Question

Martinus beijerinck developed the enrichment culture technique to isolate metabolically-distinct microbes from complex natural samples, like soil and water, by manipulating the

Answer 1

By manipulating the culture conditions and nutrients.  

Enrichment culture refers to the application of some kind of growth media to favor the development of a specific microorganism over the others, elevating a sample for the microorganism, which is of interest. This is usually attained by administrating nutrients or favorable environmental conditions, which permit the development of the desired organism.