Mitochondria are derived from bacteria.
"Mitochondria are bacteria. But that's the part that when I wrote a paper about this in undergrad, you'll be proud of me. I I wrote a whole paper about how mitochondria were bacteria when I was in like junior year." (said at 0:28:20)
The endosymbiotic theory of mitochondrial origin is established evolutionary biology. Modern genomic and phylogenetic analyses demonstrate that all eukaryotic mitochondria derived from an ancestral endosymbiotic alphaproteobacterium that integrated into an archaeal host cell. While modern mitochondria function as specialized cellular organelles rather than independent bacteria, their bacterial ancestry is supported by overwhelming phylogenetic, genetic, and structural evidence.
- supports: The Origin and Diversification of Mitochondria. (Current biology : CB 2017)
"all mitochondria derive from a common ancestral organelle that originated from the integration of an endosymbiotic alphaproteobacterium into a host cell related to Asgard Archaea. The transition from endosymbiotic bacterium to permanent organelle entailed a massive number of evolutionary changes including the origins of hundreds of new genes and a protein import system" (abstract, passage verified)
pubmedfull study (doi) - supports: Site-and-branch-heterogeneous analyses of an expanded dataset favour mitochondria as siste… (Nature ecology & evolution 2022)
"Determining the phylogenetic origin of mitochondria is key to understanding the ancestral mitochondrial symbiosis and its role in eukaryogenesis... The consilience of evidence thus suggests that mitochondria are sister to the Alphaproteobacteria" (abstract)
pubmedfull study (doi)