Identification of an antibacterial compound, benzylideneacetone, fromXenorhabdus nematophilaagainst major plant-pathogenic bacteria

Abstract

An entomopathogenic bacterium, Xenorhabdus nematophila, is known to have potent antibiotic activities to maintain monoxenic condition in its insect host for effective pathogenesis and ultimately for optimal development of its nematode symbiont, Steinernema carpocapsae. In this study we assess its antibacterial activity against plant-pathogenic bacteria and identify its unknown antibiotics. The bacterial culture broth had significant antibacterial activity that increased with development of the bacteria and reached its maximum at the stationary growth phase. The antibiotic activities were significant against five plant-pathogenic bacterial strains: Agrobacterium vitis, Pectobacterium carotovorum subsp. atrosepticum, P. carotovorum subsp. carotovorum, Pseudomonas syringae pv. tabaci, and Ralstonia solanacearum. The antibacterial factors were extracted with butanol and fractionated using column chromatography with the eluents of different hydrophobic intensities. Two active antibacterial subfractions were purified, and the higher active fraction was further fractionated and identified as a single compound of benzylideneacetone (trans-4-phenyl-3-buten-2-one). With heat stability, the synthetic compound showed equivalent antibiotic activity and spectrum to the purified compound. This study reports a new antibiotic compound synthesized by X. nematophila, which is a monoterpenoid compound and active against some Gram-negative bacteria.

Purification and identification of two antifungal cyclic dipeptides from Bacillus cereus subsp. thuringiensis associated with a rhabditid entomopathogenic nematode especially against Fusarium oxysporum

“…is known, and several compounds with antibiotic activity have been isolated and identified. These include indoles 15 , stilbenes 16 , xenorhabdins 17 , xenocoumacin 18 , nematophin 19 , benzylineacetone 20 , xenortides and xenematide 21 , and cyclolipopeptide (PAX) 22 . These metabolites not only have diverse chemical structures, but also have a wide range of bioactivities of medicinal and agricultural interests such as antibiotic, antimycotic, insecticidal, nematicidal, antiulcer, antineoplastic and antiviral.…”

Microbial Population Dynamics in the Hemolymph of Manduca sexta Infected with Xenorhabdus nematophila and the Entomopathogenic Nematode Steinernema carpocapsae

“…X. nematophila produces several compounds that suppress aspects of the insect innate immune response. These include tyrosine-derived cell surface molecules (rhabduscin), which directly inhibit PO activity (12), and the monoterpenoid compound benzylideneacetone (13), which inhibits PLA2 activity, reduces AMP synthesis, and blocks PO activ-ity (9,14). Interestingly, benzylideneacetone itself has antimicrobial activity (13).…”

Role of Secondary Metabolites in Establishment of the Mutualistic Partnership between Xenorhabdus nematophila and the Entomopathogenic Nematode Steinernema carpocapsae

“…Thus, in the presence of X. nematophila, this sensitive competitor was eliminated in the absence of ngrA-derived antimicrobial compounds. X. nematophila produces nematophin and other indole-derived compounds that possess antibiotic activity (15,16), as well as benzylideneacetone, which possesses both antimicrobial and immunosuppressive activities (13). X. nematophila may also produce other unidentified compounds that are active against transient species.…”

“…The compounds synthesized by three of the NRPS clusters and the two stand-alone NRPSs have been characterized. X. nematophila also produces antimicrobial compounds not known to be synthesized by NRPS genes, such as nematophin and other indole derivatives, and benzylideneacetone (13)(14)(15)(16).…”