Showing papers in "Fems Microbiology Letters in 1995"
TL;DR: An overview of the diversity of biosynthetic polyhydroxyalkanoic acids and the importance of bacterial anabolism and catabolism, which provide the coenzyme A thioesters of the respective hydroxyalkanoing acids as substrates to these PHA synthases, is emphasized.
Abstract: An overview is provided on the diversity of biosynthetic polyhydroxyalkanoic acids, and all hitherto known constituents of these microbial storage compounds are listed. The occurrence of 91 different hydroxyalkanoic acids reflects the low substrate specificity of polyhydroxyalkanoic acid synthases which are the key enzymes of polyhydroxyalkanoic acid biosynthesis. In addition, the importance of bacterial anabolism and catabolism, which provide the coenzyme A thioesters of the respective hydroxyalkanoic acids as substrates to these PHA synthases, is emphasized.
1,103 citations
TL;DR: Analysis of predicted amino acid sequences of these genes revealed strong conservation of both primary and secondary structure, suggesting that the particulate methane monooxygenase and ammonia mono Oxygenase are evolutionarily related enzymes despite their different physiological roles in these bacteria.
Abstract: Genes encoding paniculate methane monooxygenase and ammonia monooxygenase share high sequence identity. Degenerate oligonucleotide primers were designed, based on regions of shared amino acid sequence between the 27-kDa polypeptides, which are believed to contain the active sites, of particulate methane monooxygenase and ammonia monooxygenase. A 525-bp internal DNA fragment of the genes encoding these polypeptides ( pmoA and amoA ) from a variety of methanotrophic and nitrifying bacteria was amplified by PCR, cloned and sequenced. Representatives of each of the phylogenetic groups of both methanotrophs ( α- and γ-Proteobacteria) and ammonia-oxidizing nitrifying bacteria ( β-and y-Proteobacteria) were included. Analysis of the predicted amino acid sequences of these genes revealed strong conservation of both primary and secondary structure. Nitrosococcus oceanus AmoA showed higher identity to PmoA sequences from other members of the γ-Proteobacteria than to AmoA sequences. These results suggest that the particulate methane monooxygenase and ammonia monooxygenase are evolutionarily related enzymes despite their different physiological roles in these bacteria.
859 citations
TL;DR: The understanding of the biochemical and genetic basis of resistance to Bt can help design appropriate management tactics to delay or reduce the evolution of resistance in insect populations.
Abstract: Current knowledge of biochemical mechanisms of insect resistance to Bacillus thuringiensis is reviewed. Available information on resistance inheritance and on patterns of cross-resistance is included. Modification of the binding sites for B. thuringiensis insecticidal crystal proteins has been found in different populations of three insect species. This resistance mechanism seems to be inherited as a single recessive or partially recessive major gene, and the resistance levels reached are high. Altered proteolytic processing of B. thuringiensis crystal proteins has been suggested to be involved in one case of resistance. From the available data it seems that binding site modification is the most significant resistance mechanism under field conditions.
407 citations
TL;DR: The resulting enhancement to catalysed proton efflux from the cell represents a considerable energy demand, yet may help to counteract the adverse effects for homeostasis of the increased membrane permeability that results from stress.
Abstract: Sublethal heat and ethanol exposure induce essentially identical stress responses in yeast. These responses are characterized by the induction of heat shock proteins, proteins requiring a temperature above about 35 °C or ethanol levels above a threshold level of 4–6% (v/v) for strong induction. One induced protein, Hsp104, contributes to both thermotolerance and ethanol tolerance, while others are anti-oxidant enzymes. Heat and ethanol stress cause similar changes to plasma membrane protein composition, reducing the levels of plasma membrane H+-ATPase protein and inducing the plasma membrane-associated Hsp30. Both stresses also stimulate the activity of the fraction of H+-ATPase remaining in the plasma membrane. The resulting enhancement to catalysed proton efflux from the cell represents a considerable energy demand, yet may help to counteract the adverse effects for homeostasis of the increased membrane permeability that results from stress.
