Endosymbiotic Diatoms Research Articles

Dinotoms possess two evolutionary distinct autophagy-related ubiquitin-like conjugation systems

Autophagy is an intracellular degradation mechanism by which cytoplasmic materials are delivered to and degraded in the lysosome-fused autophagosome (autolysosome) and proposed to have been established at an early stage of eukaryotic evolution. Dinoflagellates harboring endosymbiotic diatoms (so-called “dinotoms”), which retain their own nuclei and mitochondria in addition to plastids, have been investigated as an intermediate toward the full integration of a eukaryotic phototroph into the host-controlled organelle (i.e., plastid) through endosymbiosis. Pioneering studies systematically evaluated the degree of host governance on several metabolic pathways in the endosymbiotic diatoms (ESDs). However, little attention has been paid to the impact of the endosymbiotic lifestyle on the autophagy operated in the ESDs. In this study, we searched for ATG3, ATG4, ATG5, ATG7, ATG8, ATG10, and ATG12, which are required for autophagosome formation, in the RNA-seq data from dinotoms Durinskia baltica and Kryptoperidinium foliaceum. We detected two evolutionally distinct sets of the ATG proteins in the dinotom species, one affiliated with the dinoflagellate homologs and the other with the diatom homologs in phylogenetic analyses. The results suggest that the ATG proteins descended from the diatom taken up by the dinoflagellate host persist for autophagosome formation and, most likely, autophagy.

Lunar cycles and rainy seasons drive growth and reproduction in nummulitid foraminifera, important producers of carbonate buildups

Representatives of the foraminifer Nummulites are important in Earth history for timing Cenozoic shallow-water carbonates. Taphonomic complexity explains the construction of carbonate buildups, but reproduction and life span of the constructing individuals are unknown. During the 15-month investigation period, asexually reproduced schizonts and gamonts showed equal proportions in the first half of this period, whereas gamonts predominated in the second half. Oscillations in cell growth are mainly caused by light intensities during chamber construction when minor differences in water depth increase the photosynthetic rate of endosymbiotic diatoms during neap tides. The continuous reproduction rate of N. venosus throughout the year is increased in subtropical calms by higher summer temperatures and the marginal input of inorganic nutrients during rainy seasons. The expected life span of both gamonts and schizonts are 18 months.

Variable thermal stress tolerance of the reef-associated symbiont-bearing foraminifera Amphistegina linked to differences in symbiont type

Adaptation, acclimatization and symbiont diversity are known to regulate thermal tolerance in corals, but the role of these mechanisms remains poorly constrained in other photosymbioses, such as large benthic foraminifera (LBFs), which are known to bleach at temperatures that are likely to be exceeded in the near future. LBFs inhabit a broad range of shallow-water settings. Within species, differences in thermal tolerance have been found among populations from different habitats, but it is not clear whether such differences occur among LBFs inhabiting similar habitats, but differing in other aspects, such as symbiont type. To this end, we compared responses to thermal stress in specimens from a population of Amphistegina lessonii, an abundant Indo-Pacific species, to specimens of Amphistegina gibbosa, its Atlantic counterpart, from a similar environment but two different water depths (5 and 18 m). Test groups of each species were exposed in a common experiment to three thermal stress scenarios over a four-week period. Growth, respiration, mortality and motility were measured to characterize the holobiont response. Coloration, photosynthesis and chlorophyll a content were measured to determine the response of the endosymbiotic diatoms. The photosymbionts were characterized by genetic fingerprinting. Our results show that, although groups of A. gibbosa were collected from different habitats, their responses were similar, indicating only marginally higher tolerance to thermal peaks in specimens from the shallower site. In contrast, species-specific differences were stronger, with A. lessonii showing higher tolerance to episodic stress and less pronounced impacts of chronic stress on motility, growth and photosymbiont performance. These interspecies variations are consistent with the presence of different and more diverse symbiont assemblages in A. lessonii compared with A. gibbosa. This study demonstrates the importance of considering symbiont diversity in the assessment of intra- and interspecific variations in stress responses in LBFs.

