Glutamine-hydrolyzing GMP Synthase Gene (guaA) Regulates Siderophore Synthesis in the Nitrogen-fixing Bacterium (NFB) Kosakonia radicincitans GXGL-4A

The nitrogen-fixing bacterium Kosakonia radicincitans GXGL-4A can produce siderophore to sequester iron, which is essential for survival and bacteriostasis. In this investigation, a mutant, M246-2, resulting from Tn5 insertion mutagenesis of the strain GXGL-4A, was found to have lost the ability to synthesize siderophores. Whole-genome sequencing of the mutant M246-2 revealed that the insertion site is within the nucleotide sequence of the gua A gene encoding glutamine-hydrolyzing guanosine monophosphate (GMP) synthase. The deletion of the gua A gene ( ∆gua A) resulted in the loss of the ability to produce siderophores in the strain GXGL-4A and a significant slowdown in the bacterial growth curve. Moreover, the intracellular GMP contents in the strains M246-2 and ∆gua A were statistically significantly reduced compared to the wild-type strain GXGL-4A. The bacterial functional complementation and gua A gene deletion experiments revealed that the gua A gene modulated the siderophore synthesis in the strain GXGL-4A. The results of differential transcriptome analysis showed that the transcription levels of genes related to the siderophore synthesis in the mutant M246-2 had no significant changes compared to the wild-type strain GXGL-4A, suggesting that the gua A gene may modulate the siderophore synthesis of the strain GXGL-4A through a complex mechanism at the non-transcriptional level.