To investigate the molecular diversity of symbiotic algae at the latitudinal limits of their distribution, the ribosomal RNA gene sequences (rDNA) of the dinoflagellate Symbiodinium in benthic Cnidaria (corals, sea anemones etc.) on Bermuda (32°N) and in the Mediterranean and NE Atlantic (35 to 53°N) were analysed. The algae in Bermudian Cnidaria were identified as Symbiodinium of Phylotypes A, B and C, as previously described for benthic Cnidaria in the Caribbean (12 to 27°N). The algae in every sample of sea anemones (Anemonia spp. and Cereus pedunculatus) in the NE Atlantic and Mediterranean were a previously undescribed group within Phylotype A, possibly endemic to this high latitude region.
The photosynthetic response to irradiance (PI response) of dinoflagellate algae of the genus Symbiodinium was quantified immediately after isolation from symbiosis with 9 species of corals and allied taxa on Bermuda. Significant variation in PI parameters was identified among the algal isolates, but no consistent differences between representatives of different Symbiodinium phylotypes were obtained. In a parallel analysis of Montastraea franksi, a dominant Bermudian coral species, colonies from 4 to 16 m (all bearing Symbiodinium of Phylotype B) were acclimated to high light conditions. The photoacclimatory response was slight. It included an increase in the dark respiration rate by algae from all collection depths, increased light use efficiency and decreased saturating irradiance of algae from 4 m, and increased maximal photosynthetic rate per unit chlorophyll (chl), but not per cell, for algae from 8 and 16 m. We conclude that generalisations about differences between the photosynthetic traits between Symbiodinium phylotypes are not valid, and that the wide depth distribution of M. franksi cannot be attributed to either depth-dependent association with multiple Symbiodinium phylotypes with different photosynthetic properties or strong photoacclimatory capabilities of its complement of Symbiodinium. These data suggest that Symbiodinium phylotype is not generally an important determinant of the abundance and distribution of symbioses on coral reefs. KEY WORDS: Symbiosis · Symbiodinium · Zooxanthellae · PI response · Molecular diversity
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Matrix metalloproteinases (MMPs) play a crucial role in enzymatically digesting cartilage extracellular matrix (ECM) components, resulting in degraded cartilage with altered mechanical loading capacity. Overexpression of MMPs is often caused by trauma, physiologic conditions and by disease. To understand the synergistic impact MMPs have on cartilage biomechanical properties, MMPs from two subfamilies: collagenase (MMP-1) and gelatinase (MMP-9) were investigated in this study. Three different ratios of MMP-1 (c) and MMP-9 (g), c1:g1, c3:g1 and c1:g3 were considered to develop a degradation model. Thirty samples, harvested from bovine femoral condyles, were treated in groups of 10 with one concentration of enzyme mixture. Each sample was tested in a healthy state prior to introducing degradative enzymes to establish a baseline. Samples were subjected to indentation loading up to 20% bulk strain. Both control and treated samples were mechanically and histologically assessed to determine the impact of degradation. Young’s modulus and peak load of the tissue under indentation were compared between the control and degraded cartilage explants. Cartilage degraded with the c3:g1 enzyme concentration resulted in maximum 33% reduction in stiffness and peak load compared to the other two concentrations. The abundance of collagenase is more responsible for cartilage degradation and reduced mechanical integrity.
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