Webster, Nicole S., Webb, Richard I., Ridd, Michael J., Hill, Russell T., and Negri, Andrew P. (2001) The effects of copper on the microbial community of a coral reef sponge. Environmental Microbiology, 3 (1). pp. 19-31.

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Abstract

Marine sponges often harbour communities of symbiotic microorganisms that fulfil necessary functions for the well-being of their hosts. Microbial communities associated with the sponge Rhopaloeides odorabile were used as bioindicators for sublethal cupric ion (Cu²⁺) stress. A combined strategy incorporating molecular, cultivation and electron microscopy techniques was adopted to monitor changes in microbial diversity. The total density of sponge-associated bacteria and counts of the predominant cultivated symbiont (α-proteobacterium strain NW001) were significantly reduced in response to Cu²⁺ concentrations of 1.7 µg l⁻¹ and above after 14 days of exposure. The number of operational taxonomic units (OTUs) detected by restriction fragment length polymorphism (RFLP) decreased by 64% in sponges exposed to 223 µg l⁻¹ Cu²⁺ for 48 h and by 46% in sponges exposed to 19.4 µg l⁻¹ Cu²⁺ for 14 days. Electron microscopy was used to identify 17 predominant bacterial morphotypes, composing 47% of the total observed cells in control sponges. A reduction in the proportion of these morphotypes to 25% of observed cells was evident in sponges exposed to a Cu²⁺ concentration of 19.4 µg l⁻¹. Although the abundance of most morphotypes decreased under Cu²⁺ stress, three morphotypes were not reduced in numbers and a single morphotype actually increased in abundance. Bacterial numbers, as detected using fluorescence in situ hybridization (FISH), decreased significantly after 48 h exposure to 19.4 µg l⁻¹ Cu²⁺. Archaea, which are normally prolific in R. odorabile, were not detected after exposure to a Cu²⁺ concentration of 19.4 µg l⁻¹ for 14 days, indicating that many of the microorganisms associated with R. odorabile are sensitive to free copper. Sponges exposed to a Cu²⁺ concentration of 223 µg l⁻¹ became highly necrosed after 48 h and accumulated 142 ± 18 mg kg⁻¹ copper, whereas sponges exposed to 19.4 µg l⁻¹ Cu²⁺ accumulated 306 ± 15 mg kg⁻¹ copper after 14 days without apoptosis or mortality. Not only do sponges have potential for monitoring elevated concentrations of heavy metals but also examining changes in their microbial symbionts is a novel and sensitive bioindicator for the assessment of pollution on important microbial communities.

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