Implication of amino acid metabolism and cell surface integrity for the thermotolerance mechanism in the thermally adapted acetic acid bacterium Acetobacter pasteurianus TH-3

IMPORTANCE

Acetobacter pasteurianus, an industrial vinegar-producing strain, is suffered by fermentation stress such as fermentation heat and/or high concentrations of acetic acid. By an experimental evolution approach, we have obtained a stress-tolerant strain, exhibiting significantly increased growth and acetic acid fermentation ability at higher temperatures. In this study, we report that only the three gene mutations of ones accumulated during the adaptation process, ansP, dctD, and glnD, were sufficient to reproduce the increased thermotolerance of A. pasteurianus. These mutations resulted in cell envelope modification, including increased phospholipid and lipopolysaccharide synthesis, increased respiratory activity, and cell size reduction. The phenotypic changes may cooperatively work to make the adapted cell thermotolerant by enhancing cell surface integrity, nutrient or oxygen availability, and energy generation.

Periplasmic dehydroshikimate dehydratase combined with quinate oxidation in Gluconobacter oxydans for protocatechuate production

Protocatechuate (3,4-dihydroxybenzoate) has antioxidant properties and is a raw material for the production of muconic acid, which is a key compound in the synthesis of polymers such as nylon and polyethylene terephthalate. Gluconobacter oxydans strain NBRC3244 has a periplasmic system for oxidation of quinate to produce 3-dehydroquinate. Previously, a periplasmic 3-dehydroshikimate production system was constructed by heterologously expressing Gluconacetobacter diazotrophicus dehydroquinate dehydratase in the periplasm of G. oxydans strain NBRC3244. 3-Dehydroshikimate is converted to protocatechuate by dehydration. In this study, we constructed a G. oxydans strain that expresses the Acinetobacter baylyi quiC gene, which encodes a dehydroshikimate dehydratase of which the subcellular localization is likely the periplasm. We attempted to produce protocatechuate by co-cultivation of two recombinant G. oxydans strains-one expressing the periplasmically targeted dehydroquinate dehydratase and the other expressing A. baylyi dehydroshikimate dehydratase. The co-cultivation system produced protocatechuate from quinate in a nearly quantitative manner.

Heterologous expression of membrane-bound alcohol dehydrogenase-encoding genes for glyceric acid production using Gluconobacter sp. CHM43 and its derivatives

In contrast to D-glyceric acid (D-GA) production with 99% enantiomeric excess (ee) by Acetobacter tropicalis NBRC 16470, Gluconobacter sp. CHM43 produced 19.6 g L^-1 of D-GA with 73.7% ee over 4 days of incubation in flask culture. To investigate the reason for this enantiomeric composition of GA, the genes encoding membrane-bound alcohol dehydrogenase (mADH) of A. tropicalis NBRC 16470, composed of three subunits (adhA, adhB, and adhS), were cloned using the broad-host-range vector pBBR1MCS-2 and heterologously expressed in Gluconobacter sp. CHM43 and its ΔadhAB ΔsldBA derivative TORI4. Reverse-transcription quantitative real-time polymerase chain reaction demonstrated that adhABS genes from A. tropicalis were expressed in TORI4 transformants, and their membrane fraction exhibited mADH activities of 0.13 and 0.31 U/mg with or without AdhS, respectively. Compared with the GA production of TORI4-harboring pBBR1MCS-2 (1.23 g L^-1), TORI4 transformants expressing adhABS and adhAB showed elevated GA production of 2.46 and 3.67 g L^-1, respectively, suggesting a negative effect of adhS gene expression on GA production as well as mADH activity in TORI4. Although TORI4 was found to produce primarily L-GA with 42.5% ee, TORI4 transformants expressing adhABS and adhAB produced D-GA with 27.6% and 49.0% ee, respectively, demonstrating that mADH of A. tropicalis causes a sharp increase in the enantiomeric composition of D-GA. These results suggest that one reason for D-GA production with 73.7% ee in Gluconobacter spp. might be a property of the host, which possibly produces L-GA intracellularly. KEY POINTS: • Membrane-bound ADH from Acetobacter tropicalis showed activity in Gluconobacter sp. • D-GA production from glycerol was performed using recombinant Gluconobacter sp. • Enantiomeric excess of D-GA was affected by both membrane and intracellular ADHs.

