Chemotaxis toward phytoplankton drives organic matter partitioning among marine bacteria

Abstract

The microenvironment surrounding individual phytoplankton cells is often rich in dissolved organic matter (DOM), which can attract bacteria by chemotaxis. These "phycospheres" may be prominent sources of resource heterogeneity in the ocean, affecting the growth of bacterial populations and the fate of DOM. However, these effects remain poorly quantified due to a lack of quantitative ecological frameworks. Here, we used video microscopy to dissect with unprecedented resolution the chemotactic accumulation of marine bacteria around individual Chaetoceros affinis diatoms undergoing lysis. The observed spatiotemporal distribution of bacteria was used in a resource utilization model to map the conditions under which competition between different bacterial groups favors chemotaxis. The model predicts that chemotactic, copiotrophic populations outcompete nonmotile, oligotrophic populations during diatom blooms and bloom collapse conditions, resulting in an increase in the ratio of motile to nonmotile cells and in the succession of populations. Partitioning of DOM between the two populations is strongly dependent on the overall concentration of bacteria and the diffusivity of different DOM substances, and within each population, the growth benefit from phycospheres is experienced by only a small fraction of cells. By informing a DOM utilization model with highly resolved behavioral data, the hybrid approach used here represents a new path toward the elusive goal of predicting the consequences of microscale interactions in the ocean.bacteria-phytoplankton interactions | motility | competition | microbial loop | dissolved organic matter

Interkingdom Cross-Feeding of Ammonium from Marine Methylamine-Degrading Bacteria to the Diatom Phaeodactylum tricornutum

“…As our results suggest that interactions of diatoms with MMA-degrading bacteria are profitable in marine environments, it appears to be an attractive hypothesis that diatoms may release molecules to attract methylamine-degrading bacteria. In agreement with this hypothesis, it has been shown that bacteria can employ chemotaxis to approach and get established within the phycosphere (8,(50)(51)(52). To our knowledge, molecules that specifically attract methylotrophic bacteria are not known so far.…”

Ubiquitous marine bacterium inhibits diatom cell division

“…A thin boundary layer of fluid termed 'the phycosphere' surrounds algal cells (Bell and Mitchell, 1972). In the phycosphere, molecular gradients are governed by diffusion (Lazier and Mann, 1989) and altered by the activities of bacteria that accumulate through chemotaxis (Stocker and Seymour, 2012;Smriga et al, 2016) and reproduction. As the thickness of diffusive boundary layers scales with surface area (Karp-Boss et al, 1996), larger phytoplankton may harbor more bacteria than smaller phytoplankton.…”

Determination and Analysis of Kinetic Parameters of Heterotrophic Bacteria in Mathematical Simulation

“…From the above equations (Eqs. [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18], the maximum rate of growth is calculated from the slope as shown in the following table. From Table 3 it can be seen that the results of the maximum specific growth rate of heterotrophic bacteria show that the use of BI-2000 electrolyte respiration rate analyzer, the range is large and the range is roughly 7.72 d-1-10.05 d-1, the average is 8.6 d -1 compared with ASM1 model.…”

“…Therefore, it is very important to determine the kinetic parameters of heterotrophic bacteria. As a method recommended by International Water Association (IWA), respiration measurement has applied successfully to the determination of stoichiometry and kinetic parameters of wastewater (Smriga et al, 2016) and for the determination of Chemical Oxygen Demand (COD) components .…”