Prokaryote evolution

The theory of autopoiesis claims that adaptation should be understood as a precondition, and not as a constraint, guiding the evolution of social and living systems. This premise is at first sight incompatible with the perspective of the neo-Darwinian theory of evolution. In the case of speciation (phylogenesis) the varying adaptation to the environment is here, in fact, understood as a determinant factor arranging how organisms are selected. Nevertheless, the present study tests out a perspective on evolutionary biology, which is compatible with the implications of the theory of autopoiesis and can demonstrate a productive explanatory potential for evolutionary biology. In this way, it is possible to demonstrate an approach to solving the problems being intensively discussed in (neo-Darwinian) evolutionary biology. Namely, the problems of the units to be selected in evolution, or of rendering the meaning and function of the evolutionary development of sexuality comprehensible, or of relativizing the problem of altruism in evolution. Also, explanations for the so-called Cambrian Explosion and the fundamental difference between the evolution of prokaryotic and eukaryotic forms of life can be derived. And finally, the perspective so so developed permits us to determine the relation of biotic and social evolution in a differentiated manner.

The study of microbial fossils involves a broad array of disciplines and covers a vast diversity of topics, of which we review a select few, summarizing the state of the art. Microbes are found as body fossils preserved in different modes and have also produced recognizable structures in the rock record (microbialites, microborings). Study of the microbial fossil record and controversies arising from it have provided the impetus for the assembly and refining of powerful sets of criteria for recognition of bona fide microbial fossils. Different types of fossil evidence concur in demonstrating that microbial life was present in the Archean, close to 3.5 billion years ago. Early eukaryotes also fall within the microbial realm and criteria developed for their recognition date the oldest unequivocal evidence close to 2.0 billion years ago (Paleoproterozoic), but Archean microfossils >3 billion years old are strong contenders for earliest eukaryotes. In another dimension of their contribution to the fossil record, microbes play ubiquitous roles in fossil preservation, from facilitating authigenic mineralization to replicating soft tissue with extracellular polymeric substances, forming biofilms that inhibit decay of biological material, or stabilizing sediment interfaces. Finally, studies of the microbial fossil record are relevant to profound, perennial questions that have puzzled humanity and science—they provide the only direct window onto the beginnings and early evolution of life; and the methods and criteria developed for recognizing ancient, inconspicuous traces of life have yielded an approach directly applicable to the search for traces of life on other worlds.

ABSTRACT: A new genus, Desserobdella, is described to accommodate the leech Clepsine picta Verrill, 1872 which feeds exclusively on amphibians of northern and central North America. This leech belongs to the subfamily Glossiphoniinae and therefore deposits cocoons directly onto the substrate. The genus Desserobdella n.gen. has the following diagnostic characteristics: (i) two pairs of coalesced eyes; (ii) one pair of diffuse salivary glands; and (iii) a single pair of saccular mycetomes containing prokaryotic endosymbionts. Members of the new genus are distinguished from species of the closely related genus Placobdella Blanchard, 1893 on the basis of their salivary gland structure; Placobdella species have two pairs of compact salivary glands versus the single pair of diffuse salivary glands of the genus Desserobdella n.gen. Congenitors of the new genus are Desserobdella cryptobranchii (Johnson and Klemm, 1977) n.comb., Desserobdella michiganensis (Sawyer, 1972) n.comb., and Desserobdella phalera (Graf, 1899) Jones and Woo, 1990. Desserobdella picta n.gen. et comb. exhibited a stereotypical sequence of feeding behaviours on Rana catesbeiana tadpoles which involved picking at the site of proboscis insertion prior to probing, probing, and finally blood-feeding with the posterior sucker released.

A group of prokaryotic actin-related proteins (PARP) with an Mr of 43000 was detected in Actinobacillus pleuropneumoniae. These proteins were enriched by a depolymerization/polymerization cycle, under similar conditions to those used to polymerize muscle actin, and purified by affinity chromatography on a DNase I-Sepharose column. Three isoforms of A. pleuropneumoniae PARP (Ap-PARP) with pI values of 5.8, 6.15 and 6.2 were detected. Ap-PARP were recognized by four different anti-actin antibodies (one anti-muscle and three anti-cytoplasmic isoforms). Ap-PARP were also recognized by antibodies against Anabaena variabilis PARP (Av-PARP) and against actin-binding proteins such as alpha-actinin and spectrin, and also by a monoclonal antibody against heat-shock cognate protein 70 (Hsc70). Specific binding of phalloidin to Ap-PARP was detected both in permeabilized cells and in vitro. Purified Ap-PARP can polymerize under similar conditions to those required for skeletal muscle actin polymerization and the filaments formed appear to be decorated with myosin subfragment-1(S1) as observed by transmission electron microscopy. The amino acid composition of Ap-PARP revealed more similarities to muscle gamma-actin and the cytoplasmic beta-actin isoform than to eukaryotic actin-related proteins.