Relocation of dehydroquinate dehydratase to the periplasmic space improves dehydroshikimate production with Gluconobacter oxydans strain NBRC3244

3-Dehydroshikimate (3-DHS) is a key intermediate for the synthesis of various compounds, including the antiviral drug oseltamivir. The Gluconobacter oxydans strain NBRC3244 intrinsically oxidizes quinate to produce 3-dehydroquinate (3-DHQ) in the periplasmic space. Even though a considerable activity is detected in the recombinant G. oxydans homologously overexpressing type II dehydroquinate dehydratase (DHQase) encoded in the aroQ gene at a pH where it grows, an alkaline shift of the culture medium is required for 3-DHS production in the middle of cultivation. Here, we attempted to adopt type I DHQase encoded in the aroD gene of Gluconacetobacter diazotrophicus strain PAL5 because the type I DHQase works optimally at weak acid, which is preferable for growth conditions of G. oxydans. In addition, we anticipated that subcellular localization of DHQase is the cytoplasm, and therefore, transports of 3-DHQ and 3-DHS across the cytoplasmic membrane are rate-limiting steps in the biotransformation. The Sec- and TAT-dependent signal sequences for secretion were attached to the N terminus of AroD to change the subcellular localization. G. oxydans that expresses the TAT-AroD derivative achieved 3-DHS production at a tenfold higher rate than the reference strain that expresses wild-type AroD even devoid of alkaline shift. Enzyme activity with the intact cell suspension and signal sequence cleavage supported the relocation of AroD to the periplasmic space. The present study suggests that the relocation of DHQase improves 3-DHS production in G. oxydans and represents a proof of concept for the potential of enzyme relocation in metabolic engineering. KEY POINTS: • Type-I dehydroquinate dehydratase (DHQase) was expressed in Gluconobacter oxydans. • Cytoplasmic DHQase was relocated to the periplasmic space in G. oxydans. • Relocation of DHQase in G. oxydans improved 3-dehydroshikimate production.

Thermal adaptation of acetic acid bacteria for practical high-temperature vinegar fermentation

Thermotolerant microorganisms are useful for high-temperature fermentation. Several thermally adapted strains were previously obtained from Acetobacter pasteurianus in a nutrient-rich culture medium, while these adapted strains could not grow well at high temperature in the nutrient-poor practical culture medium, "rice moromi." In this study, A. pasteurianus K-1034 originally capable of performing acetic acid fermentation in rice moromi was thermally adapted by experimental evolution using a "pseudo" rice moromi culture. The adapted strains thus obtained were confirmed to grow well in such the nutrient-poor media in flask or jar-fermentor culture up to 40 or 39 °C; the mutation sites of the strains were also determined. The high-temperature fermentation ability was also shown to be comparable with a low-nutrient adapted strain previously obtained. Using the practical fermentation system, "Acetofermenter," acetic acid production was compared in the moromi culture; the results showed that the adapted strains efficiently perform practical vinegar production under high-temperature conditions.

Donghicola mangrovi sp. nov., a member of the family Rhodobacteraceae isolated from mangrove forest in Thailand

Two novel Gram-stain-negative, rod-shaped and non-motile bacterial strains, designated B5-SW-15^T and C2-DW-16, were isolated from water collected in mangrove forests in Ranong Province, Thailand. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strains B5-SW-15^T and C2-DW-16 belonged to the genus Donghicola and were most closely related to Donghicola tyrosinivorans DSM 100212^T (98.2 and 98.1 %, respectively) and Donghicola eburneus DSM 29127^T (97.7 and 97.6 %, respectively). The average nucleotide identity and digital DNA-DNA hybridization values between strain B5-SW-15^T, strain C2-DW-16 and related species were 95.8 and 71.6 % (to strain C2-DW-16), 76.8 and 21.3 % (to D. tyrosinivorans DSM 100212^T) and 80.3 and 24.2 % (to D. eburneus DSM 29127^T), respectively. The predominant cellular fatty acids (>5 %) were summed feature 8 (C_18 : 1  ω6c and/or C_18 : 1  ω7c), C_16 : 0 and C_12 : 1 3-OH. Ubiquinone Q-10 was the sole respiratory quinone. DNA G+C contents of the isolates were 61.0 and 61.2 mol% based on whole genome sequences. Strains B5-SW-15^T and C2-DW-16 contained aminolipid, phosphatidylcholine, phosphatidylethanolamine and phosphatidylglycerol as the major polar lipids. On the basis of the results from phenotypic, chemotaxonomic and phylogenetic analyses, strains B5-SW-15^T and C2-DW-16 constitute a novel species of the genus Donghicola in the family Rhodobacteraceae for which the name Donghicola mangrovi sp. nov. is proposed. The type strain is B5-SW-15^T (=BCC 56522^T=TBRC 9562^T=KCTC 72743^T).

