the synthesis of an oligosaccharide in protein N-glycosylation. Previously, this gene was cloned and shown to complement the rhk1 mutation. In this study, the RHK2 gene, which complements the rhk2 mutation, was cloned. The RHK2 gene was found to be identical to the essential gene STT3, which encodes a subunit of the oligosaccharyltransferase complex. This complex transfers the core oligosaccharide to proteins. The rhk2 mutants showed supersensitivity to several drugs (Calcofluor White, caffeine and FK506), suggesting that these strains have cell-wall defects. Activity staining of invertase in an acrylamide gel indicated that it was underglycosylated. These results suggest that one or more mannoproteins are involved in the cytocidal process of HM-1.
A variant of Saccharomyces cerevisiae pep4 strain with improved oligotrophic proliferation, cell survival and heterologous secretion of α-amylase by D.-C. Chen; S.-Y. Chen; M.-F. Gee; J.-T. Pan; T.-T. Kuo (pp. 185-192).
A variant of Saccharomyces cerevisiae pep4 strain 20B12, with improved oligotrophic proliferation, cell survival and secretion of heterologous mouse α-amylase, is described. Previously we reported a procedure to enrich NI transformants that are not inhibited by cytotoxic expression of hepatitis B virus surface antigen in the secretion pathway of the protease-A-deficient (pep4) strain. To use the NI cells as a host for heterologous expression, we tried to amend the introduced pYAS/12S vector and obtain a host strain, NI-C, with stable NI phenotype and trp1 marker restored. Southern analysis of genomic DNA of NI-C suggested that the original pYAS/12S was abnormally rearranged and not completely corrected. Further assay showed that the viability and mitotic ability of the NI-C strain were increased. While using the NI-C strain as host for plasmid transformation and heterologous expression of mouse α-amylase, we observed that transformed colonies grew more quickly and secreted more α-amylase than general yeast strains. A further test showed that the NI-C strain was able to use mouse α-amylase as a positive selection marker to form transformed colonies on nitrogen-starved plates that contain starch as the sole carbon source. The results imply that the NI-C variant is an improved pep4 strain that can be used for heterologous expression and for the development of new selective markers in the yeast transformation system.
Cloning and overexpression in Escherichia coli of the gene encoding dihydroxyacetone kinase isoenzyme I from Schizosaccharomyces pombe, and its application to dihydroxyacetone phosphate production by N. Itoh; Y. Tujibata; J. Q. Liu (pp. 193-200).
The gene dak1 encoding a dihydroxyacetone kinase (DHAK) isoenzyme I, one of two isoenzymes in the Schizosaccharomyces pombe IFO 0354 strain, was cloned and sequenced. The dak1 gene comprises 1743 bp and encodes a protein of 62 245 Da. The deduced amino acid sequence showed a similarity to a putative DHAK of Saccharomyces cerevisiae and DHAK of Citrobacter freundii. The dak1 gene was expressed at a high level in Escherichia coli, and the recombinant enzyme was purified to homogeneity and characterized. The acetone powder of recombinant E. coli cells was used to produce dihydroxyacetone phosphate.
Cloning of the transketolase gene and the effect of its dosage on aromatic amino acid production in Corynebacterium glutamicum by M. Ikeda; K. Okamoto; R. Katsumata (pp. 201-206).
