UC San Diego

Marine bacteria are responsible for a significant portion of decomposition and recycling of the organic matter produced by primary production. Moreover, these bacteria can impact the distribution of organic matter within the water column by driving aggregation and sinking of various particles in a pathway known as the biological carbon pump. The process of aggregation can be driven by bacteria which are able to stick to one another as well as to particles. While bacteria within the ocean experience a nutrient depleted environment with occasional encounters of nutrient hotspots, we know little about how this may impact their aggregative behaviors. After examining eleven strains derived from nine species of marine bacteria cultured in minimal medium with twenty-nine distinct carbon sources, distinct patterns in aggregation and growth behaviors of these bacteria have emerged. We observed many cases in which cell-cell aggregation can be triggered during growth by the presence of certain dissolved nutrients. Each strain has a unique combination of nutrients which support growth or aggregation. We categorize the strains into three types of responses: constitutive-aggregator, selective-aggregator, and non-aggregators. Constitutive and selective aggregators appear to be metabolic generalists, while non-aggregators show a preference for growth on acids. In a few cases aggregation occurred without bacterial growth. Certain carbon sources had a bias towards triggering aggregation in strains which grew with them, while others demonstrated an even split between growth with and without aggregation. The findings indicate a trend in aggregation behaviors which appears to be nutrient and strain specific.