Engineering phosphoribosylpyrophosphate synthetase in Methylobacterium radiotolerans for lettuce growth and quality...

A bacterial strain designated DS15 was isolated from the leaves of Salvia miltiorrhiza and characterized to assess its plant growth-promoting (PGP) traits. Based on 16 S rRNA gene and genome alignment, DS15 strain was identified as Methylobacterium radiotolerans. Its PGP traits, including indole acetic acid (IAA) production, phosphate solubilization, and siderophore secretion were determined. Foliar application of DS15 strain significantly increased 35.0% of fresh weight of lettuce seedlings grown in a standard growth chamber compared to the control group. Genomic analysis revealed the presence of multiple genes associated with plant growth promotion, including aldB, ltaE, phnI, phnN, as well as phosphoketolase pathway genes such as xfp, ack, and acs in DS15 strain. The introduction of the PRS mutation (an aspartic acid to an asparagine residue, D38N) in the DS15 strain, resulting in DS15^PTR strain, enhanced its growth under low concentrations of methanol and multi-carbon (C2 to C5) substrates. The DS15^PTR strain showed a notable enhancement in the phyllosphere colonization, and its application further promoted the growth of lettuce seedlings. A follow-up experiment in an agricultural solar greenhouse was performed to assess the efficiency of the DS15^PTR strain in improving lettuce growth and quality, including vitamin C and total flavonoid content. In conclusion, these findings highlight the potential of M. radiotolerans DS15 with the PRS mutation as an effective PGP bacterium, indicating its application in enhancing crop productivity and advancing sustainable agriculture.