Spear John R.

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Spear
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John R.
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  • Article
    Ancestral absence of electron transport chains in Patescibacteria and DPANN
    (Frontiers Media, 2020-08-17) Beam, Jacob P. ; Becraft, Eric D. ; Brown, Julia M. ; Schulz, Frederik ; Jarett, Jessica K. ; Bezuidt, Oliver ; Poulton, Nicole J. ; Clark, Kayla ; Dunfield, Peter F. ; Ravin, Nikolai V. ; Spear, John R. ; Hedlund, Brian P. ; Kormas, Konstantinos Ar. ; Sievert, Stefan M. ; Elshahed, Mostafa S. ; Barton, Hazel A. ; Stott, Matthew B. ; Eisen, Jonathan A. ; Moser, Duane P. ; Onstott, Tullis C. ; Woyke, Tanja ; Stepanauskas, Ramunas
    Recent discoveries suggest that the candidate superphyla Patescibacteria and DPANN constitute a large fraction of the phylogenetic diversity of Bacteria and Archaea. Their small genomes and limited coding potential have been hypothesized to be ancestral adaptations to obligate symbiotic lifestyles. To test this hypothesis, we performed cell–cell association, genomic, and phylogenetic analyses on 4,829 individual cells of Bacteria and Archaea from 46 globally distributed surface and subsurface field samples. This confirmed the ubiquity and abundance of Patescibacteria and DPANN in subsurface environments, the small size of their genomes and cells, and the divergence of their gene content from other Bacteria and Archaea. Our analyses suggest that most Patescibacteria and DPANN in the studied subsurface environments do not form specific physical associations with other microorganisms. These data also suggest that their unusual genomic features and prevalent auxotrophies may be a result of ancestral, minimal cellular energy transduction mechanisms that lack respiration, thus relying solely on fermentation for energy conservation.
  • Preprint
    Unexpected diversity and complexity of the Guerrero Negro hypersaline microbial mat
    ( 2006-02-26) Ley, Ruth E. ; Harris, J. Kirk ; Wilcox, Joshua ; Spear, John R. ; Miller, Scott R. ; Bebout, Brad M. ; Maresca, Julia A. ; Bryant, Donald A. ; Sogin, Mitchell L. ; Pace, Norman R.
    We applied nucleic acids-based molecular methods, combined with estimates of biomass (ATP), pigments and microelectrode measurements of chemical gradients, to map microbial diversity vertically on the mm-scale in a hypersaline microbial mat from Guerrero Negro, Baja California Sur, Mexico. To identify the constituents of the mat, small-subunit ribosomal RNA genes were amplified by PCR from community genomic DNA extracted from layers, cloned and sequenced. Bacteria dominated the mat and displayed unexpected and unprecedented diversity. The majority (1336) of 1586 bacterial 16S rRNA sequences generated were unique, representing 752 species (≥97% rRNA sequence identity) in 42 of the main bacterial phyla, including 15 novel candidate phyla. The diversity of the mat samples differentiated according to the chemical milieu defined by concentrations of O2 and H2S. Chloroflexi formed the majority of the biomass by percentage of bulk rRNA and of clones in rRNA gene libraries. This result contradicts the general belief that Cyanobacteria dominate these communities. Although Cyanobacteria constituted a large fraction of the biomass in the upper few mm (>80% of total rRNA and photosynthetic pigments), Chloroflexi sequences were conspicuous throughout the mat. Filamentous Chloroflexi were identified by fluorescent in-situ hybridization within the polysaccharide sheaths of the prominent cyanobacterium Microcoleus chthonoplastes in addition to free-living in the mat. The biological complexity of the mat far exceeds that observed in other polysaccharide-rich microbial ecosystems, such as human and mouse distal guts, and suggests that positive feedbacks exist between chemical complexity and biological diversity.