313
they are isolated from. Syringopeptins are produced by different strains of P. syringae. Syringopeptin shows antimicrobial activity against some gram-positive bacteria and fungi. It is highly active against Botrytis cinerea and Bacillus megaterium.
The antimicrobial properties of syringomycin and syringopeptides can be attributed
to their ability to produce pores in the plasma membranes of target cells. Corpeptins
are another group of lipodepsipeptides produced in the cultures of Pseudomonas
corrugata, the causal agent of tomato pith necrosis, with surfactant, antimicrobial
and phytotoxic activities. Fuscopeptins A and B are produced by the plant pathogen
P. fuscovaginae, the causative agent of ‘sheath brown rot’ of cultivated and wild
gramineae. They form pores in the membrane to bring about their antimicrobial
activity (Coraiola et al. 2008).
Tolaasin is a 1985-Da lipodepsipeptide secreted in the culture medium of
P. tolaasi, a saprophytic bacterium infecting edible mushrooms. Tolaasins are
reported to have detergent-like action at high concentrations with the ability to dissolve eukaryotic membranes. Tolaasins are active against many basidiomycetes and
gram-positive bacteria but inactive against gram-negative bacteria (Bassarello et al.
2004). Viscosin is a lipopeptide biosurfactant produced by P. flourescens that is
active against the plant pathogen pythium. Viscosinamide is a cyclic depsipeptide
isolated from P. flourescens with antibiotic and biosurfactant properties. It is active
against the plant pathogens Pythium ultimum and Rhizoctnoia solani both in vitro
and in planta (Haas and Défago 2005).
Other Antimicrobials Tabtoxin (Fig. 12.7d) is a dipeptide biotoxin belonging to the
monocyclic β-lactam class of antibiotics produced by Pseudomonas syringae pv.
tabaci, P. syringae pv. coronafaciens and P. syringae pv. garca. It consists of a
Tabtoxin β-lactam (TβL) linked to threonine by a peptide bond. Tabtoxin is also
known as the wildfire toxin due to its role in wildfire disease in tobacco. It is the
precursor to the antibiotic tabtoxinine β-lactam, which unlike other β-lactam antibiotics exerts its effect by inhibiting glutamine synthetase. Tabtoxin shows strong
antimicrobial activity. Phaseolotoxins are biotoxins produced by P. syringae pv.
phaseolicola and P. syringae pv. actinidiae that cause halo blight in legumes and
bacterial canker on Kiwi fruit respectively. The structure consists of a tripeptide
made of ornithine, alanine and homoarginine linked to a sulfodiaminophosphinyl
moiety. Phaseolotoxins exert their antimicrobial activity by inhibiting ornithine carbonyl transferase responsible for the conversion of ornithine and carbamoyl phosphate to citrulline in the urea cycle.
Pyrrolnitrin (Fig. 12.7e) is an antifungal antibiotic produced by certain species of
pseudomonas like Pseudomonas pyrrocinia, P. chlororaphis and P. cepacia.
Pyrrolnitrin is active against superficial and systemic mycoses involving Candida
albicans, Cryptococcus neoformans, Blastomyces dermatitidis, Sporotrichum
schenckii, and Histoplasma capsulatum. It antagonizes the growth of plant fungi
like Botrytis cinerea, Rhizoctonia solani and Sclerotinia sclerotiorum. Pyrolnitrin
prevents fungal growth by inhibiting the respiratory electron transport system.
12 Antimicrobials from Microbes
they are isolated from. Syringopeptins are produced by different strains of P. syringae. Syringopeptin shows antimicrobial activity against some gram-positive bacteria and fungi. It is highly active against Botrytis cinerea and Bacillus megaterium.
The antimicrobial properties of syringomycin and syringopeptides can be attributed
to their ability to produce pores in the plasma membranes of target cells. Corpeptins
are another group of lipodepsipeptides produced in the cultures of Pseudomonas
corrugata, the causal agent of tomato pith necrosis, with surfactant, antimicrobial
and phytotoxic activities. Fuscopeptins A and B are produced by the plant pathogen
P. fuscovaginae, the causative agent of ‘sheath brown rot’ of cultivated and wild
gramineae. They form pores in the membrane to bring about their antimicrobial
activity (Coraiola et al. 2008).
Tolaasin is a 1985-Da lipodepsipeptide secreted in the culture medium of
P. tolaasi, a saprophytic bacterium infecting edible mushrooms. Tolaasins are
reported to have detergent-like action at high concentrations with the ability to dissolve eukaryotic membranes. Tolaasins are active against many basidiomycetes and
gram-positive bacteria but inactive against gram-negative bacteria (Bassarello et al.
2004). Viscosin is a lipopeptide biosurfactant produced by P. flourescens that is
active against the plant pathogen pythium. Viscosinamide is a cyclic depsipeptide
isolated from P. flourescens with antibiotic and biosurfactant properties. It is active
against the plant pathogens Pythium ultimum and Rhizoctnoia solani both in vitro
and in planta (Haas and Défago 2005).
Other Antimicrobials Tabtoxin (Fig. 12.7d) is a dipeptide biotoxin belonging to the
monocyclic β-lactam class of antibiotics produced by Pseudomonas syringae pv.
tabaci, P. syringae pv. coronafaciens and P. syringae pv. garca. It consists of a
Tabtoxin β-lactam (TβL) linked to threonine by a peptide bond. Tabtoxin is also
known as the wildfire toxin due to its role in wildfire disease in tobacco. It is the
precursor to the antibiotic tabtoxinine β-lactam, which unlike other β-lactam antibiotics exerts its effect by inhibiting glutamine synthetase. Tabtoxin shows strong
antimicrobial activity. Phaseolotoxins are biotoxins produced by P. syringae pv.
phaseolicola and P. syringae pv. actinidiae that cause halo blight in legumes and
bacterial canker on Kiwi fruit respectively. The structure consists of a tripeptide
made of ornithine, alanine and homoarginine linked to a sulfodiaminophosphinyl
moiety. Phaseolotoxins exert their antimicrobial activity by inhibiting ornithine carbonyl transferase responsible for the conversion of ornithine and carbamoyl phosphate to citrulline in the urea cycle.
Pyrrolnitrin (Fig. 12.7e) is an antifungal antibiotic produced by certain species of
pseudomonas like Pseudomonas pyrrocinia, P. chlororaphis and P. cepacia.
Pyrrolnitrin is active against superficial and systemic mycoses involving Candida
albicans, Cryptococcus neoformans, Blastomyces dermatitidis, Sporotrichum
schenckii, and Histoplasma capsulatum. It antagonizes the growth of plant fungi
like Botrytis cinerea, Rhizoctonia solani and Sclerotinia sclerotiorum. Pyrolnitrin
prevents fungal growth by inhibiting the respiratory electron transport system.
12 Antimicrobials from Microbes