Kreb cycle is an aerobic process, and to your question about bacteria doing Kreb cycle ?
That is a no also, because the Kreb cycle occurs at the matrix of the mitochondria, and bacteria does not have mitochondria.
Also, lets use Lamark's theory such as "use it or lose it" where way back then, whenever the animal is aerobic it could go through Kreb and the electron transport chain. Electron transport chain needs oxygen as last electron acceptor. Maybe back 2 million years ago, the anaerobes could go through Kreb cycle, but CANNOT go through etc. Since this been going on for several centuries, the anaerobes realized that going through Kreb cycle route does not benefits them at all. So eventually they turn to fermentation.
Okay, yeah really. Y'all are overlooking this.