title: The cyanobacterium Mastigocladus fulfills the nitrogen demand of a terrestrial hot spring microbial mat.
abstract: Cyanobacteria from Subsection V (Stigonematales) are important components of microbial mats in non-acidic terrestrial hot springs. Despite their diazotrophic nature (N2 fixers), their impact on the nitrogen cycle in such extreme ecosystems remains unknown. Here, we surveyed the identity and activity of diazotrophic cyanobacteria in the neutral hot spring of Porcelana (Northern Patagonia, Chile) during 2009 and 2011-2013. We used 16S rRNA and the nifH gene to analyze the distribution and diversity of diazotrophic cyanobacteria. Our results demonstrate the dominance of the heterocystous genus Mastigocladus (Stigonematales) along the entire temperature gradient of the hot spring (69-38 °C). In situ nitrogenase activity (acetylene reduction), nitrogen fixation rates (cellular uptake of (15)N2) and nifH transcription levels in the microbial mats showed that nitrogen fixation and nifH mRNA expression were light-dependent. Nitrogen fixation activities were detected at temperatures ranging from 58 °C to 46 °C, with maximum daily rates of 600 nmol C2H4 cm(-2) per day and 94.1 nmol N cm(-2) per day. These activity patterns strongly suggest a heterocystous cyanobacterial origin and reveal a correlation between nitrogenase activity and nifH gene expression during diurnal cycles in thermal microbial mats. N and C fixation in the mats contributed ~3 g N m(-2) per year and 27 g C m(-2) per year, suggesting that these vital demands are fully met by the diazotrophic and photoautotrophic capacities of the cyanobacteria in the Porcelana hot spring.
authors.affiliation: Department of Molecular Genetics and Microbiology, Faculty of Biological Sciences, Pontificia Universidad Católica de Chile, Santiago, Chile.
authors.forename: María
authors.initials: M
authors.lastname: Estrella Alcamán
authors.affiliation: Laboratoire d'Océanographie Microbienne, Observatoire Océanologique, Sorbonne Universités, UPMC Univ Paris 06, UMR 7621, Banyuls/mer, France.|CNRS, UMR 7621, Laboratoire d'Océanographie Microbienne, Observatoire Océanologique, Banyuls/mer, France.|Department of Oceanography, Interdisciplinary Center for Aquaculture Research (INCAR) and COPAS SURAUSTRAL Program, University of Concepción, Concepción, Chile.
authors.forename: Camila
authors.initials: C
authors.lastname: Fernandez
authors.affiliation: Instituto Andaluz de Ciencias de la Tierra (CSIC-Univ. Granada), Armilla, Granada, Spain.
authors.forename: Antonio
authors.identifier: http://orcid.org/0000-0002-7240-1570
authors.initials: A
authors.lastname: Delgado
authors.affiliation: Department of Ecology, Environment and Plant Sciences and Science for Life Laboratory, Stockholm University, Stockholm, Sweden.
authors.forename: Birgitta
authors.initials: B
authors.lastname: Bergman
authors.affiliation: Department of Molecular Genetics and Microbiology, Faculty of Biological Sciences, Pontificia Universidad Católica de Chile, Santiago, Chile.|Center for Climate and Resilience Research (CR)2, Santiago, Chile.
authors.forename: Beatriz
authors.initials: B
authors.lastname: Díez
mesh_terms: D000114:Acetylene / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D044822:Biodiversity; D002677:Chile; D000458:Cyanobacteria / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism; D004269:DNA, Bacterial / Q000235:genetics / Q000378:metabolism; D017753:Ecosystem; D045482:Hot Springs / Q000382:microbiology*; D009584:Nitrogen / Q000378:metabolism*; D009586:Nitrogen Fixation / Q000235:genetics / Q000502:physiology; D009591:Nitrogenase / Q000378:metabolism; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D012336:RNA, Ribosomal, 16S / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D012333:RNA, Messenger; D012336:RNA, Ribosomal, 16S; D010088:Oxidoreductases; D009591:Nitrogenase; C029130:nitrogenase reductase; D009584:Nitrogen; D000114:Acetylene