A Thermostable Xylanase from a Thermophilic Acidophilic Bacillus sp.

Bacillus sp. 11-IS, a strain of thermophilic acidophilic bacteria, produced an extracellular xylanase during growth on xylan. The enzyme purified from the culture supernatant solution was homogeneous on disc-gel electrophoresis. The molecular weight was calculated to be 56,000 by SDS-gel electrophoresis. The enzyme had a pH optimum for activity at 4.0, and its stability range was pH 2.0 ~ 6.0. The temperature optimum was 80°C (10-min assay); however, the enzyme retained full activity after incubation at 70°C for 15 min. The enzyme acted on carboxymethyl cellulose (CMC) and cellulose, as well as on xylan. The Michaelis constants for larchwood xylan and CMC were calculated to be 1.68 mg xylose eq/ml and 0.465 mg glucose eq/ml, respectively. The predominant hydrolysis products from larchwood xylan were xylobiose, xylotriose, and xylose; the release of arabinose from rice-straw arabinoxylan was not detected. CMC was cleaved to cellobiose and larger oligosaccharides. Thus, the enzyme is considered to be an endoenzyme which degrades the β-1,4-glycosyl linkages in xylan and cellulose.     

Isolation and Characterization of Acidic Peptides in Soy Sauce

A soy sauce sample was fractionated by gel filtration on a Sephadex G–15 column, then the fractions were subfractionated on the basis of acidity by ion exchange chromatography on a QAE-Sephadex A–25 column. The acidic subfractions with various acidities were further fractionated, using a preparative amino acid analyzer and by paper chromatography to separate the acidic peptide components.

Four dipeptides and sugar derivatives of ten dipeptides and two tripeptides were isolated and characterized as the major acidic peptides in soy sauce. However, it was difficult to anticipate any direct contribution of these peptides to the flavor construction in soy sauce on the basis of their contents and taste intensities.     

Enzymatic Conversion of 1-Hydroxy-2-naphthoate in Phenanthrene-grown Aeromonas sp. S45P1

Soybean seedlings were grown at 28°C in the dark or the light for 12 days, and four classes of sterol lipids, sterol esters (SE), free sterols (St), acylated steryl glycosides (ASG) and steryl glycosides (SG), were isolated from the cotyledons by solvent extractions, Florisil column chromatography, and thin-layer chromatography (TLC), successively. Each sterol lipid (SE, ASG and SG) obtained was hydrolyzed and then separately divided into sterol, fatty acid and/ or sugar fractions. The hydrolysates and St were analyzed mainly by gas-liquid chromatography (GLC).

Under the two conditions tested, the main sterol lipid class was St during germination, the minor one being SG. With the progress of germination, St and ASG decreased under both conditions tested, whereas SE and SG increased, especially SE in the light-grown seedlings. The changing patterns of sterol and sugar compositions of ASG resembled those of SG, but those of fatty acid composition differed between SE and ASG. In general, the changes in fatty acid compositions of SE and ASG were more marked in the light-grown seedlings than in the dark-grown ones.     

多氯联苯的生物修复

多氯联苯(Polychlorinated biphenyls,PCBs)是一种持久性有机污染物,对人类和自然环境具有很大的威胁,降解PCBs一直是研究的热点。在目前的研究方法中生物降解最具潜力,生物降解主要分为微生物降解、植物修复和微生物-植物共同修复3个方面。文章着重介绍了微生物降解PCBs菌株的分离,降解相关基因的克隆和改造;同时对植物修复,植物与微生物共同修复以及植物转基因修复进行了讨论。     

Structural features of cytochrome P450 1A associated with the absence of EROD activity in liver of the loricariid catfish Pterygoplichthys sp

The Amazon catfish genus Pterygoplichthys (Loricariidae, Siluriformes) is closely related to the loricariid genus Hypostomus, in which at least two species lack detectable ethoxyresorufin-O-deethylase (EROD) activity, typically catalyzed by cytochrome P450 1 (CYP1) enzymes. Pterygoplichthys sp. liver microsomes also lacked EROD, as well as activity with other substituted resorufins, but aryl hydrocarbon receptor agonists induced hepatic CYP1A mRNA and protein suggesting structural/functional differences in Pterygoplichthys CYP1s from those in other vertebrates. Comparing the sequences of CYP1As of Pterygoplichthys sp. and of two phylogenetically related siluriform species that do catalyze EROD (Ancistrus sp., Loricariidae and Corydoras sp., Callichthyidae) showed that these three proteins share amino acids at 17 positions that are not shared by any fish in a set of 24 other species. Pterygoplichthys and Ancistrus (the loricariids) have an additional 22 amino acid substitutions in common that are not shared by Corydoras or by other fish species. Pterygoplichthys has six exclusive amino acid substitutions. Molecular docking and dynamics simulations indicate that Pterygoplichthys CYP1A has a weak affinity for ER, which binds infrequently in a productive orientation, and in a less stable conformation than in CYP1As of species that catalyze EROD. ER also binds with the carbonyl moiety proximal to the heme iron. Pterygoplichthys CYP1A has amino acid substitutions that reduce the frequency of correctly oriented ER in the AS preventing the detection of EROD activity. The results indicate that loricariid CYP1As may have a peculiar substrate selectivity that differs from CYP1As of most vertebrate.     

