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 <i>Pantoea alhagi</i> 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 <i>P. alhagi</i> NX-11 remains unclear. This study focused on sequencing the complete genome of <i>P. alhagi</i> NX-11 and identifying an alhagan synthesis gene cluster (<i>LQ939_RS12550</i> to <i>LQ939_RS12700</i>). Gene annotation revealed that alhagan biosynthesis in <i>P. alhagi</i> NX-11 follows the Wzx/Wzy-dependent pathway. Furthermore, transcriptome analysis of <i>P. alhagi</i> NX-11 highlighted significant upregulation of four glycosyltransferase genes (<i>alhH</i>, <i>wcaJ</i>, <i>alhK</i>, and <i>alhM</i>) 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, <i>alhH</i> and <i>alhK</i>, 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 <i>P. alhagi</i> NX-11.