306
Class II bacteriocins are small-molecular-weight peptides which do not contain
modified residues or linkages other than disulfide bridges. Coagulin (4612 Da), a
pediocin-like protease-sensitive antibacterial peptide produced by B. coagulans,
belongs to this group. Coagulin shows antimicrobial activity against bacteria such
as Enterococcus, Leuconostoc, Listeria and Pediococcus. Coagulin is active at temperatures up to 60 °C and within 4–8 pH range.
Antimicrobial proteins or peptides that are not well characterized but are similar
to bacteriocins in activity are called bacteriocin-like inhibitory substances. Cerein
7A & 7B, MXRI & 8A are peptide antibiotics from B. cereus. They have a broad
spectrum of antibacterial activity against gram-positive pathogens and are used as
natural food biopreservatives. Tochicin (10.5 kDa) and a family of Thuricins are
bacteriocin-like inhibitory substances identified from B. thuringiensis, a soil bacillus phylogenetically similar to B. cereus. Thuricin S is a well-characterized thuricin
with a molecular weight less than 10 KDa and activity against Listeria monocytogenes, Salmonella enterica and Pseudomonas aeruginosa. Thuricin H and Thuricin
17 are other members of the thuricin group with a broad spectrum of activity. Other
bacteriocins produced by genus Bacillus include Lichenin produced by B. licheniformis 26–103 RA strain, Megacin produced by B. megaterium and polyfermenticin
SCD produced by B. polyfermenticus. Bacteriocins are used as preservatives in food
systems, agents of biocontrol of phytopathogens and precursors of antibiotics.
Nonribosomally Biosynthesized Peptides Nonribosomal peptides include a group
of peptide antibiotics synthesized by nonribosomal peptide synthetases independent
of mRNA. The genus Bacillus produces several peptides using the nonribosomal
mechanism, including iturins (cyclopeptides), fengycins and surfactins (macrolactones). Iturins (Fig. 12.5a) consist of a group of lipopeptides isolated from the culture media of various strains of B. subtilis and B. amyloliquefacians. They are
amphiphilic in nature and contain a characteristic ring of seven amino acid residues
including an invariable D-Tyr-2, with the constant chiral sequence LDDLLDL
closed by a C14–C17 aliphatic β-amino acid. They exhibit antimicrobial activities
against a wide variety of pathogenic yeasts and fungi but antibacterial activities are
limited to few species like Micrococcus luteus. The antifungal properties of iturins
are due to its interaction with the cell membranes of target cells and the formation
of ion-conducting pores resulting in increased permeability of ions. The iturin group
of antimicrobials includes A, C, D and E isoforms, Bacillomycin D, F and L and
Mycosubtilin. Iturin A is antagonistic to Fusarium oxysporum, the phytopathogen
causing potato disease. Iturins that inhibit fungal plant pathogens are also produced
by B. amyloliquefaciens strains B94 and FZB42. Bacillomycin D produced by B.
amyloliquefaciens strain FZB42 was shown to suppress the Fusarium oxysporum.
The iturin A operon is 38–40 kb in size and consists of four reading frames ItuA,
ItuB, ItuC and ItuD.
The fengycin (Fig. 12.5b) class of lipopeptides, including plipastatin, is produced by several species of Bacillus like B. subtilis, B. cereus, B. amyloliquefaciens
and B. globijii. These bioactive molecules are lipodecapeptides comprised of a
D. Francis
Class II bacteriocins are small-molecular-weight peptides which do not contain
modified residues or linkages other than disulfide bridges. Coagulin (4612 Da), a
pediocin-like protease-sensitive antibacterial peptide produced by B. coagulans,
belongs to this group. Coagulin shows antimicrobial activity against bacteria such
as Enterococcus, Leuconostoc, Listeria and Pediococcus. Coagulin is active at temperatures up to 60 °C and within 4–8 pH range.
Antimicrobial proteins or peptides that are not well characterized but are similar
to bacteriocins in activity are called bacteriocin-like inhibitory substances. Cerein
7A & 7B, MXRI & 8A are peptide antibiotics from B. cereus. They have a broad
spectrum of antibacterial activity against gram-positive pathogens and are used as
natural food biopreservatives. Tochicin (10.5 kDa) and a family of Thuricins are
bacteriocin-like inhibitory substances identified from B. thuringiensis, a soil bacillus phylogenetically similar to B. cereus. Thuricin S is a well-characterized thuricin
with a molecular weight less than 10 KDa and activity against Listeria monocytogenes, Salmonella enterica and Pseudomonas aeruginosa. Thuricin H and Thuricin
17 are other members of the thuricin group with a broad spectrum of activity. Other
bacteriocins produced by genus Bacillus include Lichenin produced by B. licheniformis 26–103 RA strain, Megacin produced by B. megaterium and polyfermenticin
SCD produced by B. polyfermenticus. Bacteriocins are used as preservatives in food
systems, agents of biocontrol of phytopathogens and precursors of antibiotics.
Nonribosomally Biosynthesized Peptides Nonribosomal peptides include a group
of peptide antibiotics synthesized by nonribosomal peptide synthetases independent
of mRNA. The genus Bacillus produces several peptides using the nonribosomal
mechanism, including iturins (cyclopeptides), fengycins and surfactins (macrolactones). Iturins (Fig. 12.5a) consist of a group of lipopeptides isolated from the culture media of various strains of B. subtilis and B. amyloliquefacians. They are
amphiphilic in nature and contain a characteristic ring of seven amino acid residues
including an invariable D-Tyr-2, with the constant chiral sequence LDDLLDL
closed by a C14–C17 aliphatic β-amino acid. They exhibit antimicrobial activities
against a wide variety of pathogenic yeasts and fungi but antibacterial activities are
limited to few species like Micrococcus luteus. The antifungal properties of iturins
are due to its interaction with the cell membranes of target cells and the formation
of ion-conducting pores resulting in increased permeability of ions. The iturin group
of antimicrobials includes A, C, D and E isoforms, Bacillomycin D, F and L and
Mycosubtilin. Iturin A is antagonistic to Fusarium oxysporum, the phytopathogen
causing potato disease. Iturins that inhibit fungal plant pathogens are also produced
by B. amyloliquefaciens strains B94 and FZB42. Bacillomycin D produced by B.
amyloliquefaciens strain FZB42 was shown to suppress the Fusarium oxysporum.
The iturin A operon is 38–40 kb in size and consists of four reading frames ItuA,
ItuB, ItuC and ItuD.
The fengycin (Fig. 12.5b) class of lipopeptides, including plipastatin, is produced by several species of Bacillus like B. subtilis, B. cereus, B. amyloliquefaciens
and B. globijii. These bioactive molecules are lipodecapeptides comprised of a
D. Francis