A new peptide antibiotic, aibellin, that had the efficiency enhancing activity on rumen fermentation, was isolated from the culture broth of the fungus, Verticimonosporium ellipticum D 1 528, and its primary structure was elucidated from spectrometric analysis and chemical degradation.Aibellin is a 20-residue peptaibol, and it has a unique structural feature in the novel C-terminal amino alcohol. Moreover, aibellin is the first peptaibol that possesses two acidic amino acids in the C-terminal region and a Phe residue in the middle of the sequence.In ruminants, the positive correlation between an increase in feed conversion and enhanced propionate production in the rumenafter the treatment of ionophore antibiotics such as monensin and lasalocid has been reported1~3). These antibiotics enhance propionate production and reduce methanogenesis, thus leading to greater efficiency of energy metabolism in ruminant animals3'40.During our search for novel ruminant growth performance enhancers from microbial sources using an in vitro rumenfermentation system, a newlinear peptide antibiotic, aibellin, was found in the culture broth of the fungus Verticimonosporium ellipticum D1528. Aibellin was found to enhance propionate production and to reduce methanogenesis by rumen microorganisms5).In this paper, we report the isolation and structural elucidation of aibellin. Aibellin had structural

A new icosapeptide, aibellin, markedly modified rumen fermentation in vitro. Batch culture experiments with mixed rumen microorganisms showed that 12.5 to 25 mg/L of aibellin enhanced propionate production and reduced methanogenesis without significantly affecting production of total VFA, protozoal survival, or cellulose digestion. Aibellin had essentially the same effects in continuous culture with hay powder and concentrate. Monensin (5 mg/L) had similar effects on propionate production and methanogenesis, but total VFA, protozoa, and cellulolysis were decreased even by this low concentration of monensin. Commercially available peptide antibiotics also were compared with aibellin. Of the antibiotics examined, only graminicidin D (7.5 to 15 mg/L) enhanced propionate production and reduced methanogenesis. However, gramicidin D decreased total VFA, protozoa, and cellulolysis even at 7.5 mg/L. Alamethicin (7.5 to 15 mg/L), which resembles aibellin in its structure, did not increase propionate production but raised the percentage of propionate because of reduced production of total VFA. Alamethicin depressed methanogenesis but also decreased protozoal survival and cellulose digestion. These in vitro experiments indicate that aibellin could be a useful and potent modifier of rumen fermentation.

Aibellin was administered in feed to goats (16 to 18 kg of BW) for 12 d. At 80 mg/d, the molar percentage of propionate in rumen fluid increased significantly in 8 d, and the effect lasted for as long as 10 d after administration ceased. Total VFA concentration, protozoa numbers, and NDF digestibility were not depressed significantly at this dosage but were reduced at 100 mg/d with little further increase in the molar percentage of propionate. Therefore, the optimal dosage of aibellin was 80 mg/d under our experimental conditions. In contrast, monensin (30 mg/d) and gramicidin D (60 mg/d) decreased total VFA concentration and protozoa numbers when supplemented to obtain molar percentages of propionate comparable to 80 mg/d of aibellin. From these results, aibellin may be easier and safer to use than monensin and gramicidin D to modify rumen fermentation.

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AntibioticsAntibiotics U 1200 MK7924, a Novel Metabolite with Nematocidal Activity from Coronophora gregaria -[isolation and structure elucidation of the novel polyketide (I)]. -(KUMAZAWA*, S.; KANDA, M.; UTAGAWA, M.; CHIBA, N.; OHTANI, H.; MIKAWA, T.; J. Antibiot. 56 (2003) 7, 652-654; Sch. Food Nutr. Sci., Univ. Shizuoka, Yada, Shizuoka 422, Japan; Eng.) -Staver 52-227