Prokaryotic assemblages of halophilic protists in laboratory cultures

The modern ecosystems began to be formed in the Proterozoic Eon. The Proterozoic fossil record includes bacteria and cyanobacteria, heterotrophic and autotrophic protists, multicellular thallophytes, and metazoans. The gradual increase of the oxygen pressure in the atmosphere took place during the Proterozoic causing a great diversification of eukaryotic life and the origin of metazoans. The first autotrophic protists (acritarchs) originated in the Palaeoproterozoic and reached a high level of diversification in the early Neoproterozoic, when the first heterotrophic protists and biomineralized forms appeared. Several thallophytic groups may have originated during the Palaeoproterozoic, while the Rhodophyta probably radiated during the Mesoproterozoic, and Chlorophyta during the Neoproterozoic. The glacial episodes in the Neoproterozoic led to a mass extinction among protists. The Late Vendian ecosystems reveal deeply renewed assemblages of planktonic protists, problematic metazoan fauna (Ediacara Fauna), ichnofossils and slightly mineralized metazoans (Cloudina). The bioturbation characteristic for these ecosystems appears in form of small, simple and shallow burrows. The biotic turnover at the Neoproterozoic/Cambrian boundary is expressed by a mass extinction and the origin of new primary producers and consumers. The Cambrian rocks show a higher degree of bioturbation, suggesting a drastic change in the techniques of exploitation of the nutrients accumulated in the sediments.

Intermittent ponds of the New Jersey Pinelands are valuable ecosystems that support a diverse array of organisms including protists that play key roles in nutrient cycling and energy transfer within food webs. We used 18S-V9 DNA metabarcoding to explore protistan assemblages and their variation along a human-impact gradient in 30 natural and man-made Pinelands ponds. Heterotrophic protists were more diverse and abundant than phototrophs, especially in ponds surrounded by forest. Ciliates were the most abundant, while both ciliates and cercozoans were the most diverse taxonomic groups. Other prominent groups included amoebozoans, apicomplexans, peronosporomycetes, ochrophytes, dinoflagellates, and green algae. Protistan assemblage composition varied primarily with pH and along the land cover – eutrophication gradient. The most notable pattern in assemblage composition was a higher abundance of large-celled green algae in stormwater basins − man-made ponds with relatively low water quality, typically found in residential areas. While protistan assemblages in pond sediments were more diverse than those on submerged plants or artificial substrates, the latter still reflected the same environmental gradients as natural microhabitats.

Abstract1. Results from the few field studies that have tried to relate seston taxonomic and fatty acid (FA) composition suggest that phytoplankton composition only partially explains seston FA composition. However, in these studies, the heterotrophic components of seston (i.e. bacteria and heterotrophic protists) have not been accounted for.2. The general premise of this article was that including the contribution of heterotrophs to seston biomass can improve understanding of the variability in seston FA composition. This was tested for an oligotrophic clearwater lake, in which the taxonomic and FA compositions of seston, fractionated into three size classes, were monitored every 2 weeks over a growth season. The relationship between seston taxonomic and FA composition was studied using canonical correlation analyses.3. Because of their relative richness in branched FA and lack of highly unsaturated FAs (HUFA) compared to autotrophs and other protists, the contribution of bacteria to seston biomass was shown to explain an important part of the differences in FA composition between the different seston size classes. Phytoplankton seasonal succession also affected the FA composition of seston but only for size classes that were dominated by autotrophs.4. The results also indicated that heterotrophic protists such as ciliates and heterotrophic nanoflagellates might substantially influence the seston FA, and especially, HUFA, composition.5. The per cent of variability in seston FA composition that was explained by its taxonomic composition was still relatively low, even when taking account of heterotrophs. Hence, other possible influences, such as phytoplankton species composition, physiological state and the contribution of terrestrial detritus, need investigation.

