Xanthomonas axonopodispv.citri enters the VBNC state after copper treatment and retains its virulence

Abstract

The most severe form of citrus canker disease is caused by Xanthomonas axonopodis pv. citri (Xac) and affects all types of important citrus crops, reducing fruit yield and quality. Copper-based products are routinely used as a standard control measure for citrus canker. In this work we demonstrate that copper treatment induces the viable but nonculturable (VBNC) state in Xac but does not prevent the development of symptoms in susceptible plants. Short-term exposures to different concentrations of copper solutions were assayed to determine which treatment resulted in Xac nonculturability. Treatment of 10(6) mL(-1) Xac cells for 10 min in a 135-muM CuSO(4) solution (equivalent to three times the free soluble copper concentration applied in one field treatment) resulted in nonculturability. However, 16% of cells were viable based on 5-cyano-2,3-ditolyl tetrazolium chloride staining and 1% were capable of producing canker lesions after infiltrating grapefruit plants. If induction of the VBNC state in Xac cells were to occur under field conditions, this would have to be taken into consideration for an effective control of canker disease.

Response of Xylella fastidiosa to Zinc: Decreased Culturability, Increased Exopolysaccharide Production, and Formation of Resilient Biofilms under Flow Conditions

“…When Zn was added to PD2, an early decrease in the viability and culturability of X. fastidiosa was seen. These results suggest that X. fastidiosa may be able to enter a VBNC state in vitro and are consistent with observations from other bacteria incubated in the presence of compounds that induce the VBNC, such as Cu (78,82,83). Interestingly, Enterococcus spp.…”

“…Therefore, if aggregates were still found in the samples after thorough mixing, the comparison of the relative numbers of cells on the different fractions (e.g., culturable versus viable) would still be valid. The VBNC state is relevant to virulence, since cells in this state may remain virulent or "revive" and reacquire virulence once harsh conditions disappear or upon contact with the host (80,82,83).…”

Development of an Efficient Real-Time Quantitative PCR Protocol for Detection ofXanthomonas arboricolapv. pruni inPrunusSpecies

“…pruni colonies. In addition, we must also consider the possibility of the existence of a nonculturable condition of this bacterium, as described previously for other Xanthomonas species (7,10,17). Viable but nonculturable bacteria would be not considered part of the bacterial population and may therefore be undervalued by culture plating but may be included in the estimation by PCR.…”

Statement in response to the comments submitted by the US phytosanitary authorities on a previous EFSA opinion (EFSA Journal 2011;9(12):2461) regarding the export of Florida citrus fruit to the EU

“…citri was observed under laboratory conditions (Cubero and Graham, 2002), and that Xanthomonas citri subsp. citri cells also entered the VBNC state after copper treatment and retained their virulence (Del Campo et al, 2009)…”