Leptospira interrogans short-term transcriptional response to plasma-like medium and glutamine

The adaptation and survival of bacterial pathogens in a host involves a complex series of processes, with bacterial metabolism as a critical checkpoint and facilitator of infection. The pathogen Leptospira interrogans expands from a small inoculum to reach high bloodstream titers before colonizing host kidneys; however the supporting metabolic programs and the role of the host environment are largely unknown, and tools to investigate these host-pathogen metabolic interactions in a controlled in vitro setting are in their infancy. Here, we built upon the concept of human plasma-like medium (HPLM) to develop a more physiological system for L. interrogans culture. This supplemented HPLM (sHPLM) supported robust growth, and we used RNA-sequencing analyses to demonstrate the fidelity of the transcriptome of sHPLM cultures to in vivo models. Through the use of sHPLM, we identified the amino acid glutamine as a major nitrogen source supplying the biosynthetic activities of L. interrogans. Further study of the role of glutamine revealed that exposure altered the proliferative behavior and biofilm formation of L. interrogans, although RNA-sequencing revealed few strong transcriptional consequences of this environmental signal. This work adds to our understanding of the metabolic mechanisms supporting L. interrogans infection which could be targeted for new anti-leptospiral therapies. We propose a dual, pathogen-supporting role for glutamine: as a metabolic fuel for continued biosynthesis and replication, and as a metabolite signal to inform pathogen adaptation in the process of host infection. Overall design: L. interrogans grown in standard EMJH medium at 30 degrees Celsius was cultured for four hours at late exponential phase density in either fresh EMJH, sHPLM at 37 degrees Celsius, or EMJH with 550uM glutamine.