Search

Infertile and heavy-metal-contaminated croplands are widely distributed and threaten global food security. Plant growth-promoting bacteria provide an option for alleviating the agricultural problems. In this study, the endophytic bacteria Rahnella victoriana B38 (Accession No. OK658118) and Bacillus paramycoides N38 (Accession No. OK658562) were isolated from Brassica napus. Their plant growth-promoting effects and mechanisms were investigated by gnotobiotic and pot experiments, and extracellular metabolites analysis. The results revealed that both B38 and N38 significantly increased shoot and root length in B. napus and fresh weight, root length, pod number, and total pod weight of Arabidopsis thaliana (p < 0.05). In addition, they promoted Arabidopsis growth under arsenic (As) stress by significantly increasing fresh weight and root length and decreasing the As content by 55.81% and 30.47%, respectively (p < 0.05). Thus, these bacteria were able to protect Arabidopsis from As stress by reducing As accumulation in plants. B38 and N38 release gamma-aminobutyric acid (GABA) and enzymes including proteases, cellulases, and lipases, which can increase soil nutrient availability. Substances related to plant biomass increasing and As-stress alleviation, including indoleacetic acid (IAA), GABA, putrescine, quinic acid, trans-zeatin, N-acetylglutamic, 3-indolepropionic acid, putrescine, and lathyrine were also detected. Therefore, they could represent ideal microbial biofertilizer candidates for increasing crop yields and alleviating As accumulation in plants. [ABSTRACT FROM AUTHOR]

Cyanobacterial blooms are a worldwide problem, especially in freshwaters. As one of the most abundant co-existing organisms of algae, bacteria play critical roles in cyanobacteria growth, particularly the cyanobactericidal bacteria which can efficiently kill cyanobacteria. Recent years, cyanobactericidal bacteria are highly recognized as a method that could potentially block cyanobacterial blooms. Many studies have been conducted to assess their effects on the termination of cyanobacteria blooms and explore their cyanobactericidal mechanisms, e.g., attacking by cell to cell or releasing specific compounds, the physiological, metabolic, and transcriptional disturbance on cyanobacteria. In this review, the present state of research on cyanobactericidal bacteria for the bloom-causing cyanobacteria species is summarized. The challenges in applying cyanobactericidal bacteria in the control of natural cyanobacterial blooms are discussed. [ABSTRACT FROM AUTHOR]

Mercury (Hg) methylation and demethylation is supposed to simultaneously exist in the environment and form a cycle, which determines the net production of methylmercury (MeHg). Exploring the mechanisms of MeHg formation and degradation, and its final fate in the natural environment is essential to understanding the biogeochemical cycle of Hg. However, MeHg demethylation has been less studied in the past years comparing with Hg methylation, particularly in anaerobic microorganisms whose demethylation role has been under-evaluated. This review described the current state of knowledge on biotic (microorganisms) and abiotic demethylation (photodegradation, chemical degradation) of MeHg. The decomposition of MeHg performed by microorganisms has been identified as two different pathways, reductive demethylation (RD) and oxidative demethylation (OD). Anaerobic and aerobic microorganisms involved in the process of RD and OD, influencing factors as well as research background and histories are systematically described in this review. It is predicted that the photodegradation mechanism, as well as anaerobic microorganisms involved in MeHg formation and degradation cycle will be the focus of future research. [ABSTRACT FROM AUTHOR]

Interspecific mycelial interactions between white rot fungi are always accompanied by an increased production of laccase. In this study, the potential of the white rot fungus Dichomitus squalens to enhance laccase production during interactions with two other white rot fungi, Trametes versicolor or Pleurotus ostreatus, was assessed. To probe the mechanism of laccase induction and the role that laccase plays during combative interaction, we analyzed the differential gene expression profile of the laccase induction response to stressful conditions during fungal interaction. We further confirmed the expression patterns of 16 selected genes by qRT-PCR analysis. We noted that many differentially expressed genes (DEGs) encoded proteins that were involved in xenobiotic detoxification and reactive oxygen species (ROS) generation or reduction, including aldo/keto reductase, glutathione S-transferases, cytochrome P450 enzymes, alcohol oxidases and dehydrogenase, manganese peroxidase and laccase. Furthermore, many DEG-encoded proteins were involved in antagonistic mechanisms of nutrient acquisition and antifungal properties, including glycoside hydrolase, glucanase, chitinase and terpenoid synthases. DEG analyses effectively revealed that laccase induction was likely caused by protective responses to oxidative stress and nutrient competition during interspecific fungal interactions. [ABSTRACT FROM AUTHOR]

