Hans Reichenbach

Myxothiazol, a new inhibitor of the cytochrome b-c1 segment of the respiratory chain☆

Myxothiazol inhibited oxygen consumption of beef heart mitochondria in the presence and absence of 2,4-dinitrophenol, as well as NADH oxidation by submitochondrial particles. The doses required for 50% inhibition were 0.58 mol myxothiazol/mol cytochrome b for oxygen consumption of beef heart mitochondria, and 0.45 mol/mol cytochrome b for NADH oxidation by submitochondrial particles. Difference spectra with beef heart mitochondria and with cell suspensions of Saccharomyces cerevisiae revealed that myxothiazol blocked the electron transport within the cytochrome b-c1 segment of the respiratory chain. Myxothiazol induced a spectral change in cytochrome b which was different from and independent of the shift induced by antimycin. Myxothiazol did not give the extra reduction of cytochrome b typical for antimycin. Studies on the effect of mixtures of myxothiazol and antimycin on the inhibition of NADH oxidation indicated that the binding sites of the two inhibitors are not identical.

Myxobacteria, producers of novel bioactive substances

Myxobacteria are soil bacteria that move by gliding and have an astonishing life cycle culminating in fruiting body formation. In a research program at the Gesellshaft für Biotechnologische Forschung over the past 25 years the organisms have been shown to be a rich source of potentially useful secondary metabolites. So far about 80 different basic compounds and 450 structural variants have been characterized. Many of those compounds were new. It is particularly remarkable that myxobacteria specialize in mechanisms of action that are very rare with other producers. Thus 20 new electron transport inhibitors, 10 substances that act on the cytoskeleton, four inhibitors of nucleic acid polymerases, and one inhibitor of fungal acetyl-CoA carboxylase, a novel mechanism of action, have been found. Journal of Industrial Microbiology & Biotechnology (2001) 27, 149–156.

Steroid biosynthesis in prokaryotes: identification of myxobacterial steroids and cloning of the first bacterial 2,3(S)‐oxidosqualene cyclase from the myxobacterium Stigmatella aurantiaca

Steroids, such as cholesterol, are synthesized in almost all eukaryotic cells, which use these triterpenoid lipids to control the fluidity and flexibility of their cell membranes. Bacteria rarely synthesize such tetracyclic compounds but frequently replace them with a different class of triterpenoids, the pentacyclic hopanoids. The intriguing mechanisms involved in triterpene biosynthesis have attracted much attention, resulting in extensive studies of squalene‐hopene cyclase in bacteria and (S)‐2,3‐oxidosqualene cyclases in eukarya. Nevertheless, almost nothing is known about steroid biosynthesis in bacteria. Only three steroid‐synthesizing bacterial species have been identified before this study. Here, we report on a variety of sterol‐producing myxobacteria. Stigmatella aurantiaca is shown to produce cycloartenol, the well‐known first cyclization product of steroid biosynthesis in plants and algae. Additionally, we describe the cloning of the first bacterial steroid biosynthesis gene, cas, encoding the cycloartenol synthase (Cas) of S. aurantiaca. Mutants of cas generated via site‐directed mutagenesis do not produce the compound. They show neither growth retardation in comparison with wild type nor any increase in ethanol sensitivity. The protein encoded by cas is most similar to the Cas proteins from several plant species, indicating a close evolutionary relationship between myxobacterial and eukaryotic steroid biosynthesis.

The Genus Lysobacter

The species classified in the genus Lysobacter are Gram-negative rods that move by gliding. The cells are slender and cylindrical, with rounded ends (Figs. 1 and 2). They typically measure 0.4−0.6 × 2−5 μm, but in the population there are also always long to very long (up to 70 μm) cells and filaments. The cell shape and the occurrence of long cells are both very characteristic for the genus. Lysobacter cells resemble the vegetative cells of certain myxobacteria, specifically of the genera Polyangium and Sorangium, with which the lysobacters were confused for many years. They also share with the myxobacteria a high GC content of their DNA of 65 to 70 mol%. Due to the gliding movements of the cells, the colonies of Lysobacter are spreading or swarming on solid media and may become very large and extremely thin (Figs. 3 and 4). Sometimes the organisms produce copious amounts of slime, and the colonies then become thick and deliquescent, but colonies with a wrinkled and dry surface also occur. Lysobacter colonies may be white or cream-colored but often they are greenish-yellow, purplish-red, or brown, although their color is often rather pale. Some strains produce an unpleasant odor reminiscent of certain pseudomonads or of pyridine. In agitated liquid cultures, the lysobacters grow as homogeneous cell suspensions, but, as with all gliding bacteria, the suspended cells are unable to translocate. The Lysobacter species live in soil, decaying organic matter, and fresh water, sometimes in large populations. Many strains are of considerable ecological and biotechnological interest as producers of exoenzymes and of antibiotics.

Myxothiazol, a new antibiotic interfering with respiration.

Myxothiazol, a new antibiotic from the myxobacterium Myxococcus fulvus, inhibited the growth of many yeasts and fungi at concentrations between 0.01 and 3 micrograms/ml. It was generally inactive against bacteria. The inhibitory effect was cytostatic. With Candida albicans, Saccharomyces cerevisiae, and Mucor hiemalis, the growth inhibition was neutralized by glucose. Soon after being added to a cell suspension, the compound almost completely blocked oxygen consumption.

Intracellular location of flexirubins in Flexibacter elegans (Cytophagales).

The inner and outer membranes of 2 strains of Gram-negative Flexibacter elegans, Fx e1 and Fx 3/4, could be separated on sucrose density gradients after the cells had been converted into spheroplasts, and the spheroplasts had been lysed in presence of EDTA and the detergent Brij 58. The light fraction (rho = 1.14 g . cm-3) contained the components of the respiratory chain in high concentrations, but only low amounts of the lipopolysaccharide component, 2-keto-3-deoxyoctonic acid, and was thus mainly material from the inner membrane. The heavy fraction (rho = 1.175 g . cm-3) contained only traces of respiratory chain enzymes, but the majority of the 2-keto-3-deoxyoctonic acid, and was thus mainly material from the outer membrane. The flexirubin pigments were found almost quantitatively in the latter fraction. Strain Fx 3/4 produced carotenoids in addition to flexirubins; in this case the flexirubins were located in the outer, and the carotenoids in the inner membrane.