Ecological and Biological Response of Benthic Foraminifera Under Oxygen-Depleted Conditions: Evidence from Laboratory Approaches

Laboratory experiments are a valuable way to elucidate physiological and ecological processes of benthic foraminifera under oxygen-depleted conditions. Experimentally tested survival rates and other experiments show high tolerance of many species under low oxic to anoxic conditions. Laboratory observations raised different assumptions to explain the physiological adaptations to this tolerance. Denitrification processes seem to be one important mechanism. Nevertheless, foraminifera try to colonize sediment horizons with optimal species-specific oxygen concentrations. Experimental settings demonstrated the importance of oxygen gradients for the orientation in sediments. At the same time, foraminifera change the oxygen concentration in their microenvironment by respiration. Despite high bioturbation, they do not appear to influence the flux of oxygen into the sediment. Experimental working in oxygen-depleted environments needs a reliable determination of living foraminifera during the experiment, e.g., different biochemical techniques. Additionally, electrochemical or optical oxygen sensors that measure the oxygen concentration are necessary

First Steps in Eukaryogenesis: Physical phenomena in the origin and evolution of chromosome structure

Our present understanding of the origin and evolution of chromosomes differs considerably from current understanding of the origin and evolution of the cell itself. Chromosome origins have been less prominent in research, as the emphasis has not shifted so far appreciably from the phenomenon of primeval nucleic acid encapsulation to that of the origin of gene organization, expression, and regulation. In this work we discuss some reasons why preliminary steps in this direction are being taken. We have been led to examine properties that have contributed to raise the ancestral prokaryotic programmes to a level where we can appreciate in eukaryotes a clear departure from earlier themes in the evolution of the cell from the last common ancestor. We shift our point of view from the evolution of cell morphology to the point of view of the genes. In particular, we focus attention on possible physical bases for the way transmission of information has evolved in eukaryotes, namely, the inactivation of whole chromosomes. The special case of the inactivation of the X chromosome in mammals is discussed, paying particular attention to the physical process of the spread of X inactivation in monotremes (platypus and echidna). When experimental data is unavailable some theoretical analysis is possible based on the idea that in certain cases collective phenomena in genetics, rather than chemical detail, are better correlates of complex chemical processes

Mechanisms of organelle division and inheritance and their implications regarding the origin of eukaryotic cells

Mitochondria and plastids have their own DNAs and are regarded as descendants of endosymbiotic prokaryotes. Organellar DNAs are not naked in vivo but are associated with basic proteins to form DNA-protein complexes (called organelle nuclei). The concept of organelle nuclei provides a new approach to explain the origin, division, and inheritance of organelles. Organelles divide using organelle division rings (machineries) after organelle-nuclear division. Organelle division machineries are a chimera of the FtsZ (filamentous temperature sensitive Z) ring of bacterial origin and the eukaryotic mechanochemical dynamin ring. Thus, organelle division machineries contain a key to solve the origin of organelles (eukaryotes). The maternal inheritance of organelles developed during sexual reproduction and it is also probably intimately related to the origin of organelles. The aims of this review are to describe the strategies used to reveal the dynamics of organelle division machineries, and the significance of the division machineries and maternal inheritance in the origin and evolution of eukaryotes