Nucleic Acid Content in Crustacean Zooplankton: Bridging Metabolic and Stoichiometric Predictions

Metabolic and stoichiometric theories of ecology have provided broad complementary principles to understand ecosystem processes across different levels of biological organization. We tested several of their cornerstone hypotheses by measuring the nucleic acid (NA) and phosphorus (P) content of crustacean zooplankton species in 22 high mountain lakes (Sierra Nevada and the Pyrenees mountains, Spain). The P-allocation hypothesis (PAH) proposes that the genome size is smaller in cladocerans than in copepods as a result of selection for fast growth towards P-allocation from DNA to RNA under P limitation. Consistent with the PAH, the RNA:DNA ratio was >8-fold higher in cladocerans than in copepods, although ‘fast-growth’ cladocerans did not always exhibit higher RNA and lower DNA contents in comparison to ‘slow-growth’ copepods. We also showed strong associations among growth rate, RNA, and total P content supporting the growth rate hypothesis, which predicts that fast-growing organisms have high P content because of the preferential allocation to P-rich ribosomal RNA. In addition, we found that ontogenetic variability in NA content of the copepod Mixodiaptomus laciniatus (intra- and interstage variability) was comparable to the interspecific variability across other zooplankton species. Further, according to the metabolic theory of ecology, temperature should enhance growth rate and hence RNA demands. RNA content in zooplankton was correlated with temperature, but the relationships were nutrient-dependent, with a positive correlation in nutrient-rich ecosystems and a negative one in those with scarce nutrients. Overall our results illustrate the mechanistic connections among organismal NA content, growth rate, nutrients and temperature, contributing to the conceptual unification of metabolic and stoichiometric theories.This research was supported by the Spanish Ministries of Science and Innovation (CGL2011-23681/BOS), and Environment, Rural and Marine Affairs (OAPN2009/067); ‘Consejería de Innovación, Ciencia y Empresa – Junta de Andalucía’ (Excelencia CVI-02598; P09-RNM-5376); The Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (FORMAS) and Stockholm University’s strategic marine environmental research program ‘Baltic Ecosystem Adaptive Management’, and a Spanish government ‘Formación de Profesorado Universitario’ fellowship to F.J. Bullejos

Quantification of carbon and phosphorus co-limitation in bacterioplankton: new insights on an old topic

Because the nature of the main resource that limits bacterioplankton (e.g. organic carbon [C] or phosphorus [P]) has biogeochemical implications concerning organic C accumulation in freshwater ecosystems, empirical knowledge is needed concerning how bacteria respond to these two resources, available alone or together. We performed field experiments of resource manipulation (2×2 factorial design, with the addition of C, P, or both combined) in two Mediterranean freshwater ecosystems with contrasting trophic states (oligotrophy vs. eutrophy) and trophic natures (autotrophy vs. heterotrophy, measured as gross primary production:respiration ratio). Overall, the two resources synergistically co-limited bacterioplankton, i.e. the magnitude of the response of bacterial production and abundance to the two resources combined was higher than the additive response in both ecosystems. However, bacteria also responded positively to single P and C additions in the eutrophic ecosystem, but not to single C in the oligotrophic one, consistent with the value of the ratio between bacterial C demand and algal C supply. Accordingly, the trophic nature rather than the trophic state of the ecosystems proves to be a key feature determining the expected types of resource co-limitation of bacteria, as summarized in a proposed theoretical framework. The actual types of co-limitation shifted over time and partially deviated (a lesser degree of synergism) from the theoretical expectations, particularly in the eutrophic ecosystem. These deviations may be explained by extrinsic ecological forces to physiological limitations of bacteria, such as predation, whose role in our experiments is supported by the relationship between the dynamics of bacteria and bacterivores tested by SEMs (structural equation models). Our study, in line with the increasingly recognized role of freshwater ecosystems in the global C cycle, suggests that further attention should be focussed on the biotic interactions that modulate resource co-limitation of bacteria.This research was supported by Junta de Andalucía (Excelencia P09-RNM-5376 to JMMS) and the Spanish Ministry Ciencia e Innovación (CGL2011-23681 to PC)

Hepatic glutamine synthetase controls N⁵-methylglutamine in homeostasis and cancer

Funding: This work was funded by Cancer Research UK awards A17196 and A31287 (CRUK Beatson Institute), Cancer Research UK RadNet Glasgow Centre award A28803 (A.B.), Wellcome Trust grant WT107492Z (T.G.B. and M.M.), Cancer Research UK HUNTER accelerator award A26813 (E.H.T.), Cancer Research UK award A25045 and DRCQQR-May21\100002 (O.J.S.), Cancer Research UK award A29256 (D.T.H.), Cancer Research UK award A29799 (K.B.), Cancer Research UK award A25006 (D.Y.L.) and Cancer Research UK award A23982 (S.T.).Glutamine synthetase (GS) activity is conserved from prokaryotes to humans, where the ATP-dependent production of glutamine from glutamate and ammonia is essential for neurotransmission and ammonia detoxification. Here, we show that mammalian GS uses glutamate and methylamine to produce a methylated glutamine analog, N5-methylglutamine. Untargeted metabolomics revealed that liver-specific GS deletion and its pharmacological inhibition in mice suppress hepatic and circulating levels of N5-methylglutamine. This alternative activity of GS was confirmed in human recombinant enzyme and cells, where a pathogenic mutation in the active site (R324C) promoted the synthesis of N5-methylglutamine over glutamine. N5-methylglutamine is detected in the circulation, and its levels are sustained by the microbiome, as demonstrated by using germ-free mice. Finally, we show that urine levels of N5-methylglutamine correlate with tumor burden and GS expression in a β-catenin-driven model of liver cancer, highlighting the translational potential of this uncharacterized metabolite.Publisher PDFPeer reviewe

