Production of individual marine organic aggregates using Paramagnetic Microspheres: A new tool for examining microbial associations with aggregates

Abstract

We describe a new method to produce marine aggregates from natural organic material based on the sticking properties of transparent exopolymeric particles. Seawater samples were prescreened and ultrafiltered to concentrate the 30 kDa to 10 µm size fraction. First, we produced small magnetizable aggregates by combining glass microfibers and paramagnetic 1‐µm beads with the organic matter present in the concentrated solution. The second step involved clustering the small aggregates into a single macro‐aggregate, using a small ringshaped magnet as an aggregation nucleus. Viral and bacterial densities, determined after dissolution of the newly formed aggregates with methanol, averaged 13.8 × 106 ± 3.6 × 106 vir. agg.−1 and 4.1 × 106 ± 1.1 × 106 bact. agg.−1. Bacterial respiration and production measurements of single aggregates averaged 8.47 ± 1.72 nmol O2 agg.−1 h−1 and 1.54 ± 0.45 ng C agg.−1 h−1, respectively. Particulate organic carbon and nitrogen content of the newly formed macro‐aggregates averaged 31.92 ± 2.67 µg C agg.−1 and 3.44 ± 0.43 µg N agg.−1, respectively. This approach allows the concentration and isolation of the organic matter precursors that compose natural aggregates and provides a simple protocol for recombining those precursors into single newly formed macro‐aggregates, which can then be easily manipulated for further investigation. This method is a new tool for investigations into the interactions between microorganisms and marine aggregates and their implications at the ecosystem level, but also into the interactions between aggregates and dissolved organic or inorganic substances.