TEMPO-oxidized cellulose nanofibril film from nano-structured bacterial cellulose derived from the recently developed thermotolerant Komagataeibacter xylinus C30 and Komagataeibacter oboediens R37-9 strains

Bacterial cellulose (BC), prepared from two recently developed thermotolerant bacterial strains (Komagataeibacter xylinus C30 and Komagataeibacter oboediens R37-9), were used as a raw material to synthesize nanofibril films. Field-emission scanning electron microscope (FE-SEM) observations confirmed the ultrafine nano-structure of BC pellicle (BCP) with average fibril widths between 50 and 60 nm. The BC was directly oxidized in a TEMPO/NaBr/NaClO system at pH of 10 for 2 h. TEMPO-oxidized bacterial cellulose nanofibrils (TOBCN) were obtained by a mild mechanical treatment and the TOBCN films were prepared through heat-drying. The oxidation yielded a recovery ratio between 70 and 80% by weight with an increase in the carboxylate content of 0.9-1.0 mmol g ^-1. Nanofibrillation yields were more than 90% and the resulting high aspect ratio TOBCNs were ~6 nm in average width with >800 nm in lengths, when observed under transmission electron microscope (TEM). TOBCN film of K. xylinus C30 exhibited high transparency (79%), tensile strength (142 MPa), Young's modulus (7.13 GPa), elongation around failure (3.89%), and work of fracture (2.29 MJ m^-3), when compared to the TOBCN films of K. oboediens R37-9 at 23 °C and 50% RH. Coefficients of thermal expansion of both the TOBCN films were low at around 6 ppm K^-1.

Komagataeibacter diospyri sp. nov., a novel species of thermotolerant bacterial nanocellulose-producing bacterium

Thermotolerant bacterial nanocellulose-producing strains, designated MSKU 9^T and MSKU 15, were isolated from persimmon and sapodilla fruits, respectively. These strains were aerobic, Gram-stain-negative, had rod-shaped cells, were non-motile and formed white-cream colonies. Phylogeny based on the 16S rRNA gene sequences revealed that MSKU 9^T and MSKU 15 represented members of the genus Komagataeibacter and formed a monophyletic branch with K. swingsii JCM 17123^T and K. europaeus DSM 6160^T. The genomic analysis revealed that overall genomic relatedness index values of MSKU 9^T with K. swingsii JCM 17123^T and K. europaeus DSM 6160^T were ~90 % average nucleotide identity (ANI) and ≤58.2 % digital DNA-DNA hybridization (dDDH), respectively. MSKU 9^T and MSKU 15 can be differentiated from the closely related K. swingsii JCM 17123^T by their growth on 30 % d-glucose and ability to utilize and to form acid from raffinose and sucrose as carbon sources, and from K. europaeus DSM 6160^T by their ability to grow without acetic acid. The genomic DNA G+C contents of MSKU 9^T and MSKU 15 were 60.4 and 60.2 mol%, respectively. The major fatty acids of MSKU 9^T and MSKU 15 were summed feature 8 (C_18 : 1  ω7c and/or C_{18  : 1}ω6c). The respiratory quinone was determined to be Q10. On the basis of the results of the polyphasic taxonomic analysis, MSKU 9^T (=TBRC 9844^T=NBRC 113802^T) represents a novel species of the genus Komagataeibacter, for which the name Komagataeibacter diospyri sp. nov. is proposed.

Superfine bacterial nanocellulose produced by reverse mutations in the bcsC gene during adaptive breeding of Komagataeibacter oboediens

Nonsense mutation in the bcsC gene occurred in the ethanol-adapted strain of Komagataeibacter oboediens MSKU 3, E3 strain, resulting in the loss of the function to produce BNC. In this study, we tried to restore the BNC-producing ability of E3 strain by the following adaptive mutation through repetitive static culture, and obtained four BNC-producing revertant strains, of which the bcsC gene had InDel mutations near the frameshift mutation region in E3 strain, resulting in several amino acid alterations compared with the BcsC of MSKU 3. Each revertant produced BNCs with different productivity on the static culture. Interestingly, one of the revertants, R37-9, produced BNC with a finer structure and narrower range of fibrils width, compared to others. The genome of R37-9 strain revealed only one amino acid substitution in the bcsC gene. Thus, we concluded that N713D mutation occurred in the bcsC gene is responsible for the finer fibrils structure.

Mutated fabG gene encoding oxidoreductase enhances the cost-effective fermentation of jasmine rice vinegar in the adapted strain of Acetobacter pasteurianus SKU1108

A low-nutrient adapted strain, Acetobacter pasteurianus G-40, was successfully obtained by repetitive cultivation of A. pasteurianus 7E-13 under selective pressure. The adapted strain could grow well and produce 3.45-fold higher amounts of acetic acid than 7E-13 in jasmine rice wine containing 6% ethanol at 37 °C in a shaking flask. The G-40 strain also exhibited higher amounts of acetic acid (5.16%) in 2-L jar fermentor compared with 7E-13, where the bio-conversion yield to acetic acid from ethanol was 71% and 55.5% in the adapted strain and parental strain, respectively. In addition, genome sequence analysis of G-40 revealed that the strain has mutations in the 6 genes, of which the fabG gene encoding oxidoreductase is largely mutated by the partial recombination with a highly homologous fabG homolog present in the large plasmid of the strain. Over-expression of the mutated fabG gene and also the replacement of the original fabG gene in the chromosome with the mutated one obviously enhanced growth and acetic acid production of 7E-13 in the rice wine without any nutrient supplementation, indicating that the mutation in the fabG gene is mainly involved in higher fermentation ability under low-nutrient conditions. Thus, the results suggest that the adapted G-40 strain has proven useful for the cost-effective fermentation of rice vinegar.

