Bacteria-mediated aggregation of the marine phytoplankton Thalassiosira weissflogii and Nannochloropsis oceanica
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Bacteria-mediated aggregation of the marine phytoplankton Thalassiosira weissflogii and Nannochloropsis oceanica Nhan-An T. Tran 1,2
&
Bojan Tamburic 1,3,4
&
Christian R. Evenhuis 5
&
Justin R. Seymour 1
Received: 5 June 2020 / Revised and accepted: 9 September 2020 # The Author(s) 2020
Abstract The ecological relationships between heterotrophic bacteria and marine phytoplankton are complex and multifaceted, and in some instances include the bacteria-mediated aggregation of phytoplankton cells. It is not known to what extent bacteria stimulate aggregation of marine phytoplankton, the variability in aggregation capacity across different bacterial taxa or the potential role of algogenic exopolymers in this process. Here we screened twenty bacterial isolates, spanning nine orders, for their capacity to stimulate aggregation of two marine phytoplankters, Thalassiosira weissflogii and Nannochloropsis oceanica. In addition to phytoplankton aggregation efficiency, the production of exopolymers was measured using Alcian Blue. Bacterial isolates from the Rhodobacterales, Flavobacteriales and Sphingomonadales orders stimulated the highest levels of cell aggregation in phytoplankton cultures. When co-cultured with bacteria, exopolymer concentration accounted for 34.1% of the aggregation observed in T. weissflogii and 27.7% of the aggregation observed in N. oceanica. Bacteria-mediated aggregation of phytoplankton has potentially important implications for mediating vertical carbon flux in the ocean and in extracting phytoplankton cells from suspension for biotechnological applications. Keywords Environmental biotechnology . Microbial aggregation . Thalassiosira . Nannochloropsis . Microalgae-bacteria interactions
Introduction The ecological interactions between marine phytoplankton and bacteria can vary from mutualistic to parasitic (Amin Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10811-020-02252-8) contains supplementary material, which is available to authorized users. * Nhan-An T. Tran [email protected] 1
Faculty of Science, University of Technology Sydney, Climate Change Cluster, NSW Sydney, Australia
2
Department of Plant Sciences, University of Cambridge, Cambridge, UK
3
Water Research Centre, School of Civil and Environmental Engineering, University of New South Wales Sydney, Sydney, NSW, Australia
4
Algae and Organic Matter (AOM) Laboratory, School of Chemical Engineering, University of New South Wales Sydney, Sydney, NSW, Australia
5
Faculty of Science, University of Technology Sydney, Infection, Immunity and Innovation Institute, NSW Sydney, Australia
et al. 2012) and can strongly influence the physiology, metabolic activity, abundance and growth of both partners (Lee et al. 2000; Grossart and Simon 2007; Buchan et al. 2014). These interactions have been shown to promote microalgal growth (Seyedsayamdost et al. 2011), protect phytoplankton from pathogens (Geng and Belas 2010) or alternatively to inhibit microalgal growth (Mayali and Azam 2004), whil
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