Profound differences in the transcriptome of Campylobacter jejuni grown in two different, widely used, microaerobic atmospheres

It was noted that quantitative and qualitative differences occurred between the growth of Campylobacter in microaerobic atmospheres provided by a gas replacement jar and that in a modular atmosphere controlled system cabinet, despite the fact that oxygen levels were comparable. Hydrogen was, however, only present in the replacement mixture (3%). Investigations were therefore carried out to examine any accompanying physiological or transcriptional differences. Growth curves and motility studies using Campylobacter jejuni HPC5 showed that cultures growing in the cabinet were impaired, but only in the early stages of growth compared to growth in the jar. However, transcriptome studies highlighted profound changes in the transcript profiles of exponential cultures grown in the cabinet compared to the jar, including genes indicative of oxidative stress. Genes involved in detoxification, synthesis and modification of macromolecules, probable prophage genes and genes associated with inhibition of natural transformation showed relative increases in expression in the cabinet. Conversely, genes that function in energy metabolism, chaperones, heat shock and motility were increased in the jar, which was indicative of balanced growth. This work highlights the need to carefully annotate the different methods of atmosphere generation in the description of experiments in microarray databases; the assessment of these experimental details is crucial to overcome difficulties in comparing transcriptomic studies of campylobacter cultures between different laboratories.