Xylella fastidiosa subsp. pauca Strains Fb7 and 9a5c from Citrus Display Differential Behavior, Secretome, and Plant Virulence.

Jessica Brito De Souza,Rafael Nascimento,Paulo Adriano Zaini,Aline Gomes De Souza,Mônica Neli Alves,Aline Maria Da Silva,Hebréia Oliveira Almeida-Souza,Luiz Ricardo Goulart,Paulo Marques Pierry,Abhaya M Dandekar

doi:10.3390/ijms21186769

Abstract

Xylella fastidiosa colonizes the xylem of various cultivated and native plants worldwide. Citrus production in Brazil has been seriously affected, and major commercial varieties remain susceptible to Citrus Variegated Chlorosis (CVC). Collective cellular behaviors such as biofilm formation influence virulence and insect transmission of X. fastidiosa. The reference strain 9a5c produces a robust biofilm compared to Fb7 that remains mostly planktonic, and both were isolated from symptomatic citrus trees. This work deepens our understanding of these distinct behaviors at the molecular level, by comparing the cellular and secreted proteomes of these two CVC strains. Out of 1017 identified proteins, 128 showed differential abundance between the two strains. Different protein families were represented such as proteases, hemolysin-like proteins, and lipase/esterases, among others. Here we show that the lipase/esterase LesA is among the most abundant secreted proteins of CVC strains as well, and demonstrate its functionality by complementary activity assays. More severe symptoms were observed in Nicotiana tabacum inoculated with strain Fb7 compared to 9a5c. Our results support that systemic symptom development can be accelerated by strains that invest less in biofilm formation and more in plant colonization. This has potential application in modulating the bacterial-plant interaction and reducing disease severity.

Highlights

Xylella fastidiosa is one of the most important phytopathogenic bacteria, causing a variety of economically significant diseases worldwide [1,2]
X. fastidiosa inhabits xylem vessels and mouthparts of sap-feeding insect vectors, two dynamic microenvironments that require the ability to coordinate strong attachment to surfaces with enough motility to cope with population growth under favorable conditions
This bacterium has adapted a tunable collective behavior responsive to diffusible signaling factors that switch individual motile cells into sessile aggregates maturing into biofilms [53,54]

Summary

Introduction

Xylella fastidiosa is one of the most important phytopathogenic bacteria, causing a variety of economically significant diseases worldwide [1,2]. Among them are citrus variegated chlorosis (CVC) [3], Pierce’s disease of grapevines (PD) [4], leaf scorch diseases in almond (ALS) [5], oleander (OLS) [6], and coffee (CLS) [7] and, the most recent, olive quick decline syndrome (OQDS) described in 2013 in Southern Italy [8,9] Since this Gram-negative bacterium has been detected infecting different hosts in the Mediterranean region [10,11], and strains from subspecies pauca have been recently isolated from olive trees with OQDS symptoms in Brazil [12], confirming its status of emerging pathogen in different regions and crops. This shift in autoaggregation state is observed in many bacteria that can adapt to changes within and across hosts by employing signaling systems with diffusible signaling factors [21,22]

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Conclusion