Transketolase is a key enzyme of the nonoxidative pentose phosphate pathway. The effect of its overexpression on aromatic amino acid production was investigated in Corynebacterium glutamicum, a typical amino-acid-producing organism. For this purpose, the transketolase gene of the organism was cloned on the basis of its ability to complement a C. glutamicum transketolase mutant with pleiotropically shikimic-acid-requiring, ribose- and gluconic-acid-negative phenotype. The gene was shown by deletion mapping and complementation analysis to be located in a 3.2-kb XhoI-SalI fragment of the genome. Amplification of␣the gene by use of low-, middle-, and high-copy-number vectors in a C. glutamicum strain resulted in overexpression of transketolase activities as well as a␣protein of approximately 83kDa in proportion to the copy numbers. Introduction of the plasmids into a tryptophan and lysine co-producer resulted in copy-dependent increases in tryptophan production along with concomitant decreases in lysine production. Furthermore, the presence of the gene in high copy numbers enabled tyrosine, phenylalanine and tryptophan producers to accumulate 5%–20% more aromatic amino acids. These results indicate that overexpressed transketolase activity operates to redirect the glycolytic intermediates toward the nonoxidative pentose phosphate pathway in vivo, thereby increasing the intracellular level of erythrose 4-phosphate, a precursor of aromatic biosynthesis, in the aromatic-amino-acid-producing C. glutamicum strains.
Utilization of phenoxyacetic acid, by strains using either the ortho or meta cleavage of catechol during phenol degradation, after conjugal transfer of tfdA, the gene encoding a 2,4-dichlorophenoxyacetic acid/2-oxoglutarate dioxygenase by J. Radnoti de Lipthay; T. Barkay; J. Vekova; S. J. Sørensen (pp. 207-214).
The degradation of recalcitrant pollutants in contaminated soils and waters could be facilitated by broadening the degradative capabilities of indigenous microbes by the conjugal transfer of catabolic genes. The feasibility of establishing bacterial populations that degrade phenoxyacetic acid by conjugal transfer of tfdA, the gene encoding 2,4-dichlorophenoxyacetic acid/2-oxoglutarate dioxygenase, to phenol-degrading strains of Pseudomonas and Ralstonia was examined. The mobilizable plasmid pKJS32 served as a vector for delivery of tfdA and the regulatory gene, tfdS. Transconjugant strains that degraded phenol by an ortho cleavage of catechol grew well on phenoxyacetic acid while those employing a meta cleavage could only grow on phenoxyacetic acid in the presence of benzoic acid or after a prolonged lag period and the appearance of mutants that had gained catechol 1,2-dioxygenase activities. Thus, an ortho cleavage of catechol was essential for degradation of phenoxyacetic acid, suggesting that a product of the ortho-cleavage pathway, probably cis,cis-muconic acid, is an inducer of tfdA gene expression. Establishment of phenoxyacetic-acid-degrading soil populations by conjugal transfer of tfdA would depend on the presence of phenol-degrading recipients employ- ing an ortho cleavage of catechol.
Cloning and characterization of an endo-β-1,3(4)glucanase and an aspartic protease from Phaffia rhodozyma CBS 6938 by M. L. Bang; I. Villadsen; T. Sandal (pp. 215-222).
We describe the identification and expression cloning of two novel enzymes, a β-glucanase and an aspartic protease, secreted from the basidiomycetous yeast Phaffia rhodozyma. A cDNA library from P. rhodozyma CBS 6938 was constructed, and full-length cDNA encoding an endo-1,3(4)-β-glucanase (bg1) and an aspartic protease (pr1) were cloned by expression cloning in Saccharomyces cerevisiae W3124. The bg1 cDNA encodes a 424-residue precursor protein with a putative signal peptide. The pr1 cDNA encodes a 405-residue prepropolypeptide with an 81-residue leader peptide. The aspartic protease was purified and characterized. It has a molecular mass of 36 kDa, an isoelectric point of pH 7.5, a pH activity optimum at 4.0–6.0, and a temperature activity optimum around 40 °C. Both enzymes show only low sequence identity to other known enzymes.
A murC gene from coryneform bacteria by M. Wachi; C. D. Wijayarathna; H. Teraoka; K. Nagai (pp. 223-228).
