I'm taking a microbial physiology course and we noted that, while some archaea are phototrophic, there are no known photosynethetic archaea. Are there any physiological characteristics that make archaea less suited for photosynthesis? Or is it simply a matter of there likely being photosynthetic archaea, but they have not yet been found (which seems like it could easily be the case, given that there are many extremophilic archaea)?
There are photosynthetic archaea (such as Halobacterium) but the mechanism is different. They use rhodopsin-like ion pumps (bacteriorhodopsin and halorhodopsin) to move ions against the gradient and produce ATP via chemiosmosis (like mitochondria).