Soil is the richest source of bacteria.
 

Concept: Bacteria perform important functions in the soil, decomposing organic residues from enzymes released into the soil. 
Ingham (2009) describes the four major soil bacteria functional groups as decomposers, mutualists, pathogens, and lithotrophs. 
Each functional bacteria group plays a role in recycling soil nutrients.
Hence, option 1 is correct.