A limited concentration range of diaphorin, a polyketide produced by a bacterial symbiont of the Asian citrus psyllid, promotes the in vitro gene expression with bacterial ribosomes.

Diaphorin is a polyketide produced by "Candidatus Profftella armatura" (Gammaproteobacteria: Burkholderiales), an obligate symbiont of a devastating agricultural pest, the Asian citrus psyllid Diaphorina citri (Hemiptera: Psyllidae). Physiological concentrations of diaphorin, which D. citri contains at levels as high as 2-20 mM, are inhibitory to various eukaryotes and Bacillus subtilis (Firmicutes: Bacilli) but promote the growth and metabolic activity of Escherichia coli (Gammaproteobacteria: Enterobacterales). Our previous study demonstrated that 5-mM diaphorin, which exhibits significant inhibitory and promoting effects on cultured B. subtilis and E. coli, respectively, inhibits in vitro gene expression utilizing purified B. subtilis and E. coli ribosomes. This suggested that the adverse effects of diaphorin on B. subtilis are partly due to its influence on gene expression. However, the result appeared inconsistent with the positive impact on E. coli. Moreover, the diaphorin concentration in bacterial cells, where genes are expressed in vivo, may be lower than in culture media. Therefore, the present study analyzed the effects of 50 and 500 µM of diaphorin on bacterial gene expression using the same analytical method. The result revealed that this concentration range of diaphorin, in contrast to 5-mM diaphorin, promotes the in vitro translation with the B. subtilis and E. coli ribosomes, suggesting that the positive effects of diaphorin on E. coli are due to its direct effects on translation. This study demonstrated for the first time that a pederin-type compound promotes gene expression, establishing a basis for utilizing its potential in pest management and industrial applications.IMPORTANCEThis study revealed that a limited concentration range of diaphorin, a secondary metabolite produced by a bacterial symbiont of an agricultural pest, promotes cell-free gene expression utilizing substrates and proteins purified from bacteria. The unique property of diaphorin, which is inhibitory to various eukaryotes and Bacillus subtilis but promotes the growth and metabolic activity of Escherichia coli, may affect the microbial flora of the pest insect, potentially influencing the transmission of devastating plant pathogens. Moreover, the activity may be exploited to improve the efficacy of industrial production by E. coli, which is often used to produce various important materials, including pharmaceuticals, enzymes, amino acids, and biofuels. This study elucidated a part of the mechanism by which the unique activity of diaphorin is expressed, constructing a foundation for applying the distinct property to pest management and industrial use.

Diaphorin, a polyketide produced by a bacterial endosymbiont of the Asian citrus psyllid, adversely affects the in vitro gene expression with ribosomes from Escherichia coli and Bacillus subtilis.

Diaphorin is a polyketide produced by "Candidatus Profftella armatura" (Gammaproteobacteria), an obligate mutualist of an important agricultural pest, the Asian citrus psyllid Diaphorina citri (Hemiptera). Our previous study demonstrated that diaphorin, at physiological concentrations in D. citri, inhibits the growth and cell division of Bacillus subtilis (Firmicutes) but promotes the growth and metabolic activity of Escherichia coli (Gammaproteobacteria). This unique property of diaphorin may aid microbial mutualism in D. citri, potentially affecting the transmission of "Candidatus Liberibacter spp." (Alphaproteobacteria), the pathogens of the most destructive citrus disease Huanglongbing. Moreover, this property may be exploited to promote microbes' efficiency in producing industrial materials. However, the mechanism underlying this activity is unknown. Diaphorin belongs to the family of pederin-type compounds, which inhibit protein synthesis in eukaryotes by binding to eukaryotic ribosomes. Therefore, as a first step to assess diaphorin's direct influence on bacterial gene expression, this study examined the effect of diaphorin on the in vitro translation using ribosomes of B. subtilis and E. coli, quantifying the production of the green fluorescent protein. The results showed that the gene expression involving B. subtilis and E. coli ribosomes along with five millimolar diaphorin was 29.6% and 13.1%, respectively, less active than the control. This suggests that the diaphorin's adverse effects on B. subtilis are attributed to, at least partly, its inhibitory effects on gene expression. Moreover, as ingredients of the translation system were common other than ribosomes, the greater inhibitory effects observed with the B. subtilis ribosome imply that the ribosome is among the potential targets of diaphorin. On the other hand, the results also imply that diaphorin's positive effects on E. coli are due to targets other than the core machinery of transcription and translation. This study demonstrated for the first time that a pederin congener affects bacterial gene expression.