To assess the contribution of n-3 essential lipids by heterotrophic protists in the pelagic food webs, we examined the kinetics and efficiency of long-chain n-3 essential fatty acid (LCn-3EFA) production of 2 common heterotrophic protists, Oxyrrhis marina and Gyrodinium dominans, fed an alga (Dunaliella tertiolecta) deficient in both eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). D. tertiolecta was rapidly ingested and consumed by the heterotrophic protists. Growth rates ranged from 0.77 to 0.82 and 0.78 to 0.92 d(-1) in O. marina and G. dominans, respectively. LCn-3EFA production in the 2 heterotrophic protists reached the highest levels at the highest protist cell density in the feeding experiments, equivalent to a production of 1.9 +/- 0.3 mu g EPA and 22.3 +/- 6.4 mu g DHA by O. marina and 4.7 +/- 0.5 mu g EPA and 16.5 +/- 1.1 mu g DHA by G. dominans per mg algal carbon consumed. Both protists contained much higher levels of DHA, a nutrient critical for neural and visual development for marine organisms at higher trophic levels, compared to the good food quality alga Rhodomonas salina. This suggests that the LCn-3EFA contribution by heterotrophic protists to the pelagic food webs is quantitatively significant and may be crucial for the production and recruitment of species at higher trophic levels, particularly at times of blooms dominated by algal species deficient in LCn-3EFAs or when the primary producer standing stock is dominated by pico- and nanoplankton during non-bloom periods.

The dark ocean is one of the largest biomes on Earth, with critical roles in organic matter remineralization and global carbon sequestration. Despite its recognized importance, little is known about some key microbial players, such as the community of heterotrophic protists (HP), which are likely the main consumers of prokaryotic biomass. To investigate this microbial component at a global scale, we determined their abundance and biomass in deepwater column samples from the Malaspina 2010 circumnavigation using a combination of epifluorescence microscopy and flow cytometry. HP were ubiquitously found at all depths investigated down to 4000 m. HP abundances decreased with depth, from an average of 72±19 cells ml(-1) in mesopelagic waters down to 11±1 cells ml(-1) in bathypelagic waters, whereas their total biomass decreased from 280±46 to 50±14 pg C ml(-1). The parameters that better explained the variance of HP abundance were depth and prokaryote abundance, and to lesser extent oxygen concentration. The generally good correlation with prokaryotic abundance suggested active grazing of HP on prokaryotes. On a finer scale, the prokaryote:HP abundance ratio varied at a regional scale, and sites with the highest ratios exhibited a larger contribution of fungi molecular signal. Our study is a step forward towards determining the relationship between HP and their environment, unveiling their importance as players in the dark ocean's microbial food web.

The food vacuole stain LysoTracker Green ® was used to enumerate heterotrophic pro- tists on a standard model flow cytometer. Appropriate stain concentration and staining time were determined using cultures of protists. Stained heterotrophic protists consistently formed distinct populations within cytograms of green fluorescence versus forward scatter. Cytometric counts of cultured species were compared to direct counts using light microscopy at cell abundances ranging from 10 3 to 10 6 cells ml -1 . A regression of these data was highly significant and yielded a slope of 0.95. Stained populations were accurately counted during lag, exponential and early stationary growth phases. Growth rates calculated from cytometric counts were not statistically different from those based on microscopy. The method was applied to 26 natural plankton samples, and general region definitions on the cytograms were established that identified heterotrophic protistan assemblages. Ar egression of cytometric counts versus direct counts yielded a slope of 1.16. LysoTracker Green ® can only be used with live samples because preservation destroys membrane potential, resulting in loss of fluorescence. However, the flow cytometric method employing LysoTracker Green ® is highly applicable for monitoring the growth of many heterotrophic protists in cultures and has the potential to be extremely useful for field samples, providing comparable counts to microscopical methods while allowing much faster sample processing.

The distribution and structure of heterotrophic protist communities and size-fractionated chlorophyll a were studied during the Korea Deep Ocean Study 98 (KODOS 98) research expedition (July 1998) in the northeast equatorial Pacific Ocean (5–11°N). Areas of convergence and divergence formed at the boundaries of the South Equatorial Current (SEC), North Equatorial Current (NEC), and North Equatorial Counter Current (NECC) during the expedition. Water column physicochemical characteristics significantly influenced the size structure of heterotrophic protist communities. Intense vertical mixing and high nutrient and chlorophyll a concentrations characterized SEC and NECC areas, which were affected by converging and diverging water masses, respectively. Nanophytoplankton dominated in SEC and NECC areas; both areas also had relatively high heterotrophic protist biomasses (average 743 µg C m−2). NEC areas were characterized by a stratified vertical structure, low nutrient and chlorophyll a concentrations, and picophytoplankton dominance. The heterotrophic protist biomass in NEC areas averaged 414 µg C m−2; nanoprotists ( 20 µm size classes in both water columns. The biomass of heterotrophic protists significantly correlated with the net-, nano-, and picophytoplankton biomass in SEC/NECC areas and with the nano- and picophytoplankton biomass in NEC areas. Heterotrophic protists and phytoplankton also showed strong positive correlation in the study area. The size structure of the phytoplankton biomass coincided with that of heterotrophic protists; the heterotrophic protist biomass positively correlated with the protists’ prey source. These relationships suggest that the community structure of heterotrophic protists and the microbial food web depended on size classes within the phytoplankton biomass. Microzooplankton grazing and phytoplankton growth rates were higher in SEC/NECC areas than in NEC areas. In contrast, the potential primary production grazed by microzooplankton was relatively high in NEC areas (127.3%) compared with SEC/NECC areas (94.6%). Our results indicate that the relative importance and size structure of heterotrophic protists might vary according to two distinct water column structures.

