Siliceous protozoan plates in lake sediments

The silicified plates of certain testate amoebae have the necessary characteristics to be useful paleoindicators. These plates are usually abundant and well preserved in sedimentary deposits, where they can be studied using the same preparation techniques developed for other siliceous microfossils. Individual plates can usually be identified to the generic and, in some cases, to the species level. A preliminary survey of plates recorded in the surficial (top centimetre) sediments of 38 Adirondack Mountain (NY) lakes suggests that these testaceans may reflect catchment features (e.g. bog development) more closely than lakewater characteristics. The siliceous, species-specific scales of heliozoans are also shown to preserve in sedimentary profiles.     

Transmissibility of Bacterial Endosymbionts Between Isolates of Acanthamoeba Spp.

ABSTRACT. Experimental transmission of two bacterial endosymbionts to symbiont-free isolates of Acanthamoeba spp. was studied to determine specificity of the host-symbiont relationship. Both symbionts originated from amoebic isolates displaying an identical mitochondrial DNA Eco RI fingerprint (group AcUW II). Symbioses were readily established in one amoebic isolate which displayed a homologous mtDNA fingerprint (group AcUW II). Exposure of a heterologous amoebic isolate (group AcUW IV) to the two symbionts resulted in either cell death or encystation without the establishment of symbioses. While symbioses were established with an amoebic isolate from a second heterologous group (AcUW I), a unique membranous sheath appeared and persisted around one of the symbionts which did not exist in the original host. An isolate representing a third heterologous amoebic group (AcUW VI) was variable in its susceptibility with one symbiont unable to infect the host and the other becoming established only after an initial reaction in which trophozoites rounded-up and floated off the substrate. These studies suggest that a specific recognition system exists between particular isolates of Acanthamoeba and their symbionts, and that the appearance of a killer phenotype is related to contact between mismatched, though recognized, pairs.     

Transfer of the Thecate Amoeba Lecythium mutabilis to a Novel Genus Omnivora (Fiscullidae,Thecofilosea, Cercozoa)

Thecofilosea is a class in Cercozoa (Rhizaria) comprising mainly freshwater‐inhabiting algivores. Recently, numerous isolates of thecofilosean amoebae have been cultured and were characterized by an integrated morphological and molecular approach. As attempts to establish a culture of Lecythium mutabilis repeatedly failed, it was not yet investigated by molecular means. We isolated single cells of L. mutabilis directly from their habitat and successfully sequenced the V4 region of their SSU rDNA. Phylogenetic analyses showed that L. mutabilis is not directly related to the genus Lecythium and instead branches within the Fiscullidae (Tectofilosida, Thecofilosea). Accordingly, we transfer the species L. mutabilis to a novel genus Omnivora gen. nov.     

Molecular investigation of Phryganella acropodia Hertwig et Lesser, 1874 (Arcellinida,Amoebozoa)

Phryganella acropodia Hertwig and Lesser, 1874, is one of the most common and abundant testate amoeba species. It represents the type species of the genus Phryganella Penard, 1902, which in turn is the type genus for the suborder Phryganellina (Arcellinida) Bovee, 1985, but despite its taxonomic importance it was not yet analyzed with molecular methods. We established two cultures of putative Phryganella acropodia, designed Phryganellina-specific primers, amplified SSU rDNA data and subjected these sequences to phylogenetic analyses. Morphological and genetic differences were found between both strains. With SSU rDNA phylogenetic analyses we confirm that Phryganella acropodia branches with Phryganella paradoxa Penard, 1902 and Cryptodifflugia Penard, 1890 in the Phryganellina. We thus give further evidence that pseudopodia morphology in the Arcellinida is a character of high taxonomic value, as suggested by Bovee and Jung when erecting the suborder Phryganellina. Moreover, we provide evidence for cryptic diversity and for the first time confirm the existence of a naked life stage in Arcellinida by molecular means.     

Evaluating the use of dominant microbial consumers (testate amoebae) as indicators of blanket peatland restoration

Peatlands represent globally-important ecosystems and carbon stores. However, large areas of peatland have been drained for agriculture, or peat has been harvested for use as fuel or in horticulture. Increasingly, these landscapes are being restored through ditch blocking and rewetting primarily to improve biodiversity and promote peat accumulation. To date we have little knowledge of how these interventions influence the microbial communities in peatlands. We compared the responses of dominant microbial consumers (testate amoebae) to drainage ditch restoration relative to unblocked ditches in a UK upland blanket peatland (Migneint, North Wales). Two techniques were used for restoration: (i) dammed ditches with re-profiling; and (ii) dammed ditches with pools of open water behind each dam. Testate communities in the inter-ditch areas changed markedly over time and between treatments illustrating the potential of this group of organisms as indicators of blanket peatland restoration status. However, the responses of testate amoebae to peat rewetting associated with restoration were partially obscured by inter-annual variability in weather conditions through the course of the experiment. Although there was considerable variability in the response of testate amoebae communities to peatland drain blocking, there were clearly more pronounced changes in samples from the dammed and reprofiled treatments including an increase in diversity, and the appearance of unambiguous wet-indicator species in relatively high abundances (including Amphitrema stenostoma, Archerella flavum, Arcella discoides type, Difflugia bacillifera and Difflugia bacillarium). This reflects a shift towards overall wetter conditions across the site and the creation of new habitats. However, water-table was not a significant control on testate amoebae in this case, suggesting a poor relationship between water table and surface moisture in this sloping blanket peatland. Our findings highlight the potential of testate amoebae as bioindicators of peatland restoration success; however, there is a need for caution as mechanisms driving change in the microbial communities may be more complex than first assumed. Several factors need to be taken into account when implementing biomonitoring studies in peatlands including: (i) the natural variability of the peatland ecosystem under changing weather conditions; (ii) any disturbance connected with the restoration procedures; and (iii) the timescales over which the ecosystem responds to the management intervention. Our results also suggest an indicator species approach based on population dynamics may be more appropriate for biomonitoring peatland restoration than examining changes at the community level.     

