The effects of copper on the microbial community of a coral reef sponge.
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 (alpha-proteobacterium strain NW001) were significantly reduced in response to Cu2+ concentrations of 1.7 microg 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 microg l(-1) Cu2+ for 48 h and by 46% in sponges exposed to 19.4 microg 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 microg l(-1). Although the abundance of most morphotypes decreased under Cu2+ stress, three morphotypes were not reduced in numbers and a single morpho-type actually increased in abundance. Bacterial numbers, as detected using fluorescence in situ hybridization (FISH), decreased significantly after 48 h exposure to 19.4 microg l(-1) Cu2+. Archaea, which are normally prolific in R. odorabile, were not detected after exposure to a Cu2+ concentration of 19.4 microg 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 microg l(-1) became highly necrosed after 48 h and accumulated 142 +/- 18 mg kg(-1) copper, whereas sponges exposed to 19.4 microg 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.
Australian Institute of Marine Science, Department of Microbiology, James Cook University, Townsville, Queensland.
N S
NS
Webster
R I
RI
Webb
M J
MJ
Ridd
R T
RT
Hill
A P
AP
Negri
D020561:Alphaproteobacteria / Q000254:growth & development* / Q000378:metabolism / Q000648:ultrastructure; D000818:Animals; D001105:Archaea / Q000254:growth & development* / Q000378:metabolism / Q000648:ultrastructure; D003063:Cnidaria / Q000382:microbiology*; D003300:Copper / Q000378:metabolism*; D017753:Ecosystem; D004784:Environmental Monitoring; D017404:In Situ Hybridization, Fluorescence; D008854:Microscopy, Electron; D010802:Phylogeny; D016133:Polymerase Chain Reaction; D012150:Polymorphism, Restriction Fragment Length; D011161:Porifera / Q000382:microbiology*; D012329:RNA, Bacterial / Q000032:analysis; D012336:RNA, Ribosomal, 16S / Q000032:analysis
D012329:RNA, Bacterial; D012336:RNA, Ribosomal, 16S; D003300:Copper