Antibiotics reduce Pocillopora coral‐associated bacteria diversity, decrease holobiont oxygen consumption and activate immune gene expression

Abstract

Corals are important models for understanding invertebrate host-microbe interactions; however, to fully discern mechanisms involved in these relationships, experimental approaches for manipulating coral-bacteria associations are needed.Coral-associated bacteria affect holobiont health via nutrient cycling, metabolic exchanges and pathogen exclusion, yet it is not fully understood how bacterial community shifts affect holobiont health and physiology. In this study, a combination of antibiotics (ampicillin, streptomycin and ciprofloxacin) was used to disrupt the bacterial communities of 14 colonies of the reef framework-building corals Pocillopora meandrina and P. verrucosa, originally collected from Panama and hosting diverse algal symbionts (family Symbiodiniaceae). Symbiodiniaceae photochemical efficiencies and holobiont oxygen consumption (as proxies for coral health) were measured throughout a 5-day exposure. Antibiotics altered bacterial community composition and reduced alpha and beta diversity, however, several bacteria persisted, leading to the hypothesis that these bacteria are either antibiotics resistant or occupy internal niches that are shielded from antibiotics. While antibiotics did not affect Symbiodiniaceae photochemical efficiency, antibiotics-treated corals had lower oxygen consumption rates. RNAseq revealed that antibiotics increased expression of Pocillopora immunity and stress response genes at the expense of cellular maintenance and metabolism functions. Together, these results reveal that antibiotic disruption of corals' native bacteria negatively impacts holobiont health by decreasing oxygen consumption and activating host immunity without directly impairing Symbiodiniaceae photosynthesis, underscoring the critical role of coral-associated bacteria in holobiont health. They also provide a baseline for future experiments that manipulate Pocillopora corals' symbioses by first reducing the diversity and complexity of coral-associated bacteria.

Microbiome depletion and recovery in the sea anemone, Exaiptasia diaphana , following antibiotic exposure

“…It is likely that our colony forming unit assay, which allowed us to show that bacterial load is reduced in treated anemones, missed key bacterial groups that remain refectory to cultivation on marine agar. However, our results are consistent with previous work in cnidarians which showed that antibiotics reduced the abundance of bacteria within the host microbiome following 5–7 days of exposure ( 33 , 35 , 46 , 47 ). Surprisingly, our community composition analysis revealed that the microbiome only shifted in treated anemones during recovery.…”

“…1 ). The priming stage enables the initial depletion of the Aiptasia microbiome ( 43 ), while exposure to each of the antibiotic solutions during the treatment phase helps to reduce the cnidarian microbial load ( 33 , 35 , 42 , 47 ). Throughout the experiment, anemones were reared in six-well plates at 25°C and 12 h light:12 h dark cycle using 44 ± 15 µmol photon/m 2 /s light levels, in either artificial seawater (ASW; control group; Coral Pro Red Sea Salt Salinity 35 ppt) or 0.2 µm filtered artificial seawater (FASW; treatment groups).…”

Microbiome depletion and recovery in the sea anemone,Exaiptasia diaphana, following antibiotic exposure

“…In our study, we showed that antibiotic solutions decreased the microbial load and composition of the Aiptasia microbiome. Our primary finding is consistent with previous work in cnidarians which showed that antibiotics reduced the abundance of bacteria within the host microbiome following 5-7 days of exposure (31,33,43,44). Surprisingly, our community composition analysis revealed that the microbiome only shifted in treated anemones during recovery.…”

“…1A). The priming stage enables the initial depletion of the Aiptasia microbiome (40), while exposure to each of the antibiotic solutions during the treatment phase helps to reduce the cnidarian microbial load (31,32,44,50).…”

Microbial influence on the larval survival of Japanese eel Anguilla japonica: Antibiotic-mediated alterations and biomarker isolation

“…Zhongshania (ASV 23) is dominant in sediments and seawater polluted with crude oil and aromatic compounds, and potentially degrade alkane and aromatics, respectively [ 47 , 48 ]. The bacteria in the genus Kordiimonas (ASV 27 and 38) are common within coral holobiont and are thought to be one of the bacteria with important functions [ 49 ]. Aliikangiella (ASV 41) had a differentially abundant ASV in large size oysters than in small size oysters, indicating that it appears to have roles in nutrient absorption and energy acquisition [ 50 ].…”