397 citations
TL;DR: Cereulide causes emesis through the 5-HT3 receptor and stimulation of the vagus afferent and it is found that the purified cereulide caused swelling of mitochondria of HEp-2 cells.
Abstract: A vacuole-formation substance, cereulide of Bacillus cereus, is an emetic toxin in animals. Both oral administration and intraperitoneal injection of cereulide caused dose-dependent emesis in Suncus murinus, a new animal model of emesis. Vagotomy or a 5-HT3 receptor antagonist completely abolished this emetic effect. Therefore, cereulide causes emesis through the 5-HT3 receptor and stimulation of the vagus afferent. We also found that our purified cereulide caused swelling of mitochondria of HEp-2 cells.
347 citations
TL;DR: Genomic DNA fragment patterns of strains from animal sources were different from each other and also from those of strains isolated in hospitals and from sewage treatment plants, suggesting the dissemination of the vanA determinant among different enterococcal strains of distinct ecological origin.
Abstract: Glycopeptide-resistant Enterococcus faecium strains were isolated from a pig farm and a poultry farm both using avoparcin as a food additive. Such organisms were not isolated in a hen's eggs-producing farm not using avoparcin. Glycopeptide-resistant enterococci were also detected in broiler chicken carcasses that were delivered to a hospital's kitchen. The resistance was determined by the vanA gene as indicated by the detection of the inducible 39-kDa cytoplasmic membrane protein and of a vanA -specific DNA sequence amplified by polymerase chain reaction. Genomic DNA fragment patterns of strains from animal sources were different from each other and also from those of strains isolated in hospitals and from sewage treatment plants. This findings suggest the dissemination of the vanA determinant among different enterococcal strains of distinct ecological origin.
326 citations
TL;DR: This paper presents a hypothesis on the importance of initial microbial adhesion in the overall process of biofilm formation, based on the realization that dynamic shear conditions exist in many environments, such as in the oral cavity, or on rocks and ship hulls.
Abstract: This paper presents a hypothesis on the importance of initial microbial adhesion in the overall process of biofilm formation. The hypothesis is based on the realization that dynamic shear conditions exist in many environments, such as in the oral cavity, or on rocks and ship hulls. Recognizing that an entire biofilm is detached during high shear once the bond between the initially adhering organisms and a surface (often constituted through a so-called ‘conditioning film’) is broken, it becomes clear that research should focus on detachment rather than adhesion. Experiments were done in a parallel plate flow chamber in which attempts were made to detach adhering oral streptococci from glass by applying a high shear caused by the passage of a bubble, giving an air-liquid interface. Detachment of streptococci from bare glass and from an initially adhering actinomycete strain appeared not to occur. However, substantial detachment of adhering streptococci occurred when adhesion was mediated through a salivary conditioning film, presumably because of cohesive failure in the conditioning film.
233 citations
TL;DR: In this paper, a strain of Lentinula (Lentinus) edodes, strain LS4, produces manganese-dependent peroxidase (MnP) and laccase, but not lignin peroxideidase, when grown on a defined medium with glucose as sole carbon source.
Abstract: Lentinula (Lentinus) edodes, strain LS4, produces manganese-dependent peroxidase (MnP) and laccase, but not lignin peroxidase, when grown on a defined medium with glucose as sole carbon source. MnP production is suppressed by nitrogen whereas highest levels of laccase were observed when the fungus was grown under high nitrogen (26 mM) conditions. Both the titre and time of appearance of MnP were affected by the concentration of Mn in the culture medium with highest enzyme levels recorded in cultures supplemented with 1.1 ppm Mn. Purified MnP from L. edodes LS4 has an apparent Mr of 59000 and a pI of 5.6, and differs in several respects from a MnP isolated from L. edodes grown on a commercial wood substrate.