Durinskia baltica (Dinophyceae), a newly recorded species and genus from China, and its systematics

Abstract A freshwater dinoflagellate was identified as Durinskia baltica (Levander) Carty & Cox by morphological characteristics, with the plate formula: Po, x, 4′, 2a, 6″, 5c, 4s, 5‴, 2″″. Durinskia was a newly recorded dinoflagellate genus for China with two anterior intercalary plates and six characteristic precingular plates. Partial sequences of the small and large subunit ribosomal DNA and internal transcribed spacer sequences for the dinoflagellate cells were obtained from field samples. Molecular phylogenetic results indicated Durinskia species could cluster into a monophyletic group, which were distinct from Peridinium species. According to morphological and molecular evidence, it was agreed that the genus Durinskia was separated from the genus Peridinium, which could be a polyphyletic group. In addition, D. baltica was an infrequent diatom‐harboring dinoflagellate which was known to possess an endosymbiotic diatom or diatom‐like alga. The phylogenetic analyses indicated that D. baltica had a close affinity with Peridiniopsis penardii and P. niei, common freshwater bloom‐forming species in China.

Temperature‐induced stress leads to bleaching in larger benthic foraminifera hosting endosymbiotic diatoms

Physiological mechanisms of bleaching were studied on larger benthic foraminifera (LBF) hosting endosymbiotic diatoms. Amphistegina radiata, Heterostegina depressa, and Calcarina hispida were exposed to increasing temperatures in static temperature experiments (23°C to 33°C, 6 d). Photosynthetic activity (Fv : Fm, measured with a pulse‐amplitude modulated fluorometer), chlorophyll a (a proxy for symbiont biomass), and motility (a proxy for overall fitness of the foraminifera) were reduced in specimens at 32°C to 33°C, and cytoplasm color changes associated with bleaching were observed. A 30‐d flow‐through experiment at three temperatures (26°C to 31°C) and three levels of inorganic nitrate concentration (0.5 to 1.4 µmol L−1) confirmed negative effects of temperature at 31°C for A. radiata (including growth) and H. depressa. Another Calcarina species, Calcarina mayorii, was not affected. This suggests that temperature effects are species‐specific. However, elevated nutrient concentrations did not affect any of the parameters measured. Temperatures > 30°C stress the foram–diatom endosymbiosis in some LBF species, which may lead to subsequent bleaching of the host. Given that a 2–3°C increase led to rapid bleaching of most species, we propose that, similar to corals, these species are threatened by sea‐surface temperature increase predicted for tropical reef waters in the near future.

Morphological differences and molecular phylogeny of freshwater blooming species, Peridiniopsis spp. (Dinophyceae) from China

In 2008–2010, several freshwater dinoflagellate blooms caused by Peridiniopsis spp. were observed in China. P. penardii and P. niei sampled from various geographical localities were examined by means of light and scanning electron microscopy. After comparing morphological and molecular differences, the new freshwater variety Peridiniopsis penardii var. robusta var. nov. (Peridiniales, Dinophyceae) found in Manwan Reservoir, Yunnan Province was described. The new variety differed from P. penardii since it possessed numerous robust antapical spines and a conspicuous apical spine. Molecular phylogenetic analyses based on SSU, LSU and ITS indicated P. niei, P. penardii and P. penardii var. robusta were closely related with P. kevei, and clustered into a monophyletic clade. The new variety possessed an endosymbiotic diatom which was similar to P. penardii and P. kevei, whereas the endosymbiont was not present in cells of P. niei. The endosymbiont SSU and ITS phylogenies showed that the endosymbionts of these three dinoflagellates were closely related to members of Thalassiosirales. Furthermore it was concluded that the endosymbionts might originate from Discostella-like species.

EVOLUTIONARY ANALYSES OF THE NUCLEAR-ENCODED PHOTOSYNTHETIC GENE psbO FROM TERTIARY PLASTID-CONTAINING ALGAE IN DINOPHYTA(1).

Although the dinophytes generally possess red-algal-derived secondary plastids, tertiary plastids originating from haptophyte and diatom ancestors are recognized in some lineages within the Dinophyta. However, little is known about the nuclear-encoded genes of plastid-targeted proteins from the dinophytes with diatom-derived tertiary plastids. We analyzed the sequences of the nuclear psbO gene encoding oxygen-evolving enhancer protein from various algae with red-algal-derived secondary and tertiary plastids. Based on our sequencing of 10 new genes and phylogenetic analysis of PsbO amino acid sequences from a wide taxon sampling of red algae and organisms with red-algal-derived plastids, dinophytes form three separate lineages: one composed of peridinin-containing species with secondary plastids, and the other two having haptophyte- or diatom-derived tertiary plastids and forming a robust monophyletic group with haptophytes and diatoms, respectively. Comparison of the N-terminal sequences of PsbO proteins suggests that psbO genes from a dinophyte with diatom-derived tertiary plastids (Kryptoperidinium) encode proteins that are targeted to the diatom plastid from the endosymbiotic diatom nucleus as in the secondary phototrophs, whereas the fucoxanthin-containing dinophytes (Karenia and Karlodinium) have evolved an additional system of psbO genes for targeting the PsbO proteins to their haptophyte-derived tertiary plastids from the host dinophyte nuclei.