Complete Genome Sequencing and Comparative Genomic Analysis of the Thermotolerant Acetic Acid Bacterium, Acetobacter pasteurianus SKU1108, Provide a New Insight into Thermotolerance

Acetobacter pasteurianus SKU1108 is a typical thermotolerant acetic acid bacterium. In this study, the complete genome sequence of the SKU1108 strain was elucidated, and information on genomic modifications due to the thermal adaptation of SKU1108 was updated. In order to obtain a clearer understanding of the genetic background responsible for thermotolerance, the SKU1108 genome was compared with those of two closely related complete genome strains, thermotolerant A. pasteurianus 386B and mesophilic A. pasteurianus NBRC 3283. All 24 "thermotolerant genes" required for growth at higher temperatures in the thermotolerant Acetobacter tropicalis SKU1100 strain were conserved in all three strains. However, these thermotolerant genes accumulated amino acid mutations. Some biased mutations, particularly those that occurred in xanthine dehydrogenase XdhA, may be related to thermotolerance. By aligning whole genome sequences, we identified ten SKU1108 strain-specific regions, three of which were conserved in the genomes of the two thermotolerant A. pasteurianus strains. One of the regions contained a unique paralog of the thermotolerant gene xdhA, which may also be responsible for conferring thermotolerance. Thus, comparative genomics of complete genome sequences may provide novel insights into the phenotypes of these thermotolerant strains.

A Novel Type of Formaldehyde-Oxidizing Enzyme from the Membrane ofAcetobactersp. SKU 14

Membrane-bound NADP-independent formaldehyde-oxidizing enzyme was purified to homogeneity from the membrane of Acetobacter sp. SKU 14 isolated in Thailand. The enzyme was solubilized from the membrane fraction of glycerol-grown cells with 1% Tween 20 at pH 2.85, and purified to homogeneity through the steps of column chromatographies on DEAE-Sephadex A-50 and Q-Sepharose in the presence of 0.1% Tween 20 and 0.1% Triton X-100. The enzyme purified together with a cytochrome c showed a single protein band on native-PAGE, and was dissociated into three different subunits upon SDS-PAGE with molecular masses of 78 kDa, 55 kDa, and 18 kDa. The purified enzyme was finally characterized as a quinoprotein alcohol dehydrogenase (QADH), and this is the first indication that QADH highly oxidizes formaldehyde. The substrate specificity of the enzyme was found to be broad toward aldehydes and alcohols, and alcohols, especially n-butanol, n-propanol, and ethanol, were oxidized more rapidly than formaldehyde.

Influence of Acetobacter pasteurianus SKU1108 aspS gene expression on Escherichia coli morphology

The aspS gene encoding Aspartyl-tRNA synthetase (AspRS) from a thermotolerant acetic acid bacterium, Acetobacter pasteurianus SKU1108, has been cloned and characterized. The open reading frame (ORF) of the aspS gene consists of 1,788 bp, encoding 595 amino acid residues. The highly conserved Gly-Val-Asp-Arg ATP binding motif (motif 3) is located at the position 537-540 in the C-terminus. Deletion analysis of the aspS gene upstream region suggested that the promoter is around 173 bp upstream from the ATG initiation codon. Interestingly, transformation with the plasmids pGEM-T138, pUC138, and pCM138 synthesizing 138 amino acid C-terminal fragments of AspRS, that carry the ATP binding domain, caused E. coli cell lengthening at 37 and 42°C. Moreover, E. coli harboring pUC595 (synthesizing all 595 amino acids) and a disordered aspS gene in pGEM-T138 had normal rod shapes. The normal rod shape was observed in E. coli harboring pD539V following site-directed mutagenesis of the ATP binding domain. We propose that over-production of truncated C-terminal peptides of AspRS may cause sequestration of intracellular ATP in E. coli, leaving less ATP for cell division or shaping cell morphology.