225 citations
TL;DR: A gel-stabilized system with counter gradients of CH4 and O2 was used to grow methanotrophs from wetland, agricultural and forest soils and lake sediment as discussed by the authors.
Abstract: A gel-stabilized system with counter gradients of CH4 and O2 was used to grow methanotrophs from wetland, agricultural and forest soils and lake sediment. Columns of semi-solid nitrate- or ammonium-minerai salts medium were continuously flushed at opposite ends with CH4 and O2 to create opposing concentration gradients of the two gases. Methanotrophs grew from all samples except forest soil, and were visible as thin bands after 5 to 15 days of incubation. The position of growth was CH4 and O2 concentration-dependent and occurred at the point of maximum possible CH4 oxidation, where both substrates were completely consumed. Evidence was obtained for denitrification and nitrification activities concomitant with CH4 oxidation. This approach may be useful to isolate methanotrophs with different CH4 and O2 requirements and to study their interactions with other groups of bacteria in nature.
210 citations
TL;DR: Using phenotypic test systems and genotypic analysis, it has been shown that the mutant strain J96-M1 has lost the hlyII, prs and cnf1 genes.
Abstract: The uropathogenic Escherichia coli strain J96 (04:K6) is able to produce four adherence factors [P-fimbriae (pap and prs), F1C-fimbriae (foc) and Type 1-fimbriae (fim)], two α-hemolysins (hfyI and II) and the cytotoxic necrotizing factor type 1 (cnf1). Using phenotypic test systems and genotypic analysis, it has been shown that the mutant strain J96-M1 has lost the hlyII, prs and cnf1 genes. The three virulence associated determinants are linked on one particular region on the chromosome, which is termed ‘pathogenicity island II’ (Pai II).
202 citations
TL;DR: The δ-endotoxin crystal of the mosquitocidal bacterium Bacillus thuringiensis subsp. israelensis contains four major 0-endoxins as discussed by the authors.
Abstract: The δ-endotoxin crystal of the mosquitocidal bacterium Bacillus thuringiensis subsp. israelensis contains four major 0-endotoxins. Expression systems were devised to synthesize each of the four toxins at concentrations at which they formed inclusion bodies in an acrystalliferous mutant of Bacillus thuringiensis. The relative activities of these inclusions were then determined against Aedes aegypti larvae. Bioassays of mixtures of the individual toxins revealed a number of synergistic interactions which explained in part why the native crystal is considerably more toxic than any of the individual toxins.
TL;DR: Spectra of some Bacillus strains showed expression of poly-β-hydroxybutyric acid granules, capsules and endospores simultaneously and some particular cell components can be detected and identified by Fourier Transform infrared spectroscopy of intact bacteria.
Abstract: Some particular cell components can be detected and identified by Fourier Transform infrared spectroscopy (FT-IR) of intact bacteria. Typical marker bands were used to identify these bacterial cell components. Polypeptide capsules were detected in several Bacillus species by a band typical for α-helical structures and by strong carboxylate stretching vibrations. Formation of endospores in clostridia and bacilli was discovered using marker bands for dipicolinic acid. Spectra of some Bacillus strains showed expression of poly-β-hydroxybutyric acid granules, capsules and endospores simultaneously.
TL;DR: The domains, which represent the functional building units of peptide synthetases, appear to act as independent enzymes whose specific linkage order forms the protein-template that defines the sequence of the incorporated amino acids.
Abstract: Peptide synthetases are large multienzyme complexes that catalyze the non-ribosomal synthesis of a structurally diverse family of bioactive peptides. They possess a multidomain structure and employ the thiotemplate mechanism to activate, modify and link together by amide or ester bonds the constituent amino acids of the peptide product. The domains, which represent the functional building units of peptide synthetases, appear to act as independent enzymes whose specific linkage order forms the protein-template that defines the sequence of the incorporated amino acids. Two types of domains have been characterized in peptide synthetases of bacterial and fungal origin: type I comprises about 600 amino acids and contains at least two modules involved in substrate recognition, adenylation and thioester formation, whereas type II domains carry in addition an insertion of about 430 amino acids that may function as a N-methyltransferase module. The role of other genes associated with bacterial operons encoding peptide synthetases is also discussed.
