315
and Bacillus megaterium. None of these antibiotics are active against gram-negative
organisms.
Ripostatins are a group of RNAP inhibitor antibiotic isolated from myxobacteria.
Ripostatin A, B and C were isolated from Sorangium cellulosum Soce377. Ripostatin
A and B are 14-membered macrolide antibiotics with double bonds at positions 2, 5
and 8. Ripostatin C is noncyclic in structure, and all the three ripostatins share a
terminal phenyl ring. Ripostatin A and B are active against S. aureus and E. coli
tolC. Ripostatin C does not show antimicrobial activity. Ripostatin B (Fig. 12.8b)
showed minor activity against fungi like Nadsonia fulvescens and Debaryomyces
hansenii. Sorangicins are another group of antimicrobials isolated from the sporangium genus of myxobacteria. Sorangicin A, Sorangicin B and Sorangiosides were
isolated by activity-based screening of the fermentation broth of Sporangium cellulosum So ce12. The structure contains a core macrocyclic hydrolacton with seven
carbon–carbon double bonds. The macrocycle consists of three pyran rings, one
being a trisubstituted dihydropyran ring and the other two tetrasubstituted tetrahydro pyran rings. Sorangicin A and B are highly active against gram-positive bacteria, including Mycobacterium phlei and Nocardia corallina. Gram-negative
bacteria were only inhibited at high concentrations. Etnangien characterized by a
22-membered polyhydroxylated macrolide ring is also isolated from strains of
Sorangium cellulosum (Irschik et al. 2007). It shows a broad spectrum of activity
against gram-positive bacteria, including mycobacteria.
12.4.5.3 Inhibitors of Protein Synthesis
Some of the antimicrobial molecules derived from myxobacteria act by inhibiting
protein synthesis in target cells. Althiomycin (Fig. 12.8c) is a sulfur-containing antibiotic originally isolated from Streptomyces althioticus. It is also produced by the
genera cystobacter and myxococcus of myxobacteria as well as the insect pathogen
Serratia marcescens. The chemical structure of althiomycin is comprised of an
oxime group, a thiazole, a thiazoline and a methoxypyrrolinone ring. Althiomycin
shows a broad spectrum of antimicrobial activity against both gram-positive and
gram-negative bacteria, including Klebsiella pneumoniae, S. aureus, and
Corynebacterium diphtheriae. Angiolam A is a lactam-lactone antibiotic containing
a 19-member macrocyclic ring with methyl, carbonyl and hydroxyl groups and a
single carbon–carbon double bond. It is isolated from Angiococcus disciformis An
d30. Angiolam is a bacteriostatic antibiotic with a narrow spectrum of activity limited to few members of gram-positive Bacillaceae, including Clostridium perfringens. Myxovalargin A and its derivatives myxovalargin B and C are peptide
antibiotics produced by Myxococcus fulvus strain Mx f65. They are composed of a
linear peptide chain made of 14 amino acids, including nonproteogenic amino acids
like 3-methylbutyric acid, α,β-dehydrovaline, α,β-dehydroleucine and (S)-βtyrosine. Myxovalargins are active against gram-positive bacteria like Micrococcus
luteus and Corynebacterium mediolanum.
12 Antimicrobials from Microbes
and Bacillus megaterium. None of these antibiotics are active against gram-negative
organisms.
Ripostatins are a group of RNAP inhibitor antibiotic isolated from myxobacteria.
Ripostatin A, B and C were isolated from Sorangium cellulosum Soce377. Ripostatin
A and B are 14-membered macrolide antibiotics with double bonds at positions 2, 5
and 8. Ripostatin C is noncyclic in structure, and all the three ripostatins share a
terminal phenyl ring. Ripostatin A and B are active against S. aureus and E. coli
tolC. Ripostatin C does not show antimicrobial activity. Ripostatin B (Fig. 12.8b)
showed minor activity against fungi like Nadsonia fulvescens and Debaryomyces
hansenii. Sorangicins are another group of antimicrobials isolated from the sporangium genus of myxobacteria. Sorangicin A, Sorangicin B and Sorangiosides were
isolated by activity-based screening of the fermentation broth of Sporangium cellulosum So ce12. The structure contains a core macrocyclic hydrolacton with seven
carbon–carbon double bonds. The macrocycle consists of three pyran rings, one
being a trisubstituted dihydropyran ring and the other two tetrasubstituted tetrahydro pyran rings. Sorangicin A and B are highly active against gram-positive bacteria, including Mycobacterium phlei and Nocardia corallina. Gram-negative
bacteria were only inhibited at high concentrations. Etnangien characterized by a
22-membered polyhydroxylated macrolide ring is also isolated from strains of
Sorangium cellulosum (Irschik et al. 2007). It shows a broad spectrum of activity
against gram-positive bacteria, including mycobacteria.
12.4.5.3 Inhibitors of Protein Synthesis
Some of the antimicrobial molecules derived from myxobacteria act by inhibiting
protein synthesis in target cells. Althiomycin (Fig. 12.8c) is a sulfur-containing antibiotic originally isolated from Streptomyces althioticus. It is also produced by the
genera cystobacter and myxococcus of myxobacteria as well as the insect pathogen
Serratia marcescens. The chemical structure of althiomycin is comprised of an
oxime group, a thiazole, a thiazoline and a methoxypyrrolinone ring. Althiomycin
shows a broad spectrum of antimicrobial activity against both gram-positive and
gram-negative bacteria, including Klebsiella pneumoniae, S. aureus, and
Corynebacterium diphtheriae. Angiolam A is a lactam-lactone antibiotic containing
a 19-member macrocyclic ring with methyl, carbonyl and hydroxyl groups and a
single carbon–carbon double bond. It is isolated from Angiococcus disciformis An
d30. Angiolam is a bacteriostatic antibiotic with a narrow spectrum of activity limited to few members of gram-positive Bacillaceae, including Clostridium perfringens. Myxovalargin A and its derivatives myxovalargin B and C are peptide
antibiotics produced by Myxococcus fulvus strain Mx f65. They are composed of a
linear peptide chain made of 14 amino acids, including nonproteogenic amino acids
like 3-methylbutyric acid, α,β-dehydrovaline, α,β-dehydroleucine and (S)-βtyrosine. Myxovalargins are active against gram-positive bacteria like Micrococcus
luteus and Corynebacterium mediolanum.
12 Antimicrobials from Microbes