Molecular cloning and characterization of two inducible NAD⁺-adh genes encoding NAD⁺-dependent alcohol dehydrogenases from Acetobacter pasteurianus SKU1108

The cytosolic NAD⁺-dependent alcohol dehydrogenases (NAD⁺-ADHs) are induced in the quinoprotein ADH-(PQQ-ADH) defective Acetobacter pasteurianus SKU1108 mutant during growth in an ethanol medium. The adhI and adhII genes, which encode NAD⁺-ADH I and ADH II, respectively, of this strain have been cloned and characterized. Sequence analyses have revealed that the adhI gene consists of 1029 bp coding for 342 amino acids, which share 99.71% identity with the same protein from A. pasteurianus IFO 3283. Conversely, the adhII gene is composed of 762 bp encoding for a polypeptide of 253 amino acids, which exhibit 99.60% identity with the A. pasteurianus IFO 3283 protein. ADH I is a member of the group I Zn-dependent long-chain ADHs, while the ADH II belongs to the group II short-chain dehydrogenase/reductase NAD⁺-ADHs. The NAD⁺-adh gene disruptants exhibited a growth reduction when grown in an ethanol medium. In Escherichia coli, ethanol induced adhI and adhII promoter activities by approximately 1.5 and 2.0 times, respectively, and the promoter activity of the adhII gene exceeded that of the adhI gene by approximately 3.5 times. The possible promoter regions of the adhI and adhII genes are located at approximately 81-105 bp and 74-92 bp, respectively, from their respective ATG start codons. Their repressor regions might be located in proximity to these promoters and may repress gene expression in the wild-type, where the membrane-bound ADH effectively functions.

Morphology, genetic diversity, temperature tolerance and toxicity of Cylindrospermopsis raciborskii (Nostocales, Cyanobacteria) strains from Thailand and Japan

Cylindrospermopsis raciborskii is a planktonic, nostocalean cyanobacterium, which produces an alkaloid heptatoxin, cylindrospermopsin. We performed morphological observations, 16S rDNA sequence analysis, PCR fingerprint analysis of short tandemly repeated repetitive (STRR) sequences, temperature tolerances and toxin analysis to characterize 24 strains of this toxic cyanobacterium isolated from Thailand and Japan. All strains shared common morphological traits characteristic of C. raciborskii and showed high 16S rDNA sequence similarity, forming a defined cluster together with the reference strains from Australia. In particular, some of the Thai strains shared 99.9% to 100% similarity with the Australian strains. Various combinations of STRR primers revealed different and unique DNA band patterns among strains of C. raciborskii. The phylogenetic tree revealed two main clusters of C. raciborskii strains, the Thai/Japan-Shinobazugaike cluster (cluster I) and the Japan-Gonoike cluster (cluster II). Cluster I was further divided into two subclusters, A (only Thai strains) and B (one Thai strain and the Japan-Shinobazugaike strains). Thus, the results from 16S rDNA and STRR analyses showed no clear geographical distinction between Japanese and Thai strains and between Thai and Australian strains. Thai strains were separated into adaptive and non-adaptive groups to low temperature (15 and 17.5 degrees C) and Japanese strains were composed of only low-temperature-adaptive ones. The toxin cylindrospermopsin was detected in some strains of cluster I-A and in one strain of cluster II. We conclude that C. raciborskii is a species that has recently begun to invade, and a species with different physiological strains or ecotypes in temperature tolerance; the toxin is synthesized without any relation to phylogenetic or genetic clusters and to geography.

Purification and characterization of two NAD-dependent alcohol dehydrogenases (ADHs) induced in the quinoprotein ADH-deficient mutant of Acetobacter pasteurianus SKU1108

High NAD-dependent alcohol dehydrogenase (ADH) activity was found in the cytoplasm when a membrane-bound, quinoprotein, ADH-deficient mutant strain of Acetobacter pasteurianus SKU1108 was grown on ethanol. Two NAD-dependent ADHs were separated and purified from the supernatant fraction of the cells. One (ADH I) is a trimer, consisting of an identical subunit of 42 kDa, while the other (ADH II) is a homodimer, having a subunit of 31 kDa. One of the two ADHs, ADH II, easily lost the activity during the column chromatographies, which could be stabilized by the addition of DTT and MgCl2 in the column buffer. ADH I but not ADH II contained approximately one zinc atom per subunit. The N-terminal amino acid analysis indicated that ADH I and ADH II have homology to the long-chain and short-chain ADH families, respectively. ADH I showed a preference for primary alcohols, while ADH II had a preference for secondary alcohols. The two ADHs showed clear difference in their kinetics on ethanol, acetaldehyde, NAD, and NADH. The physiological function of both ADH I and ADH II are also discussed.

