No abstract

This study investigated the bulk nitrogen isotopic composition and fractionation of marine and freshwater cyanobacteria growing at the expense of atmospheric dinitrogen gas (N 2 ) or nitrate (NO { 3 ). In agreement with previous studies, cyanobacteria using N 2 had d 15 N values ranging from 22% to 21% and fractionated by 2-3% against atmospheric N 2 . When grown on NO { 3 , the analyzed cyanobacteria had a remarkably large range in d 15 N, from 214% to 1%, and fractionated by 4-19% relative to the supplied NO { 3 . Interestingly, several of the NO { 3 -utilizing cyanobacteria expressed a nitrogen isotopic signal similar to the one expected for diazotrophic species. Extrapolation to the natural environment indicates that d 15 N signals considered to be associated with dinitrogen fixation could also be generated by NO { 3 utilization, depending on the isotopic composition of the nitrogen source, the degree of fractionation, and the type of cyanobacterium involved.

N 2 -fixing cyanobacteria play an essential role in sustaining primary productivity in contemporary oceans and freshwater systems. However, the significance of N 2 -fixing cyanobacteria in past nitrogen cycling is difficult to establish as their preservation potential is relatively poor and specific biological markers are presently lacking. Heterocystous N 2 -fixing cyanobacteria synthesize unique long-chain glycolipids in the cell envelope covering the heterocyst cell to protect the oxygen-sensitive nitrogenase enzyme. We found that these heterocyst glycolipids are remarkably well preserved in (ancient) lacustrine and marine sediments, unambiguously indicating the (past) presence of N 2 -fixing heterocystous cyanobacteria. Analysis of Pleistocene sediments of the eastern Mediterranean Sea showed that heterocystous cyanobacteria, likely as epiphytes in symbiosis with planktonic diatoms, were particularly abundant during deposition of sapropels. Eocene Arctic Ocean sediments deposited at a time of large Azolla blooms contained glycolipids typical for heterocystous cyanobacteria presently living in symbiosis with the freshwater fern Azolla, indicating that this symbiosis already existed in that time. Our study thus suggests that heterocystous cyanobacteria played a major role in adding "new" fixed nitrogen to surface waters in past stratified oceans.nitrogen fixation | intact polar lipids | cyanobacterial biomarkers | symbiosis | saproprel

A novel archaeal lytic virus targeting species of the genus was isolated using strain Gö1 as the host. Due to its spherical morphology, the virus was designated hanosarcinapherical irus (MetSV). Molecular analysis demonstrated that MetSV contains double-stranded linear DNA with a genome size of 10,567 bp containing 22 open reading frames (ORFs), all oriented in the same direction. Functions were predicted for some of these ORFs, i.e., such as DNA polymerase, ATPase, and DNA-binding protein as well as envelope (structural) protein. MetSV-derived spacers in CRISPR loci were detected in several published draft genomes using bioinformatic tools, revealing a potential protospacer-adjacent motif (PAM) motif (TTA/T). Transcription and expression of several predicted viral ORFs were validated by reverse transcription-PCR (RT-PCR), PAGE analysis, and liquid chromatography-mass spectrometry (LC-MS)-based proteomics. Analysis of core lipids by atmospheric pressure chemical ionization (APCI) mass spectrometry showed that MetSV and both contain archaeol and glycerol dialkyl glycerol tetraether without a cyclopentane moiety (GDGT-0). The MetSV host range is limited to strains growing as single cells (, and). In contrast, strains growing as sarcina-like aggregates were apparently protected from infection. Heterogeneity related to morphology phases in cultures allowed acquisition of resistance to MetSV after challenge by growing cultures as sarcina-like aggregates. CRISPR/Cas-mediated resistance was excluded since neither of the two CRISPR arrays showed MetSV-derived spacer acquisition. Based on these findings, we propose that changing the morphology from single cells to sarcina-like aggregates upon rearrangement of the envelope structure prevents infection and subsequent lysis by MetSV. Methanoarchaea are among the most abundant organisms on the planet since they are present in high numbers in major anaerobic environments. They convert various carbon sources, e.g., acetate, methylamines, or methanol, to methane and carbon dioxide; thus, they have a significant impact on the emission of major greenhouse gases. Today, very little is known about viruses specifically infecting methanoarchaea that most probably impact the abundance of methanoarchaea in microbial consortia. Here, we characterize the first identified -infecting virus (MetSV) and show a mechanism for acquiring resistance against MetSV. Based on our results, we propose that growth as sarcina-like aggregates prevents infection and subsequent lysis. These findings allow new insights into the virus-host relationship in methanogenic community structures, their dynamics, and their phase heterogeneity. Moreover, the availability of a specific virus provides new possibilities to deepen our knowledge of the defense mechanisms of potential hosts and offers tools for genetic manipulation.

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