The upstream flanking region of the ftsQ and ftsZ genes of Brevibacterium flavum MJ233, which belongs to the coryneform bacteria, was amplified by the inverse polymerase chain reaction method and cloned in Escherichia coli. Complementation analysis of E. coli mutant with a defective cell-wall synthesis mechanism with the cloned fragment and its DNA sequencing indicated the presence of the murC gene, encoding UDP-N-acetylmuramate:l-alanine ligase involved in peptidoglycan synthesis, just upstream from the ftsQ gene. The B. flavum murC gene could encode a protein of 486 amino acid residues with a calculated molecular mass of 51 198 Da. A 50-kDa protein was synthesized by the B. flavummurC gene in an in vitro transcription/translation system using E. coli S30 lysate. These results indicate that the genes responsible for cell-wall synthesis and cell division are located as a cluster in B. flavum similar to the E. coli mra region.
Bacterial growth in space flight: logistic growth curve parameters for Escherichia coli and Bacillus subtilis by M. A. Kacena; G. A. Merrell; B. Manfredi; E. E. Smith; D. M. Klaus; P. Todd (pp. 229-234).
Previous investigations have reported that bacterial suspension cultures grow to higher stationary concentrations in space flight than on Earth; however, none of these investigations included extensive ground controls under varied inertial conditions. This study includes extensive controls and cell-growth data taken at several times during lag phase, log phase, and stationary phase of Escherichia coli and Bacillus subtilis. The Marquardt-Levenberg, least-squares fitting algorithm was used to calculate kinetic growth parameters from the logistic bacterial growth equations for space-flight and control growth curves. Space-flight cultures grew to higher stationary-phase concentrations and had shorter lag-phase durations. Also, evidence was found for increased exponential growth rate in space.
Effects of yeast extract on the production and the quality of the exopolysaccharide, zooglan, produced by Zoogloea ramigera 115SLR by S. Guillouet; J. H. Choi; C. K. Rha; A. J. Sinskey (pp. 235-240).
Although many studies have examined the influence of culture conditions on the production and composition of polysaccharides, little is known about the factors influencing the quality of exopolysaccharides (EPS). In this work we studied the effect of yeast extract on the production, composition and molecular weight of the EPS zooglan produced by Zoogloea ramigera 115SLR. This bacterium was grown on a new completely defined synthetic medium and on a medium containing yeast extract. Growth and polysaccharide production performances were comparable on the two media with a glucose to exopolysaccharide conversion yield of 35% (g/g). The polysaccharides produced on these two media have an identical composition but a different molecular weight and molecular weight distribution. The yeast extract medium leads to a more homogeneous polysaccharide solution.
Investigation of lignin-carbohydrate complexes in kraft pulps by selective enzymatic treatments by M. Tenkanen; T. Tamminen; B. Hortling (pp. 241-248).
The occurrence of covalent bonds between residual lignin and polysaccharides in birch and pine kraft pulps was investigated by specific enzymatic treatments. Pure enzymes degrading cellulose, xylan and mannan were used both separately and in combination. Comparison of the molar masses of polysaccharides and lignin in the orginal pulps and in the residual pulps after enzymatic treatments showed that residual lignin in birch kraft pulp is linked at least to xylan. A minor portion may also be linked to cellulose. In pine kraft pulp some of the residual lignin appears to be linked to cellulose, glucomannan and xylan. The linkages between lignin and cellulose and hemicelluloses may be either native or formed during pulp processing. The results also provided new information on the synergistic action of cellulose- and hemicellulose-degrading enzymes on pulp fibres. The synergism appears to be mainly due to the structure of the pulp fibres, with different layers of cellulose sheets, hemicelluloses and lignin. On the other hand the results also provided information about fibre structure. The degradation of xylan clearly enhanced the action of enzymes on cellulose, suggesting that xylan partially covers the cellulose. A similar phenomenon was not observed in the simultaneous hydrolysis of glucomannan and cellulose. However, the results suggest that glucomannan does interact with cellulose, possibly by non-covalent linkages.
Influence of environmental factors on lipase production by Lactobacillus plantarum by M. Fátima Silva Lopes; A. E. Cunha; J. J. Clemente; M. J. Teixeira Carrondo; M. T. Barreto Crespo (pp. 249-254).
