Search Results (6)

The GntR is a transcriptional regulator generally known as a gluconate-operon repressor to specifically regulate the transportation and phosphorylation of gluconate. In the present study we report the cloning of the GntR-encoding gene of the industrial 2-ketogluconate (2KGA)-producer Pseudomonas plecoglossicida JUIM01, which is involved in the regulation of gluconate metabolism, along with the identification of some of its target genes and its operator sequence. GntR is a 36.36-kDa cytoplasmic and hydrophobic DNA-binding transcriptional regulator belonging to the LacI family. The knockout of gntR resulted in the significant upregulation of the transcription of the gluconate kinase gene gntK and, to a lesser extent, the permease gene gntP, as well as downregulation of genes involved in glucose uptake (oprB-1, gltB, gltF, gltG, and gltK) and those involved in 2-ketogluconate (2KGA) transport (kguT) and catabolism (kguE, kguK, and kguD). These results indicated that GntR positively regulated glucose and 2KGA transport and catabolism, while negatively affecting GntP-mediated gluconate uptake and gluconate phosphorylation by GntK. Electrophoretic mobility shift assay (EMSA) and DNase I footprinting analyses confirmed that GntR interacted with operator sequences in the divergent promoter regions of gntK and gntP, as well as in the gntR promoter region. A putative operator sequence (consensus 5′-AG-N₂-AGCGCT-N-TCT-3′) was identified. These data suggest that GntR positively regulates genes involved in glucose uptake/transport and 2KGA transport/catabolism, while repressing its own expression as well as that of genes involved in gluconate transport/catabolism. These findings not only elucidate the regulation of GntR and its target genes in P. plecoglossicida, but also provide valuable insights for optimizing industrial 2KGA production. Full article

Pseudomonas plecoglossicida JUIM01 is an industrial 2-keto-d-gluconate (2KGA)-producing strain. However, its regulation mechanism of 2KGA metabolism remains to be clarified. Among other reported Pseudomonas species, the 2-ketogluconate utilization operon (kgu operon) plays key roles in 2KGA catabolism. In this study, the structural genes of the kgu operon and its promoter in P. plecoglossicida JUIM01 were identified using reverse transcription PCR and lacZ reporter gene fusion. The results showed the kgu operon in P. plecoglossicida was composed of four structural genes: kguE, kguK, kguT, and kguD. The ptxS gene located upstream of kguE was excluded from the kgu operon. Then, the knockout and corresponding complementation strains of kguE, kguK, kguT, and kguD were constructed, respectively, to prove the kgu operon was involved in 2KGA catabolism of P. plecoglossicida. The knockout stains, especially JUIM01ΔkguE, showed potential as industrial production strains for 2KGA. Moreover, the transcriptional regulation mechanism of PtxS on the kgu operon was elucidated using multiple methods. In P. plecoglossicida, the LacI-family transcription regulator PtxS could recognize a 14 bp palindrome (5′-TGAAACCGGTTTCA-3′) within the promoter region of the kgu operon and specifically bind to a 26 bp region where the palindrome was located. As the binding sites overlapped with the transcription start site of the kgu operon, the binding of PtxS possibly hindered the binding of RNA polymerase, thus repressing the transcription of the kgu operon and further regulating 2KGA catabolism. 2KGA bound to PtxS as an effector to dissociate it from the kgu operon promoter region, so as to relieve the transcription repression. The results will provide strategies for improving the product accumulation in 2KGA industrial production and theoretical bases for the construction of a Pseudomonas chassis. Full article

