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PubMed2005

Herbicidal and antioxidant responses of transgenic rice overexpressing Myxococcus xanthus protoporphyrinogen oxidase.

We analyzed the herbicidal and antioxidant defense responses of transgenic rice plants that overexpressed the Myxococcus xanthus protoporphyrinogen oxidase gene. Leaf squares of the wild-type incubated with oxyfluorfen were characterized by necrotic leaf lesions and increases in conductivity and malonyldialdehyde levels, whereas transgenic lines M4 and M7 did not show any change with up to 100 microM oxyfluorfen. The wild-type had decreased F(v)/F(m) and produced a high level of H(2)O(2) at 18 h after foliar application of oxyfluorfen, whereas transgenic lines M4 and M7 were unaffected. In response to oxyfluorfen, violaxanthin, beta-carotene, and chlorophylls (Chls) decreased in wild-type plants, whereas antheraxanthin and zeaxanthin increased. Only a slight decline in Chls was observed in transgenic lines at 48 h after oxyfluorfen treatment. Noticeable increases of cytosolic Cu/Zn-superoxide dismutase, peroxidase isozymes 1 and 2, and catalase were observed after at 48 h of oxyfluorfen treatment in the wild-type. Non-enzymatic antioxidants appeared to respond faster to oxyfluorfen-induced photodynamic stress than did enzymatic antioxidants. Protective responses for the detoxification of active oxygen species were induced to counteract photodynamic stress in oxyfluorfen-treated, wild-type plants. However, oxyfluorfen-treated, transgenic plants suffered less oxidative stress, confirming increased herbicidal resistance resulted from dual expression of M. xanthus Protox in chloroplasts and mitochondria.

Antioxidants↗
PubMed1997

Biochemical characterization of Pkn2, a protein Ser/Thr kinase from Myxococcus xanthus, a Gram-negative developmental bacterium.

Pkn2, a protein Ser/Thr kinase, from the developmental bacterium Myxococcus xanthus was expressed under a T7 promoter in Escherichia coli and purified. Purified Pkn2 retained the autophosphorylation activity with the Km value of 177 microM for ATP and 73 nmol/min/mg for Vmax. The optimum pH and temperature were determined to be 7.5 and 35 degrees C, respectively. The autophosphorylation activity was inhibited by staurosporine with the IC50 value of 400 nM while H-7 and genistein had little effect on this kinase. Pkn2 appears to be unique for its higher manganese dependence. This is the first biochemical characterization of the prokaryotic protein Ser/Thr kinase.

Bacterial Proteins↗
PubMed2003

Lanthanum fixation by Myxococcus xanthus: cellular location and extracellular polysaccharide observation.

Myxococcus xanthus is a soil bacterium of the myxobacteria group and is abundant in almost all soils. Its role in soil ecology is considered significant. One noteworthy characteristic of the bacterium is that it produces large quantities of extracellular polymeric substances (EPS). It is also known that its biomass has the capacity to fix heavy metals. Here it is reported that M. xanthus was able to accumulate 0.6 mmol of La per g of wet biomass and/or 0.99 mmol per g of dry biomass. Transmission Electron Microscopy (TEM) observation of M. xanthus cells treated with La showed that a substantial amount of this cation was fixed in the EPS and in the cell wall. Smaller amounts were also observed in the cytoplasm. Fixed La appeared as phosphate in all cellular locations. The results given here also show that the use of La enables TEM observation of the M. xanthus EPS as a dense fibrillar net surrounding the cells. This technique is relatively easy and prevents EPS collapse, which occurs frequently during the fixation and dehydration procedures commonly used in preparations for TEM observations. Since antibodies are no longer required, the La stain can be carried out without delaying bacterial cell cultivation or isolation. In addition, the presence of La in cell cytoplasm without cell degeneration suggests that this microorganism could be used as a model in the study of bacteria-lanthanide interactions.

Biomass↗
PubMed1997

Comparative heavy metal biosorption study of brewery yeast and Myxococcus xanthus biomass.

The biosorption for La2+, Co2+, Mn2+, UO2(2+), Pb2+, Ag+, Zn2+, Cd2+ and Cr2+ by wet and dry biomass form Myxococcus xanthus obtained from laboratory cultures and Saccharomyces cerevisiae from the brewing industry has been studied. M. xanthus biomass was found to be the most efficient biosorbent for all of the metals assayed. However, due to the fact that S. cerevisiae is a low cost residual by-product from the brewing industry, and at the same time yields good levels of biosorption, it is considered in this work to be of great interest for use as a detoxifier of heavy metals contaminated waters. In addition, the use of sodium carbonate as a desorbent agent is discussed where it was possible to recover up to 94,53% of UO2(2+) by both M. xanthus and S. cerevisiae biomass.

Absorption↗
PubMed2000

Effect of culture conditions on the formation of struvite by Myxococcus xanthus.

