Abstract
Microalgal–bacterial interactions are commonly found in marine environments and are well known in diatom cultures maintained in laboratory. These interactions also exert strong effects on bacterial and algal diversity in the oceans. Small green eukaryote algae of the class Mamiellophyceae (Chlorophyta) are ubiquitous and some species, such as Ostreococcus spp., are particularly important in Mediterranean coastal lagoons, and are observed as dominant species during phytoplankton blooms in open sea. Despite this, little is known about the diversity of bacteria that might facilitate or hinder O. tauri growth. We show, using rDNA 16S sequences, that the bacterial community found in O. tauri RCC4221 laboratory cultures is dominated by γ-proteobacteria from the Marinobacter genus, regardless of the growth phase of O. tauri RCC4221, the photoperiod used, or the nutrient conditions (limited in nitrogen or phosphorous) tested. Several strains of Marinobacter algicola were detected, all closely related to strains found in association with taxonomically distinct organisms, particularly with dinoflagellates and coccolithophorids. These sequences were more distantly related to M. adhaerens, M. aquaeoli and bacteria usually associated to euglenoids. This is the first time, to our knowledge, that distinct Marinobacter strains have been found to be associated with a green alga in culture.
Highlights
Phytoplankton, together with viruses, bacteria, and micrograzers constitute different communities of species which all play fundamental roles in the functioning of microbial food web (Buchan et al, 2014)
The latency and decline phases are advantageous for the development of LNA bacteria while the exponential phase is more suitable for the development of HNA bacteria
The proportion of LNA bacteria increases when cultivated in F/2-ESAW 50%N and F/2ESAW 10%P media compared to L1-MOLA medium and are predominant in F/2-ESAW medium whatever the photoperiod condition (Figure 3B)
Summary
Phytoplankton, together with viruses, bacteria, and micrograzers constitute different communities of species which all play fundamental roles in the functioning of microbial food web (Buchan et al, 2014). Phytoplankton and bacterial communities are closely linked in coastal marine environments (Fuhrman et al, 1980; Rooney-Varga et al, 2005; Amin et al, 2015) and bacterial–algal interactions play a major role in determining bacterial and algal diversity in the ocean (Schäfer et al, 2002). Detailed knowledge of these interactions is crucial for understanding marine ecosystems. Bacteria can even kill the algae by the secretion of algicidal compounds (Mayali and Azam, 2004)
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