Abstract
Climate fluctuations have been linked to an increased prevalence of disease in seaweeds, including the red alga Delisea pulchra, which is susceptible to a bleaching disease caused by the bacterium Nautella italica R11 under elevated seawater temperatures. To further investigate the role of temperature in the induction of disease by N. italica R11, we assessed the effect of temperature on the expression of the extracellular proteome (exoproteome) in this bacterium. Label-free quantitative mass spectrometry was used to identify 207 proteins secreted into supernatant fraction, which is equivalent to 5% of the protein coding genes in the N. italica R11 genome. Comparative analysis demonstrated that expression of over 30% of the N. italica R11 exoproteome is affected by temperature. The temperature-dependent proteins include traits that could facilitate the ATP-dependent transport of amino acid and carbohydrate, as well as several uncharacterized proteins. Further, potential virulence determinants, including two RTX-like proteins, exhibited significantly higher expression in the exoproteome at the disease inducing temperature of 24°C relative to non-inducing temperature (16°C). This is the first study to demonstrate that temperature has an influence exoproteome expression in a macroalgal pathogen. The results have revealed several temperature regulated candidate virulence factors that may have a role in macroalgal colonization and invasion at elevated sea-surface temperatures, including novel RTX-like proteins.
Highlights
Seaweeds are key ecosystem engineers of temperate marine coastal habitats
We identified 207 proteins in the supernatant fraction of N. italica R11 (Supplementary Table S1), which corresponds to over 5% of the protein coding genes in the genome
This study is the first to demonstrate that N. italica R11 modulates the expression of a subset of its exoproteome in response to temperature, and it provides the foundation for future investigations into the function of the temperaturedependent secreted proteins in the pathogenicity and/or environmental persistence of N. italica R11
Summary
Seaweeds (macroalgae) are key ecosystem engineers of temperate marine coastal habitats. A combination of laboratory and Exoproteome Analysis of a Seaweed Pathogen field experiments have demonstrated that under increased host stress (such as that imposed by higher temperatures) D. pulchra has reduced levels of its natural chemical defense (furanones) (Campbell et al, 2011; Case et al, 2011). This reduced algal defense results in the increased susceptibility to infection by bacterial pathogens, including the Roseobacter species Nautella italica R11 R11) under the elevated seasurface temperatures of 24◦C (Campbell et al, 2011; Case et al, 2011; Fernandes et al, 2011; Kumar et al, 2016)
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