The science of studying genomic fragments from microbial communities, allowing researchers to study genes from a collection of multiple species, is called:
pharmacogenomics
transcriptomics
metagenomics
proteomics

metagenomics

Explanation:

Metagenomics is the study of the collective genome of the microorganisms obtain from the environment. The study can provide details of the microbial diversity and ecology for a particular environment. It allows the identification of the specific microbial species from the mixture of genomic samples. The metagenomics is useful in solving the problems related to other fields such as medicine, agriculture, engineering and ecology.