The amount of struvite (MgNH4PO4 x 6H2O) produced by Myxococcus xanthus as well as the culture parameter values (pH, total phosphorus, total Kjeldahl nitrogen) were dependent on the culture medium used. Struvite formation started during the exponential phase and the maximum concentration was observed at the beginning of stationary growth phase. The addition of each medium component to the liquid culture influenced the amount of crystal produced. This amount did not depend on the pH increase during the culture period. The moment of the bacterial growth phase, at which each medium component was added, influenced the struvite formation.

Bacteriological Techniques↗
PubMed1999

Identification and characterization of five cspA homologous genes from Myxococcus xanthus.

Escherichia coli contains a large CspA family consisting of nine homologues, in which four are cold-shock inducible and one is stationary-phase inducible. Here, we demonstrate that Myxococcus xanthus possesses at least five CspA homologues, CspA to CspE. Hydrophobic residues forming a hydrophobic core, and aromatic residues, which are included in functional motifs RNP-1 and RNP-2 involved in binding to RNA and ssDNA, are well conserved. These facts suggest that M. xanthus CspA homologues have a similar structure and function as E. coli CspA. However, in contrast to the E. coli CspA family, the expression of M. xanthus csp genes as judged by primer extension analysis is not significantly regulated by temperature changes, except for cspB of which expression was reduced to less than 10% upon heat shock at 42 degrees C. Such constitutive expression of the csp genes may be important for M. xanthus, a soil-dwelling bacterium, to survive under conditions of exposure to various environmental changes in nature.

Amino Acid Sequence↗
PubMed1997

Trans-acting regulation of antibiotic TA genes in Myxococcus xanthus.

Two regulatory mutations of Myxococcus xanthus, which cause an increase in the transcription of genes required for antibiotic TA synthesis, were mapped by transduction and their effect on transcription of four TA genes examined. The two regulatory mutations were closely linked and located within the 40-kb TA gene cluster on the M. xanthus chromosome. Recombinants were constructed which contained one of the regulatory mutations and promoter probes in the four different TA genes. Both regulatory mutations enhanced transcription of three of the four TA genes. However, construction of a strain containing the over-expression regulatory mutation in a wild-type background produced less antibiotic than the parental strain.

Anti-Bacterial Agents↗
PubMed1997

Cloning and sequencing of two genes, prtA and prtB, from Myxococcus xanthus, encoding PrtA and PrtB proteases, both of which are required for the protease activity.

The sequence of a 1955-bp TaqI DNA fragment from Myxococcus xanthus was determined. This fragment contains two complete genes, designated prtA and prtB. The prtA and prtB ORFs extend over 828 and 798 bp, respectively. They are separated only by 3 nt and appear to be present in a polycistronic transcriptional unit. A typical lipoprotein signal sequence is present at the N terminus of the two deduced polypeptides. The aa sequence of PrtA shows a high degree of identity to the region adjacent to the Ser residue belonging to the catalytic triad of serine proteases from Staphylococcus aureus and Enterococcus faecalis. It also exhibits features characteristic of trypsin-like serine proteases in that it contains the same pattern of variable and conserved regions. The deduced aa sequence of PrtB reveals a signature zinc-binding consensus motif (HEXXHXXGXXH/Met-turn) characteristic of the class of metalloproteases called metzincins. Plasmids containing prtA, prtB, or both were constructed. Protease activity studies of Escherichia coli clones containing these plasmids showed that both genes are necessary for this activity, whatever their cis or trans position. As prtB produces a putative membrane-bound lipoprotein of 266 aa, the protease activation must occur at the membrane level.

Amino Acid Sequence↗
PubMed1999

Cloning and characterization of a Myxococcus xanthus cytochrome P-450 hydroxylase required for biosynthesis of the polyketide antibiotic TA.

The antibiotic TA, a complex macrocyclic polyketide of Myxococcus xanthus, is produced, like many other polyketides, through successive condensations of acetate by a type I polyketide synthase (PKS) mechanism. The chemical structure of this antibiotic and the mechanism by which it is synthesized indicate the need for several post-modification steps, such as a specific hydroxylation at C-20. Previous studies have shown that several genes, essential for TA biosynthesis, are clustered in a region of at least 36kb, which was subsequently cloned and analyzed. In this study, we report the analysis of a DNA fragment, containing a specific cytochrome P-450 hydroxylase, presumably responsible for the sole non-PKS hydroxylation at position C-20. Functional analysis of the cytochrome P-450 hydroxylase gene through specific gene disruption confirms that it is essential for the production of an active TA molecule.

Amino Acid Sequence↗
PubMed2001

A novel gene from Myxococcus xanthus that facilitates membrane translocation of an extracellular endoglucanase in Escherichia coli?

Expression in Escherichia coli of the Myxococcus xanthus gene celA, which encodes an extracellular endoglucanase, resulted in CelA being distributed between cytoplasm, periplasm and membrane. The presence of an adjacent open reading frame downstream from the full celA gene, or the absence of a putative lipoprotein signal sequence, confined CelA distribution to the periplasm and membrane, or to the cytoplasm and periplasm, respectively.

