Cause of Psoriasis: Likely Virus or Cell-Wall-Deficient Bacteria/Mycoplasma
I think that the cause is some type of pathogen like virus, mycoplasma  or some CWD (cell wall deficient) bacteria (maybe Streptococcus since a lot of psoriatics develop psoriasis after a Strep throat (Streptococcal pharyngitis)– however we should consider also the effects of antibiotics which most people use for strep throat).
It is quite possible that some type of virus is involved which infects the CWD bacteria/mycoplasma and changes its behavior and just this combination of pathogens leads to psoriasis. There is also a chance that psoriasis plaques can be caused by some bacteria (which have normal cell wall) in the skin, however in my opinion it is very unlikely because the antibiotics would cure the plaques in a few days in the most people, which is not the case despite taking the strong antibiotics (the most antibiotics work by inhibiting the bacterial cell wall synthesis) for a few weeks.
Some of the black dots are the bacteria in the blood of psoriatic
I think these pathogens – CWD bacteria, mycoplasma or virus – are located in the skin where the psoriasis plaques are formed. Don’t the plaques look like the bacterial colonies in the petri dish? Or maybe like a mold on the bread? Yes, the pathogens when spreading they usually form the circles. Mycoplasma is very similar to virus since it doesn’t have a cell wall (which is targeted by antibiotics) but still spreads forming the circles.
|Mold on the food looks similar like the guttate psoriasis|
Actually it doesn’t matter if psoriasis is caused by bacteria, virus or mycoplasma in the skin. Because all three will be destroyed when enough oxygen gets to the skin since they are low life forms that live in anaerobic environment – the places with just very low oxygen content or even completely without oxygen. The oxygen kills many harmful bacteria, helps the immune system to fight off the infections and supports it to work more effectively. 
Always in any disease look for the infections. The pathogens use many different ways how to invade the human body and subvert the immune system.