LAUSR

The viable but nonculturable (VBNC) state is a unique survival strategy of bacteria in response to stress conditions. It was confirmed that Clavibacter michiganensis, the causal agent of bacterial canker in tomato, could be induced into the VBNC state by exposure to CuSO4 in an oligotrophic solution. RNA-Seq analysis was used to monitor the mechanisms of the VBNC state during CuSO4 induction in C. michiganensis. The results identified that numerous genes involved in stringent response, copper resistance, and stress resistance were up-regulated, and some involved in cell division were down-regulated significantly. The study investigated the importance of Rel, which is an essential enzyme in the synthesis of the molecular alarmone ppGpp, via the generation of a Δrel mutant and its complementation strain. Biological characterization revealed that deficiency of rel reduced the bacterial growth, production of exopolysaccharides, and pathogenicity, as well as ppGpp production. The Δrel mutant increased the sensitivity to environmental stress, exhibiting reduced growth on minimal media, and a propensity to enter the VBNC state in response to CuSO4. These findings have important implications for the understanding of survival mechanism and management of Clavibacter michiganensis and other phytopathogenic bacteria.