Actinobacillus succinogenes sp. nov., a novel succinic-acid-producing strain from the bovine rumen.
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Strain 130ZT was isolated from the bovine rumen. It is a facultatively anaerobic, pleomorphic, Gram-negative rod. It exhibits a 'Morse code' form of morphology, which is characteristic of the genus Actinobacillus. Strain 130ZT is a capnophilic, osmotolerant succinogen that utilizes a broad range of sugars. It accumulates high concentrations of succinic acid (> 70 g l-1). Strain 130ZT is positive for catalase, oxidase, alkaline phosphatase and beta-galactosidase, but does not produce indole or urease. Acid but no gas is produced from D-glucose and D-fructose. 16S rRNA sequence analysis places strain 130ZT within the family Pasteurellaceae; the most closely related members of the family Pasteurellaceae have 16S rRNA similarities of 95.5% or less with strain 130ZT. Strain 130ZT was compared with Actinobacillus lignieresii and the related Bisgaard Taxa 6 and 10. Based upon morphological and biochemical properties, strain 130ZT is most similar to members of the genus Actinobacillus within the family Pasteurellaceae. It is proposed that strain 130ZT be classified as a new species, Actinobacillus succinogenes. The type strain of Actinobacillus succinogenes sp. nov. is ATCC 55618T. (+info)
Polynucleotide probes that target a hypervariable region of 16S rRNA genes to identify bacterial isolates corresponding to bands of community fingerprints.
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Temperature gradient gel electrophoresis (TGGE) is well suited for fingerprinting bacterial communities by separating PCR-amplified fragments of 16S rRNA genes (16S ribosomal DNA [rDNA]). A strategy was developed and was generally applicable for linking 16S rDNA from community fingerprints to pure culture isolates from the same habitat. For this, digoxigenin-labeled polynucleotide probes were generated by PCR, using bands excised from TGGE community fingerprints as a template, and applied in hybridizations with dot blotted 16S rDNA amplified from bacterial isolates. Within 16S rDNA, the hypervariable V6 region, corresponding to positions 984 to 1047 (Escherichia coli 16S rDNA sequence), which is a subset of the region used for TGGE (positions 968 to 1401), best met the criteria of high phylogenetic variability, required for sufficient probe specificity, and closely flanking conserved priming sites for amplification. Removal of flanking conserved bases was necessary to enable the differentiation of closely related species. This was achieved by 5' exonuclease digestion, terminated by phosphorothioate bonds which were synthesized into the primers. The remaining complementary strand was removed by single-strand-specific digestion. Standard hybridization with truncated probes allowed differentiation of bacteria which differed by only two bases within the probe target site and 1.2% within the complete 16S rDNA. However, a truncated probe, derived from an excised TGGE band of a rhizosphere community, hybridized with three phylogenetically related isolates with identical V6 sequences. Only one of the isolates comigrated with the excised band in TGGE, which was shown to be due to identical sequences, demonstrating the utility of a combined TGGE and V6 probe approach. (+info)
Studies on time-kill kinetics of different classes of antibiotics against veterinary pathogenic bacteria including Pasteurella, Actinobacillus and Escherichia coli.
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A systematic analysis of the bacteriostatic/bactericidal effect of several antibiotics used in veterinary medicine was carried out by time-kill kinetic analysis using P. haemolytica, P. multocida, A. pleuropneumoniae, and E. coli. The antibiotics tested were enrofloxacin, danofloxacin, erythromycin, tilmicosin, penicillin G, ceftiofur and tetracycline. Unexpectedly, the antibiotics well characterized as bacteriostatic agents against human pathogens such as tetracycline and macrolides, showed bactericidal activity against P. haemolytica and A. pleuropneumoniae. In contrast, tetracycline and erythromycin were bacteriostatic and tilmicosin was bactericidal against P. multocida. In addition, P. multocida was killed by fluoroquinolones at a slower rate than the other bacteria. Spectrum analysis revealed that ceftiofur and tilmicosin were good substrates of the universal efflux pump, AcrA/B, but penicillin and tetracycline were not. The fluoroquinolones were modest substrates for AcrA/B. (+info)
Utilization of electrically reduced neutral red by Actinobacillus succinogenes: physiological function of neutral red in membrane-driven fumarate reduction and energy conservation.
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Neutral red (NR) functioned as an electronophore or electron channel enabling either cells or membranes purified from Actinobacillus succinogenes to drive electron transfer and proton translocation by coupling fumarate reduction to succinate production. Electrically reduced NR, unlike methyl or benzyl viologen, bound to cell membranes, was not toxic, and chemically reduced NAD. The cell membrane of A. succinogenes contained high levels of benzyl viologen-linked hydrogenase (12.2 U), fumarate reductase (13.1 U), and diaphorase (109.7 U) activities. Fumarate reductase (24.5 U) displayed the highest activity with NR as the electron carrier, whereas hydrogenase (1.1 U) and diaphorase (0.8 U) did not. Proton translocation by whole cells was dependent on either electrically reduced NR or H2 as the electron donor and on the fumarate concentration. During the growth of Actinobacillus on glucose plus electrically reduced NR in an electrochemical bioreactor system versus on glucose alone, electrically reduced NR enhanced glucose consumption, growth, and succinate production by about 20% while it decreased acetate production by about 50%. The rate of fumarate reduction to succinate by purified membranes was twofold higher with electrically reduced NR than with hydrogen as the electron donor. The addition of 2-(n-heptyl)-4-hydroxyquinoline N-oxide to whole cells or purified membranes inhibited succinate production from H2 plus fumarate but not from electrically reduced NR plus fumarate. Thus, NR appears to replace the function of menaquinone in the fumarate reductase complex, and it enables A. succinogenes to utilize electricity as a significant source of metabolic reducing power. (+info)
Microbial utilization of electrically reduced neutral red as the sole electron donor for growth and metabolite production.
