Intracellular Mycobacterium tuberculosis Exploits Multiple Host Nitrogen Sources during Growth in Human Macrophages

Abstract

Summary: Nitrogen metabolism of Mycobacterium tuberculosis (Mtb) is crucial for the survival of this important pathogen in its primary human host cell, the macrophage, but little is known about the source(s) and their assimilation within this intracellular niche. Here, we have developed 15N-flux spectral ratio analysis (15N-FSRA) to explore Mtb’s nitrogen metabolism; we demonstrate that intracellular Mtb has access to multiple amino acids in the macrophage, including glutamate, glutamine, aspartate, alanine, glycine, and valine; and we identify glutamine as the predominant nitrogen donor. Each nitrogen source is uniquely assimilated into specific amino acid pools, indicating compartmentalized metabolism during intracellular growth. We have discovered that serine is not available to intracellular Mtb, and we show that a serine auxotroph is attenuated in macrophages. This work provides a systems-based tool for exploring the nitrogen metabolism of intracellular pathogens and highlights the enzyme phosphoserine transaminase as an attractive target for the development of novel anti-tuberculosis therapies. : Borah et al. measured nitrogen uptake and assimilation in Mycobacterium tuberculosis during replication in host macrophages using 15N-flux spectral ratio analysis (15N-FSRA), a systems-based tool. The biosynthetic and transport systems of the identified nitrogen sources involved in serine biosynthesis are potential drug targets. Keywords: Mycobacterium tuberculosis, tuberculosis, host macrophages, intracellular pathogen, nitrogen metabolism, systems biology, isotopic labeling, flux analysis, host metabolism, amino acid