Antibiotic pollution alters the microbiome and reduces primary production and growth in the seagrass Cymodocea nodosa (Ucria) Ascherson

Abstract

Antibiotics are considered a contaminant of emerging concern that can affect marine plants and their associated microbiome. To date, limited information is available about the effects of antibiotic pollution on seagrasses. Here, we conducted a seven-day mesocosm experiment in which we exposed the seagrass Cymodocea nodosa to a cocktail of ampicillin, streptomycin, and amoxicillin (with two total concentration exposure levels of 20 and 200 μ g L 1 2 1 ). At the end of the incubation, we assessed phyllosphere and rhizosphere microbiome composition, plant growth, and carbon metabolism. We found that the seagrass community switched from a highly autotrophic in control (19.41 mmol C m d m 2 d 1 ) to a moderately heterotrophic in the high-exposure treatment ( 2.74 mmol C ). This decrease in net community production was attributed to (i) a reduction in photosynthetic pigments (from 20 % to 41 %) due to antibiotic-induced oxidative stress in the seagrass chloroplasts and (ii) a change in the phyllosphere that showed lower species richness and abundance (from x0.3 to x0.7-fold lower) in exposure treatments compared to control. Although most bacterial families showed a reduced relative abundance under antibiotic stress, some taxa, including Pseudoalteromonadaceae, Halomonadaceae, and Cellvibrionaceae, were markedly enriched in the phyllosphere. Our results show that phyllosphere bacterial community is more sensitive to antibiotic pollution in the seawater column than rhizosphere community. Long-term antibiotic stress may also promote the development of seagrass diseases. Overall, our results suggest that antibiotic exposure may reduce seagrass growth and health and may compromise their function as a blue carbon sink.