Abstract
Algal-bacterial associations were studied in unialgal xenic cultures of Synedra acus subsp. radians, Asterionella formosa and Fragillaria crotonensis planktonic diatoms from Lake Baikal, using epifluorescent and scanning electron microscopy. It was found that rod- and ovoid-shaped bacteria colonized cell walls of diatoms. Cloning and sequencing of fragments of 16S rRNA gene in diatom cultures revealed members of Gammaproteobacteria (Pseudomonas sp.), Betaproteobacteria (Janthinobacterium sp., Hydrogenophaga sp., Methylophilus sp.), Bacteroidetes (Flavobacterium sp., Pedobacter sp.), and Acinobacteria (Nocardioides sp.).
Highlights
Phytoplankton and bacteria play a key role in biogeochemical cycles in aquatic ecosystems (Cole, 1982; Azam, Malfatti, 2007)
Diatom cells differed in size (Table 1, Fig. 2)
Free-living bacteria and diatom-attached bacteria were found in cultures
Summary
Phytoplankton and bacteria play a key role in biogeochemical cycles in aquatic ecosystems (Cole, 1982; Azam, Malfatti, 2007). Diatom cells are surrounded by phycosphere containing extracellular metabolites that stimulate growth of heterotrophic bacteria (Amin et al, 2012; Seymour et al, 2017). Relationships between diatoms and bacteria vary from symbiotic to commensal to parasitic (Cole, 1982; Amin et al, 2012). Heterotrophic bacteria associated with phytoplankton consume organic matter produced by live algae or generated during their lysis (Riemann et al, 2000; Azam, Malfatti, 2007). Composition and physiological characteristics of diatom-associated bacteria are typically studied using lab cultures (Schäfer et al, 2002; Grossart et al, 2005; Sison-Mangus et al, 2014; Mila et al, 2018). Bacteria produce vitamins necessary for microalgae growth (Croft et al, 2005)
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