For the first decade following its description in 1954, the Calvin-Benson cycle was considered the sole pathway of autotrophic CO assimilation. In the early 1960s, experiments with fermentative bacteria uncovered reactions that challenged this concept. Ferredoxin was found to donate electrons directly for the reductive fixation of CO into alpha-keto acids via reactions considered irreversible. Thus, pyruvate and alpha-ketoglutarate could be synthesized from CO, reduced ferredoxin and acetyl-CoA or succinyl-CoA, respectively. This work opened the door to the discovery that reduced ferredoxin could drive the Krebs citric acid cycle in reverse, converting the pathway from its historical role in carbohydrate breakdown to one fixing CO. Originally uncovered in photosynthetic green sulfur bacteria, the Arnon-Buchanan cycle has since been divorced from light and shown to function in a variety of anaerobic chemoautotrophs. In this retrospective, colleagues who worked on the cycle at its inception in 1966 and those presently working in the field trace its development from a controversial reception to its present-day inclusion in textbooks. This pathway is now well established in major groups of chemoautotrophic bacteria, instead of the Calvin-Benson cycle, and is increasingly referred to as the Arnon-Buchanan cycle. In this retrospective, separate sections have been written by the authors indicated. Bob Buchanan wrote the abstract and the concluding comments. [ABSTRACT FROM AUTHOR]

Previous research found that the water-level fluctuating zone (WLFZ) of the Three Gorges Reservoir (TGR) was an Hg-sensitive area. However, little research has been conducted on the distribution of Hg-methylating microorganisms in this area. The goal of this research was to provide an initial description of the distribution of the dsrB (for sulfate-reducing bacteria) and hgcA (one gene confirmed for Hg methylation) genes. Different types of soil were selected to analyze the abundance of the dsrB and hgcA in different periods, in inundated soil (SI, ≤155 m, which becomes sediment during the wet period, SS) and in non-inundated soil (≥175 m, SN) from Shibao, a typical WLFZ of the TGR. A significant positive correlation was observed between dsrB and hgcA abundance and MeHg concentrations, suggesting that microorganisms with these genes contribute to Hg methylation. Principal component analysis (PCA) indicated that dsrB diversity was highest in SI, followed by SS; SS had the highest diversity of hcgA. Six phylogenetic trees were constructed and showed that more strains were present in SI than in SS. HgcA sequences in SS were confined to three evolutionarily distant clades, δ-Proteobacteria, a methanogen group, and a Clostridia group, which was relatively rare among most clades. [ABSTRACT FROM AUTHOR]

The effect of a non-cellulolytic bacterium W2-10 ( Geobacillus sp.) on the cellulose-degrading activity of a cellulolytic bacterium CTL-6 ( Clostridium thermocellum) was determined using cellulose materials (paper and straw) in peptone cellulose solution (PCS) medium under aerobic conditions. The results indicated that in the co-culture, addition of W2-10 resulted in a balanced medium pH, and may provide the required anaerobic environment for CTL-6. Overall, addition of W2-10 was beneficial to CTL-6 growth in the adverse environment of the PCS medium. In co-culture with W2-10, the CTL-6 cellulose degradation efficiency of filter paper and alkaline-treated wheat straw significantly increased up to 72.45 and 37.79 %, respectively. The CMCase activity and biomass of CTL-6 also increased from 0.23 U ml −1 and 45.1 μg ml −1 (DNA content) up to 0.47 U ml −1 and 112.2 μg ml −1, respectively. In addition, co-culture resulted in accumulation of acetate and propionate up to 4.26 and 2.76 mg ml −1. This was a respective increase of 2.58 and 4.45 times, in comparison to the monoculture with CTL-6. [ABSTRACT FROM AUTHOR]

