Distinct glycoconjugate cell surface structures make the pelagic diatom Thalassiosira rotula an attractive habitat for bacteria

Abstract

Interactions between marine diatoms and bacteria have been studied for decades. However, the visualization of physical interactions between these diatoms and their colonizers is still limited. To enhance our understanding of these specific interactions, a new Thalassiosira rotula isolate from the North Sea (strain 8673) was characterized by scanning electron microscopy and confocal laser scanning microscopy (CLSM) after staining with fluorescently labeled lectins targeting specific glycoconjugates. To investigate defined interactions of this strain with bacteria the new strain was made axenic and co‐cultivated with a natural bacterial community and in two‐ or three‐partner consortia with different bacteria of the Roseobacter group, Gammaproteobacteria and Bacteroidetes. The CLSM analysis of the consortia identified six out of 78 different lectins as very suitable to characterize glycoconjugates of T. rotula. The resulting images show that fucose‐containing threads were the dominant glycoconjugates secreted by the T. rotula cells but chitin and to a lesser extent other glycoconjugates were also identified. Bacteria attached predominantly to the fucose glycoconjugates. The colonizing bacteria showed various attachment patterns such as adhering to the diatom threads in aggregates only or attaching to both the surfaces and the threads of the diatom. Interestingly the colonization patterns of single bacteria differed strikingly from those of bacterial co‐cultures, indicating that interactions between two bacterial species impacted the colonization of the diatom. Our observations help to better understand physical interactions and specific colonization patterns of distinct bacterial mono‐ and co‐cultures with an abundant diatom of costal seas.

The diatom Thalassiosira rotula induces distinct growth responses and colonization patterns of Roseobacteraceae, Flavobacteria and Gammaproteobacteria

“…This strain was isolated from T. rotula and presumably is a member of the bacterial core community of this diatom (Amin et al, 2015;Mönnich et al, 2020). Previous observations showed that this strain adheres to tuft-like structures of this diatom, which are visible only by CLSM after staining with fluorescent lectins, and/or forms aggregates (Tran et al, 2023). Our findings are in line with these observations but our microscopic inspection did not detect the tuft-like structures visible by CLSM.…”

“…However, physical interactions and colonization patterns of these bacteria and algae and aggregates have been studied only little. It has been shown that Roseobacteraceae and Flavobacteriales colonize distinct surface structures of diatom cells and aggregates (Bennke et al, 2013; Grossart, 1999; Tran et al, 2023). However, it is still unknown whether distinct bacterial taxa dwelling in association with algae preferentially colonize algal cells or their aggregated organic matter such as EPS or Transparent Exopolymeric Particles (TEP; Passow, 2000) or do not establish tight physical interactions and prefer to remain free‐living.…”

“…To deepen our understanding of DCOL and AGG bacteria we set up experiments with an axenic diatom, Thalassiosira rotula , and studied its colonization by members of Roseobacteraceae , Flavobacteriaceae and Gammaproteobacteria . This diatom belongs to one of the globally most prominent diatom genera (Malviya et al, 2016) and we used an isolate obtained recently from the North Sea (Tran et al, 2023). To test the hypothesis that different bacteria and bacterial consortia exhibit distinct colonization patterns of DCOL and AGG cells, strains of Roseobacteraceae and Flavobacteriaceae , either isolated from or known to co‐occur with this diatom were grown together with T. rotula in two or three partner treatments.…”

Marine particle microbiomes during a spring diatom bloom contain active sulfate-reducing bacteria

“…3a), are known to form aggregates (Thornton 2002). For example, several species of Thalassiosira extrude long chitin fibrils, which prevent sinking and bind exopolymeric substances (EPS) also produced by the algal cells (Den et al 2023, Herth & Barthlott 1979). This creates a favorable environment for bacteria to attach, which can in turn stimulate algal EPS production (Gärdes et al 2011).…”

The cell surface of a diatom from the bacterial perspective

“…Using these methods, Tran et al (2023) investigate diatom‐bacteria interactions and the diversity of glycoconjugates of Thalassiosira rotula , a widely distributed diatom in marine environments. The authors screened 78 commercially available fluorescent lectins and found six lectins that bind to glycoconjugates on T. rotula cells.…”