Biosynthesis of the Nematode Attractant 2-Heptanone and Its Co-evolution Between the Pathogenic Bacterium Bacillus nematocida and Non-pathogenic Bacterium Bacillus subtilis

Abstract

Methylketones are broadly distributed in nature and perform a variety of functions. Most microorganisms are thought to produce methylketone by abortive β-oxidation of fatty acid catalytic metabolism. However, two methylketone synthetase genes in wild tomatoes are reported to synthesize methylketone using intermediates of the fatty acids biosynthetic pathway. In our previous study on Trojan horse-like interactions between the bacterium Bacillus nematocida B16 and its host worm, the chemical 2-heptanone was found to be an important attractant for the hosts. So here we used this model to investigate the genes involved in synthesizing 2-heptanone in microorganisms. We identified a novel methylketone synthase gene yneP in B. nematocida B16 and found enhancement of de novo fatty acid synthesis during 2-heptanone production. Interestingly, a homolog of yneP’ existed in the non-pathogenic species Bacillus subtilis 168, a close relative of B. nematocida B16 that was unable to lure worms, but GC-MS assay showed no 2-heptanone production. However, overexpression of yneP’ from B. subtilis in both heterologous and homologous systems demonstrated that it was not a pseudogene. The transcriptional analysis between those two genes had few differences under the same conditions. It was further shown that the failure to detect 2-heptanone in B. subtilis 168 was at least partly due to its conversion into 6-methyl-2-heptanone by methylation. Our study revealed methylketone biosynthesis of Bacillus species, and provided a co-evolution paradigm of second metabolites during the interactions between pathogenic/non-pathogenic bacteria and host.

Fungal–bacterial interaction selects for quorum sensing mutants with increased production of natural antifungal compounds

“…The release of the fap regulon in association to the chemical condition derived from the global change produced by the mutation may be favoring branched-chain fatty acid biosynthesis pathways and/or decarboxilation of intermediates ketoacids that promote the synthesis of 2-ketones. Accordingly, a recent report showed an enhancement of de novo fatty acid synthesis in Bacillus nematocida B16 during 2-heptanone production 30 .…”

Biosynthesis of 2-Heptanone, a Volatile Organic Compound with a Protective Role against Honey Bee Pathogens, by Hive Associated Bacteria

“…The analysis was performed following the method of Reference [16], with modifications. Each sample was composed of 10 mL of CFS in a 20-mL glass vial, with 2 g of NaCl added and closed with an aluminum-silicone/PTFE septum.…”

“…Methylketones can be synthetized by bacteria, fungi, plants, insects and mammals and have been found in numerous natural environments, having various biological roles [16]. In plants, for example, these compounds are highly effective for protection against pests [17].…”

“…2-heptanone produced by lactic acid bacteria (i.e., Lactobacillus casei and Lactobacillus paracasei) is known to contribute to aroma development in many dairy products [18]. Furthermore, this volatile compound was found to be synthetized by species of Bacillus during host-pathogen interactions [16] and by Bacillus amyloliquefaciens with antifungal properties against Fusarium oxysporum [19]. Even though this volatile compound has various bioactive roles of potential practical interest, its biosynthetic pathway has been scarcely investigated.…”

“…In 2005, two methylketone synthetases from wild tomatoes (Lycopersicon hirsutum) were reported to use intermediates of the fatty acids biosynthetic pathway to synthesize methylketones [17]. In bacteria, a methylketone synthase involved in the production of 2-heptanone was identified in Bacillus nematocida [16].…”