From the culture supernatant of the myxobacterium, Myxococcus fulvus strain Mx f50, an antibiotic activity was isolated which blocked growth of many Gram-positive and several Gramnegative bacteria, but not of yeasts and fungi. The activity consisted of two closely related compounds, myxopyronins A and B. The myxopyronins appear to be new antibiotics, and seem to specifically inhibit bacterial RNA polymerase.In this article, we present data on a new antibacterial compound, myxopyronin ( Fig. 1)1), which was discovered in a screening program for antibiotics from myxobacteria.After myxothiazol">, myxovirescin3>, myxovalargin4), and myxalamid1>, this is now the fifth new antibiotic which we could isolate from these unusual and little studied organisms. In addition, we found two antibiotics, pyrrolnitrine> and althiomycin7>, that were already known from other bacteria. We describe here the fermentation and •2H0O; pH adjusted to 7.2 before autoclaving. In this medium, the organism grew as a homogeneous cell suspension.

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Squalene and three sterols were isolated from Nannocystis exedens (Myxobacterales). The sterol content was about 0.4% of the dry weight; squalene content was in the same range. The main component was identified as cholest-8(9)-en-3~-01.[ 14C]Mevalonate was readily incorporated into the sterols. The bacterium was not inhibited by nystatin or amphotericin B. I N T R O D U C T I O NDuring an investigation into the carotenoids of Nannocystis exedens, a ubiquitous soil bacterium (Reichenbach, 1970), substantial amounts of steroid-like lipids were discovered. In addition, a substance with the retention time of squalene appeared in the gas-liquid chromatogram. As steroids are quite unusual in prokaryotes, we decided to isolate and characterize these compounds. METHODSStruins und culture conditions. Nunnocystis r.redens strain Na e l ( = N . r.wdrns HR 1 = German Collection of Microorganisms DSM 71 ; type strain : Reichenbach, 1970) was used for the chemical investigation. The organism was cultivated in 1 litre Erlenmeyer flasks containing 300 ml PL liquid medium [consisting of Probion LS 600 (single cell protein; Hoechst), 1 %; MgSOJ. 7H10, 0.1 %; and CaCl?. 2H10, 0.1 7;; pH 7.0, autoclaved]. The flasks were shaken at 30 "C at 160 r.p.m. From 8.7 1 of culture, 235 g of wet cells were obtained, corresponding to about 6 0 g dry wt. Alternatively the organism was grown in MDI medium [consisting of Casitone (Difco), 0.30;; CaCI?. 2H,O, 0.050,{; MgSO,. 7 H Z 0 , 0.2%; cyanocobalamine, 0.5 mg I-' ; and trace elements solution; pH 7.2, autoclaved]. Cell yields were much lower in this medium. The incorporation experiments were performed with N . osetlens strain Na el58 ( = N . e.wdens HR 2), isolated in 1980 from field soil collected near Cairo, Egypt.Isolation of'steroids. The wet cell mass (235 g) was extracted three times with 250 ml acetone, and the aqueous acetone solution was extracted three times with 200 ml toluene. After removal of the toluene under vacuum, there remained 1.1 g of crude material. GLC of an aliquot, with cholesterol as a standard, showed that this material contained about 220 mg of steroids. The crude material was dissolved in CH,Cl,/methanol ( 1 : I , v/v) and chromatographed on a column (850 x 35 mm) of Sephadex LH-20 with CH,Cl,/methanol as the eluant. There were 90 fractions of 15 ml each, and steroids could be demonstrated by TLC in fractions 48 to 65 (total residue 300 mg). This material was chromatographed on a silica gel column (Lobar column size B, self-packed with LiChrosorb Si60 silica gel, 10 pm particles; Merck) with hexane/acetone (6 :4, v/v) as the eluant. GLC of the 170 fractions (1 ml each) showed the steroids to be in fractions 51 to 86 (total residue 210 mg).Atwfj.ricu/ chrcmufogruphy. For TLC, silica gel on aluminium sheets (Merck) was used, with acetone/hexane (35 : 65, v/v) as the solvent, the steroids having an Rf of 0.6.The acetylated steroids were chromatographed on silica gel (Kieselgel 60 HFZSs; Merck) impregnated with 10% (w/w) AgNO, and activated by heating at 110 "C for 30 ...

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