CYTOLOGICAL EXAMINATION AND LOCATION OF SYMBIONTS IN "LIVING SANDS" - BACULOGYPSINA

Specimens of the “living star-sand,” Baculogypsina sphaerulata , were collected from Lizard Island, Great Barrier Reef, Australia. Detailed cytological study of these algal-bearing foraminifera helped us to understand for the first time the relationship of the endosymbiotic diatoms to the complex morphology of the Baculogypsina test and its canal systems. We find that the symbionts are widely distributed in most of the chamberlets, especially in the umbilical and central parts of the test. In the proloculus and inner chamberlets, the symbionts are somewhat less abundant. Furthermore, the fossil canal liners and the expanded internal pore domes were empty of individual symbionts. It is now clear that regarding B. sphaerulata there is no special relationship between the symbionts and the homologs of the pores and liners as found in Amphistegina spp.

Serial replacement of diatom endosymbionts in two freshwater dinoflagellates, Peridiniopsis spp. (Peridiniales, Dinophyceae)

Y. Takano, G. Hansen, D. Fujita and T. Horiguchi. 2007. Serial replacement of diatom endosymbionts in two freshwater dinoflagellates, Peridiniopsis spp. (Peridiniales, Dinophyceae). Phycologia 47: 41–53. DOI: 10.2216/07-36.1Two freshwater armoured dinoflagellates, Peridiniopsis cf. kevei from Japan and Peridiniopsis penardii from Japan and Italy, were examined by means of light, scanning and transmission electron microscopy. Morphological studies indicated that the two dinoflagellates had similar type of cellular structure and possessed an endosymbiotic diatom. The diatom endosymbiont, which contained a eukaryotic nucleus, chloroplasts and mitochondria, was separated from the dinoflagellate cytoplasm by a single unit membrane. The dinoflagellate cytoplasm contained a triple-membrane-bound eyespot, in addition to typical dinoflagellate organelles. Molecular phylogenetic analyses based on small subunit ribosomal RNA gene (SSU rDNA) revealed a close relationship between these two dinoflagellates. They formed a clade with other dinoflagellates possessing a diatom endosymbiont, suggesting a single origin of diatom-harbouring dinoflagellates. On the contrary, the phylogenetic analyses based on plastid-encoded rbcL and nuclear-encoded SSU rDNA of the endosymbionts included the endosymbiont of these two freshwater dinoflagellates in the Thalassiosira/Skeletonema-clade (Centrales), whereas the endosymbionts of other diatom-containing dinoflagellates, except for Peridinium quinquecorne, were closely related to members of the Bacillariaceae (Pennales), most likely a Nitzschia-like diatom. The discrepancy between the host phylogeny and the endosymbiont phylogeny suggested, as in the case of Peridinium quinquecorne, that there was a serial replacement of endosymbionts from original a pennate Nitzschia-like diatom to a centric diatom, such as Thalassiosira (or possibly Skeletonema).

New tools for resolving phylogenies: a systematic revision of the Convolutidae (Acoelomorpha, Acoela)

