XadA2 Adhesin Decreases Biofilm Formation and Transmission of Xylella fastidiosa subsp. pauca.

Mariana Bossi Esteves,João Roberto Spotti Lopes,Tiago De Melo Sales,Julia Lopes Nalin,Karla Kudlawiec,Alessandra Alves De Souza,Rodrigo Piacentini Paes De Almeida,Anne Sicard,Raquel Caserta Salviatto

doi:10.3390/insects11080473

Abstract

Xylella fastidiosa is a vector-borne bacterium that causes diseases in many plants of economic interest. The bacterium–vector initial interactions involve bacterial membrane-bound adhesins that mediate cell attachment to the foregut of insect vectors. We investigated the role of the afimbrial adhesin XadA2 in the binding and biofilm formation of X. fastidiosa subsp. pauca to vector surfaces in vitro, as well as its potential to disrupt pathogen transmission. We showed that XadA2 has binding affinity for polysaccharides on sharpshooter hindwings, used as a proxy for the interactions between X. fastidiosa and vectors. When in a medium without carbon sources, the bacterium used wing components, likely chitin, as a source of nutrients and formed a biofilm on the wing surface. There was a significant reduction in X. fastidiosa biofilm formation and cell aggregation on vector wings in competition assays with XadA2 or its specific antibody (anti-XadA2). Finally, pathogen acquisition and transmission to plant were significantly reduced when the vectors acquired X. fastidiosa from an artificial diet supplemented with anti-XadA2. These results show that XadA2 is important in mediating bacterial colonization in the insect and that it could be used as a target for blocking X. fastidiosa transmission.

Highlights

Vector-borne bacterial plant pathogens are responsible for some of the most important emerging plant diseases today [1]
50–60 adult individuals of each species were placed inside screened cages with V. condensata or Ocimum basilicum (Lamiaceae) plants for rearing healthy individuals of B. xanthophis or M. leucomelas and S. sagata, respectively, as described previously [12]
No difference was found in absorbance values over the 6-hour evaluation period when X. fastidiosa-green fluorescent protein (GFP) was incubated in X. fastidiosa medium (XFM) with or without XadA2 (F = 2,679; d.f. = 1; p = 0.153) (Figure 1B), demonstrating that the addition of this protein did not influence the formation of cell aggregates by the bacterium

Summary

Introduction

Vector-borne bacterial plant pathogens are responsible for some of the most important emerging plant diseases today [1]. Xylella fastidiosa is a bacterium that causes several diseases in agricultural crops of economic interest, including citrus variegated chlorosis (CVC), Pierce’s disease (PD) of grapevines and olive quick decline syndrome (OQDS) [2,3]. It is naturally disseminated among host plants by xylem-sap feeding insects, known as sharpshooter leafhoppers (Hemiptera: Cicadellidae: Cicadellinae) and spittlebugs (Hemiptera: Cercopoidea) [4]. Previous studies have shown that initial interactions of X. fastidiosa with the foregut of vectors, the retention site of the pathogen, are mediated by adhesion proteins on the bacterial cell surface, which are classified as fimbrial and afimbrial adhesins [5]. Killiny and Almeida [5,6] demonstrated that the adhesins HxfA, Insects 2020, 11, 473; doi:10.3390/insects11080473 www.mdpi.com/journal/insects

Methods

Results

Discussion

Conclusion