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 50:25-38 (2007) - DOI: https://doi.org/10.3354/ame01155 Grazing of large-sized bacteria by sea-ice heterotrophic protists on the Mackenzie Shelf during the winter–spring transition Andrea Riedel1,2,*, Christine Michel2, Michel Gosselin1 1Institut des sciences de la mer (ISMER), Université du Québec à Rimouski, 310 allée des Ursulines, Rimouski, Québec G5L 3A1, Canada 2Fisheries and Oceans Canada, Freshwater Institute, 501 University Crescent, Winnipeg, Manitoba R3T 2N6, Canada *Email: andrea.niemi@dfo-mpo.gc.ca ABSTRACT: Heterotrophic bacterial dynamics were assessed in the sea ice and surface waters on the Mackenzie Shelf (Beaufort Sea), from 5 March to 3 May 2004. On 11 occasions, heterotrophic protist bacterivory was assessed from the disappearance of fluorescently labeled bacteria (FLB) in sea-ice samples collected from areas of high and low snow cover. Concurrently, sea-ice and surface water samples were analyzed for dissolved organic carbon (DOC), exopolymeric substances (EPS) and chlorophyll a concentrations, and protist and bacterial abundances. Total bacterial abundances were significantly higher in the sea ice than in surface waters. However, DOC concentrations and abundances of large (≥0.7 µm) bacteria were not significantly higher in the sea ice as compared to surface waters. This suggests that DOC was being released from the sea ice, potentially supporting the growth of large-sized bacteria at the ice–water interface. Heterotrophic protist (HP) bacterivory averaged 57% d–1 of large-sized bacterial abundances in the sea ice with ingestion rates averaging 768 and 441 bacteria HP–1 d–1, under high and low snow cover, respectively. High concentrations of EPS during the sea-ice algal bloom may have interfered with the grazing activities of heterotrophic protists as indicated by the significant negative correlations between ingestion rates and EPS-carbon concentrations under high (τ = –0.57, p < 0.05) and low (τ = –0.56, p < 0.05) snow cover. Bacterivory satisfied heterotrophic protist carbon requirements prior to, but not during, the sea-ice algal bloom, under high and low snow cover. EPS may have been an additional carbon source for the heterotrophs, especially during the sea-ice algal bloom period. This study provides evidence of an active heterotrophic microbial food web in first-year sea ice, prior to and during the sea-ice algal bloom. This study also highlights the significance of DOC and EPS as integral components of the microbial food web within the sea ice and surface waters of Arctic shelves. KEY WORDS: Bacteria · FLB · Grazing · DOC · EPS · Sea ice · Arctic Full text in pdf format PreviousNextCite this article as: Riedel A, Michel C, Gosselin M (2007) Grazing of large-sized bacteria by sea-ice heterotrophic protists on the Mackenzie Shelf during the winter–spring transition. Aquat Microb Ecol 50:25-38. https://doi.org/10.3354/ame01155 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 50, No. 1. Online publication date: December 12, 2007 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2007 Inter-Research.

