Before revision:  A generically observed mechanism that drives URLanization is interaction among the individual elements---which may represent cells, bacteria, or even enzymes---via chemical signals. We develop a systematic coarse-graining scheme using which we can construct a general theoretical framework to study many-body effects in chemotactic populations. The framework unveils a polarization-induced coupling term , which originates from quorum effects and can compete with the chemotactic drift term.
After revision:  A generically observed mechanism that drives URLanization is interaction among the individual elements---which may represent cells, bacteria, or even enzymes. Here we propose a novel mechanism for such interactions, in the context of chemotaxis , which originates from quorum effects and can compete with the chemotactic drift term.