Lscβ and lscγ, two novel levansucrases of Pseudomonas syringae pv. actinidiae biovar 3, the causal agent of bacterial canker of kiwifruit, show different enzymatic properties

Bacterial canker disease caused by Pseudomonas syringae pv. actinidiae (Psa) biovar 3 involved all global interest since 2008. We have found that in Psa3 genome, similarly to other P. syringae, there are three putative genes, lsc alpha, lsc beta and lsc gamma, coding for levansucrases. These enzymes, breaking the sucrose moiety and releasing glucose can synthetize the fructose polymer levan, a hexopolysaccharide that is well known to be part of the survival strategies of many different bacteria. Considering lsc alpha non-coding because of a premature stop codon, in the present work we cloned and expressed the two putatively functional levansucrases of Psa3, lsc beta and lsc gamma, in E. coli and characterized their biochemical properties such as optimum of pH, temperature and ionic strength. Interestingly, we found completely different behaviour for both sucrose splitting activity and levan synthesis between the two proteins; lsc gamma polymerizes levan quickly at pH 5.0 while lsc beta has great sucrose hydrolysis activity at pH 7.0. Moreover, we demonstrated that at least in vitro conditions, they are differentially expressed suggesting two distinct roles in the physiology of the bacterium. (c) 2021 Elsevier B.V. All rights reserved.

Automated summary

Research on the bacterial canker disease caused by Pseudomonas syringae pv. actinidiae (Psa) biovar 3 has identified three potential genes coding for levansucrases in the Psa3 genome. Through cloning and expression in E. coli, lsc beta and lsc gamma were characterized for their different biochemical properties, indicating distinct roles in sucrose hydrolysis and levan synthesis, suggesting potential differential functions in the physiology of the bacterium.