Changes in bacterioplankton composition under different phytoplankton regimens

Area of Science:

• Marine microbial ecology
• Oceanography
• Bacterioplankton and phytoplankton interactions

Background:

• Empirical studies show links between phytoplankton and bacterioplankton, often correlating chlorophyll a with bacterial abundance and production.
• However, knowledge of these interactions at the specific taxonomic group level remains limited.

Purpose of the Study:

• To investigate the influence of distinct phytoplankton communities on bacterioplankton composition.
• To identify specific bacterial taxa responding to different phytoplankton bloom types.

Main Methods:

• Seawater microcosm experiments were conducted in the northwestern Mediterranean Sea.
• Turbulence was used to induce phytoplankton blooms dominated by diatoms, while still conditions favored phytoflagellates.
• Bacterioplankton community composition was analyzed using denaturing gradient gel electrophoresis (DGGE) of 16S rRNA gene fragments and sequencing.

Main Results:

• Changes in phytoplankton composition, induced by turbulence, led to shifts in bacterioplankton community structure.
• Specific bacterial phylotypes, including Roseobacter, Bacteroidetes (Cryomorphaceae, Flavobacteriaceae), Alphaproteobacteria, and Gammaproteobacteria, were associated with different phytoplankton bloom conditions.
• Flavobacteriaceae members showed a strong response to phytoplankton blooms, suggesting their role in organic matter processing.

Conclusions:

• Phytoplankton species composition quantitatively and qualitatively influences bacterioplankton species composition.
• Bacterioplankton communities are highly responsive to the type of phytoplankton bloom, indicating specific ecological roles.
• This highlights the importance of phytoplankton diversity in structuring marine microbial food webs.