Esofagites em pacientes com síndrome de imunodeficiência adquirida: estudo histológico e imunoistoquímico Esophagitis in patients with acquired human immunodeficiency syndrome: an histological and immunohistochemistry study

RACIONAL: A maioria dos pacientes com síndrome da imunodeficiência adquirida cursa com sintomas gastrointestinais ao longo da sua evolução. A alta prevalência e morbidade das esofagites nesses pacientes são amplamente reconhecidas. OBJETIVOS: Graduar, histologicamente, as esofagites; identificar os agentes associados, tais como Candida sp, citomegalovírus, herpes vírus e micobactérias; identificar, através da imunoistoquímica, os seguintes agentes: citomegalovírus, herpes vírus I e II, vírus Epstein-Barr, vírus do papiloma humano e vírus da imunodeficiência adquirida; verificar a contribuição da imunoistoquímica para o diagnóstico dos agentes infecciosos; verificar a associação entre os achados histológicos e endoscópicos; verificar a relevância do número de fragmentos na caracterização dos agentes etiológicos. MÉTODOS: Estudaram-se, retrospectivamente, biopsias esofagianas em 227 pacientes com síndrome da imunodeficiência adquirida. Utilizaram-se as colorações de hematoxilina e eosina, PAS ("periodic acid of Schiff"), prata de Grocott e Ziehl-Nielsen, assim como a imunoistoquímica para a detecção de infecções por agentes oportunistas. Aspectos endoscópicos também foram avaliados. RESULTADOS: A esofagite inespecífica acentuada, localizada no terço inferior, foi o tipo mais freqüente. A Candida sp foi o agente mais encontrado, seguida de citomegalovírus, herpes vírus e micobactérias. A presença de placa e ulceração sugeriu o diagnóstico de candidíase e esofagite por citomegalovírus, respectivamente. O herpes vírus I não foi encontrado isolado e sim associado ao herpes vírus II. Não houve imunorreatividade para o vírus Epstein-Barr e o vírus da imunodeficiência adquirida. O número de fragmentos nas amostras não influenciou na detecção do agente etiológico. CONCLUSÃO: Os achados endoscópicos de lesão em placa ou de úlcera estão associados com os diagnósticos de Candida sp e citomegalovírus, respectivamente. O emprego da técnica de imunoistoquímica auxilia no diagnóstico das esofagites virais e torna possível detectar o citomegalovírus em esôfagos normais à endoscopia e/ou ao exame histopatológico.<br>BACKGROUND: Almost all patients with acquired immunodeficiency virus syndrome will have gastrointestinal symptoms during the course of their illness. The high prevalence and complications of esophagitis are well documented. AIM: Graduate esophagitis; identify microorganisms like Candida sp, cytomegalovirus, herpesvirus and mycobacteria; identify by immunohistochemical staining viral agents cytomegalovirus, herpesvirus I, herpesvirus II, Epstein-Barr Virus, human papilloma virus and human immunodeficiency virus; verify how immunohistochemistry changes the profile of esophagitis; verify the association between the histological and endoscopical findings; verify the relevance of the number of fragments studied in the characterization of the histological agents. METHODS: We studied retrospectively esophageal biopsies in 227 patients with acquired immunodeficiency virus syndrome using hematoxylin and eosin, PAS (periodic acid of Schiff), Groccott and Ziehl-Nielsen stains and immunoperoxidase stains to detect opportunistic agents. Endoscopic aspects were studied. RESULTS: The non-specific esophagitis grade III, in the inferior third of the esophagus, was the most frequent type. Candida sp was the most frequent agent, followed by viruses cytomegalovirus, herpesvirus and mycobacteria. The presence of plaque and ulceration suggested the diagnosis of esophageal candidiasis and cytomegalovirus esophagitis. Immunohistochemical allowed the characterization of cytomegalovirus and of herpesvirus in those cases where other techniques could not achieve it, furthermore the cytomegalovirus was also found in histological normal cases, making the use of this technique advisable in routine diagnosis. The herpesvirus I was not found isolated but associated to herpesvirus II. We have not found immunoreactivity for the Epstein-Barr virus and the human immunodeficiency virus. The number of fragments does not seem to influence the detection of the etiologic agent. CONCLUSION: The endoscopic findings of plaques or ulcers are associated with candidiasis or cytomegalovirus esophagitis. Immunohistochemisty improved the diagnosis of viral infections. It is possible to detect cytomegalovirus infections in endoscopic and histologic normal cases