ABSTRACTProtists play key roles in aquatic food webs as primary producers, predators, nutrient recyclers, and symbionts. However, a comprehensive view of protist diversity in freshwaters has been challenged by the immense environmental heterogeneity among lakes worldwide. We assessed protist diversity in the surface waters of 366 freshwater lakes across a north temperate to subarctic range covering nearly 8.4 million km2 of Canada. Sampled lakes represented broad gradients in size, trophic state, and watershed land use. Hypereutrophic lakes contained the least diverse and most distinct protist communities relative to nutrient-poor lakes. Greater taxonomic variation among eutrophic lakes was mainly a product of heterotroph and mixotroph diversity, whereas phototroph assemblages were more similar under high-nutrient conditions. Overall, local physicochemical factors, particularly ion and nutrient concentrations, elicited the strongest responses in community structure, far outweighing the effects of geographic gradients. Despite their contrasting distribution patterns, obligate phototroph and heterotroph turnover was predicted by an overlapping set of environmental factors, while the metabolic plasticity of mixotrophs may have made them less predictable. Notably, protist diversity was associated with variation in watershed soil pH and agricultural crop coverage, pointing to human impact on the land-water interface that has not been previously identified in studies on smaller scales. Our study exposes the importance of both within-lake and external watershed characteristics in explaining protist diversity and biogeography, critical information for further developing an understanding of how freshwater lakes and their watersheds are impacted by anthropogenic stressors.IMPORTANCE Freshwater lakes are experiencing rapid changes under accelerated anthropogenic stress and a warming climate. Microorganisms underpin aquatic food webs, yet little is known about how freshwater microbial communities are responding to human impact. Here, we assessed the diversity of protists and their myriad ecological roles in lakes varying in size across watersheds experiencing a range of land use pressures by leveraging data from a continental-scale survey of Canadian lakes. We found evidence of human impact on protist assemblages through an association with lake trophic state and extending to agricultural activity and soil characteristics in the surrounding watershed. Furthermore, trophic state appeared to explain the distributions of phototrophic and heterotrophic protists in contrasting ways. Our findings highlight the vulnerability of lake ecosystems to increased land use and the importance of assessing terrestrial interfaces to elucidate freshwater ecosystem dynamics.

Protist entrapment in newly formed sea ice in the Coastal Arctic Ocean

1. The taxonomic composition, abundance and biomass of heterotrophic protists (ciliates, heterotrophic flagellates (HF), rhizopods and actinopods) in the sediment and water column of shallow inlets of the Southern Baltic was studied under a variety of environmental conditions during 1996–1997. A shallow, highly eutrophic station and a deeper, less eutrophic station were compared. 2. Community biomass ranged from 0.12 to 0.34 μg C cm−3 in the water column and from 1.5 to 105 μg C cm−3 in the sediment. Heterotrophic protists dominated zooplankton biomass at both stations (73% and 84% mean contribution), while they were of minor importance within the zoobenthos. Expressed per unit area, benthic biomass contributed a significant part (44% and 49%) to the total heterotrophic protistan community at both stations. 3. Although the methodology for counting ciliates and HF was focussed on a high taxonomic resolution, the results reveal some general trends in the distribution of heterotrophic protists: protozooplankton biomass was dominated by flagellates (80% mean biomass contribution) at the shallow station and by ciliates (73% mean biomass contribution) at the deep station. In the benthos at both stations, ciliates were the dominant protozoans, followed by the hitherto little‐studied rhizopods (25% and 35% mean biomass contribution) and flagellates. 4. The degree of benthic–pelagic coupling differed between taxonomic groups. Benthic and pelagic communities of ciliates showed little taxonomic overlap. In contrast, many heterotrophic flagellate species were found both in the benthos and in the pelagic. These benthic–pelagic species contributed significantly to the biomass of HF in the water column. The planktonic rhizopod community consisted of a subset of those species found in the benthos. 5. The abundance of benthic and pelagic protists was positively correlated at the shallow station, but taxonomic data indicate that the direct exchange between benthic and pelagic communities was only partly responsible.

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 260:33-41 (2003) - doi:10.3354/meps260033 Effects of high pH on the growth and survival of six marine heterotrophic protists Maria Fenger Pedersen, Per Juel Hansen* Marine Biological Laboratory, University of Copenhagen, Strandpromenaden 5, 3000 Helsingør, Denmark *Corresponding author. Email: pjhansen@zi.ku.dk ABSTRACT: The pH tolerance of the ciliates Balanion comatum, Favella ehrenbergii, Rimostrombidium caudatum and R. veniliae and the dinoflagellates Gyrodinium dominans and Oxyrrhis marina was studied using laboratory cultures at specific pH levels and prey concentrations. The results of these experiments divided the tested species into 2 groups: pH-tolerant species and pH-non-tolerant species. The tolerant group consisted of B. comatum, which experienced a reduction in growth when pH exceeded 9.5, and O. marina, which maintained its maximum growth within the pH limit of the experiment (pH 9.9). The pH-non-tolerant group consisted of 3 ciliates and 1 dinoflagellate. The most pH sensitive species were F. ehrenbergii, R. caudatum and R. veniliae. Their growth rate became affected at pH 8.8 to 8.9 and they did not grow when pH exceeded 9.0. The more tolerant species of this group, G. dominans, experienced a reduction in its growth when pH exceeded 9.2, and negative growth when pH exceeded 9.4. In a different set of experiments with the same species, the algae were allowed to grow and thereby raise the pH. In these experiments, the pH-sensitive species F. ehrenbergii, R. caudatum and R. veniliae all died within 24 h when pH exceeded 9.3, whereas some cells of the more tolerant dinoflagellate G. dominans were able to survive at pH values around 10 for up to 5 d. Thus, heterotrophic protists differ in their pH limits for growth and in their survival response when exposed to pH exceeding their limits for growth. In nature, algal blooms may lead to elevated pH (>9). Our results suggest that such pH levels will kill many, but not all, heterotrophic protists. This may, at least temporarily, lead to a reduction in grazing control of such algal blooms, thereby further allowing their growth and persistence. KEY WORDS: pH tolerance · Ciliates · Dinoflagellates · Balanion comatum · Rimostrombidium caudatum · Rimostrombidium veniliae · Gyrodinium dominans · Favella ehrenbergii · Oxyrrhis marina Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 260. Online publication date: September 30, 2003 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2003 Inter-Research.

