Mechanism of Photoregulated Carotenogenesis in Rhodotorula minuta VII. Action Spectrum for Photoinduced Carotenogenesis

An action spectrum for photoinduced carotenogenesis in the yeast,Rhodotorula minuta, was determined over the wavelength rangefrom 250 nm to 770 nm. The action spectrum had a prominent peak at about 280 nm, withshoulders at 340, 370 and 400 nm. In addition, at wavelengthsfrom 260 nm to 400 nm, all slopes of fluence-response curveswere approximately equal, and reciprocity was obtained at eachwavelength tested. The action spectrum obtained was different from any action spectrumso far reported for photoinduced carotenogenesis and suggeststhat a new type of chromoprotein plays a major role as a photoreceptor. ³Present address: Koshi Agricultural Extension Office of FukuiPrefecture, Matsumoto, Fukui, 910 Japan (Received March 31, 1989; Accepted December 8, 1989)     

Untersuchungen an Myxococcus xanthus

Ohne Zusammenfassung     

Microcyst Germination in Myxococcus xanthus

Germination of glycerol-prepared microcysts of Myxococcus xanthus was studied. The sequence of morphological events during germination resembled that of germinating fruiting body-microcysts. The turbidity drop of a culture of germinating microcysts could be described by McCormick's formula derived for germinating Bacillus spores. The rate of uptake of labeled glycine and acetate did not change during germination. Temperature, aeration, and pH optima for germination were the same as for vegetative cell growth. Germination was induced by protein hydrolysates and the individual amino acids glycine, alanine, valine, aspartic acid, and glutamic acid. A number of organic compounds, including sugars, alcohols, aldehydes, ketones, organic acids, and chelating agents, did not induce germination. The inorganic ions HPO(4) (2-), Mg(++), Ca(++), and NH(4) (+) induced germination, although ionic strength was not a factor. Microcysts incubated in distilled water at concentrations greater than about 10(9) cells/ml germinated; supernatant fluid from such suspensions (germination factor) induced germination of less concentrated suspensions. The activity of germination factor was resistant to boiling, but was lost on charring and dialysis. Germination of microcysts and growth of vegetative cells was equally sensitive to a variety of metabolic inhibitors, including penicillin and chloramphenicol. Germination was more resistant than vegetative growth to inhibition by antibiotics of the streptomycin family and by actinomycin D.     

Gliding movements in Myxococcus xanthus.

Prokaryotic gliding motility is described as the movement of a cell on a solid surface in the direction of the cell's long axis, but its mechanics are unknown. To investigate the basis of gliding, movements of individual Myxococcus xanthus cells were monitored by employing a video microscopy method by which displacements as small as 0.03 micron could be detected and speeds as low as 1 micron/min could be resolved. Single cells were observed to glide with speeds varying between 1 and 20 microns/min. We found that speed variation was due to differences in distance between the moving cell and the nearest cell. Cells separated by less than one cell diameter (0.5 micron) moved with an average speed of 5.0 micron/min, whereas cells separated by more than 0.5 micron glided with an average speed of 3.8 microns/min. The power to glide was found to be carried separately at both ends of a cell.     

Regulated exopolysaccharide production in Myxococcus xanthus

Myxococcus xanthus fibrils are cell surface-associated structures composed of roughly equal amounts of polysaccharide and protein. The level of M. xanthus polysaccharide production under different conditions in the wild type and in several mutants known to have alterations in fibril production was investigated. Wild-type exopolysaccharide increased significantly as cells entered the stationary phase of growth or upon addition of Ca2+ to growing cells, and the polysaccharide-induced cells exhibited an enhanced capacity for cell-cell agglutination. The activity of the key gluconeogenic pathway enzyme phosphoenolpyruvate carboxykinase (Pck) also increased under these conditions. Most fibril-deficient mutants failed to produce polysaccharide in a stationary-phase- or Ca2+-dependent fashion. However, regulation of Pck activity was generally unimpaired in these mutant strains. In an stk mutant, which overproduces fibrils, polysaccharide production and Pck activity were constitutively high under the conditions tested. Polysaccharide production increased in most fibril-deficient strains when an stk mutant allele was present, indicating that these fibril-deficient mutants retained the basic cellular components required for fibril polysaccharide production. In contrast to other divalent cations tested, Sr2+ effectively replaced Ca2+ in stimulating polysaccharide production, and either Ca2+ or Sr2+ was required for fruiting-body formation by wild-type cells. By using transmission electron microscopy of freeze-substituted log-phase wild-type cells, fibril material was observed as a cell surface-associated layer of uniform thickness composed of filaments with an ordered structure.     

Cytochemistry of Phosphatases in Myxococcus xanthus

An Mg(2+)-dependent and a K(+)-stimulated adenosine triphosphatase were localized by cytochemistry at or near both surfaces of the cytoplasmic membrane of Myxococcus xanthus. An alkaline and an acid phosphatase resided at the external surface of the membrane or in the periplasm. All enzymes could be extracted from partially fixed cells with Mg(2+)-deficient buffers. Suboptimal external phosphate elicited dissociation of adenosine triphosphatase from the membrane but not that of the unspecific phosphatases. The dissociated enzymes migrated into the cytoplasm where they were associated mainly with cytoplasmic aggregates.     

Myxococcus xanthus biomass as biosorbent for lead

This paper deals with lead biosorption by Myxococcus xanthus biomass in which dry biomass, accumulating up to 1.28 mmol of lead g(-1), is demonstrated to be a more efficient biosorbent than wet biomass. Dry biomass biosorption was found to be very rapid, reaching equilibrium after 5-10 min. Culture age, the initial lead concentration and pH affected this process, but temperature did not. Furthermore, by using sodium citrate as a desorbent agent, 92.17% of the biosorbed lead could be recovered. It was also established that the biosorbed lead is located on the cellular wall and within the characteristic extracellular polysaccharide of this micro-organism.     

