Abstract
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.
Highlights
Vibrio harveyi is a heterotrophic Gram-negative luminous bacterium inhabiting marine environments and showing a preference for temperate and tropical waters
In order to learn more about Vibrio spp. responses to global warming (GW) and their possible contribution to survival and pathogenicity of Vibrio spp., we studied phenotypical and gene expression changes that occur during the time-dependent adaptation of V. harveyi in seawater microcosm at 30 °C which is close to the upper limit of sea surface temperature (SST) recently observed in some regions of the globe[36,37]
To investigate the combined impact of elevated temperatures and limitation of carbon on Vibrio species, we used V. harveyi as a model organism and studied its persistence in seawater microcosms at 30 °C known to be within the upper limit of sea surface temperature observed in some areas of the global oceans[50]
Summary
Effects of prolonged incubation of V. harveyi cells in seawater at 30 °C on their culturability and morphology. While determining culturable populations in aliquots withdrawn at different time points and analyzed by spreading on MA plates, a 10-fold decrease in the number of culturable cells was observed after three weeks of incubation (Fig. 1). Besides monitoring cell culturability and morphological changes, V. harveyi adaptation was analyzed at the whole transcriptome level To carry out this analysis, total RNA was isolated from the initial inoculate (control) and from V. harveyi cells after their incubation in sterile seawater for 12 h, 3, 6, 14 and 21 days. Electrophoretic profiles of RNA samples isolated from cells incubated for 14 and 21 days revealed that they contained a considerable fraction of degraded RNA (apparently accumulating due to cell damage beginning after prolong incubation of V. harveyi cells in seawater (Fig. 3). While clusters 2 and 3 were primarily represented by metabolic genes (e.g. genes controlling carboxylic acid and nucleotide metabolism, respectively), the other two (clusters 4 and 6) comprised the genes playing important roles in the processing of genetic information (namely, transcription and translation, respectively)
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