302
a synthetic derivative of rifamycin that has largely replaced isoniazid in treatment
of tuberculosis especially when isoniazid resistance is indicated. Rifamycin exerts
its effect by binding to prokaryotic RNA polymerases and prevents the synthesis of
mRNA in target organisms. The broad-spectrum antibiotic phosphomycin was
originally isolated from S. fradiae although now it is produced by chemical synthesis. The antibiotic originally known as phosphonomycin prevents cell wall formation in target organisms by binding and inactivating the enzyme
UDP-N-acetylglucosamine- 3-enolpyruvyltransferase, also known as MurA which
is essential for the biosynthesis of peptidoglycan. Cycloserine, an unusual amino
acid derivative effective against Mycobacterium tuberculosis sold under the trade
name Seromycin, was originally isolated from S. orchidaccus. Cycloserine acts by
inhibiting cell wall biosynthesis and is known to have neurological side effects as
the drug penetrates the central nervous system. Caboxamycin (Fig. 12.3e), a benzoxazole antibiotic, was isolated from a marine strain Streptomyces sp. NTK 937.
Unlike other benzoxazoles isolated from Streptomyces, Caboxamycin exhibited a
broad spectrum of antimicrobial activity. It was effective against gram-positive
bacteria like Bacillus subtilis, Staphylococcus lentus, S. epidermidis and the yeast
Candida glabrata. It shows weak inhibition of biofilms formed by Staphylococcus
xylosus and inhibits phytopathogenic bacteria Xanthomonas campestris and
Ralstonia solanacearum (Hohmann et al. 2009). Meonomycins, the only group of
antibiotics that directly inhibits bacterial peptidoglycan glycosyltransferases, are
produced by at least four Streptomyces species like S. ghanaensis, S. bambergiensis, S. ederensis and S. geysiriensis. They show antimicrobial activity against
gram-positive bacteria (Ostash and Walker 2010). Essramycin (Fig. 12.3f), a triazolpyramidine antibiotic with a broad spectrum of activity, was isolated from
Streptomyces sp., isolate Merv8102. It shows antimicrobial action against both
gram-positive and gram-negative bacteria with significant activity against
Pseudomonas aeruginosa (El-Gendy et al. 2008).
12.4.2 Genus Bacillus
The genus Bacillus comprises of gram-positive rod-shaped bacteria belonging to
the family Bacillaceae of the phylum Firmicutes. The bacteria are mostly obligate
aerobes, while some are facultative anaerobes. They are widely distributed in the
environment with both free-living and parasitic species. Many of the members are
mesophiles, but some are extremophiles. They are characterized by the ability to
form endospores under stressful environmental conditions. They are mobile by virtue of the presence of peritrichous flagella. The bacteria are chemoorganotrophs that
rely on organic substances for energy.
12.4.2.1 Antimicrobials from Bacillus
Bacteria of the genus Bacillus are well-known producers of secondary metabolites
like antibiotics and siderophores (Table 12.1). Most of the antibiotics produced by
Bacillus spp. are polypeptides of low molecular weight that are synthesized either
D. Francis
a synthetic derivative of rifamycin that has largely replaced isoniazid in treatment
of tuberculosis especially when isoniazid resistance is indicated. Rifamycin exerts
its effect by binding to prokaryotic RNA polymerases and prevents the synthesis of
mRNA in target organisms. The broad-spectrum antibiotic phosphomycin was
originally isolated from S. fradiae although now it is produced by chemical synthesis. The antibiotic originally known as phosphonomycin prevents cell wall formation in target organisms by binding and inactivating the enzyme
UDP-N-acetylglucosamine- 3-enolpyruvyltransferase, also known as MurA which
is essential for the biosynthesis of peptidoglycan. Cycloserine, an unusual amino
acid derivative effective against Mycobacterium tuberculosis sold under the trade
name Seromycin, was originally isolated from S. orchidaccus. Cycloserine acts by
inhibiting cell wall biosynthesis and is known to have neurological side effects as
the drug penetrates the central nervous system. Caboxamycin (Fig. 12.3e), a benzoxazole antibiotic, was isolated from a marine strain Streptomyces sp. NTK 937.
Unlike other benzoxazoles isolated from Streptomyces, Caboxamycin exhibited a
broad spectrum of antimicrobial activity. It was effective against gram-positive
bacteria like Bacillus subtilis, Staphylococcus lentus, S. epidermidis and the yeast
Candida glabrata. It shows weak inhibition of biofilms formed by Staphylococcus
xylosus and inhibits phytopathogenic bacteria Xanthomonas campestris and
Ralstonia solanacearum (Hohmann et al. 2009). Meonomycins, the only group of
antibiotics that directly inhibits bacterial peptidoglycan glycosyltransferases, are
produced by at least four Streptomyces species like S. ghanaensis, S. bambergiensis, S. ederensis and S. geysiriensis. They show antimicrobial activity against
gram-positive bacteria (Ostash and Walker 2010). Essramycin (Fig. 12.3f), a triazolpyramidine antibiotic with a broad spectrum of activity, was isolated from
Streptomyces sp., isolate Merv8102. It shows antimicrobial action against both
gram-positive and gram-negative bacteria with significant activity against
Pseudomonas aeruginosa (El-Gendy et al. 2008).
12.4.2 Genus Bacillus
The genus Bacillus comprises of gram-positive rod-shaped bacteria belonging to
the family Bacillaceae of the phylum Firmicutes. The bacteria are mostly obligate
aerobes, while some are facultative anaerobes. They are widely distributed in the
environment with both free-living and parasitic species. Many of the members are
mesophiles, but some are extremophiles. They are characterized by the ability to
form endospores under stressful environmental conditions. They are mobile by virtue of the presence of peritrichous flagella. The bacteria are chemoorganotrophs that
rely on organic substances for energy.
12.4.2.1 Antimicrobials from Bacillus
Bacteria of the genus Bacillus are well-known producers of secondary metabolites
like antibiotics and siderophores (Table 12.1). Most of the antibiotics produced by
Bacillus spp. are polypeptides of low molecular weight that are synthesized either
D. Francis