The effect of detergents and lipids on the properties of the outer-membrane protein OmcA from Shewanella oneidensis

The protein OmcA from the bacterium Shewanella oneidensis was purified to homogeneity, and characterized using UV–vis spectroelectrochemistry, EPR, and circular dichroism (far- and near-UV regions). EPR spectroscopy showed that many different c-type hemes are present in the protein: high-spin, low-spin, and highly anisotropic low-spin hemes were all detected. The protein was shown to bind tightly to artificial membranes (liposomes) composed of dioleoylphosphatidylglycerol and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (60:40 molar ratio), which mimic the natural environment. However, on the basis of the spectroscopic and electrochemical studies, binding to liposomes does not appear to significantly alter either the structure or the properties of OmcA. On the other hand, the electrochemical properties of OmcA are noticeably changed in the presence of the detergents used during the initial purification stages. In particular, the reduction potentials of two out of the ten OmcA hemes appear to shift in the presence of detergent, perhaps because these hemes are solvent-exposed.     

The role of hyperiid parasites as a trophic link between jellyfish and fishes

The trophic interactions between the scyphozoan medusa Chrysaora plocamia and the palm ruff Seriolella violacea were investigated off northern Chile and showed that large numbers of hyperiid amphipods parasitizing the medusa may channel energy back to the fishes, which feed on the parasites. The biomass of hyperiids eaten by the fish was a function of the biomass of hyperiids parasitizing the medusa. This temporally available food supply may enhance fish recruitment. The large number of hyperiids parasitizing diverse jellyfish species represents a missing trophic link in current efforts to understand the effects of jellyfish blooms on marine food webs.