TL;DR: The mechanism of action of specific immunity proteins, which protect the producer strains from the lethal action of their own products (producer self-protection), are discussed.
Abstract: Proteinaceous antimicrobial compounds are produced by a diversity of species ranging from bacteria to humans. This review focuses on the mode of action of pore-forming bacteriocins produced by Gram-positive bacteria. The mechanism of action of specific immunity proteins, which protect the producer strains from the lethal action of their own products (producer self-protection), are also discussed.
TL;DR: This review describes this non-culturable state in V. vulnificus, and its role in the ecology, physiology, and epidemiology of this pathogen.
Abstract: Vibrio vulnificus is a serious human pathogen, accounting for 95% of all seafood-related deaths in the United States. During the winter months, when coastal water temperatures drop below 10 °C, investigators have repeatedly reported their inability to isolate this estuarine bacterium from the environment. We now realize that this apparent ‘die-off’ is actually due to entry of the cells into a ‘viable but non-culturable’ state, a survival response to the low temperature stress. Cells in this state appear dormant, and cannot be cultured in or on routine bacteriological media, but are capable of returning to the actively metabolizing state when the environmental stress is removed. This review describes this non-culturable state in V. vulnificus, and its role in the ecology, physiology, and epidemiology of this pathogen.
TL;DR: The combination of polymerase chain reaction-restriction fragment length polymorphism and plasmid analysis allowed us to investigate nosocomial outbreaks due to clinical isolates of multi-resistant Klebsiella pneumoniae in three hospitals.
Abstract: To rapidly characterise TEM-derived extended-spectrum β-lactamases a fast and easy method using polymerase chain reaction-restriction fragment length polymorphism was developed. This method was validated with ten reference TEM-type extended-spectrum β-lactamases. The mutations involved in TEM-20 and TEM-21, which were previously reported only with biochemical analysis, were then characterised. TEM-20 differed from TEM-19 by a silent mutation at position 925 (A for G), and TEM-21 differed from TEM-3 and TEM-14 by a single mutation (G for A) in an unreported position 660, involving an amino acid substitution, arginine for histidine, at position 153. Moreover, a new extended-spectrum β-lactamase conferring low resistance to ceftazidime (TEM-29), was described. TEM-29 derived from TEM-1, with an amino acid substitution, his-164. Finally, the combination of polymerase chain reaction-restriction fragment length polymorphism and plasmid analysis allowed us to investigate nosocomial outbreaks due to clinical isolates of multi-resistant Klebsiella pneumoniae in three hospitals.
TL;DR: For suspended organisms, flow cytometry provides a powerful means of measurement of a wide range of characteristics and for microbes in aggregates or growing on surfaces may be obtained by use of confocal scanning laser microscopy.
Abstract: Assessment of the vigour, vitality or viability of microorganisms must be done on an individual basis and thus requires the non-invasive interrogation of single organisms. For suspended organisms, flow cytometry provides a powerful means of measurement of a wide range of characteristics. Similar information for microbes in aggregates or growing on surfaces may be obtained by use of confocal scanning laser microscopy. For instance, membrane potential-sensitive fluorophores can distinguish between vigorous, frail and dead cells.
TL;DR: Results indicate that presumptive killer yeast strains, together with their killer toxins, may have potential as novel antimycotic biocontrol agents.
Abstract: A total of 17 presumptive killer yeast strains were tested in vitro for growth inhibitory and killing activity against a range of fungal pathogens of agronomic, environmental and clinical significance. Several yeasts were identified which displayed significant activity against important pathogenic fungi. For example, isolates of the opportunistic human pathogen, Candida albicans, were generally very sensitive to Williopsis mrakii killer yeast activity, whilst killer strains of Saccharomyces cerevisiae and Pichia anomala markedly inhibited the growth of certain wood decay basidiomycetes and plant pathogenic fungi. Results indicate that such yeasts, together with their killer toxins, may have potential as novel antimycotic biocontrol agents.