Molecular sequence data, morphological characters of spermatozoa, and newly obtained morphological characters of penis musculature are used here to revise the systematics of the family Convolutidae (Acoela). Species having isodiametric penes with non-anastomosing longitudinal muscles are transferred to the family Isodiametridae fam. nov. Species with longitudinal penis muscle fibres that anastomose or cross-over each other remain in the Convolutidae. Some species of the genera Convoluta and Conaperta (Convolutidae) are transferred to the genus Isodiametra gen. nov. (Isodiametridae fam. nov.). The genus Stomatricha (Otocelididae) is transferred to the family Convolutidae. Convoluta opisthandropora (Convolutidae) is transferred to the genus Pseudohaplogonaria (Haploposthiidae). Aphanostoma sanguineum (Convolutidae) is transferred to the genus Pseudactinoposthia (Actinoposthiidae). Zusammenfassung Molekulare Sequenzdaten, Spermien-Morphologie und erstmals ermittelte morphologische Merkmale der Penismuskulatur werden herangezogen, um die Verwandtschaftsverhaltnisse innerhalb der Familie Convolutidae (Acoela) neu zu beleuchten. Dabei werden Arten mit isodiametrischen Penes mit nicht anastomosierender Langsmuskulatur in die neue Familie Isodiametridae gestellt, wahrend Arten mit longitudinalen Penis-Muskelfasern, die sich verbunden oder einanderuberkreuzen, innerhalb der Convolutidae belassen. Einige Arten der Gattungen Convoluta und Conaperta (Convolutidae) werden in die neue Gattung Isodiametra gen. nov. (Isodametridae fam. nov.) gestellt. Die Gattung Stomatricha (Otocelididae) wird in die Familie Convolutidae uberfuhrt. Convoluta opisthandropora (Convolutidae) wird in die Gattung Pseudohaplogonaria (Haploposthiidae) gestellt und Aphanostoma sanguineum (Convolutidae) in die Gattung Pseudactinoposthia (Actinoposthiidae).

Isolation and identification of endosymbiotic diatoms from planktonic and benthic species of foraminifera

Isolation and identification of endosymbiotic diatoms from planktonic and benthic species of foraminifera

Diatom symbionts in larger foraminifera from Caribbean hosts

Larger foraminifera, as a group, are the hosts for many different types of algae. The majority of modern families host small (< 10 μm) pennate endosymbiotic diatoms. In these, the host/symbiont relationship is not finical. Studies from hosts harvested from Indo-Pacific habitats have shown some symbiont species are found with greater frequency than others, but any one of twenty different diatom species may be found in the same host. This study examined the endosymbionts from two diatom-bearing hosts from the Caribbean, Amphistigina gibbosa and Heterostegina antillarum. A high number of hosts harbored more than one symbiont species. A new variety of Nitzschia frustulum was involved in many (33%) of the symbioses. Many of the isolates of this taxon, if it is to be considered only one, are extremely aberrant forms for the genus. Another common (18%) isolate was an unidentified species of Navicula. A highly variable Amphora sp. was also isolated. These taxa will require more detailed examination in the future. Many of the isolates from the Caribbean hosts also were known as endosymbionts from previous studies: Nitzschia laevis N. frustulum var. symbiotica N. valdestriata, Amphora tenerrima, Navicula muscatini, Cocconeis andersoni and Fragillaria shiloi. A number of endosymbiotic species, common in Indo-Pacific hosts, were not found in the Caribbean hosts studied. The results of the present study are in consonance with those of previous studies.

Identification and Distribution of Endosymbiotic Diatoms in Larger Foraminifera

The diatom endosymbionts have been isolated in culture from over 2,000 specimens of larg iner a (Amphistegina lessonii, A. lobifera, Heterostegina depressa, Borelis schlumbergi, Operculina ammonoides, Calcarina calcar) harvested from Red Sea, Indian Ocean, Hawaii, Palau, and the Great Barrier Reef stations. Twenty different species or varieties of diatoms were collectively isolated from the 6 host species in the total samples. Nitzschia frustulum var. symbiotica was the most commonly (33.7% of total hosts) isolated endosymbiont. Next most common were Nitzschia panduriformis var. continua, Fragilaria shiloi, Nitzschia laevis, and Amphora roettgerii, respectively, representing 14.5, 9.9, 8.7, and 6% of the isolations. More than half of the isolations were made in the vacinity of the H. Steinitz Marine Biology Laboratory on the Gulf of Elat, Red Sea so that the results have to be interpreted with that bias in mind. N. frustulum var. symbiotica was the most frequently isolated endosymbiont at all sites where more than 75 organisms were studied. Significant numbers of N. frustulum var. symbiotica, N. laevis and N. panduriformis var. continua were isolated from hosts collected at every depth. Fragilaria shiloi, in contrast, was rarely isolated from hosts at depths greater than 25m. Achnanthes maceneryae, Amphora sp.(J) and Protokeelia hottingeri were only collected in hosts harvested at depths greater than 25m. Although host species harbored more than one endosymbiont species some bias was observed. Nitzschia laevis and F. shiloi were the most common symbionts of B. schlumbergeri. A. maceneryae and N. laevis were isolated in over 55% of all the 0. ammonoides studied. Most larger foraminifera were the hosts for only a single species of symbiont (71%) at a time; a second symbiont species was found in the remainder. Studies of the microflora on substrates on which larger foraminifera were feeding showed no correlation between potential diet and the endosymbiotic diatoms present in foraminifera harvested from the same substrates. Endosymbiotic diatoms were extremely rare (<0. 5%) in the habitat where the foraminifera were feeding.