Decomposition of lignocelluloses by cooperative microbial actions is an essential process of carbon cycling in nature and provides a basis for biomass conversion to fuels and chemicals in biorefineries. In this study, structurally stable symbiotic aero-tolerant lignocellulose-degrading microbial consortia were obtained from biodiversified microflora present in industrial sugarcane bagasse pile (BGC-1), cow rumen fluid (CRC-1), and pulp mill activated sludge (ASC-1) by successive subcultivation on rice straw under facultative anoxic conditions. Tagged 16S rRNA gene pyrosequencing revealed that all isolated consortia originated from highly diverse environmental microflora shared similar composite phylum profiles comprising mainly Firmicutes, reflecting convergent adaptation of microcosm structures, however, with substantial differences at refined genus level. BGC-1 comprising cellulolytic Clostridium and Acetanaerobacterium in stable coexistence with ligninolytic Ureibacillus showed the highest capability on degradation of agricultural residues and industrial pulp waste with CMCase, xylanase, and β-glucanase activities in the supernatant. Shotgun pyrosequencing of the BGC-1 metagenome indicated a markedly high relative abundance of genes encoding for glycosyl hydrolases, particularly for lignocellulytic enzymes in 26 families. The enzyme system comprised a unique composition of main-chain degrading and side-chain processing hydrolases, dominated by GH2, 3, 5, 9, 10, and 43, reflecting adaptation of enzyme profiles to the specific substrate. Gene mapping showed metabolic potential of BGC-1 for conversion of biomass sugars to various fermentation products of industrial importance. The symbiotic consortium is a promising simplified model for study of multispecies mechanisms on consolidated bioprocessing and a platform for discovering efficient synergistic enzyme systems for biotechnological application. [ABSTRACT FROM AUTHOR]

The membraneless bioelectrochemical reactor (Ml-BER) is useful for dark hydrogen fermentation. The effect of the electrochemical reaction on microorganisms in the Ml-BER was investigated using glucose as the substrate and compared with organisms in a membraneless non-bioelectrochemical reactor (Ml-NBER) and bioelectrochemical reactor (BER) with a proton exchange membrane. The potentials on the working electrode of the Ml-BER and BER with membrane were regulated to −0.9 V (versus Ag/AgCl) to avoid water electrolysis with a carbon electrode. The Ml-BER showed suppressed methane production (19.8 ± 9.1 mg-C·L·day) and increased hydrogen production (12.6 ± 3.1 mg-H·L·day) at pH 6.2 ± 0.1, and the major intermediate was butyrate (24.9 ± 2.4 mM), suggesting efficient hydrogen fermentation. In contrast, the Ml-NBER showed high methane production (239.3 ± 17.9 mg-C·L·day) and low hydrogen production (0.2 ± 0.0 mg-H·L·day) at pH 6.3 ± 0.1. In the cathodic chamber of the BER with membrane, methane production was high (276.3 ± 20.4 mg-C·L·day) (pH, 7.2 ± 0.1). In the anodic chamber of the BER with membrane (anode-BER), gas production was low because of high lactate production (43.6 ± 1.7 mM) at pH 5.0 ± 0.1. Methanogenic archaea were not detected in the Ml-BER and anode-BER. However, Methanosarcina sp. and Methanobacterium sp. were found in Ml-NBER. Prokaryotic copy numbers in the Ml-BER and Ml-NBER were similar, as were the bacterial community structures. Thus, the electrochemical reaction in the Ml-BER affected hydrogenotrophic and acetoclastic methanogens, but not the bacterial community. [ABSTRACT FROM AUTHOR]

