Vertebrates as vectors of cellular slime moulds in temperate forests

Diversity of Dictyostelid Cellular Slime Molds, Including Two Species New to Science, in Forest Soils of Changbai Mountain, China

Dictyostelid cellular slime molds (dictyostelids) are protists that are common inhabitants of most soils, where they feed upon bacteria. Changbai Mountain is the highest mountain in northeast China. Soil samples collected on Changbai Mountain yielded 11 isolates representing six species of dictyostelid samples. Two of these species (Dictyostelium robusticaule and Heterostelium recretum) were found to be new to science, based on morphology, SSU rDNA sequences, and an ATPase subunit 1 gene (atp1) phylogeny. The present study also demonstrated that the increased accuracy and lower costs associated with the use of atp1 sequences make them a complement of SSU rDNA sequences for identifying dictyostelids. Changbai Mountain is characterized by a higher diversity of dictyostelids than indicated by the few previous reports. Moreover, the data for Changbai Mountain, compared with comparable data for Taiwan, suggest that differences in diversity at the family level are possibly related to latitude. Mixed broadleaf-conifer forests produced more isolates and species than broadleaf forests at the same elevation and also had the highest species richness, which indicates an effect of vegetation on dictyostelids. However, the pattern of slightly decreasing diversity with increasing elevation in dictyostelids was also apparent. IMPORTANCE Dictyostelium robusticaule and Heterostelium recretum are two new species of dictyostelids reported in this study. The potential use of atp1 sequences is a complement of SSU rDNA sequences for the identifying dictyostelids. A pattern of slightly decreasing diversity with increasing elevation in dictyostelids was observed, with the conditions that exist at lower elevations apparently more suitable for dictyostelids, whereas differences of diversity observed at the family level are possibly related to latitude.

Additional new species suggest high dictyostelid diversity on Madagascar

Dictyostelids are a monophyletic group of sorocarp-forming social amoebae in the major eukaryotic division Amoebozoa. Members of this taxon, which is made up of almost 200 described species, are common in terrestrial soils globally. Still, the alpha diversity is not well known in many areas, and new species are frequently recovered. The highest species richness is found in the tropics. Here, five new species are described from soil samples collected in Madagascar. These species-Cavenderia basinodulosa, C. canoespora, Heterostelium radiatum, H. versatile, and Raperostelium stabile-are described based on both morphological characteristics and molecular data, with sequence data from the rDNA small subunit (SSU). The five new species are morphologically disparate, ranging from relatively small, robust taxa such as R. stabile to taxa with variable morphologies such as the larger H. radiatum and H. versatile and the yellow-tinted and irregularly branched species C. canoespora and C. basinulosa. These new species, together with earlier work where 13 other species were described from the island, suggest that there is a range of genetically diverse and highly morphologically variable dictyostelid taxa occurring on Madagascar, suggesting biogeographic patterns even within these very small organisms.

Dictyostelid Cellular Slime Molds from Christmas Island, Indian Ocean

Reported here are the results of a study for dictyostelids carried out on Christmas Island, Indian Ocean. Six isolates representing four species of dictyostelid cellular slime molds were obtained from two of the four localities from which samples were collected on the island. Two of the species (Dictyostelium insulinativitatis and D. barbarae) belong to the Dictyosteliaceae, genus Dictyostelium, and are new to science. These are described based on both morphology and phylogeny. The diversity and abundance of dictyostelids on Christmas Island appear to be low, which might in part be due to the abundance of land crabs, which considerably reduce the extent of the litter layer on the forest floor.

Christmas Island (10°30′S, 105°40′E) is an Australian external territory located in the Indian Ocean, approximately 350 km south of Java and Sumatra and about 1,550 km northwest of the closest point on the Australian mainland. In May 2017, 20 samples of soil/humus were collected on Christmas Island and processed for dictyostelid cellular slime molds. Four species were recovered. Two of these (Dictyostelium purpureum and Cavenderia aureostipes) are common and widely distributed throughout the world, but two other species (Dictyostelium insulinativitatis sp. nov. and Dictyostelium barbarae sp. nov.) were found to be new to science and are described here.

IMPORTANCE Reported here are the results of a study for dictyostelids carried out on Christmas Island, Indian Ocean. Six isolates representing four species of dictyostelid cellular slime molds were obtained from two of the four localities from which samples were collected on the island. Two of the species (Dictyostelium insulinativitatis and D. barbarae) belong to the Dictyosteliaceae, genus Dictyostelium, and are new to science. These are described based on both morphology and phylogeny. The diversity and abundance of dictyostelids on Christmas Island appear to be low, which might in part be due to the abundance of land crabs, which considerably reduce the extent of the litter layer on the forest floor.

