A proposed phylogeny of the flagellated protostelids.

The flagellated members of the group of mycetozoans known as protostelids have been recognized for some time to be members of a monophyletic group which also includes the myxomycetes. This inference was based primarily upon comparisons of the flagellar apparatus of the amoeboflagellate state. However, more detailed comparisons based on the whole life history and comparisons with an outgroup were necessary to have information sufficient to determine the interrelationships within the group. Recent studies of the other states of the life history of protostelids have provided a wealth of additional morphological and developmental characters such that an in depth phylogenetic analysis is possible. The results show that the group can be resolved into two major clades, one of which contains the myxomycetes and the myxomycete-like protostelid genera, Protosporangium, Clastostelium, and Ceratiomyxa, and another which contains the protostelid genera Planoprotostelium, Cavostelium, and Ceratiomyxella. As the myxomycetes appear to be part of the ingroup, and not a sister group to the protostelids, L.S. Olive's subclass Protostelia must be considered paraphyletic.     

Ultrastructural studies of protostelids: The cyst stage ofCavostelium bisporum

Summary The ultrastructure of encystment stages in the flagellate protostelidCavostelium bisporum was studied with sectioned material fixed in sequential glutaraldehyde-OsO₄.Major features of encystment were (1) intensive release of vesicles via the plasmalemma, (2) deposition just exterior to the plasmalemma of membranous structures similar to the latter, (3) disappearance of food vacuoles with their concentrically lamellate, membranous residues, and (4) alterations in the complex of kinetosomes, microtubules, and Golgi apparatus that characterizes the flagellate stage. In view of the possible phylogenetic origin of myxomycetes from the protostelids, the ultrastructure of encystment in the two groups is compared.Supported by U.S. National Science Foundation, Grant GB-7392.Partially supported by FundaÇÃo de Amparo à Pesquisa, SÃo Paulo, Brasil.     

Chemoattractants of Distyostelium discoideum (Protozoa: Sarcomastigophora, Eumycetozoa)

The authors summarize data on interaction of protozoan Dictyostelium discoideum with folia acid and cyclic adenozinmonophosphate as chemoattractants. These substances play role of antagonists in the life cycle of Dictyostelium discoideum: one disperses cells in space and another gathers them into groups forming and organism. Analysis of interaction between Dictyostelium discoideum and environment allows to reveal that Deictyosteliceae has unique mechanism of adaptation of shortage of feeding resource--forming of multicellular organism with functional differentiation of cells. This mechanism could be found at different hierarchical levels of living organisms.     

Species pool: the concept,its determination and significance for community restoration

Abstract. The concept of species pool is reviewed. It is suggested to maintain the terms regional pool and local pool but replace actual pool by community pool. The regional and local pool are considered as selections from the regional and local flora based on ecological similarity. It is also suggested to include in the community pool a selection of species present only as diaspores in the diaspore bank (including diaspores from the seed rain), the selection being based on the same ecological criteria. Four approaches to determine the species pool are discussed: ecological, functional and phytosociological similarity, and an experimental approach. The phytosociological approach appears to be promising. The species pool is elaborated as a fuzzy set in the sense that each species of a community or a local or regional flora is a member of any community, local or regional species pool with different degrees of membership. This membership is defined as a probability of a species to become part of the community pool of a target community which is a function of the ecological (environmen-tal/functional/phytosociological) similarity of the species with the target community; the shortness of the distance of its nearest populations, the frequency/abundance, the dispersal capacity, the actual presence of dispersal mechanisms, the germinability of newly arrived diaspores, and the longevity of seeds (viability) in the diaspore bank. The information on species pools is needed for designing experiments where the number of species in a community is to be manipulated, for instance in restoration management.     

Improved Culture Flask for Obligate Anaerobes

An improved flask system for the growth of extremely oxygen-sensitive bacteria in liquid culture is described. The improvement described utilizes an all-glass, neoprene-stoppered flask designed for growth of 50- to 1,000-ml cultures of bacteria with continuous gassing.     