mmonia accumulation is one of the main causes of the loss of methane production observed during fermentation. We investigated the effect of addition of carbon fiber textiles (CFT) to thermophilic methanogenic bioreactors with respect to ammonia tolerance during the process of degradation of artificial garbage slurry, by comparing the performance of the reactors containing CFT with the performance of reactors without CFT. Under total ammonia-N concentrations of 3,000 mg L, the reactors containing CFT were found to mediate stable removal of organic compounds and methane production. Under these conditions, high levels of methanogenic archaea were retained at the CFT, as determined by 16S rRNA gene analysis for methanogenic archaea. In addition, Methanobacterium sp. was found to be dominant in the suspended fraction, and Methanosarcina sp. was dominant in the retained fraction of the reactors with CFT. However, the reactors without CFT had lower rates of removal of organic compounds and production of methane under total ammonia-N concentrations of 1,500 mg L. Under this ammonia concentration, a significant accumulation of acetate was observed in the reactors without CFT (130.0 mM), relative to the reactors with CFT (4.2 mM). Only Methanobacterium sp. was identified in the reactors without CFT. These results suggest that CFT enables stable proliferation of aceticlastic methanogens by preventing ammonia inhibition. This improves the process of stable garbage degradation and production of methane in thermophilic bioreactors that include high levels of ammonia. [ABSTRACT FROM AUTHOR]

idification is one of the most common and serious problems inducing process failure in anaerobic digesters. The production of volatile fatty acids (VFAs) mainly triggers acidic shock. However, little is known about the bacteria involved in the processes of acidogenic metabolism, such as fermentation and reductive acetogenesis. Here, the metabolic responses of a methanogenic community to the acidification and resulting process deterioration were investigated using transcriptional profiling of both the 16S rRNA and formyltetrahydrofolate synthetase (FTHFS) genes. The 16S rRNA-based analyses demonstrated that the dynamic shift of bacterial populations was closely correlated with reactor performance, especially with VFA accumulation levels. The pH drop accompanied by an increase in VFAs stimulated the metabolic activation of an uncultured Chloroflexi subphylum I bacterium. The subphylum has been characterized as a fermentative carbohydrate degrader using culture- and molecular-based ecophysiological assays. At the beginning of VFA accumulation, FTHFS genes were expressed; the transcripts were derived from phylogenetically predicted homoacetogens, suggesting that reductive acetogenesis was operated by hitherto unidentified bacteria. When acetate concentrations were high, the FTHFS expression ceased and Thermoanaerobacterium aciditolerans proliferated selectively. This thermoacidophilic bacterium would play a decisive role in acetate production via fermentative metabolism. The results of this study reveal for the first time that an uncultured Chloroflexi, T. aciditolerans, and novel homoacetogens were metabolically associated with acidic shock and subsequent VFA accumulation in an anaerobic digester. [ABSTRACT FROM AUTHOR]

Bioelectrochemical reactors (BERs) with a cathodic working potential of −0.6 or −0.8 V more efficiently degraded cellulosic material, i.e., filter paper (57.4-74.1% in 3 days and 95.9-96.3% in 7 days) than did control reactors without giving exogenous potential (15.4% in 3 days and 64.2% in 7 days). At the same time, resultant conversions to methane and carbon dioxide in cathodic working chamber of BERs by application of electrochemical reduction in 3 days of operation were larger than control reactors. However, cumulative methane production in cathodic BERs was similar to those in control reactors after 7 days of operation. Microscopic observation and 16S rRNA gene analysis showed that microbial growth in the entire consortium was higher after 2 days of operation of cathodic BERs as compared with the control reactors. In addition, the number of methanogenic 16S rRNA gene copies in cathodic BERs was higher than in control reactors. Moreover, archaeal community structures constructed in cathodic BERs consisted of hydrogenotrophic methanogen-related organisms and differed from those in control reactors after 2 days of operation. Specifically, the amount of Methanothermobacter species in cathodic BERs was higher within archaeal communities than in those control reactors after 2 days of operation. Electrochemical reduction may be effective for accelerating microbial growth in the start-up period and thereby increasing microbial treatment of cellulosic waste and methane production. [ABSTRACT FROM AUTHOR]

