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Abstract
BackgroundXylella fastidiosa is limited to the xylem of the plant host and the foregut of insect vectors (sharpshooters). The mechanism of pathogenicity of this bacterium differs from other plant pathogens, since it does not present typical genes that confer specific interactions between plant and pathogens (avr and/or hrp). The bacterium is injected directly into the xylem vessels where it adheres and colonizes. The whole process leads to the formation of biofilms, which are considered the main mechanism of pathogenicity. Cells in biofilms are metabolically and phenotypically different from their planktonic condition. The mature biofilm stage (phase of higher cell density) presents high virulence and resistance to toxic substances such as antibiotics and detergents. Here we performed proteomic analysis of proteins expressed exclusively in the mature biofilm of X. fastidiosa strain 9a5c, in comparison to planktonic growth condition.ResultsWe found a total of 456 proteins expressed in the biofilm condition, which correspond to approximately 10% of total protein in the genome. The biofilm showed 37% (or 144 proteins) different protein than we found in the planktonic growth condition. The large difference in protein pattern in the biofilm condition may be responsible for the physiological changes of the cells in the biofilm of X. fastidiosa. Mass spectrometry was used to identify these proteins, while real-time quantitative polymerase chain reaction monitored expression of genes encoding them. Most of proteins expressed in the mature biofilm growth were associated with metabolism, adhesion, pathogenicity and stress conditions. Even though the biofilm cells in this work were not submitted to any stress condition, some stress related proteins were expressed only in the biofilm condition, suggesting that the biofilm cells would constitutively express proteins in different adverse environments.ConclusionsWe observed overexpression of proteins related to quorum sensing, proving the existence of communication between cells, and thus the development of structuring the biofilm (mature biofilm) leading to obstruction of vessels and development of disease. This paper reports a first proteomic analysis of mature biofilm of X. fastidiosa, opening new perspectives for understanding the biochemistry of mature biofilm growth in a plant pathogen.
Highlights
Xylella fastidiosa is limited to the xylem of the plant host and the foregut of insect vectors
X. fastidiosa is transmitted by leafhoppers into the xylem vessel where it colonizes and blocks the movement of water and nutrients, causing typical disease symptoms according to the host
It has been reported that X. fastidiosa biofilm presents at least 5 phases of biofilm formation where 20 days corresponds to a mature biofilm [14]
Summary
Xylella fastidiosa is limited to the xylem of the plant host and the foregut of insect vectors (sharpshooters). The bacterium is injected directly into the xylem vessels where it adheres and colonizes. Cells in biofilms are metabolically and phenotypically different from their planktonic condition. Xylella fastidiosa is a slow growing Gram-negative bacterium involved in many economically important plant diseases, such as citrus variegated chlorosis (CVC) in sweet orange, Pierce’s disease (PD) in grapevine and other species such as coffee and plum. X. fastidiosa is transmitted by leafhoppers into the xylem vessel where it colonizes and blocks the movement of water and nutrients, causing typical disease symptoms according to the host. A number of changes in gene regulation that cause the adhering cells to become phenotypically and metabolically distinct from their planktonic counterparts [3]. Important factors include cell density, as well as the extent and duration of cell-to-cell contact, the concentrations of diffusible substances and/or the ability to establish concentration gradients of diffusible substances and oxygen availability
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