Identification and functional characterization of a fructose-inducible phosphotransferase system in Sp7.

Plant growth-promoting rhizobacterium Sp7 utilizes fructose efficiently via a fructose phosphotransferase system (Fru-PTS). Its genome encodes two putative Fru-PTS, each consisting of FruB (EIIA), FruK (Pfk), and FruA (EIIBC) proteins. We compared the proteomes of Sp7 grown with malate or fructose as sole carbon source, and noticed upregulation of the constituent proteins of Fru-PTS1 only on fructose. Inactivation of gene of both the Fru-PTS showed that Fru-PTS1 is the main PTS involved in fructose utilization. Overexpression of in Sp7 enhanced its growth on fructose showing improved consumption of fructose. This suggested that fructose utilization in Sp7 is limited due to the limitation of EIIBC component. A FruR-type regulator, encoded divergently to the Fru-PTS1 operon, was required for chemotaxis toward fructose. Although not an absolute necessity for the growth of fructose, FruR was required for the optimal growth of fructose. The promoter was activated by fructose and repressed by malate, but FruR does not seem to regulate its expression. A 27-nucleotide stem-loop structure located between the -125 and -99 promoter proximal region of was involved in fructose inducibility and malate repression. Fructose also upregulated several proteins involved in the biogenesis of a Type 6 secretion system. Here, we have shown that Sp7 was able to inhibit the growth of and in the presence of fructose, and that an intact T6SS was required for contact-dependent growth inhibition of the two Gram-negative bacteria.IMPORTANCE, a plant growth-promoting rhizobacterium, has limited ability to utilize carbohydrates and sugars. Although it is known to utilize fructose via a fructose phosphotransferase system (fructose-PTS), the genes involved in fructose utilization and the role of fructose in its biology were not well characterized. This study has shown that out of the two units of fructose-PTS encoded in its genome, fructose-PTS1 plays the major role in fructose utilization. Overexpression of the membrane component (EIIBC) improved the growth of on fructose. The ability of fructose to induce proteins of the Type 6 Secretion System (T6SS) enables to cause contact-dependent inhibition of the growth of as well as . This is the first report on the fructose inducibility of T6SS in , which may provide a handle to control the growth of undesirable bacteria using T6SS of in a mixed culture.