Csp1, a cold shock protein homolog in Xylella fastidiosa influences cell attachment, pili formation, and gene expression

Authors: Wei, Wei; SAWYER, TERESA - Oregon State University; Burbank, Lindsey

Submitted to: Microbiology Spectrum
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/7/2021
Publication Date: 11/17/2021
Citation: Wei, W., Sawyer, T., Burbank, L.P. 2021. Csp1, a cold shock protein homolog in Xylella fastidiosa influences cell attachment, pili formation, and gene expression. Microbiology Spectrum. 9(3). Article e01591-21. https://doi.org/10.1128/Spectrum.01591-21.
DOI: https://doi.org/10.1128/Spectrum.01591-21

Interpretive Summary: Xylella fastidiosa is a disease-causing bacterial pathogen of many economically important crops including grapevine. This pathogen grows within the water-transporting vessels of plant hosts, where it may encounter many stressors such as nutrient limitation, temperature fluctuations, and other adverse conditions that can be detrimental to bacteria survival. Many bacterial pathogens adapt to stressful environments by using cold shock proteins (Csps) that help the cell perform essential functions under duress. Despite their name, some cold shock proteins are involved in cell processes unrelated to temperature, such as aiding in disease development. This study characterizes how Csp1, a temperature-independent cold shock protein in X. fastidiosa, contributes to bacterial survival and disease. Removing Csp1 makes X. fastidiosa less able to survive for extended periods of time and disrupts many of the processes used by the bacteria to spread and grow within plants. The findings from this study shed light on the biology of this economically important pathogen and can be used to design better disease management and control strategies.

Technical Abstract: Bacterial cold shock-domain proteins (CSPs) are conserved nucleic acid binding chaperones that play important roles in adaptation to environmental changes and stressors, as well as in pathogenesis. Csp1 is a temperature-independent cold shock protein homolog in Xylella fastidiosa, a bacterial plant pathogen of grapevine and other economically important crops. Csp1 contributes to stress tolerance and virulence in X. fastidiosa. However, besides general single stranded nucleic acid binding activity, relatively little is known about the specific function(s) of this protein. To further investigate the role(s) of Csp1, we compared phenotypic differences between wild type X. fastidiosa strain Stag’s Leap and a csp1 deletion mutant ('csp1). We observed a significant decrease in cellular aggregation and surface attachment with the 'csp1 strain compared to the wild type in liquid medium. Transmission electron microscopy imaging revealed that 'csp1 had reduced pili formation compared to the wild type and complemented strains. Pili influence X. fastidiosa aggregation and attachment, which are important steps in biofilm formation. The 'csp1 strain also showed reduced survival compared to wild type after long term growth, in vitro. Since Csp1 binds DNA and RNA, its influence on bacterial gene expression was also investigated. Long-read Nanopore RNA-Seq was used to evaluate transcriptomes of wild-type Stag’s Leap and 'csp1 under standard growth conditions (28°C). RNA-Seq analysis revealed changes in expression of several genes important for attachment and biofilm formation in 'csp1 compared to wild type. One gene of intertest, pilA1, encodes a type IV pili subunit protein and was up regulated in the 'csp1 mutant. Deleting pilA1 from the Stag’s Leap genome increased surface attachment in vitro and reduced virulence in grapevines. X. fastidiosa virulence depends on bacterial attachment to host tissue and movement within and between xylem vessels. Studies in X. fastidiosa and other bacteria have also identified links between stress response and biofilm formation, suggesting that Csp1 may play a role in both virulence and stress tolerance by influencing expression of genes important for biofilm formation.