Quinoprotein alcohol dehydrogenase is involved in catabolic acetate production, while NAD-dependent alcohol dehydrogenase in ethanol assimilation in Acetobacter pasteurianus SKU1108

The relationship between quinoprotein alcohol dehydrogenase (ADH) and NAD-dependent ADH was studied by constructing quinoprotein ADH-deficient mutants. Quinoprotein ADH-deficient mutants were successfully constructed from Acetobacter pasteurianus SKU1108 by N-methyl-N'-nitro-N-nitrosoguanidine (NTG) mutagenesis and also by adhA gene disruption with a kanamycin cassette. The NTG mutant exhibited a complete loss of its acetate-producing ability and acetic acid resistance, while the disruptant also exhibited a loss of its acetic acid resistance but retained a weak ADH activity. The immunoblot analysis of quinoprotein ADH indicated that there are no appreciable ADH subunits in the membranes of both mutant strains. The NTG mutant grew better than the wild-type strain in ethanol-containing medium, despite the absence of quinoprotein ADH. In the mutant, the activities of two NAD-dependent ADHs, present in a small amount in the wild-type strain, markedly increased in the cytoplasm when cultured in a medium containing ethanol, concomitant to the increase in the activities of the key enzymes in TCA and glyoxylate cycles. The disruptant showed a poorer growth than the wild-type strain, producing a lower amount of acetic acid in ethanol culture, and it induced one of the two NAD-dependent ADHs and some of the acetate-assimilating enzymes induced in the NTG mutant. This study clearly showed that quinoprotein ADH is extensively involved in acetic acid production, while NAD-dependent ADH only in ethanol assimilation through the TCA and glyoxylate cycles in acetic acid bacteria. The differences between the NTG mutant and the disruptant are also discussed.

Purification and characterization of a novel polysaccharide involved in the pellicle produced by a thermotolerant Acetobacter strain

Acetobacter strains able to produce a thick pellicle at 37 degrees C were screened among many thermotolerant strains isolated from fruits in Thailand. As a result, Acetobacter sp. SKU 1100 was selected as the producer of a relatively thick pellicle even when cultured at higher temperatures such as 37 degrees C or 40 degrees C. This strain could produce a pellicle polysaccharide in a shaking submerged culture as well as under static culture conditions. The polysaccharide was found to be attached to the bacterial cells. Although the polysaccharide production was higher at 30 degrees C than at 37 degrees C in shaking submerged culture, the productivity in static culture was not decreased even at higher temperatures. The membrane-attached polysaccharide was purified from the SKU 1100 strain by cell disruptions using either ultrasonic treatment or lysozyme treatment, followed by ultracentrifugation, enzyme treatments, dialysis against SDS, DEAE-cellulose column chromatography, alcohol precipitation, and gel filtration chromatography. The polysaccharide purified by the sonic treatment and also by the mild conditions using lysozyme treatment had the same average molecular mass of 120 kDa. The purified polysaccharide was composed of three different monosaccharides; glucose, galactose, and rhamnose, in an approximately equimolar ratio of 1:1:1.

Purification and characterization of membrane-bound malate dehydrogenase from Acetobacter sp. SKU 14

Membrane-bound NAD(P)-independent malate dehydrogenase (EC 1.1.99.16) was purified to homogeneity from the membrane of thermotolerant Acetobacter sp. SKU 14, an isolate from Thailand. The enzyme was solubilized from the membrane fraction of glycerol-grown cells with 1% Triton X-100 in the presence of 0.1 M KCl, and purified to homogeneity through steps of column chromatographies on DEAE-Sephadex A-50 and DEAE-Toyopearl in the presence of 0.1% Triton X-100. The purified enzyme showed a single protein band in both native-PAGE and SDS-PAGE. The enzyme was a homodimer with a molecular mass of 60 kDa subunit and had noncovalently bound FAD as the cofactor. The enzyme was stable over pH 5 and had its maximum activity at pH 11.0 when ferricyanide was used as an electron acceptor. The enzyme activity was elevated by the addition of ammonium ions. The substrate specificity was very strict to only L-malate, of which the apparent Km was 10 mM and over 20 compounds involving D-malate were not oxidized by the enzyme.

L-erythrulose production by oxidative fermentation is catalyzed by PQQ-containing membrane-bound dehydrogenase