We have reported for the first time that agricultural and cellulosic waste, i.e., rice straw was directly applied to methanogenic bioreactors containing carbon fiber textiles (CFT) as supporting material. Addition of CFT to the methanogenic bioreactors enhanced the conversion of dichromate chemical oxygen demand of the substrate to methane (41%) to a greater extent than bioreactors without CFT (9%). In addition, removal of rice straw as a suspended solid was increased from 31% (in bioreactors without CFT) to 57% (in those with CFT). Methanogenic 16S rRNA gene analysis showed that the abundance of acetoclastic methanogen, genus Methanosarcina, was about 11 times higher in bioreactors with CFT (suspended fraction plus retained fraction to CFT) than in bioreactors without CFT (suspended fraction), resulting in lower concentration of acetate in bioreactors with CFT (0.4 mM) than in those without CFT (29.7 mM). On the other hand, the abundance of hydrogenotrophic methanogen, genus Methanobacterium, in bioreactors with CFT was similar to those without CFT. Bacterial communities in bioreactors with CFT were different from those in bioreactors without CFT. Our results indicated that specific microbial community and cooperative relationships between microorganisms in reactors containing CFT facilitated efficient decomposition of rice straw and its conversion to methane. [ABSTRACT FROM AUTHOR]

Adding a supporting material to a methanogenic bioreactor treating garbage slurry can improve efficiency of methane production. However, little is known on how characteristics (e.g., porosity and hydrophobicity) of the supporting material affect the bioreactor degrading garbage slurry. We describe the reactor performances and microbial communities in bioreactors containing hydrophilic or hydrophobic sheets, or fibrous hydrophilic or hydrophobic sponges. The porosity affected the efficiency of methane production and solid waste removal more than the hydrophilic or hydrophobic nature of the supporting material. When the terminal restriction fragment length polymorphism technique was used at a lower organic loading rate (OLR), microbial diversities in the suspended fraction were retained on the hydrophobic, but not the hydrophilic, sheets. Moreover, real-time quantitative polymerase chain reaction (PCR) performed at a higher OLR revealed that the excellent performance of reactors containing fibrous sponges with high porosity (98%) was supported by a clear increase in the numbers of methanogens on these sponges, resulting in larger total numbers of methanogens in the reactors. In addition, the bacterial communities in fractions retained on both the hydrophobic and hydrophilic fibrous sponges differed from those in the suspended fraction, thus increasing bacterial diversity in the reactor. Thus, higher porosity of the supporting material improves the bioreactor performance by increasing the amount of methanogens and bacterial diversity; surface hydrophobicity contributes to maintaining the suspended microbial community. [ABSTRACT FROM AUTHOR]

In anoxic rice field soil, ferric iron reduction is one of the most important terminal electron accepting processes, yet little is known about the identity of iron-reducing microorganisms. Here, we identified acetate-metabolizing bacteria by RNA-based stable isotope probing in the presence of iron(III) oxides as electron acceptors. After reduction of endogenous iron(III) for 21 days, isotope probing with 13C-labeled acetate (2 mM) and added ferric iron oxides (ferrihydrite or goethite) was performed in rice field soil slurries for 48 and 72 h. Ferrihydrite reduction coincided with a strong suppression of methanogenesis (77%). Extracted RNA from each treatment was density resolved by isopycnic centrifugation, and analyzed by terminal restriction fragment length polymorphism, followed by cloning and sequencing of 16S rRNA of bacterial and archaeal populations. In heavy, isotopically labeled RNAs of the ferrihydrite treatment, predominant 13C-assimilating populations were identified as Geobacter spp. (∼85% of all clones). In the goethite treatment, iron(II) formation was not detectable. However, Geobacter spp. (∼30%), the δ-proteobacterial Anaeromyxobacter spp. (∼30%), and novel β-Proteobacteria were predominant in heavy rRNA fractions indicating that 13C-acetate had been assimilated in the presence of goethite, whereas none were detected in the control heavy RNA. For the first time, active acetate-oxidizing iron(III)-reducing bacteria, including novel hitherto unrecognized populations, were identified as a functional guild in anoxic paddy soil. [ABSTRACT FROM AUTHOR]

