Discovering the means to control the increasing dissemination of pathogenic vibrios driven by recent climate change is challenged by the limited knowledge of the mechanisms in charge of Vibrio spp. persistence and spread in the time of global warming. To learn about physiological and gene expression patterns associated with the long-term persistence of V. harveyi at elevated temperatures, we studied adaptation of this marine bacterium in seawater microcosms at 30 °C which closely mimicked the upper limit of sea surface temperatures around the globe. We found that nearly 90% of cells lost their culturability and became partly damaged after two weeks, thus suggesting a negative impact of the combined action of elevated temperature and shortage of carbon on V. harveyi survival. Moreover, further gene expression analysis revealed that major adaptive mechanisms were poorly coordinated and apparently could not sustain cell fitness. On the other hand, elevated temperature and starvation promoted expression of many virulence genes, thus potentially reinforcing the pathogenicity of this organism. These findings suggest that the increase in disease outbreaks caused by V. harveyi under rising sea surface temperatures may not reflect higher cell fitness, but rather an increase in virulence enabling V. harveyi to escape from adverse environments to nutrient rich, host-pathogen associations.

This work was supported by the Spanish Ministry of Economy and Competitiveness grant CGL2015-70929-R, Ikerbasque (Basque Foundation for Science) and pre-doctoral grants PRE-2013-1-901 (I.M.) from the Basque Government and PIF15/101 (E.O.) from the University of the Basque Country. A.E.-C. is funded by ISCIII of the MINECO (Ref: PT17/0009/0019) and cofinanced by FEDER.