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  1. In nature, concentrations of dissolved inorganic carbon (DIC; = CO 2 + HCO 3 - + CO 3 2- ) can be low, and autotrophic organisms adapt with a variety of mechanisms to elevate intracellular DIC concentrations to enhance CO 2 fixation. Such mechanisms have been well-studied in Cyanobacteria , but much remains to be learned about their activity in other phyla. Novel multi-subunit membrane-spanning complexes capable of elevating intracellular DIC were recently described in three species of bacteria. Homologs of these complexes are distributed among 17 phyla in Bacteria and Archaea, and are predicted to consist of one, two, or three subunits. To determine whether DIC accumulation is a shared feature of these diverse complexes, seven of them, representative of organisms from four phyla, from a variety of habitats, and with three different subunit configurations were chosen for study. A high-CO 2 requiring, carbonic anhydrase-deficient ( yadF - cynT - ) strain of E. coli Lemo21(DE3), which could be rescued via elevated intracellular DIC concentrations, was created for heterologous expression and characterization of the complexes. Expression of all seven complexes rescued the ability of E. coli Lemo21(DE3) yadF - cynT - to grow under low CO 2 conditions, andmore »six of the seven generated measurably elevated intracellular DIC concentrations when their expression was induced. For complexes consisting of two or three subunits, all subunits were necessary for DIC accumulation. Isotopic disequilibrium experiments clarified that CO 2 was the substrate for these complexes. In addition, the presence of an ionophore prevented the accumulation of intracellular DIC, suggesting that these complexes may couple proton potential to DIC accumulation. IMPORTANCE To facilitate the synthesis of biomass from CO 2 , autotrophic organisms use a variety of mechanisms to increase intracellular DIC concentrations. A novel type of multi-subunit complex has recently been described, which has been shown to generate measurably elevated intracellular DIC concentrations in three species of bacteria, begging the question of whether these complexes share this capability across the 17 phyla of Bacteria and Archaea where they are found. This study shows that DIC accumulation is a trait shared by complexes with varied subunit structures, from organisms with diverse physiologies and taxonomies, suggesting that this trait is universal among them. Successful expression in E. coli suggests the possibility of their expression in engineered organisms synthesizing compounds of industrial importance from CO 2 .« less
  2. Phages (viruses that infect bacteria) play important roles in the gut ecosystem through infection of bacterial hosts, yet the gut virome remains poorly characterized. Mammalian gut viromes are dominated by double-stranded DNA (dsDNA) phages belonging to the order Caudovirales and single-stranded DNA (ssDNA) phages belonging to the family Microviridae. Since the relative proportion of each of these phage groups appears to correlate with age and health status in humans, it is critical to understand both ssDNA and dsDNA phages in the gut. Building upon prior research describing dsDNA viruses in the gut of Ciona robusta, a marine invertebrate model system used to study gut microbial interactions, this study investigated ssDNA phages found in the Ciona gut. We identified 258 Microviridae genomes, which were dominated by novel members of the Gokushovirinae subfamily, but also represented several proposed phylogenetic groups (Alpavirinae, Aravirinae, Group D, Parabacteroides prophages, and Pequeñovirus) and a novel group. Comparative analyses between Ciona specimens with full and cleared guts, as well as the surrounding water, indicated that Ciona retains a distinct and highly diverse community of ssDNA phages. This study significantly expands the known diversity within the Microviridae family and demonstrates the promise of Ciona as a model systemmore »for investigating their role in animal health.« less
  3. ABSTRACT Phage Cr39582 was induced by mitomycin C from Pseudoalteromonas sp. strain Cr6751, isolated from a marine invertebrate gut. Pseudoalteromonas phage Cr39582 has 85% pairwise nucleotide identity with phage PM2 but lacks sequence homology in the spike protein. This report supports previous bioinformatic identification of corticoviral sequences within aquatic bacterial genomes.