Oral Presentation Australian Society for Microbiology Annual Scientific Meeting 2019

Living on air: trace gases as hidden energy sources for the dormant bacterial majority (#62)

Chris Greening 1
  1. School of Biological Sciences, Monash University, Clayton, VIC, Australia

Bacteria have an extraordinary capacity to persist in response to resource limitation. To achieve this, cells enter a dormant state in which they expend energy for maintenance rather than growth. Our research program has shown that the survival of environmental and pathogenic bacteria depends on previously unrecognized metabolic flexibility, including novel respiration, fermentation, and biodegradation pathways. In this presentation, I will focus on work demonstrating that many aerobic bacteria are capable of ‘living on air’, i.e. scavenging atmospheric hydrogen and carbon monoxide as alternative energy sources. Genetic and biochemical studies show that axenic mycobacterial cultures use these gases as respiratory electron donors when exhausted for preferred organic carbon sources. These alternative metabolic pathways are tightly regulated, critical for redox homeostasis, and necessary for long-term survival. The determinants of these processes are widespread in the genomes of aerobic bacteria and we have experimentally validated that five dominant bacterial phyla scavenge these gases. At the ecosystem level, metagenomic and biogeochemical studies show that trace gas scavengers are abundant and active in aerated soil and marine ecosystems, and are particularly important for primary production in global desert soils. I will also outline ongoing work to use these principles to understand how Mycobacterium tuberculosis and various enteropathogens maintain energy needs in different reservoirs. While atmospheric hydrogen and carbon monoxide in sufficiently concentrated to support growth, they are highly dependable energy sources for persistence given their ubiquity, diffusibility, and energy content. Overall, these findings redefine the minimal nutritional requirements for life and identify trace gases as the hidden energy source supporting the dormant bacterial majority in aerated ecosystems.