Forgot your password?
New user?
New Window Opens on the Secret Life of Microbes: Scientists Develop First Microbial Profiles of Ecosystems
CAS announces the release of SciFinder Scholar for Mac OS X
Press Releases
Press Releases
| Check out our New Publishers' Select for Free Articles |
Archives of Microbiology (v.183, #5)
Lactobacillus plantarum ccl gene is non-essential, arginine-repressed and codes for a conserved protein in Firmicutes by Florence Arsène-Ploetze; Hervé Nicoloff; Françoise Bringel (pp. 307-316).
Among proteins specifically found in most gram-positive bacteria of the phylum Firmicutes, conserved proteins of the family pfam06177-DUF988-COG4708 are of unknown function. The citrulline cluster-linked (ccl) gene of Lactobacillus plantarum codes one such protein and is adjacent to the citrulline biosynthesis operon argCJBDF, a situation also found in Lactococcus lactis. This gene is well conserved among L. plantarum species, and 1 isolate out of 24 harbored two ccl copies. Northern hybridization with a ccl probe revealed two arginine-repressed transcripts with sizes corresponding to the predicted argCJBDF–ccl operon and the ccl gene alone. Transcription start sites of both transcripts were characterized. Four different 5′ ends were mapped at the argF–ccl intergenic region, resulting from either regulated transcription initiation or maturation of the transcripts. Transcriptional ccl–gusA gene fusion confirmed the promoter activity of the argF–ccl intergenic region. Thus, the ccl gene is arginine-repressed and transcribed both monocistronically and polycistronically in the argCJBDF-ccl operon. The ccl gene is not essential in L. plantarum, because a ccl gene deletion was obtained in strain CCM 1904. Although no functions were found in the tested laboratory conditions, the Ccl-like proteins may play a role in environmental conditions of life.
Keywords: Firmicutes; Lactobacillus plantarum ; Membrane protein; Pfam06177; COG4708; Arginine repression
Purification and characterization of succinate:menaquinone oxidoreductase from Corynebacterium glutamicum by Tatsuki Kurokawa; Junshi Sakamoto (pp. 317-324).
Succinate:menaquinone oxidoreductase from Corynebacterium glutamicum, a high-G+C, Gram-positive bacterium, was purified to homogeneity. The enzyme contained two heme B molecules and three polypeptides with apparent molecular masses of 67, 29 and 23 kDa, which corresponded to SdhA (flavoprotein), SdhB (iron–sulfur protein), and SdhC (membrane anchor protein), respectively. In non-denaturating polyacrylamide gel electrophoresis, the enzyme migrated as a single band with an apparent molecular mass of 410 kDa, suggesting that it existed as a trimer. The succinate dehydrogenase activity assayed using 2,3-dimethoxy-5-methyl-6-decyl-1,4-benzoquinone and 2,6-dichloroindophenol as the electron acceptor was inhibited by 2-n-heptyl-4-hydroxyquinoline N-oxide (HQNO), and the Dixon plots were biphasic. In contrast, the succinate dehydrogenase activity assayed using phenazine methosulfate and 2,6-dichloroindophenol was inhibited by p-benzoquinone and not by HQNO. These findings suggested that the C. glutamicum succinate:menaquinone oxidoreductase had two quinone binding sites. In the phylogenetic tree of SdhA, Corynebacterium species do not belong to the high-G+C group, which includes Mycobacterium tuberculosis and Streptomyces coelicolor, but are rather close to the group of low-G+C, Gram-positive bacteria such as Bacillus subtilis. This situation may have arisen due to the horizontal gene transfer.
Keywords: Succinate:quinone oxidoreductaseCorynebacterium glutamicumGram-positive bacteria
Isethionate as a product from taurine during nitrogen-limited growth of Klebsiella oxytoca TauN1 by Katharina Styp von Rekowski; Karin Denger; Alasdair M. Cook (pp. 325-330).
Klebsiella oxytoca TauN1 represents a group of isolates which utilise taurine (2-aminoethanesulfonate) quantitatively as a sole source of combined nitrogen for aerobic growth. During growth, a compound is excreted, which has now been identified as isethionate (2-hydroxyethanesulfonate). An ion-chromatographic separation of isethionate was developed to quantify the putative isethionate, whose identity was confirmed by matrix-assisted, laser-desorption ionisation time-of-flight mass spectrometry. Strain TauN1 utilised taurine (and excreted isethionate) concomitantly with growth. Cell-free extracts contained inducible taurine transaminase, which yielded sulfoacetaldehyde. A soluble, NADP-dependent isethionate dehydrogenase converted sulfoacetaldehyde to isethionate. The enzyme was partially purified and it apparently belonged to the family of short-chain alcohol dehydrogenases.
Keywords: Isethionate formation; Taurine transaminase; Isethionate dehydrogenaseKlebsiella oxytoca
Purification and characterization of an NADH oxidase from extremely thermophilic anaerobic bacterium Thermotoga hypogea by Xianqin Yang; Kesen Ma (pp. 331-337).
