Axenic growth of Coxiella burnetii.

Early metabolic studies of C. burnetii showed minimal metabolic activity of axenic (host cell-free) organisms in buffers adjusted to neutral pH. However, our understanding of the organism's physiology was greatly improved upon the discovery that C. burnetii requires an acidic pH for metabolic activation. Indeed, information gained from acid activation studies coupled with contemporary analyses using transcription microarrays, metabolic pathway reconstruction and metabolite typing, led to an axenic culture system that supports robust growth of C. burnetii. While axenic culture of C. burnetii can present some technical challenges, the technique is currently facilitating new lines of investigation and development of genetic tools. Axenic cultivation of C. burnetii should also prove useful in clinical settings.