NUTRITIVE EFFECT OF BACTERIA FROM GENUS Limnohabitans ONGROWTH OF NATURAL HETEROTROPHIC FLAGELLATE COMMUNITIES

Različiti bakterijski sojevi mogu imati različitu nutritivnu vrijednost za heterotrofne bičaše i prema tome moduliraju rast heterotrofnih bičaša i vjerovatno sastav zajednica. Ispitivan je utjecaj nutritivne kvalitete tri bakterijska soja roda Limnohabitans na rast (stopa rasta, dužina lag faze) zajednica heterotrofnih bičaša. Zabilježena je i različita raspodjela volumena heterotrofnih bičaša u različitim vremenskim fazama eksperimenta. Sva tri testirana soja pokazala su se kao značajna za rast zajednica heterotrofnih bičaša no soj T6 (neopisani soj iz roda Limnohabitans) se istaknuo kao najbolji jer pokazuje najkraću lag-fazu i najveću stopu rasta. Podatci o raspodjeli veličina heterotrfonih bičaša pokazali su kako tijekom ranih faza eksperimenta dominiraju bičaši manjeg volumena što se kako je eksperiment odmicao pomicalo prema onima većega volumena, što vjerovatno ukazuje na to da postoji snažan utjecaj specifičnog plijena ili srodnih bakterija na sastav zajednica heterotrofnih bičaša ali nema direktnih dokaza za tu tvrdnju. Rezultati ovoga rada pružaju uvid u saznanja o tome koje bakterijske vrste sudjelu u prijenosu ugljika prema hranidbenom lancu grejzera u određenim vodenim ekosustavima.Different bacteria strains can have different value as a food for heterotrophic nanoflagellates (HNF),thus modulating HNF growth and probably community composition. It was examined how a prey food quality, of three bacterial strains from genus Limnohabitans effects on growth of HNF communities(growth rate, lenght of lag phase). There was a different volume distribution of heterotrophic nanoflagellates in different time-course stages of the experiment. All three tested strains demonstrated significant growth of HNF communities, but strain T6 (undescribed strain of genus Limnohabitans) is singeld out as the best because it shows the shortest lag-phase and the biggest growth rate during the experiment. Data on size distribution of HNF showed time-course shift of communities, from smaller flagellates that were dominant during the begining of the experiment, to the bigger ones in the last stages of the experiments.This probably indicates that there is prey-specific effect of bacteria on HNFcommunity composition but without any direct evidence supporting this theory. The results of this work show important insight regarding the question which bacteria strains are active in carbon transfer to the grazer food chain

NUTRITIVE EFFECT OF BACTERIA FROM GENUS Limnohabitans ONGROWTH OF NATURAL HETEROTROPHIC FLAGELLATE COMMUNITIES

Različiti bakterijski sojevi mogu imati različitu nutritivnu vrijednost za heterotrofne bičaše i prema tome moduliraju rast heterotrofnih bičaša i vjerovatno sastav zajednica. Ispitivan je utjecaj nutritivne kvalitete tri bakterijska soja roda Limnohabitans na rast (stopa rasta, dužina lag faze) zajednica heterotrofnih bičaša. Zabilježena je i različita raspodjela volumena heterotrofnih bičaša u različitim vremenskim fazama eksperimenta. Sva tri testirana soja pokazala su se kao značajna za rast zajednica heterotrofnih bičaša no soj T6 (neopisani soj iz roda Limnohabitans) se istaknuo kao najbolji jer pokazuje najkraću lag-fazu i najveću stopu rasta. Podatci o raspodjeli veličina heterotrfonih bičaša pokazali su kako tijekom ranih faza eksperimenta dominiraju bičaši manjeg volumena što se kako je eksperiment odmicao pomicalo prema onima većega volumena, što vjerovatno ukazuje na to da postoji snažan utjecaj specifičnog plijena ili srodnih bakterija na sastav zajednica heterotrofnih bičaša ali nema direktnih dokaza za tu tvrdnju. Rezultati ovoga rada pružaju uvid u saznanja o tome koje bakterijske vrste sudjelu u prijenosu ugljika prema hranidbenom lancu grejzera u određenim vodenim ekosustavima.Different bacteria strains can have different value as a food for heterotrophic nanoflagellates (HNF),thus modulating HNF growth and probably community composition. It was examined how a prey food quality, of three bacterial strains from genus Limnohabitans effects on growth of HNF communities(growth rate, lenght of lag phase). There was a different volume distribution of heterotrophic nanoflagellates in different time-course stages of the experiment. All three tested strains demonstrated significant growth of HNF communities, but strain T6 (undescribed strain of genus Limnohabitans) is singeld out as the best because it shows the shortest lag-phase and the biggest growth rate during the experiment. Data on size distribution of HNF showed time-course shift of communities, from smaller flagellates that were dominant during the begining of the experiment, to the bigger ones in the last stages of the experiments.This probably indicates that there is prey-specific effect of bacteria on HNFcommunity composition but without any direct evidence supporting this theory. The results of this work show important insight regarding the question which bacteria strains are active in carbon transfer to the grazer food chain

