Marine organic aggregates are sites of high of viral accumulation; however, still little is known about their colonization processes and interactions with their local bacterial hosts. By taking advantage of a novel approach (paramagnetic functionalized microsphere method) to create and incubate artificial macroaggregates, we examined the small-scale movements of viruses and bacteria between such marine snow particles and the surrounding water. The examination of the codynamics of both free-living and attached viral and bacterial abundance, over 12 hours of incubation in virus-free water, suggests that aggregates are rather comparable to viral factories than to viral traps where a significant part of the virions production might be locally diverted to the water column. Also, the near-zero proportion of lysogenized cells measured in aggregates after mitomycin-C induction seems to indicate that lysogeny is not a prominent viral reproduction pathway in organic aggregates where most viruses might rather be virulent. Finally, we hypothesize that, contrary to bacteria, which can use both strong attachment and detachment from aggregates (two-way motion of bacteria), the adsorption of planktonic viruses appears to be numerically negligible compared to their massive export from the aggregates into the water column (one-way motion of viruses).
