Microbial metabolism covers an astonishing range of ways bacteria and other microorganisms actually extract usable energy, from familiar sugar fermentation all the way to metabolising sulfur, iron or methane in environments with no oxygen and no sunlight whatsoever. Microbial genetics, including genes that move directly between separate bacterial cells rather than only down a single parent-to-offspring lineage, is part of why that metabolic range keeps expanding, a useful metabolic trick discovered in one bacterial lineage doesn't have to stay confined to its own descendants.
Many microbes get energy in ways that don't need oxygen or sunlight at all
Beyond familiar aerobic respiration and fermentation, many microorganisms use entirely different electron acceptors in place of oxygen, sulfate, nitrate or iron among them, extracting usable energy through chemistry most other life can't rely on. Some go further still, using chemosynthesis, extracting energy directly from inorganic chemical reactions rather than from sunlight or organic food, which is exactly what lets certain microbial communities thrive in genuinely extreme environments, deep-sea hydrothermal vents and anoxic sediments among them, that would be lethal or simply unusable to most other life on Earth.
Genes can move directly between bacterial cells, independent of reproduction entirely
Horizontal gene transfer, moving genetic material directly from one bacterial cell to another through conjugation, transformation or transduction, is a genuinely different mode of genetic change from the vertical, parent-to-offspring inheritance most genetics teaching focuses on. A useful new metabolic capability discovered through mutation in one bacterial lineage can spread directly into an entirely different, unrelated lineage this way, without either lineage having to reproduce with the other at all, which is part of why microbial metabolic diversity as a whole can expand and spread considerably faster than ordinary evolutionary inheritance alone would predict.
What we're still unsure about
That microbes use a genuinely wide range of metabolic strategies, and that horizontal gene transfer moves genetic material directly between bacterial cells, are well established, extensively documented microbiology. What's more genuinely disputed is that horizontal gene transfer means a bacterial genome isn't really one stable, well-defined thing the way a plant or animal genome is usually treated, since genes can move in and out of it independent of reproduction, and exactly how much this blurs the traditional idea of a bacterial species as a distinct, coherent genetic unit remains a genuinely open, actively debated definitional question among microbiologists rather than a settled matter.
This sits inside Microbial Metabolism & Genetics, one of seven topics in Microbiology, one of six domains in Biology, one of seventeen subjects the app can quiz you on.