Dioxin-like polychlorinated biphenyl adsorbent obtained from enzymatic saccharification residue of lignocellulose

In this study, the effective utilization of lignocellulose residue as an adsorbent was investigated. Japanese cypress wood flour subjected to hydrothermal pretreatment and ball-mill grinding was saccharified with an enzyme. The residual wood flour was carbonized and activated by physical and chemical activation to produce adsorbents for persistent organic pollutant removal. The adsorption properties were investigated by pore analysis using the N₂ adsorption/desorption isotherm and adsorption tests for dioxin-like polychlorinated biphenyls in a hexane solution. The obtained adsorbents showed high production yields and adsorption properties for dioxin-like polychlorinated biphenyls.     

Isolation and characterization of a thermophilic Bacillus sp. JF8 capable of degrading polychlorinated biphenyls and naphthalene

Bacillus sp. strain JF8, which was isolated from compost, utilizes naphthalene and biphenyl as carbon sources at 60 degrees C. Biphenyl grown cells of strain JF8 barely degraded naphthalene while naphthalene grown cells did not degrade p-chlorobiphenyl, suggesting the existince of two independent degradation pathways. Isolation of JF8N, a mutant strain which can not utilize biphenyl as a carbon source while retaining the ability to utilize naphthalene, supports this hypothesis. Biphenyl grown cells of strain JF8 can degrade several polychlorinated biphenyl congeners including tetra- and pentachlorobiphenyl. bph and nah probes from mesophilic organisms failed to hybridize to strain JF8 DNA.     

Comparison of anaerobic microbial communities from Estuarine sediments amended with halogenated compounds to enhance dechlorination of 1,2,3,4-tetrachlorodibenzo-p-dioxin

A suite of experiments were conducted to ascertain whether dehalogenation of a model dioxin compound could be stimulated in marine sediments by supplementation with halogenated analogues to enrich for dehalogenating bacteria and if growth by members of the Chloroflexi-like group was associated with dioxin removal. Five halogenated compounds (tetrachlorobenzene, tetrachloroanisole, tetrachlorophenol, tetrachlorobenzoic acid and trichloroacetophenone) were added with 1,2,3,4-tetrachlorodibenzo-p-dioxin (TeCDD) to estuarine sediments from four sites in San Diego Bay and the coast of southern New Jersey to test for dioxin dehalogenation. Most of the halogenated additives were found to stimulate dechlorination of the model dioxin. Molecular analysis of the bacterial population using 16S rRNA and reductive dehalogenase genes indicated that distinct microbial populations were enriched with each halogenated co-amendment. Additionally, Chloroflexi-like ribosomal genes associated with dehalogenation were detected. For example, quantitative real-time PCR analysis of 16S rRNA and reductive dehalogenase gene copy number in the microcosms showed a positive correlation with 1,2,3,4-TeCDD reductive dechlorination in coastal sediments amended with different halogenated additives. These results suggest that specific Chloroflexi-like microorganisms related to Dehalococcoides are involved in 1,2,3,4-TeCDD reductive dechlorination.     

Temperature-dependent biotransformation of 2,4'-dichlorobiphenyl by psychrotolerant Hydrogenophaga strain IA3-A: higher temperatures prevent excess accumulation of problematic meta-cleavage products

AIMS: The present work investigates the possibility that temperature could regulate the pattern of transformation of 2,4'-chlorobiphenyl (2,4'-CB) by psychrotolerant Hydrogenophaga sp. IA3-A. Methods AND RESULTS: Transformation of 2,4'-chlorobiphenyl to 2- and 4-chlorobenzoic acid (2- and 4-CBA), and meta-cleavage products by cells of strain IA3-A incubated at 10 degrees C, 25 degrees C, 37 degrees C or 45 degrees C were monitored by UV spectrometry, HPLC and GC-MS analyses. Cultures incubated at 10 degrees C, 25 degrees C or 37 degrees C produced low amounts of CBAs and excess levels of meta-cleavage products from 2,4'-CB. Cultures incubated at 45 degrees C transformed most of the degraded 2,4'-CB to CBAs and low level of meta-cleavage product. Culture extracts contained unusual varieties of isomeric hydroxylated metabolic products. CONCLUSIONS: Efficient transformation of 2,4'-CB to CBAs was possible in cultures incubated at 45 degrees C. Evidence for the involvement of multiple pathways in the transformation of 2,4'-CB in strain IA3-A suggests that differential regulation of the pathways at different temperatures was likely responsible for the change in the pattern of transformation of 2,4'-CB in cultures incubated at 45 degrees C. Significance AND IMPACT OF THE STUDY: It may be possible to condition cells to transform chlorinated biphenyls more efficiently without accumulating excess level of toxic intermediates.     

Characterization of polychlorinated alkane mixtures—a Monte Carlo modeling approach

A Monte Carlo model was developed to characterize the molecular composition of polychlorinated alkane mixtures. The model is based upon a simulation of the free-radical chlorination process by which polychlorinated alkane mixtures are produced industrially from n-alkanes. In the model, the free-radical chlorination reaction was simulated by randomly selecting a position on a partially converted alkane molecule for target by chlorine free-radical attack. The relative reactivities of the hydrogen atoms on the alkane chain towards chlorine free-radical substitution were either determined experimentally or extrapolated from experimental results and incorporated into the model. The result of the simulation is the prediction of the detailed molecular composition of any PCA mixture. Good agreement was found when comparing the distribution of molecules predicted by the model to analytically determined distributions of real PCA mixtures. Results from the model were then coupled with rules describing the action of biological enzymes to estimate the upper limit possible for the aerobic biodegradation of PCA mixtures.