Zinc Detoxification Is Required for Full Virulence and Modification of the Host Leaf Ionome by Xylella fastidiosa

Abstract

Zinc (Zn) is an essential element for all forms of life because it is a structural or catalytic cofactor of many proteins, but it can have toxic effects at high concentrations; thus, microorganisms must tightly regulate its levels. Here, we evaluated the role of Zn homeostasis proteins in the virulence of the xylem-limited bacterium Xylella fastidiosa, causal agent of Pierce's disease of grapevine, among other diseases. Two mutants of X. fastidiosa 'Temecula' affected in genes which regulate Zn homeostasis (zur) and Zn detoxification (czcD) were constructed. Both knockouts showed increased sensitivity to Zn at physiologically relevant concentrations and increased intracellular accumulation of this metal compared with the wild type. Increased Zn sensitivity was correlated with decreased growth in grapevine xylem sap, reduced twitching motility, and downregulation of exopolysaccharide biosynthetic genes. Tobacco plants inoculated with either knockout mutant showed reduced foliar symptoms and a much reduced (czcD) or absent (zur) modification of the leaf ionome (i.e., the mineral nutrient and trace element composition), as well as reduced bacterial populations. The results show that detoxification of Zn is crucial for the virulence of X. fastidiosa and verifies our previous findings that modification of the host leaf ionome correlates with bacterial virulence.

Zinc transporters YbtX and ZnuABC are required for the virulence of Yersinia pestis in bubonic and pneumonic plague in mice

“…73-77 Therefore, the ability to avoid Zn toxicity via Zn 2+ efflux has also been shown as an important virulence factor in several bacteria. 76, 78-80 Y. pestis is a facultative intracellular pathogen and has been shown to survive in macrophages, and to a lesser extent in neutrophils. 81-85 While bioinformatics identified several systems predicted to be involved in Zn 2+ efflux in the Y. pestis KIM10+ genome, 59 their role in virulence and in preventing Zn toxicity has not been determined.…”

A Short Protocol for Gene Knockout and Complementation in Xylella fastidiosa Shows that One of the Type IV Pilin Paralogs (PD1926) Is Needed for Twitching while Another (PD1924) Affects Pilus Number and Location

“…This is because, similarly to other bacteria, almost 40% of the proteins encoded by the genome do not have a known function assigned and are annotated as hypothetical proteins (28), and, moreover, X. fastidiosa has been a difficult pathogen for genetic manipulation studies (59,60). Although transposon mutagenesis (4,8) and homologous recombination protocols (15,30,33,61) have been used, these protocols are timeconsuming and inconsistent in efficiency. This is further complicated by the fastidious and slow-growing nature of the bacterium (62).…”

Bacterial zinc uptake regulator proteins and their regulons

“…Δ zur mutants often have higher zinc contents, and suffer from increased sensitivity towards elevated concentrations of zinc, although there are exceptions to that rule, for example, in Corynebacterium diphtheriae [ 73 ]. The viability and/or virulence of Δ zur mutants of pathogenic bacteria in the host is often more or less severely compromised [ 74 , 85 , 86 , 95 ], but that is not always the case [ 75 ]. The knockout phenotypes highlight that Zur provides tolerance towards both high and low zinc: it is required not only to boost zinc uptake under limiting conditions but also to down-regulate zinc uptake in excess conditions.…”