A strain of Lactobacillus plantarum, DSMZ 12028 (Deutsch Sammlung von Mikroorganismen und Zellkulturen), isolated from a Portuguese dry fermented sausage, “chouriço”, was found to produce true lipase, producing free fatty acids from triolein (olive oil). This enzymatic activity was found in whole cells, but was negligible in comparison to lipolytic activity in culture supernatant. Therefore, only extracellular activity was studied. The effect of pH, temperature and glucose concentration on extracellular lipase production was studied in continuously stirred tank reactors, the first time this technology has been used to study the production of this enzyme in lactobacilli. Maximum lipase production was achieved at a pH of 5.5 and 30 °C and was kept at a significant level over a wide range of dilution rates (0.05–0.4 h−1); the production of lipase was still significant for low pH values, temperature and glucose concentration, conditions that are close to the ones present during chouriço ripening. The effect of glucose concentration was also studied in a batch system. The control of lipase production was found to be related both to glucose concentration in the medium and to the growth rate/dilution rate. Glucose concentration was found to be important for fast lipase production, although it did not influence the maximum lipase activity reached in a batch culture.
Hydroxylamine oxidation and subsequent nitrous oxide production by the heterotrophic ammonia oxidizer Alcaligenes faecalis by S. Otte; J. Schalk; J. G. Kuenen; M. S. M. Jetten (pp. 255-261).
Nitrous oxide (N2O), a greenhouse gas, is emitted during autotrophic and heterotrophic ammonia oxidation. This emission may result from either coupling to aerobic denitrification, or it may be formed in the oxidation of hydroxylamine (NH2OH) to nitrite (NO2 −). Therefore, the N2O production during NH2OH oxidation was studied with Alcaligenes faecalis strain TUD. Continuous cultures of A. faecalis showed increased N2O production when supplemented with increasing NH2OH concentrations. 15N-labeling experiments showed that this N2O production was not due to aerobic denitrification of NO2 −. Addition of 15N-labeled NH2OH indicated that N2O was a direct by-product of NH2OH oxidation, which was subsequently reduced to N2. These observations are sustained by the fact that NO2 − production was low (0.23 mM maximum) and did not increase significantly with increasing NH2OH concentration in the feed. The NH2OH-oxidizing capacity increased with increasing NH2OH concentrations. The apparent V max and K m were 31 nmol min−1 mg dry weight−1 and 1.5 mM respectively. The culture did not increase its growth yield and was not able to use NH2OH as the sole N source. A non-haem hydroxylamine oxidoreductase was partially purified from A. faecalis strain TUD. The enzyme could only use K3Fe(CN)6 as an electron acceptor and reacted with antibodies raised against the hydroxylamine oxidoreductase of Thiosphaera pantotropha.
Long-term survival of the plant-growth-promoting bacteria Azospirillum brasilense and Pseudomonas fluorescens in dry alginate inoculant by Y. Bashan; L. E. Gonzalez (pp. 262-266).
Two plant-growth-promoting bacteria, Azospirillum brasilense Cd and Pseudomonas fluorescens 313, immobilized in 1983 in two types of alginate-bead inoculant (with and without skim-milk supplement) and later dried and stored at ambient temperature for 14 years, were recovered in 1996. The population in each type of bead had decreased, yet significant numbers survived (105–106 cfu/g beads). Population numbers depended on the bead type and the three independent bacterial counting methods: the conventional plate-count method, indirect enzyme-linked immunosorbent assay and the limited-enrichment technique. Both bacterial species retained several of their original physiological features. When inoculated onto wheat plants, both species colonized and produced plant-growth effects equal to those of the contemporary strain from a culture collection or to their own 1983 records. This study showed that bacteria can survive in alginate inoculant over long periods.