Two new species of dictyostelid cellular slime molds in high-elevation habitats on the Qinghai-Tibet Plateau, China

Dictyostelid cellular slime molds (dictyostelids) are key components of soil microbes. The Qinghai-Tibet Plateau is characterized by unique and important forest types because of the considerable range in elevation which exists. During the period of 2012, 2013 and 2016, 12 species of dictyostelids were yielded from samples collected in this region, including two new species and three new records for China. Six other species were new records for this region. Ontogeny, morphology, ultrastructure and systematic molecular analyses (SSU & ITS) of D. minimum and D. multiforme confirm that they are Goup 4 new species. The ornamentation of the surface of dictyostelids' spores is the first time to be observed until now. In the SSU phylogenetic tree generated in the present study, Synstelium, not assigned to order and family before, was assigned to the clade Acytosteliaceae in the Acytosteliales firstly. To our knowledge, the study reported herein is the first investigation of dictyostelid biodiversity carried out at elevations above 2000 m. Sorocarp size, sorus size, spore length, ratio of sorus and sorophore, and ratio of sorus and spore size were positively correlated with increasing elevation and no linear correlated with forest type, according to the results of linear regression analysis.

Diversity of Free-Living Environmental Bacteria and Their Interactions With a Bactivorous Amoeba

A small subset of bacteria in soil interact directly with eukaryotes. Which ones do so can reveal what is important to a eukaryote and how eukaryote defenses might be breached. Soil amoebae are simple eukaryotic organisms and as such could be particularly good for understanding how eukaryote microbiomes originate and are maintained. One such amoeba, Dictyostelium discoideum, has both permanent and temporary associations with bacteria. Here we focus on culturable bacterial associates in order to interrogate their relationship with D. discoideum. To do this, we isolated over 250 D. discoideum fruiting body samples from soil and deer feces at Mountain Lake Biological Station. In one-third of the wild D. discoideum we tested, one to six bacterial species were found per fruiting body sorus (spore mass) for a total of 174 bacterial isolates. The remaining two-thirds of D. discoideum fruiting body samples did not contain culturable bacteria, as is thought to be the norm. A majority (71.4%) of the unique bacterial haplotypes are in Proteobacteria. The rest are in either Actinobacteria, Bacteriodetes, or Firmicutes. The highest bacterial diversity was found in D. discoideum fruiting bodies originating from deer feces (27 OTUs), greater than either of those originating in shallow (11 OTUs) or in deep soil (4 OTUs). Rarefaction curves and the Chao1 estimator for species richness indicated the diversity in any substrate was not fully sampled, but for soil it came close. A majority of the D. discoideum-associated bacteria were edible by D. discoideum and supported its growth (75.2% for feces and 81.8% for soil habitats). However, we found several bacteria genera were able to evade phagocytosis and persist in D. discoideum cells through one or more social cycles. This study focuses not on the entire D. discoideum microbiome, but on the culturable subset of bacteria that have important eukaryote interactions as prey, symbionts, or pathogens. These eukaryote and bacteria interactions may provide fertile ground for investigations of bacteria using amoebas to gain an initial foothold in eukaryotes and of the origins of symbiosis and simple microbiomes.

The Amoebozoa

The model organism Dictyostelium discoideum is a member of the Amoebozoa, one of the six major -divisions of eukaryotes. Amoebozoa comprise a wide variety of amoeboid and flagellate organisms with single cells measuring from 5 μm to several meters across. They have adopted many different life styles and sexual behaviors and can live in all but the most extreme environments. This chapter provides an overview of Amoebozoan diversity and compares roads towards multicellularity within the Amoebozoa with inventions of multicellularity in other protist divisions. The chapter closes with a scenario for the evolution of Dictyostelid multicellularity from an Amoebozoan stress response.

