Bacterial communities of juvenile corals infected with different Symbiodinium (dinoflagellate) clades

The coral holobiont consists of the host and its microbial partners, including the dinoflagellate endosymbiont Symbiodinium and bacteria living both on and within coral tissues. Although genetically different, Symbiodinium types have been shown to differentially affect the physiology of\ud the coral host; their effects on the bacterial partners in the association are unknown. The present study compares profiles of the bacterial communities associated with juvenile corals of Acropora millepora and A. tenuis that had been experimentally infected with 2 different clades of Symbiodinium, Clade C1 and D, to investigate possible interactions between bacterial and Symbiodinium\ud communities. Three culture-independent 16S rRNA gene profiling methods (clone library construction,\ud terminal restriction length polymorphism and denaturing gradient gel electrophoresis) revealed no discernible pattern in bacterial communities on 9 mo old juvenile corals containing different clades of zooxanthellae, suggesting that coral-associated bacteria are not linked to Symbiodinium types in hospite in early ontogeny. In contrast to bacterial profiles of adult corals, bacterial communities associated with juvenile corals were highly variable, indicating that bacterial associates are not\ud conserved in these early stages. When 12 mo old juveniles were sampled again in summer, bacterial communities associated with A. tenuis hosting Clade D Symbiodinium were dominated by sequences affiliating with Vibrio species, indicating that corals harbouring this symbiont may be more susceptible to temperature stress, allowing growth of opportunistic microbial community members possibly\ud detrimental to coral health

Methods for sampling free-living Symbiodinium (zooxanthellae) and their distribution and abundance at Lizard Island (Great Barrier Reef)

The abundance and distribution of free-living dinoflagellates in the genus Symbiodinium have important implications for the ecology of coral reefs, determining both the symbionts available to newly recruited corals and symbiont types available for uptake by adult corals during environmental stress. However, little is known about where symbiotic dinoflagellates reside outside the host, due to the difficulty of capturing and detecting unicellular organisms in the marine environment. This study presents a successful protocol for sampling Symbiodinium from both the benthos and the water column. Comparisons of two detection methods for enumerating Symbiodinium indicated that conventional microscope analysis is accurate and more efficient when estimating Symbiodinium densities in sediment samples, while an automated particle counter (FlowCAM) was more efficient in detecting cells in the water column where densities are low. Symbiodinium densities were found to be relatively high (1000–4000 cells/mL) in sediment samples and much lower (up to 80 cells/mL) in the water column, indicating that the free-living form resides mainly in the benthos. Symbiodinium densities were found to be highly variable spatially, differing significantly between two reef locations. Within sites, elevated densities of Symbiodinium along reef margins combined with significant decreases in densities one meter away from the reef, suggest that cells aggregate within the reef habitat

Coastal urbanization influences human pathogens and microdebris contamination in seafood

Seafood is one of the leading imported products implicated in foodborne outbreaks worldwide. Coastal marine environments are being increasingly subjected to reduced water quality from urbanization and leading to contamination of important fishery species. Given the importance of seafood exchanged as a global protein source, it is imperative to maintain seafood safety worldwide. To illustrate the potential health risks associated with urbanization in a coastal environment, we use next-generation high-throughput amplicon sequencing of the 16S ribosomal RNA gene combined with infrared spectroscopy to characterize and quantify a vast range of potential human bacterial pathogens and microdebris contaminants in seawater, sediment and an important oyster fishery along the Mergui Archipelago in Myanmar. Through the quantification of >1.25 million high-quality bacterial operational taxonomic unit (OTU) reads, we detected 5459 potential human bacterial pathogens belonging to 87 species that are commonly associated with gut microbiota and an indication of terrestrial runoff of human and agricultural waste. Oyster tissues contained 51% of all sequenced bacterial pathogens that are considered to be both detrimental and of emerging concern to human health. Using infrared spectroscopy, we examined a total of 1225 individual microdebris particles, from which we detected 78 different types of contaminant materials. The predominant microdebris contaminants recovered from oyster tissues included polymers (48%), followed by non-native minerals (20%), oils (14%) and milk supplement powders (14%). Emerging technologies provide novel insights into the impacts of coastal development on food security and risks to human and environmental health

Diversities of coral-associated bacteria differ with location, but not species, for three acroporid corals on the Great Barrier Reef

Patterns in the diversity of bacterial communities associated with three species of Acropora (Acropora millepora, Acropora tenuis and Acropora valida) were compared at two locations (Magnetic Island and Orpheus Island) on the Great Barrier Reef to better understand the nature and specificity of coral–microbial symbioses. Three\ud culture-independent techniques demonstrated consistent bacterial communities among replicate samples of each coral species, confirming that corals associate with specific microbiota. Profiles were also conserved among all three species of Acropora within each location, suggesting that closely related corals of the same genus harbor similar bacterial types. Bacterial community profiles of A. millepora at Orpheus Island were consistent in samples collected throughout the year, indicating a stable community despite temporal changes. However, DGGE and TRFLP\ud profiles differed on corals from different reefs. Nonmetric multidimensional scaling of T-RFLP profiles showed that samples grouped according to location rather than coral species. Although similar sequences were retrieved from clone libraries of corals at both Magnetic and Orpheus Island, differences in the relative dominant bacterial ribotypes within the libraries drive bacterial community\ud structure at different geographical locations. These results indicate certain bacterial groups associated specifically with corals, but the dominant bacterial genera differ between geographically-spaced corals