TL;DR: In this article, a simple optical method was developed for assaying cellular magnetism in culture samples of magnetic spirilla, where cells are aligned parallel to the field lines in a magnetic field, resulting in a change in light scattering.
Abstract: A simple optical method was developed for assaying cellular magnetism in culture samples of magnetic spirilla. Cells are aligned parallel to the field lines in a magnetic field, resulting in a change in light scattering. The ratio of scattering intensities at different angles of magnetic field relative to the light beam (Cmag) is used to characterize the average magnetic orientation of the cells. Cmag was found to be well correlated with the average number of particles in different magnetic cell populations. Thus, estimations of magnetosome content can be made using magnetically induced differential light scattering. The method provides a fast and sensitive tool for monitoring the magnetite formation in growing cultures of Magnetospirillum gryphiswaldense.
TL;DR: Results indicate that phenazine biosynthesis in P. aureofaciens shares similarities with the shikimic acid, enterochelin, and tryptophan biosynthetic pathways.
Abstract: The DNA sequence of five contiguous open reading frames encoding enzymes for phenazine biosynthesis in the biological control bacterium Pseudomonas aureofaciens 30–84 was determined. These open reading frames were named phzF, phzA, phzB, phzC and phzD. Protein PhzF is similar to 3-deoxy-D-arabino-heptulosonate-7-phosphate synthases of solanaceous plants. PhzA is similar to 2,3-dihydro-2,3-dihydroxybenzoate synthase (EntB) of Escherichia coli. PhzB shares similarity with both subunits of anthranilate synthase and the phzB open reading frame complemented an E. coli trpE mutant deficient in anthranilate synthase activity. Although phzC shares little similarity to known genes, its product is responsible for the conversion of phenazine-1-carboxylic acid to 2-hydroxy-phenazine-1-carboxylic acid. PhzD is similar to pyridoxamine phosphate oxidases. These results indicate that phenazine biosynthesis in P. aureofaciens shares similarities with the shikimic acid, enterochelin, and tryptophan biosynthetic pathways.
TL;DR: Various soil samples were screened for the presence of microorganisms which have the ability to degrade polyurethane compounds and the more active strain was tentatively identified as Comamonas acidovorans, which could utilize polyester-typepolyurethanes but not the polyether-type polyUREthanes as sole carbon and nitrogen sources.
Abstract: Various soil samples were screened for the presence of microorganisms which have the ability to degrade polyurethane compounds. Two strains with good polyurethane degrading activity were isolated. The more active strain was tentatively identified as Comamonas acidovorans. This strain could utilize polyester-type polyurethanes but not the polyether-type polyurethanes as sole carbon and nitrogen sources. Adipic acid and diethylene glycol were probably the main degradation products when polyurethane was supplied as a sole carbon and nitrogen source. When ammonium nitrate was used as nitrogen source, only diethylene glycol was detected after growth on polyurethane.
TL;DR: Brettanomyces anomalus is shown to metabolise p-coumaric, caffeic and ferulic acid to 4-vinyl and 4-ethyl derivatives.
Abstract: Brettanomyces anomalus is shown here to metabolise p-coumaric, caffeic and ferulic acid to 4-vinyl and 4-ethyl derivatives. We also demonstrate the transformation of vanillin to both vanillyl alcohol and vanillic acid by this yeast. The results presented here show the production of these compounds during the fermentation of this organism and also the effects of these and other simple phenolic compounds on the growth of the organism. The products were analysed and their identities were determined by TLC, HPLC and by mass spectrometry.
