Abstract
Rhodopseudomonas palustris strains PS3 and YSC3 are purple non-sulfur phototrophic bacteria isolated from Taiwanese paddy soils. PS3 has beneficial effects on plant growth and enhances the uptake efficiency of applied fertilizer nutrients. In contrast, YSC3 has no significant effect on plant growth. The genomic structures of PS3 and YSC3 are similar; each contains one circular chromosome that is 5,269,926 or 5,371,816 bp in size, with 4,799 or 4,907 protein-coding genes, respectively. In this study, a large class of genes involved in chemotaxis and motility was identified in both strains, and genes associated with plant growth promotion, such as nitrogen fixation-, IAA synthesis- and ACC deamination-associated genes, were also identified. We noticed that the growth rate, the amount of biofilm formation, and the relative expression levels of several chemotaxis-associated genes were significantly higher for PS3 than for YSC3 upon treatment with root exudates. These results indicate that PS3 responds better to the presence of plant hosts, which may contribute to the successful interactions of PS3 with plant hosts. Moreover, these findings indicate that the existence of gene clusters associated with plant growth promotion is required but not sufficient for a bacterium to exhibit phenotypes associated with plant growth promotion.
Highlights
Effect of root exudates on the growth of R. palustris strains
We identified some genes involved in the synthesis of indole-3-glycerolphosphate and indole in PS3, YSC3 and CGA009; these genes included trpBA (RPPS3_00730, RPPS3_00740, RPYSC3_00730, RPYSC3_00740, TX73_RS00360 and TX73_ RS00365) and tnaA (RPPS3_35930, RPYSC3_36170 and TX73_RS18205)
We identified many putative genes that were associated with known PGP traits in both R. palustris strains, only PS3 can successfully promote the growth of plants[13]
Summary
Effect of root exudates on the growth of R. palustris strains. A single bacterial colony was selected, inoculated into 3 mL of PNSB broth as described previously[13], and incubated for 24 h at 37 °C (200 rpm). The absorbance at 600 nm was adjusted to 1.0 using fresh PNSB broth, and 0.5 ml of the above broths were inoculated into 250-mL Erlenmeyer flasks containing 50 mL of fresh 50% Hoagland solutions as well as the root exudate solutions described above. The growth concentration was determined by measuring the optical density at 600 nm (OD600) using a spectrophotometer
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