Morris, Robert M.

Summary A hallmark of the SUP05 clade of marine Gammaproteobacteria is the ability to use energy obtained from reduced inorganic sulfur to fuel autotrophic fixation of carbon using RuBisCo. However, some SUP05 also have the genetic potential for heterotrophic growth, raising questions about the roles of SUP05 in the marine carbon cycle. We used genomic reconstructions, physiological growth experiments and proteomics to characterize central carbon and energy metabolism in Candidatus Thioglobus singularis strain PS1, a representative from the SUP05 clade that has the genetic potential for autotrophy and heterotrophy. Here, we show that the addition of individual organic compounds and 0.2 μm filtered diatom lysate significantly enhanced the growth of this bacterium. This positive growth response to organic substrates, combined with expression of a complete TCA cycle, heterotrophic pathways for carbon assimilation, and methylotrophic pathways for energy conversion demonstrate strain PS1's capacity for heterotrophic growth. Further, our inability to verify the expression of RuBisCO suggests that carbon fixation was not critical for growth. These results highlight the metabolic diversity of the SUP05 clade that harbours both primary producers and consumers of organic carbon in the oceans and expand our understanding of specific pathways of organic matter oxidation by the heterotrophic SUP05.

Summary Two phylogenetically distinct marine strains producing transparent exopolymers (TEP), designated HTCC2155 T and HTCC2160, were cultivated from Oregon coast seawater by dilution to extinction in a high throughput culturing format. When cultured in low‐nutrient seawater media, these strains copiously produced Alcian Blue‐stainable viscous TEP. Growing cells were attached to each other by the TEP in a three dimensional network. Polymerase chain reaction employing 16S rDNA primers specific for the novel isolates indicated that they are indigenous to the water column of the Atlantic and Pacific oceans. The abundance of the isolates as determined by 16S rRNA dot blots, however, indicated that they are less than 1% of the total bacterial community. In phylogenetic analyses, the strains consistently formed a new phylum‐level lineage within the domain Bacteria , together with members of the candidate phylum VadinBE97, which consists of Victivallis, the first cultured genus in the candidate phylum, and 16S rRNA gene clones from DNA extracted from marine or anaerobic terrestrial habitats. Five putative subgroups were delineated within this phylum‐level lineage, including a marine group and an anaerobic group. The isolates are Gram negative, strictly aerobic, chemoheterotrophic, and facultatively oligotrophic sphere‐shaped bacteria. The DNA G+C content of strain HTCC2155 T was 48.3 mol% and the genome size was 2.9 mb. It is proposed from these observations that the strains be placed into a new genus and a new species named Lentisphaera araneosa (type strain HTCC2155 T  = ATCC BAA‐859 T  = KCTC 12141 T ) gen. nov., sp. nov., the cultured marine representative of the Lentisphaerae phyl. nov., and the phylum be divided into two novel orders named the Lentisphaerales ord. nov. and the Victivallales ord. nov.