Bacterial fruit blotch (BFB) is a serious threat to cucurbits production worldwide. Its causal agent, Acidovorax citrulli, infects many cucurbits crops including watermelon and melon. A previous study showed that A. citrulli can enter into a viable but nonculturable (VBNC) state following exposure to copper sulfate and those VBNC cells can be resuscitated by addition of EDTA solution. VBNC A. citrulli cells challenged the traditional culture-based detection method and the resuscitated cells could be a great risk to the cucurbit production. Since copper-based bactericides are widely used for BFB management, a good knowledge of mechanism in A. citrulli VBNC state is quite important.

In this study, protein profiling in log-phase, copper-induced VBNC state and four stages of resuscitating A. citrulli cells was analysis by isobaric tags for relative and absolute quantification (iTRAQ) approach. A total of 60 proteins were differentially expressed in VBNC cells compared with log-phase cells, and 469 proteins were differentially expressed in resuscitated cells compared with VBNC cells. Expression levels of 15 in 18 selected genes tested by qPCR were consistent with the protein levels in the iTRAQ experiment.

Many proteins were associated with induction and resuscitation VBNC state in A. citrulli. In the VBNC state, energy generation associated proteins and a copper translocating P-type ATPase was remarkably enriched. While in the resuscitating process, the energy production proteins played an important role, as well as oxidative stress response and toxin-antitoxin system proteins.