A freshwater radiation of diplonemids

Diplonemids are considered marine protists and have been reported among the most abundant and diverse eukaryotes in the world oceans. Recently we detected the presence of freshwater diplonemids in Lake Biwa, Japan. However, their distribution and abundances in freshwater ecosystems remain unknown. We assessed abundance and diversity of diplonemids from several geographically distant deep freshwater lakes of the world by amplicon-sequencing, shotgun metagenomics and CARD-FISH. We found diplonemids in all the studied lakes, albeit with low abundances and diversity. We assembled long 18S rRNA sequences from freshwater diplonemids and showed that they form a new lineage distinct from the diverse marine clades. Freshwater diplonemids are a sister-group to marine isolates from coastal and bay areas, suggesting a recent habitat transition from marine to freshwater habitats. Images of CARD-FISH targeted freshwater diplonemids suggest they feed on bacteria. Our analyses of 18S rRNA sequences retrieved from single cell genomes of marine diplonemids shows they encode multiple rRNA copies that may be very divergent from each other, suggesting that marine diplonemid abundance and diversity both have been overestimated. These results have wider implications on assessing eukaryotic abundances in natural habitats by using amplicon-sequencing alone

High-resolution metagenomic reconstruction of the freshwater spring bloom

Background The phytoplankton spring bloom in freshwater habitats is a complex, recurring, and dynamic ecological spectacle that unfolds at multiple biological scales. Although enormous taxonomic shifts in microbial assemblages during and after the bloom have been reported, genomic information on the microbial community of the spring bloom remains scarce. Results We performed a high-resolution spatio-temporal sampling of the spring bloom in a freshwater reservoir and describe a multitude of previously unknown taxa using metagenome-assembled genomes of eukaryotes, prokaryotes, and viruses in combination with a broad array of methodologies. The recovered genomes reveal multiple distributional dynamics for several bacterial groups with progressively increasing stratification. Analyses of abundances of metagenome-assembled genomes in concert with CARD-FISH revealed remarkably similar in situ doubling time estimates for dominant genome-streamlined microbial lineages. Discordance between quantitations of cryptophytes arising from sequence data and microscopic identification suggested the presence of hidden, yet extremely abundant aplastidic cryptophytes that were confirmed by CARD-FISH analyses. Aplastidic cryptophytes are prevalent throughout the water column but have never been considered in prior models of plankton dynamics. We also recovered the first metagenomic-assembled genomes of freshwater protists (a diatom and a haptophyte) along with thousands of giant viral genomic contigs, some of which appeared similar to viruses infecting haptophytes but owing to lack of known representatives, most remained without any indication of their hosts. The contrasting distribution of giant viruses that are present in the entire water column to that of parasitic perkinsids residing largely in deeper waters allows us to propose giant viruses as the biological agents of top-down control and bloom collapse, likely in combination with bottom-up factors like a nutrient limitation. Conclusion We reconstructed thousands of genomes of microbes and viruses from a freshwater spring bloom and show that such large-scale genome recovery allows tracking of planktonic succession in great detail. However, integration of metagenomic information with other methodologies (e.g., microscopy, CARD-FISH) remains critical to reveal diverse phenomena (e.g., distributional patterns, in situ doubling times) and novel participants (e.g., aplastidic cryptophytes) and to further refine existing ecological models (e.g., factors affecting bloom collapse). This work provides a genomic foundation for future approaches towards a fine-scale characterization of the organisms in relation to the rapidly changing environment during the course of the freshwater spring bloom

Efekti kratkotrajne kombinovane insulinske terapije na glikoregulaciju i insulinosekretornu funkciju kod bolesnika sa tipom 2 dijabetesa i sekundarnim neuspjehom oralne terapije

