Microbiology is the study of small organisms, unicellular or cell-cluster microscopic organisms. This includes microscopic fungi and protists and bacteria, certain algae and viruses. Microbiology is a broad term which includes many branches like virology, mycology, parasitology and others.
Molecular Biology
Molecular biology is the study of biology at a molecular level. The field overlaps with other areas of biology and chemistry in particular genetics and biochemistry. Molecular biology attempts to understand the interactions between the various systems of a cell, including the interactions between DNA, RNA and protein biosynthesis and how these interactions are regulated.
Molecular Microbiology
Molecular microbiology is the molecular biology of microorganisms.