Thermotoga hypogea is an extremely thermophilic anaerobic bacterium capable of growing at 90°C. It was found to be able to grow in the presence of micromolar molecular oxygen (O2). Activity of NADH oxidase was detected in the cell-free extract of T. hypogea, from which an NADH oxidase was purified to homogeneity. The purified enzyme was a homodimeric flavoprotein with a subunit of 50 kDa, revealed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. It catalyzed the reduction of O2 to hydrogen peroxide (H2O2), specifically using NADH as electron donor. Its catalytic properties showed that the NADH oxidase had an apparent Vmax value of 37 μmol NADH oxidized min−1 mg−1 protein. Apparent Km values for NADH and O2 were determined to be 7.5 μM and 85 μM, respectively. The enzyme exhibited a pH optimum of 7.0 and temperature optimum above 85°C. The NADH-dependent peroxidase activity was also present in the cell-free extract, which could reduce H2O2 produced by the NADH oxidase to H2O. It seems possible that O2 can be reduced to H2O by the oxidase and peroxidase, but further investigation is required to conclude firmly if the purified NADH oxidase is part of an enzyme system that protects anaerobic T. hypogea from accidental exposure to O2.
Keywords: NADH oxidaseThermotoga hypogeaFlavoprotein; H2O2Extreme thermophile; Peroxidase
Characterization of a model system for the study of Nostoc punctiforme akinetes by Claudia Argueta; Michael L. Summers (pp. 338-346).
Nostoc punctiforme is a filamentous cyanobacterium that is capable of dark heterotrophy and cellular differentiation into nitrogen-fixing heterocysts, motile hormogonia, or spore-like akinetes. The study of akinete differentiation at the molecular level has been limited by the asynchronous development and limited number of akinetes formed within a filament. A system in which to study the development and genetic regulation of akinetes was investigated using a zwf mutant lacking glucose-6-phosphate dehydrogenase, the initial enzyme of the oxidative pentose phosphate pathway. Upon dark incubation in the presence of fructose, the zwf− strain ceased growth and differentiated into akinete-like cells, whereas the wild-type strain exhibited heterotrophic growth. Dark-induced zwf akinetes exhibited periodic acid–Schiff staining characteristics identical to that observed for wild-type akinetes, and synchronous induction of akinetes occurred in treated cultures. Dark-induced zwf akinetes exhibited increased resistance to the environmental stresses of desiccation, cold, or treatment with lysozyme relative to vegetative cells of both strains. Transcription of the avaK akinete marker gene was strongly induced in developing zwf akinetes as shown by Northern blotting and green fluorescent protein transcriptional reporter fusions. ATP levels did not vary significantly between dark incubated strains, indicating that a signal other than energy level may trigger akinete formation. This phenotypic and genetic evidence showing near-synchronous induction of dark-induced zwf akinetes indicates that this system will provide a valuable tool for the molecular genetic study of akinete development in N. punctiforme.
Keywords: Filamentous cyanobacteria; Akinete; Cyanobacterial development
Heme uptake genes in human and fish isolates of Photobacterium damselae: existence of hutA pseudogenes by Sandra Juíz Río; Carlos R. Osorio; Manuel L. Lemos (pp. 347-358).
The marine bacterium Photobacterium damselae includes strains classified into two distinct subspecies, namely subsp. damselae and subsp. piscicida, which have been reported to cause disease in a variety of marine animals and in humans. P. damselae strains utilize heme compounds as sole iron sources. In the present study, ten potential heme uptake and utilization genes are described in P. damselae subsp. damselae and subsp. piscicida. One gene cluster includes the genes coding for putative proteins HutZ, HutX and HutW; TonB, ExbB and ExbD, the three components of the TonB system; HutB, the putative periplasmic binding protein; HutC, the putative inner membrane permease; and HutD, the putative ABC-transporter ATP-ase. A gene coding for HutA, the outer membrane heme receptor, has also been identified, but it is not linked to the rest of the heme transport genes. RT-PCR analyses showed that heme uptake genes are arranged in three iron-regulated transcriptional units. A plasmid carrying the gene for the heme receptor HutA in combination with a plasmid carrying tonBexbBDhutBCD genes conferred to Escherichia coli 101ESD (ent) the ability to use heme and hemoglobin as iron sources. The hutA gene was present in strains isolated from humans and a variety of fish species, but it was shown to be interrupted in some subsp. piscicida strains, constituting a pseudogene. This is the first description of a heme-uptake system in a Photobacterium species, and shows some structural and functional similarities to heme-uptake systems reported in other gram-negative bacteria.
Keywords: Photobacterium damselaeIron uptake; Heme uptake; ABC transporter; Pseudogenes
Apparent incompatibility of plasmid pSfrYC4b of Sinorhizobium fredii with two different plasmids in another strain by Lihong Miao; Kui Zhou; Junchu Zhou; Dasong Chen; Fuli Xie (pp. 359-367).
Sinorhizobium fredii YC4B is a spontaneous mutant derivative of strain YC4 that is unable to nodulate soybeans. The second-largest plasmid of strain YC4B, termed pSfrYC4b (810 kb), was transferred to S. fredii HN01SR, a strain which contains three large indigenous plasmids (pSfrHN01a, pSfrHN01b and pSfrHN01c). Surprisingly, two stable indigenous plasmids (pSfrHN01a and pSfrHN01b) of strain HN01SR were cured simultaneously by the introduction of pSfrYC4b. Furthermore, a novel, unstable plasmid (pHY4) became visible in agarose gels. The electrophoretic mobility of plasmid pHY4 was slower than that shown by the cured plasmids, indicating that the molecular weight of the former is higher than that of plasmids pSfrYC4b and pSfrHN01b. Replication gene repC-like sequences were detected by polymerase chain reaction (PCR) on pSfrHN01a and pSfrYC4b, but not on pSfrHN01b. Sau3AI and PstI restriction patterns of the PCR-amplified repC-like sequences from HN01SR and YC4B were very similar.
Keywords: Sinorhizobium frediiIndigenous plasmids; Conjugative plasmid transfer; Incompatibility