Bacillus and Paenibacillus secreted polyketides and peptides involved in controlling human and plant pathogens.

Overuse of broad-spectrum antibiotics to control human and plant pathogens greatly accelerated the development of antibiotic resistance among bacteria and fungi. Therefore, usage of new approaches is necessary to control outbreaks of phytopathogenic diseases as well as multidrug-resistant human pathogens. Many of the polyketides (PKs) and lipopetides (LPs) produced by Bacillus and Paenibacillus species have been described as antimicrobial agents that can be potentially applied as sustainable bio-organic products in medicine against human pathogens and in agriculture for controlling plant pathogens. The present review provides a general information about the classification and biochemical structure of known Bacillus- and Paenibacillus-secreted PKs, as well as ribosomally and nonribosomally synthesized peptides, their functional features, gene clusters involved in their production, and the mode of action of these metabolites.

Development of a novel biological control agent targeting the phytopathogen Erwinia amylovora.

Antibiotics are used extensively to control animal, plant, and human pathogens. They are sprayed on apple and pear orchards to control the bacterium Erwinia amylovora, the causative agent of fire blight. This phytopathogen is developing antibiotic resistance and alternatives either have less efficacy, are phytotoxic, or more management intensive. The objective of our study was to develop an effective biological control agent colonizing the host plant and competing with Erwinia amylovora. It must not be phytotoxic, have a wide spectrum of activity, and be unlikely to induce resistance in the pathogen. To this end, several bacterial isolates from various environmental samples were screened to identify suitable candidates that are antagonistic to E. amylovora. We sampled bacteria from the flowers, leaves, and soil from apple and pear orchards from the springtime bloom period until the summer. The most effective bacteria, including isolates of Pseudomonas poae, Paenibacillus polymyxa, Bacillus amyloliquefaciens and Pantoea agglomerans, were tested in vitro and in vivo and formulated into products containing both the live strains and their metabolites that were stable for at least 9 months. Trees treated with the product based on P. agglomerans NY60 had significantly less fire blight than the untreated control and were statistically not different from streptomycin-treated control trees. With P. agglomerans NY60, fire blight never extended beyond the central vein of the inoculated leaf. The fire blight median disease severity score, 10 days after inoculation, was up to 70% less severe on trees treated with P. agglomerans NY60 as compared to untreated controls.