The present invention uses microfluidics droplets for studying the growth dynamics of communities of bacteria in the presence of various perturbations such as various chemicals or other microorganisms and to establish microbial assemblies model which is representative of a microbiota of interest and to examine their growth dynamics after perturbations such as with an array of chemicals or other microorganisms. In particular, the present invention refers to a method and apparatus for assessing the effect of a chemical or biological substance on the growth of microorganisms.