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Electrically reduced neutral red (NR) served as the sole source of reducing power for growth and metabolism of pure and mixed cultures of H2-consuming bacteria in a novel electrochemical bioreactor system. NR was continuously reduced by the cathodic potential (-1.5 V) generated from an electric current (0.3 to 1.0 mA), and it was subsequently oxidized by Actinobacillus succinogenes or by mixed methanogenic cultures. The A. succinogenes mutant strain FZ-6 did not grow on fumarate alone unless electrically reduced NR or hydrogen was present as the electron donor for succinate production. The mutant strain, unlike the wild type, lacked pyruvate formate lyase and formate dehydrogenase. Electrically reduced NR also replaced hydrogen as the sole electron donor source for growth and production of methane from CO2. These results show that both pure and mixed cultures can function as electrochemical devices when electrically generated reducing power can be used to drive metabolism. The potential utility of utilizing electrical reducing power in enhancing industrial fermentations or biotransformation processes is discussed. (+info)
Electricity generation in microbial fuel cells using neutral red as an electronophore.
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Neutral red (NR) was utilized as an electron mediator in microbial fuel cells consuming glucose to study both its efficiency during electricity generation and its role in altering anaerobic growth and metabolism of Escherichia coli and Actinobacillus succinogenes. A study of chemical fuel cells in which NADH, NR, and ferricyanide were the electron donor, the electronophore, and the electron acceptor, respectively, showed that electrical current produced from NADH was proportional to the concentration of NADH. Fourfold more current was produced from NADH in chemical fuel cells when NR was the electron mediator than when thionin was the electron mediator. In microbial fuel cells in which E. coli resting cells were used the amount of current produced from glucose when NR was the electron mediator (3.5 mA) was 10-fold more than the amount produced when thionin was the electron mediator (0.4 mA). The amount of electrical energy generated (expressed in joules per mole of substrate) and the amount of current produced from glucose (expressed in milliamperes) in NR-mediated microbial fuel cells containing either E. coli or A. succinogenes were about 10- and 2-fold greater, respectively, when resting cells were used than when growing cells were used. Cell growth was inhibited substantially when these microbial fuel cells were making current, and more oxidized end products were formed under these conditions. When sewage sludge (i.e., a mixed culture of anaerobic bacteria) was used in the fuel cell, stable (for 120 h) and equivalent levels of current were obtained with glucose, as observed in the pure-culture experiments. These results suggest that NR is better than other electron mediators used in microbial fuel cells and that sludge production can be decreased while electricity is produced in fuel cells. Our results are discussed in relation to factors that may improve the relatively low electrical efficiencies (1.2 kJ/mol) obtained with microbial fuel cells. (+info)
Comparative pathogenicity of different Actinobacillus suis O/K serotypes.
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The pathogenicity of Actinobacillus suis serotypes O1/K1 (strain SO4), O1/K2 (strain C84), and O2/K2 (strain H91-0380) was evaluated in specific-pathogen-free (SPF) piglets challenged by intraperitoneal inoculation with approximately 1 x 10(7) colony-forming units per mL. All 3 strains produced peritonitis, but differences were observed in the composite histopathologic scores (P = 0.001) and in their ability to spread (P = 0.008) at 7 h post challenge. The O2/K2 strain caused the most severe peritonitis and disseminated most widely to other tissues. Moderate lesions were seen with the O1/K2 strain while the O1/K1 strain caused mild lesions and remained largely localized to the peritoneum. In an attempt to explain the basis of observed differences, the serum sensitivity of 9 A. suis strains with different O and K types was assessed. Regardless of the O/K type, all of the isolates tested were serum resistant. Moreover, most A. suis isolates grew as well or better in complement-replete sera as they did in complement-depleted sera. These observations indicate that although 02 and K2 strains had a greater propensity to cause a disseminating septic inflammatory response in pigs, they were no more resistant to complement-mediated killing than O1 strains. (+info)
A gene cluster for the synthesis of serotype d-specific polysaccharide antigen in Actinobacillus actinomycetemcomitans.
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The serotype d antigen of Actinobacillus actinomycetemcomitans consists of D-glucose, D-mannose, and L-rhamnose in a molar ratio of 1:2:1. A gene cluster involved in the synthesis of serotype-specific polysaccharide antigen was cloned from the chromosomal DNA of A. actinomycetemcomitans IDH 781 (serotype d). This cluster consisted of 12 open reading frames. Insertional inactivation of six genes in this cluster resulted in loss of ability of A. actinomycetemcomitans IDH 781 cells to produce the polysaccharide. Comparing the structure of the gene cluster with similar clusters from other serotypes of A. actinomycetemcomitans, showed that eight genes are unique to serotype d; the other four genes are involved in the biosynthesis of dTDP-L-rhamnose. These results suggest that the synthesis and structure of serotype d-specific polysaccharide of A. actinomycetemcomitans is quite different from those of other serotype strains. (+info)