Bacteria are traditionally classified by their energy and carbon acquisition strategies. While some bacteria are known to be highly flexible, especially within the Proteobacteria, most are thought to be metabolically constrained. Here I provide evidence that most bacteria worldwide are in fact surprisingly versatile. Through culture-based work, we have observed that many bacteria adapt to energy starvation by consuming inorganic energy sources and survive hypoxia through fermentation. For example, bacteria from at least eight dominant phyla have been experimentally shown to scavenge atmospheric hydrogen and carbon monoxide, including those traditionally thought to be limited to organic carbon, methane, iron, or nitrite oxidation. Through culture-independent work, we have observed that these processes are widespread and active at the ecosystem scale. Most bacteria inhabiting environments worldwide, whether in soils, waters, sediments, or eukaryotic hosts, express enzymes to use alternative inorganic energy sources or mediate fermentation. Metabolic flexibility provides different advantages depending on whether environments are characterised by depletion (e.g. desert soils), variability (e.g. beach sediments), or competition (e.g. human gut) of resources. Finally, I will summarise genomic surveys and genetic studies that suggest human pathogens are also unexpectedly versatile. Metabolic flexibility is likely to be crucial for gastrointestinal colonisation and environmental survival of diarrhoeal pathogens, as well as the long-term persistence of Mycobacterium tuberculosis in the face of nutritional immunity. This multifaceted evidence suggests metabolic flexibility is a trait of the many rather than few. These findings in turn have broad implications for understanding global biodiversity, biogeochemical cycling, and infectious disease.