Hydrogenobacter thermophilus TK-6 is a thermophilic, chemolithoautotrophic, hydrogen-oxidizing bacterium that fixes carbon dioxide via the reductive tricarboxylic acid (rTCA) cycle. 2-Oxoglutarate:ferredoxin oxidoreductase (OGOR) is the key enzyme in this cycle that fixes carbon dioxide. The genome of strain TK-6 encodes at least two distinct OGOR enzymes, termed For and Kor. We report here a method for measuring the carboxylation of succinyl-CoA catalyzed by OGORs. The method involves the in vitro coupling of OGOR with ferredoxin and pyruvate:ferredoxin oxidoreductase from strain TK-6, and glutamate dehydrogenase from Sulfolobus tokodaii. Using this method, we determined both the apparent maximum velocities and the Km values of For and Kor for the carboxylation of succinyl-CoA. This is the first reported kinetic analysis of carbon fixation catalyzed by OGOR enzymes from the rTCA cycle. [ABSTRACT FROM AUTHOR]

We investigated the network relationships of bacteria in a structurally stable mixed culture degrading cellulose. The mixed culture consists of four bacterial strains (a cellulose-degrading anaerobe [strain S], a saccharide-utilizing anaerobe [strain F], a peptide- and acetate-utilizing aerobe [strain 3] and a peptide-, glucose-, and ethanol-utilizing aerobe [strain 5]). Interspecies interactions were examined by analyzing the effects of culture filtrates on the growth of the other strains and by comprehensively analyzing population dynamics in the mixed-culture systems with all possible combinations of the four bacterial strains. The persistence of strain S depends on the effects of strain 5. However, strain 5 is a disadvantaged strain because strain 3 has bacteriocidal activity on strain 5. The extinction of strain 5 is indirectly prevented by strain F that suppresses the growth of strain 3. Although strain F directly has suppressive effects on the growth of strain S, strain F is essential for the persistence of strain S, considering the indirect effects (maintaining strain 5, which is essential for the survival of strain S, by inhibiting strain 3). These indirect relationships form a bacterial network in which all the relationships including suppressive effects were well balanced to maintain the structural stability. In addition to direct metabolite interactions, such kind of indirect relationships could have a great impact on microbial community structure in the natural environment. [ABSTRACT FROM AUTHOR]

An anaerobic packed-bed reactor using carbon fiber textiles (CFT) as the supporting material was continuously operated using an artificial garbage slurry. 16S rRNA gene analysis showed that many bacteria in the biomass adhering to CFT were closely related to those observed from other anaerobic environments, although a wide variety of unidentified bacteria were also found. Dot blot hybridization results clarified that 16S rRNA levels of methanogens in the adhering biomass were higher than those in the effluent. Based on microscopic observation, the adhering biomass consisted of microorganisms, organic material, and void areas. Bacteria and Archaea detected by fluorescence in situ hybridization were distributed from the surface to the inner regions of the adhering biomass. Methanosarcina sp. tended to be more abundant in the inner part of the adhering biomass than at the surface. This is the first report to elucidate the structure of the microbial community on CFT in a packed-bed reactor. [ABSTRACT FROM AUTHOR]

A novel thermoacidophilic iron-reducing Archaeon, strain NA−1, was isolated from a hot fumarole in Manza, Japan. Strain NA-1 could grow autotrophically using H2 or S0 as an electron donor and Fe3+ as an electron acceptor, and also could grow heterotrophically using some organic compounds. Fe3+ and O2 served as electron acceptors for growth. However, S0, NO3 −, NO2 −, SO4 2−, Mn4+, fumarate, and Fe2O3 did not serve as electron acceptors. The ranges of growth temperature and pH were 60–90°C (optimum: 80°C) and pH 1.0–5.0 (optimum: pH 1.2–1.5), respectively. Cells were nearly regular cocci with an envelope comprised of the cytoplasmic membrane and a single outer S-layer. The crenarchaeal-specific quinone (cardariellaquinone) was detected, and the genomic DNA G + C content was 29.9 mol%. From 16S rDNA analysis, it was determined that strain NA-1 is closely related to Acidianus ambivalens (93.1%) and Acidianus infernus (93.0%). However, differences revealed by phylogenetic and phenotypic analyses clearly show that strain NA-1 represents a new species, Acidianus manzaensis, sp. nov., making it the first identified thermoacidophilic iron-reducing microorganism (strain NA-1T = NBRC 100595 = ATCC BAA 1057). [ABSTRACT FROM AUTHOR]