Oxidation of aromatic alcohols by laccase from Trametes versicolor mediated by the 2,2′-azino-bis-(3-ethylbenzothiazoline-6-sulphonic acid) cation radical and dication by A. Majcherczyk; C. Johannes; A. Hüttermann (pp. 267-276).
Oxidation of aromatic alcohols, such as non-phenolic lignin model compounds, by oxidised species of 2,2′-azino-bis-(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) has been investigated. The cation radical and dication formed from ABTS were both capable of oxidising aromatic alcohols to aldehydes. The reactions terminated at the level of the aldehyde and no acids were formed. The cation radical and dication worked in a cycle as an electron-transfer compound between an oxidant and alcohol. In addition to the oxidation of the primary benzyl-hydroxyl group, an oxidation of the secondary α-hydroxyl group to the ketone by the dication was possible. All distinguishing features of these reactions corresponded to the results of the oxidation performed by the laccase of Trametes versicolor in the presence of ABTS. The decomposition products from the dication alone and ABTS with laccase confirmed the supposition that the dication was involved in the laccase mediator system. A reaction mechanism based on deprotonation of the alcohol cation radical was predicted to play a key role in the irreversible followup reaction and to be the driving force of the process.
Complete transformation of 1,1,1-trichloroethane to chloroethane by a methanogenic mixed population by J. H. de Best; A. Hage; H. J. Doddema; D. B. Janssen; W. Harder (pp. 277-283).
A methanogenic mixed population in a packed-bed reactor completely transformed 1,1,1-trichloroethane (10 μM) to chloroethane by a cometabolic process. Chloroethane was not further transformed. Acetate and methanol served as electron donors. Complete transformation of 1,1,1-trichloroethane to chloroethane only occurred when sufficient electron donor was fed into the reactor. Otherwise, besides chloroethane, 1,1-dichloroethane was also found as a product. The products of 1,1,1-trichloroethane transformation also depended on the type of electron donor present. With acetate, the degree of dechlorination was higher, i.e. more 1,1,1-trichloroethane was transformed to chloroethane than with methanol. In an enrichment culture obtained from the reactor contents, 1,1,1-trichloroethane was only transformed to 1,1-dichloroethane and was not further metabolized. Methanol, acetate, formate, ethanol, 2-propanol, trimethylamine and H2, but not dimethylamine and methylamine, served as electron donors for 1,1,1-trichloroethane transformation by this enrichment culture. Both nitrate and nitrite inhibited 1,1,1-trichloroethane transformation; while nitrate completely inhibited 1,1,1-trichloroethane dechlorination, some conversion did occur in the presence of nitrite. The product(s) of this conversion remain unknown, since no chlorinated hydrocarbons were detected.
Aerobic 4-nitrophenol degradation by microorganisms fixed in a continuously working aerated solid-bed reactor by P. Ray; M. Ait Oubelli; C. Löser (pp. 284-290).
Studies of microbial purification of a model waste water containing 4-nitrophenol were carried out in a continuously working aerobic solid-bed reactor. The main emphasis was on the dynamic behaviour of the system after a sudden change in cultivation conditions and on the steady-state performance of the reactor as a function of the pollution load. A change from ammonium-free to ammonium-containing medium hardly influenced the nitrophenol degradation. The reactor responded differently to an increase in pollutant load, which was brought about by increasing either the 4-nitrophenol content or the flow of the waste water. Up to a load of 270 mg l−1 h−1 the pollutant was stably and almost completely degraded. At a higher load, only a partial 4-nitrophenol degradation took place. A mathematical model was derived to describe the processes that occurred in the reactor. By segregation into two compartments – the aqueous phase and the biofilm – account was taken of the fact that the pollutant is carried into the biofilm by diffusion and is degraded there. The observed relations between the pollutant load, the pollutant concentration in the outlet of the reactor and the reactor performance agreed with the simulated process behaviour. As the model simulation showed, the incomplete pollutant degradation at a higher reactor load was caused by oxygen limitation.