Recent research shows that the microbiome represents a crucial and inseparable component of nearly every organism. Together with the host, it forms a holobiont, in which microbes actively influence the physiology, development, and health of the organism. Despite increasing studies on marine holobionts, gelatinous zooplankton, particularly jellyfish, remain understudied as hosts. Jellyfish are characterized by seasonal population blooms that significantly influence ecological and biogeochemical processes in marine environments. To better understand and potentially manage these events, it is essential to investigate factors affecting jellyfish population dynamics, among which the microbiome may play an important role. In this study, we investigated the composition and metabolic activity of the jellyfish microbiome during the transition from a healthy to a senescent host population. Two representatives of gelatinous zooplankton were selected: the comb jelly Mnemiopsis leidyi and the scyphozoan jellyfish Aurelia aurita s.l. These species differ phylogenetically and exhibit distinct life cycles, biochemical composition, and seasonal bloom dynamics in the northern Adriatic Sea. We focused on the bacterial genera Pseudoalteromonas and Vibrio, as prior sequencing of the 16 S rRNA gene from bacterial isolates revealed their dominance in jellyfish mucus, consistent with previous studies. Using fluorescence in situ hybridization (FISH) and epifluorescence microscopy, we demonstrated that microbial density in jellyfish mucus exceeds that in ambient seawater, with Pseudoalteromonas and Vibrio as dominant genera. No major differences in total microbial density were observed between the two species; however, both exhibited a decline in microbial density and shifts in the relative abundance of the selected bacterial genera during host population development. Using the BONCAT approach combined with click chemistry, we confirmed the metabolic activity of Pseudoalteromonas and Vibrio populations in the mucus of Mnemiopsis leidyi. Host biochemical composition, which may change during aging, could influence microbiome composition and functioning. Analysis of protein and amino acid concentrations in jellyfish sampled at different population stages showed changes in both total concentrations and relative amino acid composition. Our results indicate that the microbiome represents a dynamic and potentially important factor in both the life and decay of jellyfish, and that its structure changes simultaneously with host population development and biochemical composition. Although additional studies on a larger number of specimens are required, these findings provide an important contribution to understanding the role of the microbiome in the jellyfish life cycle. Future research should further investigate how changes in host biochemical composition influence microbiome structure and clarify the role of microbial communities in jellyfish blooms within marine ecosystems.
|
