Structural levansucrase gene (lsdA) constitutes a functional locus conserved in the species Gluconacetobacter diazotrophicus

Levansucrase(EC 2.4.1.10) was identified as a constitutive exoenzyme in 14 Gluconacetobacter diazotrophicus strains recovered from different host plan ts in diverse geographical regions. The enzyme, consisting of a single 60-k Da polypeptide, hydrolysed sucrose to synthesise oligofructans and levan. S ugar-cane-associated strains of the most abundant genotype (electrophoretic type 1) showed maximal values of levansucrase production. These values wer e three-fold higher than those of the isolates recovered from coffee plants . Restriction fragment Length polymorphism analysis revealed a high degree of conservation of the levansucrase locus (lsdA) among the 14 strains under study, which represented 11 different G. diazotrophicus genotypes. Targete d disruption of the lsdA gene in four representative strains abolished thei r ability to grow on sucrose, indicating that the endophytic species G. dia zotrophicus utilises plant sucrose via levansucrase.