Hydrogenobacter thermophilus strain TK-6 was observed to grow anaerobically on nitrate as an electron acceptor when molecular hydrogen was used as an energy source. Nitrite was detected as the product of a respiratory reaction. 15NO, 15N2O, and 15N2 were detected with Na15NO3 as an electron acceptor. Western immunoblot analysis showed that cell-free extracts from cells grown on nitrate reacted with antibodies against heme cd1-type nitrite reductase from Pseudomonas aeruginosa. The positive bands, which had molecular masses similar to that of the heme cd1-type nitrite reductase, were also stained by heme staining. These results indicate that nitrite reductase of strain TK-6 is a heme cd1-type enzyme. Activity of ATP:citrate lyase, one of the key enzymes of the reductive TCA cycle, was detected in cell-free extract of cells cultivated on nitrate, which indicates that the cycle operates during anaerobic growth. [ABSTRACT FROM AUTHOR]

The autotrophic CO fixation pathway in Acidianus brierleyi, a facultatively anaerobic thermoacidophilic archaebacterium, was investigated by measuring enzymatic activities from autotrophic, mixotrophic, and heterotrophic cultures. Contrary to the published report that the reductive tricarboxylic acid cycle operates in A. brierleyi, the enzymatic activity of ATP:citrate lyase, the key enzyme of the cycle, was not detected. Instead, activities of acetyl-CoA carboxylase and propionyl-CoA carboxylase, key enzymes of the 3-hydroxypropionate cycle, were detected only when A. brierleyi was growing autotrophically. We conclude that a modified 3-hydroxypropionate pathway operates in A. brierleyi. [ABSTRACT FROM AUTHOR]

An obligately chemolithoautotrophic and aerobic hydrogen-oxidizing bacterium was isolated from a seaside saline hot spring in Izu Peninsula, Japan. The isolate was a Gram-negative, non-motile, non-spore-forming rod cell measuring 0.3 to 0.5 by 1.0 to 2.5 μm. The optimal temperature for growth was around 70°C, and no growth was observed at 40°C or 80°C. Elemental sulfur or thiosulfate could be an alternative to molecular hydrogen as the sole energy source. The DNA base composition of the isolate was 46.0 mol% G+C. 2-Methylthio-3-VI,VII-tetrahydromultiprenyl-1,4-naphthoquinone (methionaquinone) was the major component of the quinone system. C, C and C were the major components of the cellular fatty acids. These properties clearly indicate that the isolate belongs to genus Hydrogenobacter, but differed from H. thermophilus in some respects. Specifically, the isolate was a halophile which grew optimally at around 0.3-0.5 M NaCl, while H. thermophilus could not grow at such NaCl concentration levels. A new species name H. halophilus is proposed for this new halophilic isolate. [ABSTRACT FROM AUTHOR]

An obligately chemolithoautotrophic and aerobic hydrogen-oxidizing bacterium was isolated from seawater of the Shonan Coast, Kanagawa Pref., Japan. The isolate was a Gram-negative, comma-shaped rod cell measuring 0.2 to 0.5 by 1 to 2 μm. The cells occurred singly and were motile by a polar flagellum. The deoxyribonucleic acid base composition of the isolate was 44.1 mol% guanine plus cytosine. The optimal temperature for autotrophic growth on H−O−CO was around 37°C, and no growth was observed at 5° C or 45° C. The optimal pH for growth was around 6.5. NaCl was required for growth with an optimum of 0.5 M. Elemental sulfur, thiosulfate or tetrathionate was utilized, as well as molecular hydrogen, as the sole energy source. No heterotrophic growth was observed on organic media tested. To our knowledge, this is the first report of the isolation of a marine, aerobic hydrogen-oxidizing bacterium, and of an obligately chemolithoautotrophic, mesophilic and aerobic hydrogen-oxidizing bacterium. [ABSTRACT FROM AUTHOR]

