UC San Diego

As a major component of marine snow, bacteria play an important role in the ocean’s biological pump. While it has been demonstrated that bacteria effect aggregation of phytoplankton in vitro, the conditions and process of aggregation for marine bacteria remains poorly understood. In this study, we characterized the aggregation behavior of a particle-associated bacterial isolate Alteromonas sp 4B03. Based on optical density (OD600) measurement, 4B03 rapidly aggregates and disaggregates in the first hour after transferred from acetate minimal media to complex media containing peptides. To quantitatively understand 4B03’s aggregation process following introduction to peptides, we use confocal microscopy to characterize the temporal development of aggregates size distributions. Growth of aggregate size is confirmed, evident in both the drop of single cell density and an increase in the abundance of larger aggregates. Moreover, a model is built for the initial aggregation process which relates single cell dynamics to motility-based encounter rate and stickiness. The model enables estimation of cellular stickiness values using single cell counts from size distributions and measurements of cellular motility. Simulations of aggregates dynamics that take into account cell replication and single cell detachment from aggregates was done to recapitulated experimental findings. To our knowledge, this work offers the first experimental determination of cellular stickiness values in marine bacteria, which may enable incorporation of this important group of organisms into large-scale oceanographic models of aggregation.