Catalyzes the reversible isomerization of glucose-6-phosphate to fructose-6-phosphate. Required for pathogenicity. alpha-D-glucose 6-phosphate = beta-D-fructose 6-phosphate Carbohydrate biosynthesis; gluconeogenesis. Carbohydrate degradation; glycolysis; D-glyceraldehyde 3-phosphate and glycerone phosphate from D-glucose: step 2/4. Inhibited by growth in complex medium but induced by culture in plant extract. Mutation in pgi results in the inability of X.c.citri to utilize fructose or glycerol as carbon sources, to grow in plant tissue, and to cause typical canker symptoms. Belongs to the GPI family.