Fatty Acids of Myxococcus xanthus

Fatty acids were extracted from saponified vegetative cells and myxospores of Myxococcus xanthus and examined as the methyl esters by gas-liquid chromatography. The acids consisted mainly of C₁₄ to C₁₇ species. Branched acids predominated, and iso-pentadecanoic acid constituted half or more of the mixture. The other leading component (11–28%) was found to be 11-n-hexadecenoic acid. Among the unsaturated acids were two diunsaturated ones, an n-hexadecadienoic acid and an iso-heptadecadienoic acid. No significant differences between the fatty acid compositions of the vegetative cells and myxospores could be detected. The fatty acid composition of M. xanthus was found to be markedly similar to that of Stigmatella aurantiaca. It is suggested that a fatty acid pattern consisting of a large proportion of iso-branched C₁₅ and C₁₇ acids and a substantial amount of an n-16:1 acid is characteristic of myxobacteria.     

Natural transformation of Myxococcus xanthus

Myxococcus xanthus belongs to the delta class of the proteobacteria and is notable for its complex life-style with social behaviors and relatively large genome. Although previous observations have suggested the existence of horizontal gene transfer in M. xanthus, its ability to take up exogenous DNA via natural transformation has not been experimentally demonstrated. In this study, we achieved natural transformation in M. xanthus using the autonomously replicating myxobacterial plasmid pZJY41 as donor DNA. M. xanthus exopolysaccharide (EPS) was shown to be an extracellular barrier for transformation. Cells deficient in EPS production, e.g., mutant strains carrying ΔdifA or ΔepsA, became naturally transformable. Among the inner barriers to transformation were restriction-modification systems in M. xanthus, which could be partially overcome by methylating DNA in vitro using cell extracts of M. xanthus prior to transformation. In addition, the incubation time of DNA with cells and the presence of divalent magnesium ion affected transformation frequency of M. xanthus. Furthermore, we also observed a potential involvement of the type IV pilus system in the DNA uptake machinery of M. xanthus. The natural transformation was totally eliminated in the ΔpilQ/epsA and Δtgl/epsA mutants, and null mutation of pilB or pilC in an ΔepsA background diminished the transformation rate. Our study, to the best of our knowledge, provides the first example of a naturally transformable species among deltaproteobacteria.     

Cohesion-defective mutants of Myxococcus xanthus

Cohesion of Myxococcus xanthus cells involves interaction of a cell surface cohesin with a component of the extracellular matrix. In this work, two previously isolated cohesion-defective (fbd) mutants were characterized. The fbdA and fbdB genes do not encode the cohesins but are necessary for their production. Both mutants produce type IV pili, suggesting that PilA is not a major cohesin.     

Myxococcus xanthus autocide AMI.

Autocide AMI of Myxococcus xanthus was purified and shown to be a mixture of fatty acids: 46.4% saturated, 49.3% monounsaturated, and 4.3% diunsaturated. The specific autocidal activities (units per milligram) were as follows: purified AMI, 1,000; saturated fraction, 100; monounsaturated fraction, 800; diunsaturated fraction, 2,200. Model fatty acids mimicked to some extent the activity of AMI, although none of the fatty acids tested were as active as purified AMI. Spontaneous and induced mutants of M. xanthus were selected for resistance to AMI and to fatty acids. The AMI-resistant mutants were also resistant to the model fatty acids, whereas resistance to fatty acids was specific to the compound used for mutant selection. All AMI- and fatty acid-resistant mutants examined were found to be blocked in fruiting body formation. Some of these mutants were able to form normal fruiting bodies when mixed with the extracellular fluid of the parental strain. The data suggest that AMI plays a role in developmental lysis of M. xanthus.     

Heat-shock-induced proteins from Myxococcus xanthus

Optimal conditions for two-dimensional gel electrophoresis of total cellular proteins from Myxococcus xanthus were established. Using these conditions, we analyzed protein patterns of heat-shocked M. xanthus cells. Eighteen major spots and 15 minor spots were found to be induced by heat shock. From N-terminal sequences of 15 major spots, DnaK, GroEL, GroES, alkyl hydroperoxide reductase, aldehyde dehydrogenase, succinyl coenzyme A (CoA) synthetase, 30S ribosomal protein S6, and ATP synthase alpha subunit were identified. Three of the 18 major spots had an identical N-terminal sequence, indicating that they may be different forms of the same protein. Although a DnaK homologue, SglK, has been identified in M. xanthus (R. M. Weimer, C. Creghton, A. Stassinopoulos, P. Youderian, and P. L. Hartzell, J. Bacteriol. 180:5357-5368, 1998; Z. Yang, Y. Geng, and W. Shi, J. Bacteriol. 180:218-224, 1998), SglK was not induced by heat shock. In addition, there were seven substitutions within the N-terminal 30-residue sequence of the newly identified DnaK. This is the first report to demonstrate that succinyl CoA synthetase, 30S ribosomal protein S6, and ATP synthase alpha subunit are heat shock inducible.     

Myxococcus xanthus biomass as biosorbent for lead

This paper deals with lead biosorption by Myxococcus xanthus biomass in which dry biomass, accumulating up to 1·28 mmol of lead g⁻¹, is demonstrated to be a more efficient biosorbent than wet biomass. Dry biomass biosorption was found to be very rapid, reaching equilibrium after 5–10 min. Culture age, the initial lead concentration and pH affected this process, but temperature did not. Furthermore, by using sodium citrate as a desorbent agent, 92·17% of the biosorbed lead could be recovered. It was also established that the biosorbed lead is located on the cellular wall and within the characteristic extracellular polysaccharide of this micro-organism.