Genomic and Transcriptomic Analyses Identify Two Key Glycosyltransferase Genes alhH and alhK of Exopolysaccharide Biosynthesis in Pantoea alhagi NX-11

The exopolysaccharide (EPS) produced by NX-11, referred to as alhagan, enhances plant stress resistance, improves soil properties, and exhibits notable rheological properties. Despite these benefits, the exact bio-synthetic process of alhagan by NX-11 remains unclear. This study focused on sequencing the complete genome of NX-11 and identifying an alhagan synthesis gene cluster ( to ). Gene annotation revealed that alhagan biosynthesis in NX-11 follows the Wzx/Wzy-dependent pathway. Furthermore, transcriptome analysis of NX-11 highlighted significant upregulation of four glycosyltransferase genes ( , , , and ) within the alhagan synthesis gene cluster. These glycosyltransferases are crucial for alhagan synthesis. To delve deeper into this process, two upregulated and uncharacterized glycosyltransferase genes, and , were knocked out. The resulting mutants, ΔalhH and ΔalhK, showed a notable decrease in EPS yield, reduced molecular weight, and altered monosaccharide compositions. These findings contribute to a better understanding of the alhagan biosynthesis mechanism in NX-11.