High relatedness in a social amoeba: the role of kin-discriminatory segregation

A major challenge for social theory is to explain the importance of kin discrimination for the evolution of altruism. One way to assess the importance of kin discrimination is to test its effects on increasing relatedness within groups. The social amoeba Dictyostelium discoideum aggregates to form a fruiting body composed of dead stalk and live spores. Previous studies of a natural population showed that where D. discoideum occurs in the soil, multiple clones are often found in the same small soil samples. However, actual fruiting bodies usually contain only one clone. We here performed experiments to gauge the effect of kin-discriminatory segregation on increasing relatedness. We mixed co-occurring clones from this population using a relatedness level found in small soil samples. We found a lower proportion of uniclonal fruiting bodies and a lower level of relatedness compared with natural fruiting bodies. We found that the amount of relatedness increase attributable to kin-discriminatory segregation was small. These findings suggest a relatively minor influence of kin-discriminatory segregation on relatedness in D. discoideum. We discuss our results comparing with the results of previous studies, including those of wild clones and laboratory mutants. We ask why wild clones of D. discoideum exhibit a low degree of kin-discriminatory segregation, and what alternative factors might account for high relatedness in D. discoideum.

Evolution and diversity of dictyostelid social amoebae

Dictyostelid social amoebae are a large and ancient group of soil microbes with an unusual multicellular stage in their life cycle. Taxonomically, they belong to the eukaryotic supergroup Amoebozoa, the sister group to Opisthokonta (animals + fungi). Roughly half of the ~150 known dictyostelid species were discovered during the last five years and probably many more remain to be found. The traditional classification system of Dictyostelia was completely overturned by cladistic analyses and molecular phylogenies of the past six years. As a result, it now appears that, instead of three major divisions there are eight, none of which correspond to traditional higher-level taxa. In addition to the widely studied Dictyostelium discoideum, there are now efforts to develop model organisms and complete genome sequences for each major group. Thus Dictyostelia is becoming an excellent model for both practical, medically related research and for studying basic principles in cell-cell communication and developmental evolution. In this review we summarize the latest information about their life cycle, taxonomy, evolutionary history, genome projects and practical importance.

Genetic heterogeneity in wild isolates of cellular slime mold social groups

This study addresses the issues of spatial distribution, dispersal, and genetic heterogeneity in social groups of the cellular slime molds (CSMs). The CSMs are soil amoebae with an unusual life cycle that consists of alternating solitary and social phases. Because the social phase involves division of labor with what appears to be an extreme form of "altruism", the CSMs raise interesting evolutionary questions regarding the origin and maintenance of sociality. Knowledge of the genetic structure of social groups in the wild is necessary for answering these questions. We confirm that CSMs are widespread in undisturbed forest soil from South India. They are dispersed over long distances via the dung of a variety of large mammals. Consistent with this mode of dispersal, most social groups in the two species examined for detailed study, Dictyostelium giganteum and Dictyostelium purpureum, are multi-clonal.

A habitat colonisation model for spore-dispersed organisms: does it work with eumycetozoans?

Spore productivities and establishment probabilities of eumycetozoans were estimated and compared with quantitative data obtained from field surveys, using series of cultures of a given substrate. Spore numbers per spore case were found to increase from one to four in protostelids to up to 10(5)-10(6) in myxomycetes, whereas average spore size decreased slightly from 14.8 microm for protostelids to 10.3 microm in myxomycetes. Spore numbers of fructifications calculated from dimensions of spores and fruit bodies were in good agreement with direct counts carried out for six species of myxomycetes. A colonisation model is presented that estimates frequencies (as a percent of successfully colonized habitat islands), which is independent of a given density of spore rain and the sexual system of the species being considered. Whereas asexual species need a minimum spore rain of ca 0.7 spores per habitat island to reach a frequency of 50%, this figure is at least 2.4-fold higher for sexual species, depending from the incompatibility system assumed. Data from cultures indicate that the maximum potential spore rain is usually three orders of magnitude higher than the minimum figure required to create the observed frequencies. Eumycetozoans seem to follow the evolutionary trends predicted by the model. Species with sexual reproductive systems produce often more spores than asexual ones; many morphospecies have sexual and asexual strains; and back-conversion from sexual to asexual reproduction occurs occasionally.

A linear dominance hierarchy among clones in chimeras of the social amoeba Dictyostelium discoideum

Amoebae from different clones of Dictyostelium discoideum aggregate into a common slug, which migrates towards light for dispersal, then forms a fruiting body consisting of a somatic, dead stalk, holding up a head of living spores. Contributions of two clones in a chimera to spore and stalk are often unequal, with one clone taking advantage of the other's stalk contribution. To determine whether there was a hierarchy of exploitation among clones, we competed all possible pairs among seven clones and measured their relative representation in the prespore and prestalk stages and in the final spore stage. We found a clear linear hierarchy at the final spore stage, but not at earlier stages. These results suggest that there is either a single principal mechanism or additive effects for differential contribution to the spore, and that it involves more than spore/stalk competition.