Interspecific interactions in biofilms have been shown to cause the emergence of community-level properties. To understand the impact of interspecific competition on evolution, we deep-sequenced the dispersal population of mono- and co-culture biofilms of two antagonistic marine bacteria (Phaeobacter inhibens 2.10 and Pseudoalteromononas tunicata D2). we aim to understand if the presence or absence of interspecific competition influences their degree of genetic variation and, if so, which genes are affected. We applied deep-sequencing to dispersal cell populations derived from mono-culture (i.e., intraspecific competion conditions) or co-culture (i.e., interspecific competition conditions) biofilms of the two organisms over a period of 42 days.