TL;DR: Laccase is commonly found in white-rot fungi and catalyses the abstraction of one electron from the phenolic hydroxyl group to polymerize or depolymerize lignin model compounds and produces Mn(III) chelates which allow wood-decaying enzymes to penetrate wood cell walls.
Abstract: Laccase is commonly found in white-rot fungi and catalyses the abstraction of one electron from the phenolic hydroxyl group to polymerize or depolymerize lignin model compounds Laccase degrades both β-1 and β-O-4 dimers via C α - C β cleavage, C α oxidation and alkyl-aryl cleavage Also, aromatic ring cleavage may be detected following the action of laccase Laccase can also oxidize non-phenolic compounds when primary mediators, such as 2,2′-azinobis(3-ethylbenzthiazoline-6-sulfonate), are co-present Laccase produces Mn(III) chelates which allow wood-decaying enzymes to penetrate wood cell walls Laccase is considered to be capable of degrading lignin together with lignin peroxidase and manganese peroxidase
TL;DR: Data obtained showed that amplified rDNA restriction analysis is an easy, fast, reproducible and reliable tool for identification of Azospirillum strains, mainly at the species level, whereas restriction fragment length polymorphism could, in some cases, differentiate strains belonging to the same species.
Abstract: DNA fingerprints of several Azospirillum strains, belonging to the five known species A amazonense, A brasilense, A halopraeferens, A irakense and A lipoferum, were obtained by restriction analysis of the amplified 16S rDNA and by restriction fragment length polymorphism of the histidine biosynthetic genes Data obtained showed that amplified rDNA restriction analysis is an easy, fast, reproducible and reliable tool for identification of Azospirillum strains, mainly at the species level, whereas restriction fragment length polymorphism could, in some cases, differentiate strains belonging to the same species Moreover, both analyses gave congruent results in grouping strains and in the assignment of new strains to a given species
TL;DR: Iturin A passes through the cell wall and disrupts the plasma membrane with the formation of small vesicles and the aggregation of intramembranous particles, and interacts with the nuclear membrane and probably with membranes of other cytoplasmic organelles.
Abstract: The effects of iturin A, at fungicidal concentrations, on yeast cells were studied by scanning electron microscopy and by transmission electron microscopy. A depression, observed in each iturin A-treated cell, was the consequence of the release of electrolytes and other cytoplasmic components. Iturin A passes through the cell wall and disrupts the plasma membrane with the formation of small vesicles and the aggregation of intramembranous particles. Moreover, iturin A passes through the plasma membrane and interacts with the nuclear membrane and probably with membranes of other cytoplasmic organelles.
TL;DR: A procedure is described which allows the rapid permeabilization of yeast cells, Schizosac charomyces pombe and Saccharomyces cerevisiae, for quantitative in situ assays of beta-galactosidase activity and is found to be superior by being more accurate and less time-consuming.
Abstract: A procedure is described which allows the rapid permeabilization of yeast cells, Schizosaccharomyces pombe and Saccharomyces cerevisiae, for quantitative in situ assays of β-galactosidase activity. Yeast cells are permeabilized by incubation in buffer containing 0.2% of the detergent sodium lauroyl sarcosinate without any need for washing or vortexing. This procedure is equally applicable to fresh and frozen samples. It is compared to earlier reported methods and found to be superior by being more accurate and less time-consuming.
TL;DR: Both HPI and HPII are members of the RpoS regulon and elucidation of the mechanism of regulation of RPOS should contribute to the general understanding of hydroperoxidase regulation.
