Campylobacter jejuni M1 transcriptome changes during loss of culturability in water

Background: The natural environment serves as a potential reservoir for Campylobacter, the leading cause of bacterial gastroenteritis in humans. Little is understood about the mechanisms underlying variations between different strains of C. jejuni in survival characteristics in natural environments. Results: We identified three Campylobacter jejuni strains exhibiting variability in their ability to retain culturability in water at two different temperatures (4°C and 25°C). Of the three, strain C. jejuni M1 exhibited the most rapid loss of culturability whilst retaining viability. Using RNAseq transcriptomics, we characterised C. jejuni M1 gene expression in response to suspension in water by analyzing bacterial suspensions recovered immediately after introduction into water (Time 0), and from two sampling times/temperatures where considerable loss of culturability was evident, namely (i) after 24 h at 25°C, and (ii) after 72 h at 4°C. Transcript data were compared with a culture-grown control. Whilst some gene expression characteristics were shared amongst the three populations recovered from water, more genes were up-regulated than down-regulated. Many of the up-regulated genes were identified in the Time 0 sample, whereas the majority of down-regulated genes occurred in the 24 h / 25°C sample.Conclusions: Variations in expression were found amongst genes associated with oxygen tolerance, starvation and osmotic stress. However, we also found upregulation of flagellar assembly genes, accompanied by down-regulation of genes involved in chemotaxis. Our data also suggested a switch from secretion via sec to secretion via the tat system, and that the quorum sensing gene luxS may be implicated in the survival of strain M1 in water. Variations in gene expression also occurred in accessory genome regions. Our data suggest that despite the loss of culturability, strain M1 remains viable and adapts via specific changes in gene expression.