Thermotolerant Gluconobacter frateurii CHM 43 was selected for L-erythrulose production from mesoerythritol at higher temperatures. Growing cells and the membrane fraction of the strain rapidly oxidized mesoerythritol to L-erythrulose irreversibly with almost 100% of recovery at 37 degrees C. L-Erythrulose was also produced efficiently by the resting cells at 37 degrees C with 85% recovery. The enzyme responsible for mesoerythritol oxidation was found to be located in the cytoplasmic membrane of the organism. The EDTA-resolved enzyme required PQQ and Ca2+ for L-erythrulose formation, suggesting that the enzyme catalyzing meso-erythritol oxidation was a quinoprotein. Quinoprotein membrane-bound mesoerythritol dehydrogenase (QMEDH) was solubilized and purified to homogeneity. The purified enzyme showed a single band in SDS-PAGE of which the molecular mass corresponded to 80 kDa. The optimum pH of QMEDH was found at pH 5.0. The Michaelis constant of the enzyme was found to be 25 mM for meso-erythritol as the substrate. QMEDH showed a broad substrate specificity toward C3-C6 sugar alcohols in which the erythro form of two hydroxy groups existed adjacent to a primary alcohol group. On the other hand, the cytosolic NAD-denpendent meso-erythritol dehydrogenase (CMEDH) of the same organism was purified to a crystalline state. CMEDH showed a molecular mass of 60 kDa composed of two identical subunits, and an apparent sedimentation constant was 3.6 s. CMEDH catalyzed oxidoreduction between mesoerythritol and L-erythrulose. The oxidation reaction was observed to be reversible in the presence of NAD at alkaline pHs such as 9.0-10.5. L-Erythrulose reduction was found at pH 6.0 with NADH as coenzyme. Judging from the catalytic properties, the NAD-dependent enzyme in the cytosolic fraction was regarded as a typical pentitol dehydrogenase of NAD-dependent and the enzyme was independent of the oxidative fermentation of L-erythrulose production.

Purification and characterization of membrane-bound quinoprotein cyclic alcohol dehydrogenase from Gluconobacter frateurii CHM 9

A quinoprotein catalyzing oxidation of cyclic alcohols was found in the membrane fraction for the first time, after extensive screening among aerobic bacteria. Gluconobacter frateurii CHM 9 was finally selected in this study. The enzyme tentatively named membrane-bound cyclic alcohol dehydrogenase (MCAD) was found to occur specifically in the membrane fraction, and pyrroloquinoline quinone (PQQ) was functional as the primary coenzyme in the enzyme activity. MCAD catalyzed only oxidation reaction of cyclic alcohols irreversibly to corresponding ketones. Unlike already known cytosolic NAD(P)H-dependent alcohol-aldehyde or alcohol-ketone oxidoreductases, MCAD was unable to catalyze the reverse reaction of cyclic ketones or aldehydes to cyclic alcohols. MCAD was solubilized and purified from the membrane fraction of the organism to homogeneity. Differential solubilization to eliminate the predominant quinoprotein alcohol dehydrogenase (ADH), and the subsequent two steps of column chromatographies, brought MCAD to homogeneity. Purified MCAD had a molecular mass of 83 kDa by SDS-PAGE. Substrate specificity showed that MCAD was an enzyme oxidizing a wide variety of cyclic alcohols. Some minor enzyme activity was found with aliphatic secondary alcohols and sugar alcohols, but not primary alcohols, differentiating MCAD from quinoprotein ADH. NAD-dependent cytosolic cyclic alcohol dehydrogenase (CCAD) in the same organism was crystallized and its catalytic and physicochemical properties were characterized. Judging from the catalytic properties of CCAD, it was apparent that CCAD was distinct from MCAD in many respects and seemed to make no contributions to cyclic alcohol oxidation.

Membrane-bound sugar alcohol dehydrogenase in acetic acid bacteria catalyzes L-ribulose formation and NAD-dependent ribitol dehydrogenase is independent of the oxidative fermentation

To identify the enzyme responsible for pentitol oxidation by acetic acid bacteria, two different ribitol oxidizing enzymes, one in the cytosolic fraction of NAD(P)-dependent and the other in the membrane fraction of NAD(P)-independent enzymes, were examined with respect to oxidative fermentation. The cytoplasmic NAD-dependent ribitol dehydrogenase (EC 1.1.1.56) was crystallized from Gluconobacter suboxydans IFO 12528 and found to be an enzyme having 100 kDa of molecular mass and 5 s as the sedimentation constant, composed of four identical subunits of 25 kDa. The enzyme catalyzed a shuttle reversible oxidoreduction between ribitol and D-ribulose in the presence of NAD and NADH, respectively. Xylitol and L-arabitol were well oxidized by the enzyme with reaction rates comparable to ribitol oxidation. D-Ribulose, L-ribulose, and L-xylulose were well reduced by the enzyme in the presence of NADH as cosubstrates. The optimum pH of pentitol oxidation was found at alkaline pH such as 9.5-10.5 and ketopentose reduction was found at pH 6.0. NAD-Dependent ribitol dehydrogenase seemed to be specific to oxidoreduction between pentitols and ketopentoses and D-sorbitol and D-mannitol were not oxidized by this enzyme. However, no D-ribulose accumulation was observed outside the cells during the growth of the organism on ribitol. L-Ribulose was accumulated in the culture medium instead, as the direct oxidation product catalyzed by a membrane-bound NAD(P)-independent ribitol dehydrogenase. Thus, the physiological role of NAD-dependent ribitol dehydrogenase was accounted to catalyze ribitol oxidation to D-ribulose in cytoplasm, taking D-ribulose to the pentose phosphate pathway after being phosphorylated. L-Ribulose outside the cells would be incorporated into the cytoplasm in several ways when need for carbon and energy sources made it necessary to use L-ribulose for their survival. From a series of simple experiments, membrane-bound sugar alcohol dehydrogenase was concluded to be the enzyme responsible for L-ribulose production in oxidative fermentation by acetic acid bacteria.