Amino Acid Sequence↗
PubMed1998

Regulation of the expression of a gene encoding beta-endoglucanase secreted by Myxococcus xanthus during growth: role of genes involved in developmental regulation.

An endoglucanase, CelA, is secreted by Myxococcus xanthus only during exponential growth. The production of this enzyme is decreased by mutations in 5 different genes (Exc +/- phenotype), three of which correspond to asg genes which regulate the production of an early cell-to-cell signal in development. Transcription of celA is decreased in two of these Exc +/- mutants, whereas a post-transcriptional step is affected in two other Exc- mutants. Thus, asg genes, in addition to regulating the onset of development, also regulate a gene (celA) that is expressed during exponential growth and that is not involved in development.

Amino Acid Sequence↗
PubMed1991

Cell-cell interactions that direct fruiting body development in Myxococcus xanthus.

The soil bacterium, Myxococcus xanthus initiates a developmental program when nutrients are limited. This results in the formation of a multicellular fruiting body structure filled with differentiated, environmentally resistant spores. At least four cell-cell signals, cell motility, and aggregation functions are required for the completion of fruiting body formation.

Bacterial Proteins↗
PubMed2001

Lipid chemotaxis and signal transduction in Myxococcus xanthus.

The lipid phosphatidylethanolamine (PE) is the first chemoattractant to be described for a surface-motile bacterium. In Myxococcus xanthus, the specific activity of PE is determined by its fatty acid components. Two active species have been identified: dilauroyl PE and dioleoyl PE. Excitation to dilauroyl PE requires fibril appendages and the presence of two cytoplasmic chemotaxis systems, of which one (Dif) appears to mediate excitation and the other (Frz) appears to mediate adaptation. A possible mechanism for fibril-mediated signal transduction is discussed, along with the potential roles for PE chemotaxis in the context of the M. xanthus life cycle.

Chemotaxis↗
PubMed2000

Pattern formation: fruiting body morphogenesis in Myxococcus xanthus.

When Myxococcus xanthus cells are exposed to starvation, they respond with dramatic behavioral changes. The expansive swarming behavior stops and the cells begin to aggregate into multicellular fruiting bodies. The cell-surface-associated C-signal has been identified as the signal that induces aggregation. Recently, several of the components in the C-signal transduction pathway have been identified and behavioral analyses are beginning to reveal how the C-signal modulates cell behavior. Together, these findings provide a framework for understanding how a cell-surface-associated morphogen induces pattern formation.

Bacterial Proteins↗
PubMed1999

Motility in Myxococcus xanthus and its role in developmental aggregation.

The Frz signal transduction system of Myxococcus xanthus was originally thought to be a simple variation of the well-characterized Che system of the enteric bacteria. Recently, however, many additional Frz proteins, along with alternative signal transduction systems, have been discovered. Together these signal transduction pathways coordinate cell-cell behavior, permitting the complex interactions required for developmental aggregation and fruiting body formation.

Gene Expression Regulation, Bacterial↗
PubMed2002

Large-scale isolation and crystallization of epothilone D from Myxococcus xanthus cultures.

The introduction of the epothilone polyketide synthase (PKS) into Myxococcus xanthus has enabled the heterologous production of epothilone D (1) on a large scale. To isolate this valuable product from the fermentation medium, an economical, scalable, and high-yielding purification process was developed. With the crystallization of 1 from a binary solvent system that consisted of ethanol and water, the product was recovered as white crystals with a final purity of > or =97% (w/w). This is the first reported crystallization of 1.

Carbon↗
PubMed2002

A new cytotoxic epothilone from modified polyketide synthases heterologously expressed in Myxococcus xanthus.

A new epothilone, 10,11-didehydroepothilone D (5), was isolated from a strain of the heterologous host Myxococcus xanthus genetically engineered to produce epothilone D (4). The structure of 5 was determined from NMR and MS data. The epothilone polyketide synthase was further modified in a recombinant M. xanthus strain to produce 5 as the major epothilone-related metabolite. The cytotoxicity of 5 against a panel of tumor cell lines, including several with multidrug resistance, and its effect on tubulin polymerization were comparable to epothilone D (4).

Antineoplastic Agents↗
PubMed2003

Isolation and characterization of new epothilone analogues from recombinant Myxococcus xanthus fermentations.

Nine new epothilone analogues (6-8, 10, 11a, 11b, 12, 13, and 15) were isolated from fermentations of Myxococcus xanthus strains engineered with modified polyketide synthase genes. The epothilone structures were elucidated primarily through interpretation of 1D and 2D NMR data. 4-Desmethyl-10,11-didehydroepothilone D (6) displayed activity against several tumor cell lines, including a multi-drug-resistant cell line.

Antineoplastic Agents↗