Uvod. Sekundarni neuspjeh oralne terapije se definiše kao izostanak povoljnogreagovanja na oralnu terapiju koja je u prethodnom periodu bilaefikasna. Cilj rada je da se ispitaju rezidualni efekti kratkotrajne kombinovaneinsulinske terapije na glikoregulaciju i insulinosekretornu funkciju.Metode. Istraživanje je obuhvatilo 53 ispitanika sa tipom 2 dijabetesa i sekundarnimneuspjehom oralne terapije koji su tri mjeseca liječeni kombinovanominsulinskom terapijom (bazalni insulin plus metformin). Nakonprocjene akutnih efekata insulinske terapije, ispitanici su naredna tri mjesecaliječeni oralnim antihiperglikemicima koje su koristili u momentu dijagnozesekundarnog neuspjeha, nakon čega su procjenjivani rezidualni efekti.Rezultati. Tromjesečna kombinovana terapija dovela je do značajnog poboljšanjaglikoregulacije (glikemija natašte: 9,4 mmol/l vs. 6,1 mmol/l; postprandijalnaglikemija: 11,5 mmol/l vs. 7,3mmol/l; dnevni profil glikemije:10,0 mmol/l vs. 7,2 mmol/l) i parametara insulinosekretorne funkcije (insulinemija:16,63 mU/l vs. 10,8 mU/l; C-peptid: 1,53 μg/ml vs. 1,81 μg/ml) uodnosu na period kada je konstatovan sekundarni neuspjeh oralne terapije(akutni efekti). Tri mjeseca po prekidu insulinske terapije zabilježeno je samomanje pogoršanje glikoregulacije i insulinosekretorne funkcije – rezidualniefekat (glikemija: 7,1mmol/l; postprandijalna glikemija: 8,3 mmol/l; dnevniprofil glikemije: 8,4mmol/l; insulinemija: 13,3mU/l; C-peptid: 1,72 μg /ml).Zaključak. Ponovno uvođenje oralnih antidijabetika nakon kratkotrajne primjeneinsulinske terapije uslovljava lagano pogoršanje insulinosekretornefunkcije, ali su ipak svi posmatrani parametri metaboličkog statusa u prosjekuznačajno bolji u odnosu na period prije kratkotrajne primjene insulina

Cascading effects in freshwater microbial food webs by predatory Cercozoa, Katablepharidacea and ciliates feeding on aplastidic bacterivorous cryptophytes

Heterotrophic nanoflagellates (HNF) are considered as major planktonic bacterivores, however, larger HNF taxa can also be important predators of eukaryotes. To examine this trophic cascading, natural protistan communities from a freshwater reservoir were released from grazing pressure by zooplankton via filtration through 10- and 5-µm filters, yielding microbial food webs of different complexity. Protistan growth was stimulated by amendments of five Limnohabitans strains, thus yielding five prey-specific treatments distinctly modulating protistan communities in 10- versus 5-µm fractions. HNF dynamics was tracked by applying five eukaryotic fluorescence in situ hybridization probes covering 55–90% of total flagellates. During the first experimental part, mainly small bacterivorous Cryptophyceae prevailed, with significantly higher abundances in 5-µm treatments. Larger predatory flagellates affiliating with Katablepharidacea and one Cercozoan lineage (increasing to up to 28% of total HNF) proliferated towards the experimental endpoint, having obviously small phagocytized HNF in their food vacuoles. These predatory flagellates reached higher abundances in 10-µm treatments, where small ciliate predators and flagellate hunters also (Urotricha spp., Balanion planctonicum) dominated the ciliate assemblage. Overall, our study reports pronounced cascading effects from bacteria to bacterivorous HNF, predatory HNF and ciliates in highly treatment-specific fashions, defined by both prey-food characteristics and feeding modes of predominating protists

Microbial food webs in hypertrophic fishponds: Omnivorous ciliate taxa are major protistan bacterivores

Despite the importance of shallow lakes worldwide, knowledge of microbial components, the base of their food webs, remains scarce. To close this gap, we investigated planktonic microbial food webs, in particular protistan bacterivory (for both ciliates and heterotrophic nanoflagellates [HNF]), in 10 shallow hypertrophic fishponds in South Bohemia (Czech Republic). We used fluorescently labeled bacteria as bacterivory tracers to estimate how abundant protistan populations in fishponds (4–25 × 103 HNF mL−1 and 55–770 ciliates mL−1) contribute to total bacterial mortality. Fluorescence microscopy, innovative image processing tools, and quantitative protargol staining were combined to detect major bacterivorous and omnivorous ciliate taxa. We quantified bacterial production, bacterivory by individual ciliate species, total ciliates, and total protistan bacterivory in all fishponds. On average, ciliate bacterivory was comparable to that of HNF, accounting for 56% and 44% of total protistan grazing, respectively. We found that primarily bacterivorous Peritrichia (genera Vorticella, Epistylis) and Scuticociliata (Cyclidium spp.) contributed only moderately (mean 26%) to total ciliate bacterivory. Unexpectedly, but highly abundant omnivorous Halteria/Pelagohalteria (Stichotrichia) and, to a lesser extent, also omnivorous Rimostrombidium spp. (Oligotrichia) contributed significantly more (mean 71%) to total ciliate bacterivory than typical bacterivorous taxa. This suggests that unselective grazers, which feed on a broader size spectrum from bacteria to small algae, may have a considerable competitive advantage in hypertrophic environments rich in small particles. Moreover, a meta‐analysis of available literature data supports our hypothesis that the role of ciliate bacterivory increases significantly, relative to HNF bacterivory, along a trophic gradient toward hypertrophic habitats