Reactivity of Inorganic Mn and Mn Desferrioxamine B with O2, O2–, and H2O2 in Seawater

Manganese (Mn) is a required element for oceanic phytoplankton as it plays a critical role in photosynthesis, through its unique redox chemistry, as the active site in photosystem II, and in enzymes that act as defenses against reactive oxygen species (ROS), most notably for protection against superoxide (O2?), through the action of superoxide dismutase (SOD), and against hydrogen peroxide (H2O2) via peroxidases and catalases. The distribution and redox speciation of Mn in the ocean is also apparently controlled by reactions with ROS. Here we examine the connections between ROS and dissolved Mn species in the upper ocean using field and laboratory experimental data. Our results suggest it is unlikely that significant concentrations of Mn(III) are produced in the euphotic zone, as in the absence of evidence for the existence of strong Mn(III) ligands, Mn(II) reacts with O2? to form the short-lived transient manganous superoxide, MnO2+, which may react rapidly with other redox species in a manner similar to O2?. Experiments with the strong Mn(III) chelator, desferrioxamine B (DFB), in seawater indicated that the Mn(III) species are unlikely to form, as formation of the precursor Mn(II) complex is hindered due to the stability of the Ca complex with DFB.

Compound-specific isotope analysis of amino acids: A tool to unravel complex symbiotic trophic relationships

Carbon and nitrogen stable isotope ratios of amino acids (δ13CAA and δ15NAA) have been recently used to unravel trophic relationships in aquatic and terrestrial environments. However, none have studied the specific case of a symbiotic relationship. Here we use the stable isotope ratios of amino acids (AAs) to investigate the link between a scarab larva (Pericoptustruncatus) and its mite guest (Mumulaelaps, Mesostigmata: Laelapidae: Hypoaspidini). Five scenarios for the relationship between larva and mite were proposed and δ13CAA and δ15NAA respective data and patterns helped eliminate those that were inconsistent. The calculated gap of two trophic levels ruled out a parasitic trophic relationship scenario. The trophic relationship between P. truncatus was shown to most likely be commensalistic with the mites feeding on the larva's castings. Alongside this study, a comparison with the stable isotope bulk analysis method was made and demonstrated that the AA method brings a significant refinement to the results by providing a means of determining absolute tropic level without the need for prior knowledge of the isotopic composition of primary source material.