High-density planting can increase crop productivity per unit area of cultivated land. However, the application of this technology is limited by the inhibition of plant growth in the presence of neighbors, which is not only due to their competition for resources but is also caused by growth regulators. Specifically, the abscisic acid (ABA) accumulated in plants under increased density of planting has been shown to inhibit their growth. The goal of the present study was to test the hypothesis that bacteria capable of degrading ABA can reduce the growth inhibitory effect of competition among plants by reducing concentration of this hormone in plants and their environment. Lettuce plants were grown both individually and three per pot; the rhizosphere was inoculated with a strain of Pseudomonas plecoglossicida 2.4-D capable of degrading ABA. Plant growth was recorded in parallel with immunoassaying ABA concentration in the pots and plants. The presence of neighbors indeed inhibited the growth of non-inoculated lettuce plants. Bacterial inoculation positively affected the growth of grouped plants, reducing the negative effects of competition. The bacteria-induced increase in the mass of competing plants was greater than that in the single ones. ABA concentration was increased by the presence of neighbors both in soil and plant shoots associated with the inhibition of plant growth, but accumulation of this hormone as well as inhibition of the growth of grouped plants was prevented by bacteria. The results confirm the role of ABA in the response of plants to the presence of competitors as well as the possibility of reducing the negative effect of competition on plant productivity with the help of bacteria capable of degrading this hormone. Full article

The search for ways to increase plant productivity in drought conditions is of fundamental importance, since soil moisture deficiency is widespread and leads to critical crop losses. The aim of this study was to identify the effects of plant growth-promoting bacteria and humic substances on the growth, chlorophyll, flavonoids, nitrogen balance index, and concentration of cytokinins and abscisic acids in wheat plants grown in the laboratory under conditions of water deficit. An increase in the accumulation of plant mass was shown during the treatment of wheat plants with Pseudomonas plecoglossicida 2,4-D and humic substances in these conditions. It has been shown that stimulating plant growth is associated with increased root growth, which leads to an increase in the nitrogen balance index, chlorophyll, and flavonoid concentrations in treated plants. The detected increase in the concentration of chlorophyll in plants treated with P. plecoglossicida 2,4-D correlated with a decrease in the concentration of abscisic acid in plant shoots and, in plants treated with humates, with an increase in the concentration of cytokinins in shoots. The higher efficiency of treating plants with a combination of bacteria and humic substances than with any of them individually may be associated with the additive effect of these treatments on the hormonal balance. Full article

Both rhizosphere bacteria and humic substances (HSs) can promote plant growth when applied individually and even greater effects of their combination have been demonstrated. We aimed to elucidate the relative importance of the stimulating effects of HSs on bacterial growth and the effects of the combination of bacteria and HSs on plants themselves. The effects of humic (HA) and fulvic acids (FA) (components of humic substances) on the growth of Pseudomonas plecoglossicida 2,4-D in vitro were studied. We also studied the effects of this bacterial strain and HSs applied individually or in combination on the growth of wheat plants. Although the 2,4-D strain showed low ability to use HSs as the sole source of nutrition, the bacterial growth rate was increased by FA and HA, when other nutrients were available. HSs increased root colonization with bacteria, the effect being greater in the case of HA. The effects on roots and shoots increased when bacteria were associated with HSs. FA+ 2,4-D was more effective in stimulating shoot growth, while HA + 2,4-D was in the case of root growth. The latter effect is likely to be beneficial under edaphic stresses. Full article

The phytoremediation of soil contaminated with petroleum oil products relies on co-operation between plants and rhizosphere bacteria, including the plant growth-promoting effect of the bacteria. We studied the capacity of strains of Pseudomonas, selected as oil degraders, to produce plant hormones and promote plant growth. Strains with intermediate auxin production were the most effective in stimulating the seedling growth of seven plant species under normal conditions. Bacterial seed treatment resulted in about a 1.6-fold increase in the weight of barley seedlings, with the increment being much lower in other plant species. The strains P. plecoglossicida 2.4-D and P. hunanensis IB C7, characterized by highly efficient oil degradation (about 70%) and stable intermediate in vitro auxin production in the presence of oil, were selected for further study with barley. These strains increased the seed germination percentage approximately two-fold under 5% oil concentration in the soil, while a positive effect on further seedling growth was significant when the oil concentration was raised to 8%. This resulted in a 1.3–1.7-fold increase in the seedling mass after 7 days of growth, depending on the bacterial strain. Thus, strains of oil-degrading bacteria selected for their intermediate and stable production of auxin were found to be effective ameliorators of plant growth inhibition resulting from petroleum stress. Full article