His achievements have been perhaps unfairly overshadowed by those of his contemporaries, Robert Koch and Louis Pasteur, because unlike them, Beijerinck never studied human disease.

[4][5][6][7] In 1898, he published results on the filtration experiments demonstrating that tobacco mosaic disease is caused by an infectious agent smaller than a bacterium.

Beijerinck asserted that the virus was somewhat liquid in nature, calling it "contagium vivum fluidum" (contagious living fluid).

In addition to having discovered a biochemical reaction vital to soil fertility and agriculture, Beijerinck revealed this archetypical example of symbiosis between plants and bacteria.

He is often incorrectly credited with framing the microbial ecology idea that "everything is everywhere, but, the environment selects", which was stated by Lourens Baas Becking.

His low popularity with his students and their parents periodically depressed him, as he very much loved spreading his enthusiasm for biology in the classroom.

After his retirement at the Delft School of Microbiology in 1921, at age 70, he moved to Gorssel where he lived for the rest of his life, together with his two sisters.