Aquatic microbial food webs

Planktonic mixotrophic and heterotrophic dinoflagellates are ubiquitous protists and often abundant in marine environments. Recently many phototrophic dinoflagellate species have been revealed to be mixotrophic organisms and also it is suggested that most dinoflagellates may be mixotrophic or heterotrophic protists. The mixotrophic and heterotrophic dinoflagellates are able to feed on diverse prey items including bacteria, picoeukaryotes, nanoflagellates, diatoms, other dinoflagellates, heterotrophic protists, and metazoans due to their diverse feeding mechanisms. In turn they are ingested by many kinds of predators. Thus, the roles of the dinoflagellates in marine planktonic food webs are very diverse. The present paper reviewed the kind of prey which mixotrophic and heterotrophic dinoflagellates are able to feed on, feeding mechanisms, growth and ingestion rates of dinoflagellates, grazing impact by dinoflagellate predators on natural prey populations, predators on dinoflagellates, and red tides dominated by dinoflagellates. Based on this information, we suggested a new marine planktonic food web focusing on mixotrophic and heterotrophic dinoflagellates and provided an insight on the roles of dinoflagellates in the food web. © 2010 Korea Ocean Research &amp;amp; Development Institute (KORDI) and the Korean Society of Oceanography (KSO) and Springer Netherlands.

Marine plastic debris has become a significant concern in ocean ecosystems worldwide. Little is known, however, about its influence on microbial community structure and function. In 2008, we surveyed microbial communities and metabolic activities in seawater and on plastic on an oceanographic expedition through the "great Pacific garbage patch." The concentration of plastic particles in surface seawater within different size classes (2 to 5mm and >5mm) ranged from 0.35 to 3.7 particles m-3 across sampling stations. These densities and the particle size distribution were consistent with previous values reported in the North Pacific Ocean. Net community oxygen production (NCP = gross primary production - community respiration) on plastic debris was positive and so net autotrophic, whereas NCP in bulk seawater was close to zero. Scanning electron microscopy and metagenomic sequencing of plastic-attached communities revealed the dominance of a few metazoan taxa and a diverse assemblage of photoautotrophic and heterotrophic protists and bacteria. Bryozoa, Cyanobacteria, Alphaproteobacteria, and Bacteroidetes dominated all plastic particles, regardless of particle size. Bacteria inhabiting plastic were taxonomically distinct from the surrounding picoplankton and appeared well adapted to a surface-associated lifestyle. Genes with significantly higher abundances among plastic-attached bacteria included che genes, secretion system genes, and nifH genes, suggesting enrichment for chemotaxis, frequent cell-to-cell interactions, and nitrogen fixation. In aggregate, our findings suggest that plastic debris forms a habitat for complex microbial assemblages that have lifestyles, metabolic pathways, and biogeochemical activities that are distinct from those of free-living planktonic microbial communities. IMPORTANCE Marine plastic debris is a growing concern that has captured the general public's attention. While the negative impacts of plastic debris on oceanic macrobiota, including mammals and birds, are well documented, little is known about its influence on smaller marine residents, including microbes that have key roles in ocean biogeochemistry. Our work provides a new perspective on microbial communities inhabiting microplastics that includes its effect on microbial biogeochemical activities and a description of the cross-domain communities inhabiting plastic particles. This study is among the first molecular ecology, plastic debris biota surveys in the North Pacific Subtropical Gyre. It has identified fundamental differences in the functional potential and taxonomic composition of plastic-associated microbes versus planktonic microbes found in the surrounding open-ocean habitat. Author Video: An author video summary of this article is available.