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72 • "PROTIST—2016
Cryosol profiles by different processes of cryogenic mass-exchange. According to our results about half of protists communities in Cryosols have adaptive and protective mechanisms enabling long-term cryptobiosis in the inhospitable conditions of the arctic soils and permafrost. Fragments of the uppermost soil horizons that were cryoturbated, buried by solifluction and accumulated in the upper layer ofpermafrost appear to be the ecologycal niche in profiles of Turbic Cryosols that can significantly sustain viability of protists.
GENOME ANNOTATION OF ACRASIS KONA Sheikh Sanea, Fu Chengjie, Baldauf Sandra Department of Organismal Biology, Uppsala University, Sweden sanea.sheikh@ebc.uu.se
Acrasids are single-celled amoebae that can undergo aggregative multicellularity in response to adverse environmental conditions, similar to the well-studied dictyostelid social amoebas. However, acrasids are unrelated to dictyostelids (supergroup Amoebozoa), being instead the only multicellular lineage in the eukaryotic supergroup Excavata. This makes Acrasis an interesting model system to study parallel evolution of social behavior in microbes as well as to explore the diversity of eukaryotes in general. We have sequenced the genome and transcriptome of Acrasis kona and are currently preparing transcriptomes from the four main stages of its life cycle. In initial work, we assembled the complete A. kona mitochondrial genome (mtDNA) and find that it is missing 14 protein genes present in the mtDNA of its closest sequenced relative, Naegleria gruberii. We further identified 11 of these protein genes in A. kona nuclear DNA and find that they carry mitochondrial important signals (transit peptides, Fu et al. 2014). We are now using RNAseq data and the N. gruberii genome in an annotation pipeline to create a fully annotated A. kona nuclear assembly. The results will be used to investigate parallel evolution of simple multicellularity, early steps in the evolution of eukaryotes and to aid in resolution of the eukaryote tree of life by breaking up some of the longer deep branches.
CHEMOTAXIS RESPONSE OF PHYTOPLAN-
KTON TO CILIATES
Shen Z.12, Vidyarathna N.K.1, Liu H.B.1
1 - Division of Life Science, The Hong Kong University of Science and Technology, Kowloon, Hong Kong
2 - Institute of Hydrobiology, Jinan University, Guangzhou 510631, China
liuhb@ust.hk
Marine environment at the micro scale level is
heterogeneous in terms of nutrient distribution and many microbial species can actively exploit these nutrient patches. Exudates of microbes act as nutrient hotspots and also provide chemical cues to their prey or predators. In the present study we examined the chemotactic response of starved and/ or non-starved Dunaliella salina to the exudates of ciliate grazers (Euplotes vannus, Euplotes sp., and Diophrys oligothrix) by using two approaches; 1. Co-culturing oftwo species under different illumination conditions to evaluate the growth, ingestion and behavioural response of the phytoplankton and/ or ciliates and 2. Using microfluidics and image analyses to evaluate the response of D. salina to the exudates of ciliates and related nutrient media. D. salina showed different active swimming and an 'attack-like' behaviour towards ciliates under different illumination conditions, despite the high ciliate grazing rates on them. When exposed to the patches of ciliate exudates, f/2 growth medium, yeast extraction and ammonium solution, both starved and non-starved D. salina showed chemotactic accumulation on/around the exudate and nutrient patches. In both cases positive chemotaxis indices were found towards ciliate exudates suggesting that D. salina could actively uptake nutrients released by its ciliate grazers. This specific behavioural response however, could be costly to D. salina. We suggest that this behaviour could also serve as a defence mechanism thereby increasing the benefits for D. salina.
