The Effect of Light on Bacterial Activity in a Seaweed Holobiont
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Holobionts are characterized by the relationship between host and their associated organisms such as the biofilm associated with macroalgae. Considering that light is essential to macroalgae survival, the aim of this study was to verify the effect of light on the heterotrophic activity in biofilms of the brown macroalgae Sargassum furcatum during its growth cycle. Measurements of heterotrophic activity were done under natural light levels at different times during a daily cycle and under an artificial extinction of natural light during the afternoon. We also measured Sargassum primary production under these light levels in the afternoon. Both measurements were done with and without photosynthesis inhibitor and antibiotics. Biofilm composition was mainly represented by bacteria but diatoms, cyanobacteria, and other organisms were also common. When a peak of diatom genera was recorded, the heterotrophic activity of the biofilm was higher. Heterotrophic activity was usually highest during the afternoon and the presence of a photosynthesis inhibitor caused an average reduction of 17% but there was no relationship with Sargassum primary production. These results indicate that autotrophic production in the biofilm was reduced by the inhibitor with consequences on bacterial activity. Heterotrophic activity was mainly bacterial and the antibiotics chloramphenicol and penicillin were more effective than streptomycin. We suggest primary producers in the biofilm are more important to increase bacterial activity than the macroalgae itself because of coherence of the peaks of heterotrophic and autotrophic activity in biofilm during the afternoon and the effects of autotrophic inhibitors on heterotrophic activity.
KeywordsProkaryotic-eukaryotic interaction Sun light Autotrophic-heterotrophic production Leucine incorporation Specific metabolic inhibitors Brazilian upwelling
We thank the IEAPM logistic support, especially to the Department of Oceanography (specially Antônio Casarin), the Department of Chemistry, Division of Biotechnology Lab team, and LEG 10 team. We also thank Ana Carolina Mazzuco, María Soledad López, Fernanda Siviero, Estevão de Souza, Dagles Viana dos Reis, and William Romão. Thank you for the comments from the anonymous referee that improved this manuscript. This work was supported by CAPES, CNPq, and FAPERJ.
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