Although many studies have addressed the role of bacteria in the degradation of organic matter, few have examined how bacteria alter the physicochemical properties of dissolved and colloidal organic matter in coastal systems. Here, we investigate how the sticking properties of transparent exopolymeric particles (TEP) varied with DOM age in batch cultures. We show that in two contrasted sites, despite different initial TEP sticking properties and bulk concentrations, after 48 h, the sticking properties were similar and increased (i.e. TEP became stickier) with increasing DOM age. We propose that TEP occurring after 48 h of incubation are mainly of heterotrophic origin, which is in contrast to the previously identified TEP of autotrophic origin. These results highlight the potential importance of bacterial DOM production, particularly in the aphotic zone, and further underline the potential of bacterial heterotrophs to produce biologically refractory dissolved organic matter that is physically reactive (i.e. sticky).