Advances in Microbial Physiology, Volume 84 in this ongoing serial, highlights new advances in the field with this new volume presenting interesting chapters. Each chapter is written by an international board of authors. Topics of interest in this update include Mycobacterial Efflux systems, New insights in bacterial organophosphorus cycling: from human pathogens to environmental bacteria, Link between gut sulfidogenic bacteria and disease, The Formate-H2 Axis and its Importance for Microbial Physiology, Physiology of diazotrophs, Antibiotic efficacy, and Microbial metabolites as modulators of host physiology.