The incorporation of CO by the cell suspensions of an extremely thermophilic, aerobic hydrogen-oxidizing bacterium, Hydrogenobacter thermophilus was studied. After short time incubation of the cell suspensions with CO, the radiactivity was initially present in aspartate, glutamate, succinate, phosphorylated compounds, citrate, malate and fumarate. All of these compounds except phosphorylated compounds were related to the members of the tricarboxylic acid cycle. The proportion of labelled aspartate onglutamate in total radioactivity on each chromatogram decreased with incubation time, while the percentage of the radioactivity incorporated in phosphorylated compounds increased with time up to 10 s. These indicated that aspartate and glutamate is derived from primary products of CO fixation. In cell-free extracts of Hydrogenobacter thermophilus, the two key enzymes in the Calvin cycle, ribulose-1,5-bisphosphate carboxylase and phosphoribulokinase could not be detected. The key enzymes of the reductive tricarboxylic acid cycle, fumarate reductase and ATP citrate lyase were present. Activities of phosphoenolpyruvate synthetase and pyruvate carboxylase were also detected. The referse reactions (dehydrogenase reactions) of α-ketoglutarate synthase and pyruvate synthase could be detected by using methyl viologen as an electron acceptor. These findings strongly suggested that a new type of the reductive tricarboxylic acid cycle operated as the CO fixation pathway in Hydrogenobacter thermophilus. [ABSTRACT FROM AUTHOR]

The endoglucanase gene, celCCD, of Clostridium cellulolyticum has been expressed in Escherichia coli. Multiple active polypeptides were detected in the E. coli cells. The relative molecular mass (M) of two major active polypeptides were 56 000 (D56) and 38 000 (D38), which were smaller than the deduced M of the mature protein (63 401). D56 and D38 were purified from the periplasmic fraction. The N-terminal sequences of the two purified polypeptides were identical to that of the mature endoglucanase (Ala-Ile-Asn-Ser-Gln-Asp-Met-Val---) deduced from the nucleotide sequence. These data indicated that these polypeptides were produced by processing the original mature protein in the C-terminal region. The enzymatic properties of these two polypeptides were very similar, except that the specific activity of D38 was 2-3.5-fold higher than that of D56, and D38 was more heat stable than D56. [ABSTRACT FROM AUTHOR]

Two genes coding for endoglucanase activity in Clostridium cellulolyticum were cloned and expressed in Escherichia coli by using plasmid pUC18. The sizes of two fragments harbouring endoglucanase genes are 4.4 kb and 2.0 kb, respectively. The 2.0-kb fragment was identical with a reported DNA fragment encoding an endoglucanase of C. cellulolyticum. The 4.4-kb fragment was obtained first in this study. Deletion analysis showed that a 1.3-kb portion of the 4.4-kb fragment is necessary for the endoglucanase expression by its own promoter. The 4.4-kb fragment hybridized with several different fragments of the genomic DNA in C. cellulolyticum. [ABSTRACT FROM AUTHOR]

A novel thermoacidophilic iron-reducing Archaeon, strain NA−1, was isolated from a hot fumarole in Manza, Japan. Strain NA-1 could grow autotrophically using H2 or S0 as an electron donor and Fe3+ as an electron acceptor, and also could grow heterotrophically using some organic compounds. Fe3+ and O2 served as electron acceptors for growth. However, S0, NO3 −, NO2 −, SO4 2−, Mn4+, fumarate, and Fe2O3 did not serve as electron acceptors. The ranges of growth temperature and pH were 60–90°C (optimum: 80°C) and pH 1.0–5.0 (optimum: pH 1.2–1.5), respectively. Cells were nearly regular cocci with an envelope comprised of the cytoplasmic membrane and a single outer S-layer. The crenarchaeal-specific quinone (cardariellaquinone) was detected, and the genomic DNA G + C content was 29.9 mol%. From 16S rDNA analysis, it was determined that strain NA-1 is closely related to Acidianus ambivalens (93.1%) and Acidianus infernus (93.0%). However, differences revealed by phylogenetic and phenotypic analyses clearly show that strain NA-1 represents a new species, Acidianus manzaensis, sp. nov., making it the first identified thermoacidophilic iron-reducing microorganism (strain NA-1T = NBRC 100595 = ATCC BAA 1057). [ABSTRACT FROM AUTHOR]