Human Hormones and Bacterial Signaling Molecules as Growth Factors in the Human Microbiome

Abstract

It is estimated that fifty percent of the bacterial diversity of the human intestinal tract is unable to be cultured in the laboratory. Due to the role of the “human microbiome” in health and disease, there is substantial interest for its characterization. However, to properly study these organisms they must be cultivated in vitro. It has been shown that uncultured bacterial species rely on other species for growth factors not present in laboratory media, and many processes in bacteria are regulated by cellular density in a given population – a phenomenon known as autoinduction. In this study, we hypothesize that the addition of human hormones or bacterial quorum sensing factors will allow for cultivation of novel intestinal bacterial species. This was tested by comparing total colony forming units (CFU) of diluted fecal samples spread on media with and without the proposed growth factors. Increased CFU were seen on plates containing DPD (the precursor to bacterial quorum sensing signal autoinducer-2), cAMP (an inter kingdom second messenger), and norepinephrine (a human neurotransmitter). Species from Petri plates with added DPD and cAMP were reinoculated onto fresh medium, and half showed larger colony size with the added compounds. From these isolates, several rare species were identified by 16s rRNA sequencing, signifying that the addition of bacterial and host signaling factors may increase recovery of previously uncultured bacteria from the human intestinal tract. The mechanism behind this observation is currently being investigated.