Isolation and characterization of thermotolerant Gluconobacter strains catalyzing oxidative fermentation at higher temperatures

Thermotolerant acetic acid bacteria belonging to the genus Gluconobacter were isolated from various kinds of fruits and flowers from Thailand and Japan. The screening strategy was built up to exclude Acetobacter strains by adding gluconic acid to a culture medium in the presence of 1% D-sorbitol or 1% D-mannitol. Eight strains of thermotolerant Gluconobacter were isolated and screened for D-fructose and L-sorbose production. They grew at wide range of temperatures from 10 degrees C to 37 degrees C and had average optimum growth temperature between 30-33 degrees C. All strains were able to produce L-sorbose and D-fructose at higher temperatures such as 37 degrees C. The 16S rRNA sequences analysis showed that the isolated strains were almost identical to G. frateurii with scores of 99.36-99.79%. Among these eight strains, especially strains CHM16 and CHM54 had high oxidase activity for D-mannitol and D-sorbitol, converting it to D-fructose and L-sorbose at 37 degrees C, respectively. Sugar alcohols oxidation proceeded without a lag time, but Gluconobacter frateurii IFO 3264T was unable to do such fermentation at 37 degrees C. Fermentation efficiency and fermentation rate of the strains CHM16 and CHM54 were quite high and they rapidly oxidized D-mannitol and D-sorbitol to D-fructose and L-sorbose at almost 100% within 24 h at 30 degrees C. Even oxidative fermentation of D-fructose done at 37 degrees C, the strain CHM16 still accumulated D-fructose at 80% within 24 h. The efficiency of L-sorbose fermentation by the strain CHM54 at 37 degrees C was superior to that observed at 30 degrees C. Thus, the eight strains were finally classified as thermotolerant members of G. frateurii.

Bacillus subtilis spoVE gene is transcribed by sigma E-associated RNA polymerase

Expression of the Bacillus subtilis sporulation gene spoVE was examined by runoff transcription assay with an RNA polymerase preparation obtained from vegetative and sporulating cells. Transcripts from tandem promoters (P1 and P2 promoters) located just upstream of the spoVE structure gene were detected. The transcription of spoVE initiated within an hour after the onset of sporulation and coincided with the presence of RNA polymerase associated with a 33-kDa protein. Amino acid sequence analysis of the 33-kDa protein revealed that it is a sigma factor, sigma E. Reconstitution analysis of sigma E purified from the sporulating cell extracts and vegetative core RNA polymerase showed that sigma E recognizes the P2 promoter. SpoVE protein could not be synthesized in the transcription-translation coupled system prepared from vegetative cells (M. Okamoto, S. Fukui, and Y. Kobayashi, Agric. Biol. Chem. 49:1077-1082, 1985). However, addition of sigma E-associated RNA polymerase to the coupled system restored SpoVE protein synthesis. These results indicate that spoVE expression in sporulating cells is controlled essentially by sigma E-associated RNA polymerase.

In vivo expression of the Bacillus subtilis spoVE gene

In vivo expression of the Bacillus subtilis spoVE gene was studied by S1 nuclease mapping and spoVE gene fusion analysis. Transcription of spoVE is induced at about the second hour of sporulation from two closely spaced promoters designated P1 and P2. Examination of the precise transcription initiation site by high-resolution primer extension mapping indicated that the nucleotide sequences of the -10 and -35 regions of both P1 and P2 were similar to those of promoters recognized by E sigma E. Moreover, S1 nuclease mapping and translational spoVE-lacZ fusion studies with various spo mutants suggest that the expression of spoVE P2 requires the spoIIG gene product, sigma E. The sporulation of a wild-type strain was inhibited severely in the presence of a multicopy plasmid, pKBVE, carrying the spoVE promoter, indicating the possible titration of a transcriptional regulatory element(s).

Sequence of the Bacillus subtilis homolog of the Escherichia coli cell-division gene murG

The Bacillus subtilis homology of the Escherichia coli murG gene [encoding UDP-N-acetylglucosamine:N-acetylmuramyl-(pentapeptide) pyrophosphoryl-undecaprenol N-acetylglucosamine transferase] was cloned in E. coli K-12 and sequenced. The murG homolog encodes a protein of M(r) 39,936 [363 amino acid (aa) residues] of which 108 aa residues (29.8%) are identical with the E. coli murG product.