Microbiologists
Microbiologists specialize in studying microorganisms, but other biologists can study them to a lesser extent as part of their fields.
You call someone that studies metal a metallurgist.
A physicist.
a person who studies planets is a planetologist.
There is no special name for someone who studies Hebrew.
An Anthropologist.
malacologist
euclidist
Gemologists
psychologist
A numismatist.
A Zoologist