Abstract: As part of its adaptive response to oxidative stress, Escherichia coli produces two inducible hydroperoxidases called HPI and HPII. Upon exposure to sublethal levels of hydrogen peroxide, HPI expression is induced at the transcriptional level by OxyR, a member of the LysR family of autoregulators. OxyR, functioning as both a sensor and transducer, contains a critical redox-sensitive Cys residue that is oxidized by hydrogen peroxide. This is thought to induce a conformational change in the tertiary structure of the OxyR tetramer altering its DNA-binding specificity and resulting in an increase in the transcription of katG and several other OxyR-dependent genes. In contrast, synthesis of the HPII enzyme is not induced by hydrogen peroxide. Expression of both HPI and HPII is growth phase-dependent levels of HPI and HPII are 10-fold higher in stationary phase than exponential phase cultures. These growth phase-dependent increases are largely dependent on RpoS, a stationary phase specific sigma factor that is itself subject to complex transcriptional and post-transcriptional controls. Several metabolic signals have been proposed to activate the RpoS regulon including hyperosmolarity, weak acids, homoserine lactone and UDP-glucose. Since both HPI and HPII are members of the RpoS regulon, elucidation of the mechanism of regulation of RpoS should contribute to our general understanding of hydroperoxidase regulation.
TL;DR: Two hypotheses are discussed: (i) the structure of the Escherichia coli nucleoid is determined by DNA binding proteins and DNA supercoiling, representing a compaction force on the one hand, and by the coupled transcription/translation/translocation of plasma membrane and cell wall proteins, representing an expansion force.
Abstract: The mechanisms that determine chromosome structure and chromosome partitioning in bacteria are largely unknown. Here we discuss two hypotheses: (i) the structure of the Escherichia coli nucleoid is determined by DNA binding proteins and DNA supercoiling, representing a compaction force on the one hand, and by the coupled transcription/translation/ translocation of plasma membrane and cell wall proteins, representing an expansion force on the other hand; (ii) the two forces are important for the partitioning process of chromosomes.
TL;DR: An investigation of the molecular basis of the switch between aerobic and anaerobic growth was initiated by the cloning of the genes encoding the respiratory nitrate reductase from B. subtilis, which resulted in a chromosomal knock-out mutation that totally abolished nitrate respiration.
Abstract: The Gram-positive soil bacterium Bacillus subtilis, generally regarded as an aerobe, grows under strict anaerobic conditions using nitrate as an electron acceptor and should be designated as a facultative anaerobe. Growth experiments demonstrated a lag phase of 24 to 36 hours after the shift from aerobic, to the onset of anaerobic respiratory growth. Anaerobically adapted cells grew without further lag phase after their transfer to fresh anaerobic growth medium. The cells change their morphology from rods to longer filament-like structures when moved from aerobic to anaerobic respiratory growth conditions. Surprisingly, anaerobically grown B. subtilis lost the capacity for sporulation. An investigation of the molecular basis of the switch between aerobic and anaerobic growth was initiated by the cloning of the genes encoding the respiratory nitrate reductase from B. subtilis. Oligonucleotides deduced from conserved amino acid sequence regions of eubacterial respiratory nitrate reductases and related enzymes were used for the isolation of the genes. Four open reading frames with significant homology to the E. coli respiratory nitrate reductase operons (narGHIJ, narZYWV) were isolated and termed narGHJI. A chromosomal knock-out mutation of the B. subtilis nar operon totally abolished nitrate respiration.
TL;DR: The carotenoid composition of the astaxanthin-producing bacterium Agrobacterium aurantiacum was analysed under different culture conditions and a new pathway for astXanthin formation, different from that of other astaxantha-producing microorganisms, is proposed.
Abstract: The carotenoid composition of the astaxanthin-producing bacterium Agrobacterium aurantiacum was analysed under different culture conditions. Ten kinds of carotenoids, β-carotene, echinenone, β-cryptoxanthin, 3-hydroxyechinenone, canthaxanthin, 3′-hydroxyechinenone, zeaxanthin, adonirubin, adonixanthin and astaxanthin, were identified by HPLC and spectroscopical techniques. A. aurantiacum synthesized astaxanthin from β-carotene through two hydroxylation steps at C-3 and 3′, and oxidation steps at C-4 and 4′. The order of these reactions appeared to be controlled by the culture conditions. A new pathway for astaxanthin formation, different from that of other astaxanthin-producing microorganisms, is proposed.