Low-salinity transitions drive abrupt microbial response to sea-level change

The salinisation of many coastal ecosystems is underway and is expected to continue into the future because of sea-level rise and storm intensification brought about by the changing climate. However, the response of soil microbes to increasing salinity conditions within coastal environments is poorly understood, despite their importance for nutrient cascading, carbon sequestration and wider ecosystem functioning. Here, we demonstrate deterioration in the productivity of a top-tier microbial group (testate amoebae) with increasing coastal salinity, which we show to be consistent across phylogenetic groups, salinity gradients, environment types and latitude. Our results show that microbial changes occur in the very early stages of marine inundation, presaging more radical changes in soil and ecosystem function and providing an early warning of coastal salinisation that could be used to improve coastal planning and adaptation.     

Light variability and mixotrophy: Responses of testate amoeba communities and shell δ13C values to a peatland shading experiment

Paleoecological records suggest that growing season length and/or cloudiness may affect peatland carbon accumulation and testate amoeba-based environmental reconstructions, highlighting a need to understand how light intensity affects microbial communities. We shaded plots on two peatlands for two years to examine effects on testate amoeba communities, the relative abundance of mixotrophic and heterotrophic testate amoebae, transfer-function performance, and δ¹³C values of two species of mixotrophic testate amoebae. Surprisingly, relative abundance of mixotrophic species increased in shade, although compositional changes did not affect transfer-function performance. Shading did not affect δ¹³C values of Hyalosphenia papilio and Heleopera sphagni, which ranged from −23.5 to −19.6‰ and −23.2 to −19.2‰, respectively. These δ¹³C values were higher than those of potential food sources and lower than literature-derived values for Chlorella, the zoochlorellae inhabiting mixotrophic testate amoebae. δ¹³C values thus suggest that these mixotrophic species obtain some carbon from Chlorella, although coupled dietary and isotope studies are needed to quantify this contribution. More research is needed to assess impacts of light variability on peatland microbial communities; however, carbon sources are recorded by δ¹³C values of testate amoebae, indicating potential for studies of carbon cycling and how mixotrophy varies temporally and spatially.     

Gastrointestinal parasites of the Samango monkey,Cercopithecus mitis,in Natal,South Africa

Eight gastro-intestinal tracts of Cercopithecus mitis labiatus from Karkloof, Natal, and 121 fecal samples from C. m. erythrarchus from Cape Vidal, Natal, were examined for helminth parasites and/or their eggs. Fecal samples from six of the C. m. labiatus were examined for protozoan cysts. Five protozoon and six helminth species were identified from C.m labiatus. Most adult worms occurred in the caecum and colon, gut regions which also contained the highest volatile fatty acid levels. The eggs of nine helminth species were recovered from C. m. erythrarchus fecal samples; protozoans were not looked for in these samples.     

Not all free-living microorganisms have cosmopolitan distributions – the case of Nebela (Apodera) vas Certes (Protozoa: Amoebozoa: Arcellinida)

Aim  To review and critically assess the evidence that the testate amoeba species Nebela vas does not have a cosmopolitan distribution, in contradiction to the paradigm of microbial distribution that 'everything is everywhere'.
Location  Terrestrial and wetland habitats world-wide.
Methods  Relevant data were assembled on the morphology, ecology and global geographical distribution of N. vas from a comprehensive literature review of published original records. The data were collated, analysed and summarized. The roles of long-term and short-term agents of dispersal are discussed.
Results  A clear and repeated pattern has been elucidated of a microbial species, with a distinctive and unmistakeable morphology, that inhabits acid, damp terrestrial and wetland habitats in the southern cool-temperate and sub-Antarctic zones – including similar high-altitude habitats in the Tropics. It is almost entirely confined to the Gondwanaland continents and Southern Hemisphere islands. It is definitively absent from Holarctic regions. It is proposed that the continental distribution of N. vas is a consequence of continental drift following its original speciation in the Mesozoic or earlier, whereas its distribution on sub-Antarctic islands (glaciated in the Pleistocene) has been effected by dispersal from South America by wind around the Southern Ocean.
Main conclusion  Nebela vas is a proven instance of a microbial species that does not have a cosmopolitan distribution.