STRUCTURAL ORGANIZATION OF PLASTID DNA IN TWO ANOMALOUSLY PIGMENTED DINOFLAGELLATES1

ABSTRACTThe structural organization of DNA in the plastids of two anomalously pigmented dinoflagellates, Glenodinium foliaceum Stein and Gyrodinium aureolum Hulburt, was determined using the DNA‐specific fluorochrome DAPI and correlated with TEM observations. The plastids of G. foliaceum were found to possess both a peripheral DNA ring and isolated point nucleoids. This arrangement was shown to be similar to that of the diatom Asterionella formosa Hass. and may be characteristic of the Bacillariophyceae. G. aureolum exhibited a novel distribution of plastid. DNA as one or two beaded bands, whereas the plastids of the similarly pigmented haptophyte, Emiliania huxleyi (Lohm.) Hay &amp; Mohler, possessed scattered point nucleoids. These findings support the idea that G. foliaceum harbours an endosymbiotic diatom, but suggest that the plastids of G. aureolum and E. huxleyi are unrelated. The use of plastid DNA configuration as a phylogenetic marker is considered.

Effects of host cell extracts on cultures of endosymbiotic diatoms from larger foraminifera

Log phase endosymbiotic diatom species, Nitzschia valdestriata, N. laevis, N. panduriformis var. continua, N. frustulum var. subsalina and var. symbiotica, Amphora tenerima, Fragilaria shiloi and Navicula hanseniana, were aseptically exposed to an homogenate of freshly crushed foraminiferal host species (Amphistegina). To various degrees, depending upon endosymbiont species, the host homogenate affected the formation of new frustules of growing and dividing cells. F. shiloi was the most affected species. New cells were spheroids and had only vestiges of frustules or none at all. Fewer numbers of the other species tested (40 to 60%) were abnormal. The raphe and keel of affected Nitzschia spp. were usually curved and incomplete. Many cells were spherical. We infer that “host substances” are probably responsible for the maintenance of the frustule-less state in vivo and that if ingested potential endosymbionts escape digestion, they could become frustule-less after growth and cell division. Host homogenate also increased the levels of photosynthetate released by diatoms to their medium. N. valdestriata was stimulated to release 76% of its photosynthetate while other species tested were stimulated to release between one quarter to one half of their photosynthetate. Host homogenate was also effective in causing the release of 43% of the photosynthetate of a free-living diatom, Amphora sp., which was also tested in the experiment. The concentration of the metabolites released in the experiment was too low for us to identify by TLC.

A comparative study of photoadaptation in four diatoms isolated as endosymbionts from larger foraminifera

Four endosymbiotic diatoms were isolated from 2 species of larger foraminifera collected in the Red Sea and Hawaii. The photoadaptive responses of the cultured diatoms were measured at 312, 19 and 7 μW cm-2. Two of the diatoms (Fragilaria shiloi and Nitzschia laevis), both isolated from Amphistegina lessonii, grew fastest at 312 μW cm-2. The other two diatoms (N. valdestriata and N. panduriformis) which were isolated from Heterostegina depressa, grew best at 19 μW cm-2. Of the four diatoms, F. shiloi grew best at high light levels. Also in F. shiloi, chlorophyll c content per cell was directly proportional to light intensity; in contrast chlorophyll a and carotenoids increased to maxima at 19 μW cm-2. The chlorophyll a and c and carotenoid content of N. valdestriata were also maximal at 19 μW cm-2. Photosynthetic rates, measured by respirometry, suggested that the diatoms were photoinhibited at higher light intensities and did well at moderately low light intensities (175μW cm-2). The photocompensation points of all 4 diatoms were about 2% of the light available in the spring at 1-m depth at Elat on the Red Sea. At Elat the photocompensation point would lie between 40 and 50 m if the algae were free in nature. The amount of attenuation of light by the shells of the host has not yet been measured. Presumably photocompensation of the algae within hosts is reached at depths less than 40 m.