Phase-shift model for the aggregation of amoebae: a computer study.

An evolutionary scheme for the origin of chemiosmotic coupling of redox reactions and ATP synthesis is proposed. It is argued that the primitive heterotroph, which generated ATP by substrate level phosphorylation, used some of this ATP in active proton extrusion to regulate cytoplasmic pH. As fermentation substrates were used up, selection favoured organisms which produced a light-dependent redox pump for proton extrusion. This partly replaced the ATP-dependent proton extrusion, thereby economizing on fermentation substrates. The ATP-requiring mechanism was retained for dark proton extrusion. A further economic advantage would come about if the energy of the light-generated proton gradient were used to reverse the ATP-dependent proton pump, leading to chemiosmotic photophosphorylation. This hypothesis explains the origin of the two kinds of proton pump, and their occurrence in the same membrane; the origin of these two prerequisites of chemiosmotic coupling had not previously been adequately explained. The success of the proton pump based on redox loops of alternating vectorial electron and hydrogen atom carriers, rather than the apparently simpler light-driven proton pump of Halobacterium is explained in terms of the ease of converting the former type of cyclic photophosphorylation, but not the latter, into a system bringing about net redox reactions.     

Microhabitat distribution of protostelids in a Tropical Wet Forest in Costa Rica

A microhabitat study of protostelids was carried out in a Tropical Wet Forest at the La Selva Biological Station in Costa Rica. Nine species were recorded from sterile wheat straws placed out and then re-collected over a period of six weeks from two different litter microhabitats in an area of primary forest. All nine species were present on straws placed in the aerial litter microhabitat, but only six species were present on straws placed in the forest floor litter microhabitat. Total colonies, percent of straws colonized, and mean number of species per straw increased significantly over time. One species (Schizoplasmodiopsis pseudoendospora) typical of temperate litter was the overwhelming dominant on the forest floor litter, while Echinostelium bisporum, a species rare in temperate litter microhabitats, was the single most abundant species in the aerial litter microhabitat. Both of these species had significantly increased frequencies over time. Two species abundant in temperate aerial litter microhabitats and one species abundant in temperate forest floor litter were rare at La Selva. Our data conform to those obtained in an earlier study carried out in tropical forests in the mountains of Puerto Rico and provide additional support towards developing a model of microhabitat distribution of protostelids in terrestrial ecosystems.     

The chastity of amoebae: re-evaluating evidence for sex in amoeboid organisms

Amoebae are generally assumed to be asexual. We argue that this view is a relict of early classification schemes that lumped all amoebae together inside the 'lower' protozoa, separated from the 'higher' plants, animals and fungi. This artificial classification allowed microbial eukaryotes, including amoebae, to be dismissed as primitive, and implied that the biological rules and theories developed for macro-organisms need not apply to microbes. Eukaryotic diversity is made up of 70+ lineages, most of which are microbial. Plants, animals and fungi are nested among these microbial lineages. Thus, theories on the prevalence and maintenance of sex developed for macro-organisms should in fact apply to microbial eukaryotes, though the theories may need to be refined and generalized (e.g. to account for the variation in sexual strategies and prevalence of facultative sex in natural populations of many microbial eukaryotes). We use a revised phylogenetic framework to assess evidence for sex in several amoeboid lineages that are traditionally considered asexual, and we interpret this evidence in light of theories on the evolution of sex developed for macro-organisms. We emphasize that the limited data available for many lineages coupled with natural variation in microbial life cycles overestimate the extent of asexuality. Mapping sexuality onto the eukaryotic tree of life demonstrates that the majority of amoeboid lineages are, contrary to popular belief, anciently sexual, and that most asexual groups have probably arisen recently and independently. Additionally, several unusual genomic traits are prevalent in amoeboid lineages, including cyclic polyploidy, which may serve as alternative mechanisms to minimize the deleterious effects of asexuality.