*2.6. Proton Motive Force (PMF)*

As in all other bacteria, an energised cell membrane is essential for the viability and growth of *M. tb* in all metabolic states [19]. The generation and maintenance of a PMF, consisting of an electrical potential due to charge separation across the membrane and a chemical potential of protons, is, therefore, vital and occurs mainly through the proton-pumping components of the ETC [14]. A PMF of about - 110 mV has been measured both in aerobic, replicating and in hypoxic, non-growing *M. tb*, indicating that even in a non-growing state, the bacteria maintain a similarly energized membrane [19]. This PMF is less than the typical PMF range of −180 to −200 mV observed in other bacteria, a difference which has been postulated to be an adaptation to host physiological environments of low nutrient levels and/or terminal electron acceptors [39,78,90].