PELAGIC PROTISTS FEEDING ON PICO-CYANOBACTERIA AND THEIR CHLOROPHYLL CATABOLISMS
Shihongi A.1, Kinoshita Y.2, Ishikawa A.3, Tamiaki H.2, Kashiyama Y.1,2
1 - Fukui University of Technology
2 - Ritsumeikan University
3 - Mie University chiro@fukui-ut.ac.jp
Pico-phytoplanktons dominate the primary production in pelagic oligotrophic oceans. Because these settings cover roughly half areas of the Earth surface, thus relatively dilute inhabitances of pico-phytoplanktons actually represent a considerable proportion of the photosynthetic primary production on the Earth. Nonetheless, ecological/bioenergetic networks extended from these microbial phototrophs have been poorly understood due to insufficient knowledge on the prey-predator relationship, where the minute cells should evade grazing by filter-feeding zooplanktons. We have thus investigated on pelagic protists that potentially prey on picophytoplanktons based on
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microscopic observations and chemical detections of chlorophylls catabolites. Pelagic water samples from the northwestern Pacific were subdivided into hundred milliliter-scale flasks with additions oftrace medium components and/or separately cultured picocyanobacteria as preys and incubated under dim light at 5 to 10 °C. In cultures with additions of Acaryochloris marina, a cyanobacterium (9 = 2-3 ^m; nearly "pico"-scale) that produces chlorophyll d (Chl-d) instead of chlorophyll a (Chl-a) and, 132,173-cyclopheophorbide d enol (a "CPE" derived from Chl-d; cPPB-dE) was detected from the cultures after a few day of incubation. CPEs such as Chl- a-derived cPPB- aE have been reported as non-phototoxic catabolites of chlorophylls and known to be produced by many varieties of protists. Because Chl-d was not detected from any of those samples without addition of A. marina that is allochthonous to the pelagic settings, the occurrence of cPPB-dE in these experiments suggests presence of phycophagic protists that potentially feed on picophytoplanktons. Some flagellates and amoeba were actually observed to have ingested cells of A. marina from microscopic measurements.
CHARACTERIZATION OF STRAIN SRT308; A NEW HETEROTROPHIC FLAGELLATE BASAL TO EUGLENOZOA Shiratori T.1, Yazaki E.2, Inagaki Y.3, Hashimoto T.3, Ishida K.1
1 - Faculty of Life and Environmental Sciences, University of Tsukuba
2 - Graduate School of Life and Environmental Sciences, University of Tsukuba
3 - Center for Computational Sciences, University of Tsukuba
wb.takashi@gmail.com
We isolated a new heterotrophic flagellate, strain SRT308 from marine sediment sample collected in Republic of Palau on October 2013. The flagellate is round or oval shape with two long subequal flagella and shows unique rotating motion by beating the both flagella synchronously. Since the morphological combination of the flagellate is unique, the flagellate is apparently a novel lineage of eukaryotes. In molecular phylogenetic analysis using small subunit ribosomal RNA gene sequences, the flagellate shows no strong affinity with major eukaryotic lineages. Large scale phylogenetic analysis using 153 protein-coding genes placed the flagellate at the base of Euglenozoa with strong statistical support, suggesting that the flagellate is a previously undescribed member of the Discoba clade. Consistent with the position inferred from the phylogenomic analysis, the flagellate was found to
share morphological characteristics, namely discoid mitochondrial cristae and parallel basal bodies, with euglenozoans. Furthermore, the flagellate has a euglenozoan-like tripartite flagellar root system, albeit the ventral root splits into two bands, which is similar to the R2 of other typical excavates. On the other hand, the flagellate lacks some englenozoan features, such as pellicle, paraxial rod, non-tubular mastigonemes, or feeding apparatus. Based on these morphological and ultrastructural features, the early character evolution of Englenozoa, as well as that of Discoba as a whole, will be discussed.
VIABLE AMOEBOID PROTISTS FROM THE ARCTIC PERMAFROST Shmakova L.A.
Institute of Physicochemical and Biological Problems in Soil Science, Russian Academy of Sciences lushmakova@gmail.com
Viable amoeboid protists were isolated from the Arctic Late Pleistocene and Holocene permafrost buried soils and sediments. A total of 36 strains of protists of the phylum Amoebozoa have been obtained. Most isolates belong to the genera Acanthamoeba and Flamella. We also isolated Vannella, Cochliopodium, Acramoeba, Phalansterium genera. Many of them belong to new species. Two species belonging to the genus Flamella have been described. They were named Flamella pleistocenica n. sp. and Flamella beringiania n. sp. Two new species of giant Acanthamoeba viruses, Pithovirus sibericum and Mollivirus sibericum, were isolated from buried soil of the age 34 000 years, and described. These are the first representatives of the two new families of Acanthamoeba giant viruses. We isolated amoebas from the permafrost of the age up to 50,000 years. The age ofviable organisms enclosed in the samples corresponds to the time of the last freezing ofthe strata. Mechanisms allowing amoebas to survive such a long cryptobiosis are poorly understood. All amoeba species from permafrost are cyst-forming. We studied the composition of the water extract of trophozoites, unmature, and mature cysts of Acanthamoeba castellanii recovered from permafrost. It was demonstrated that the accumulation of osmolytes such as trehalose, glycerol, tyrosine phosphate, alanine, choline, and a-Glycerophosphocholin occurs during en-cystation. These substances are known to serve as cell protectants during desiccation and freezing. This study directly shows for the first time that amoeba cysts can be conserved not only for years and decades but for many thousand years and then recover, contributing to the formation of an active microbial community.
