Thermocrinis ruber gen. nov., sp. nov., A pink-filament-forming hyperthermophilic bacterium isolated from yellowstone national park

A novel hyperthermophilic bacterium was isolated from pink filamentous streamers (pink filaments) occurring in the upper outflow channel (temperature, 82 to 88 degreesC) of Octopus Spring in Yellowstone National Park, Wyo. The gram-negative cells grew at low salinity at temperatures up to 89 degreesC in the neutral to alkaline pH range. Depending on the culture conditions, the organisms occurred as single motile rods, as aggregates, or as long filaments that formed streamer-like cell masses. The novel isolate grew chemolithoautotrophically with hydrogen, thiosulfate, and elemental sulfur as electron donors and oxygen as the electron acceptor. Alternatively, under aerobic conditions, formate and formamide served as sole energy and carbon sources. The novel isolate had a 16S rRNA sequence closely related to the 16S rRNA sequence obtained from uncultivated pink filaments. It represents a new genus in the order Aquificales, the type species of which we name Thermocrinis ruber (type strain, OC 1/4 [= DSM 12173]).

Pathways of autotrophic CO2 fixation and of dissimilatory nitrate reduction to N2O in Ferroglobus placidus

The strictly anaerobic Archaeon Ferroglobus placidus was grown chemolithoautotrophically on H2 and nitrate and analyzed for enzymes and coenzymes possibly involved in autotrophic CO2 fixation. The following enzymes were found [values in parentheses = µmol min-1 (mg protein)-1]: formylmethanofuran dehydrogenase (0.2), formylmethanofuran:tetrahydromethanopterin formyltransferase (0.6), methenyltetrahydromethanopterin cyclohydrolase (10), F420-dependent methylenetetrahydromethanopterin dehydrogenase (1.5), F420-dependent methylenetetrahydromethanopterin reductase (0.4), and carbon monoxide dehydrogenase (0.1). The cells contained coenzyme F420 (0.4 nmol/mg protein), tetrahydromethanopterin (0.9 nmol/ mg protein), and cytochrome b (4 nmol/mg membrane protein). From the enzyme and coenzyme composition of the cells, we deduced that autotrophic CO2 fixation in F. placidus proceeds via the carbon monoxide dehydrogenase pathway as in autotrophically growing Archaeoglobus and Methanoarchaea species. Evidence is also presented that cell extracts of F. placidus catalyze the reduction of two molecules of nitrite to 1 N2O with NO as intermediate (0.1 µmol N2O formed per min and mg protein), showing that - at least in principle - F. placidus has a denitrifying capacity.