Hence, we undertook to investigate the mechanism of this phenomenon with respect to microbial symbiosis and adaptation. Succinatimonas hippei YIT 12066T is a strictly anaerobic, non-spore-forming, rod-shaped, Gram-negative bacterium isolated

from human feces. It is a novel species belonging to a novel genus in the lineage of Proteobacteria (phylum); Gammaproteobacteria (class); Aeromonadales (order); and Succinivibrionaceae (family). The details for the isolation of this bacterium were given previously (7). Modified GAM agar (Nissui Pharmaceutical, Tokyo Japan) and AnaeroPak system (Mitsubishi Gas Chemical, Tokyo, Japan) were used for the subsequent culture and maintenance of the strain. According to the manufacturer’s check details data, this incubation system creates anaerobic conditions of < 0.1% O2 with > 16% CO2. The composition of the modified GAM agar was described previously by Sakon et al. (11). As this strain was isolated under glove box culture conditions (88% N2, 7% H2, and 5% CO2) as described (7), the effects of the headspace gas on its growth were examined. When S. hippei YIT 12066T was cultured in modified GAM broth by using N2 as a headspace gas

to avoid any change in PLX4032 manufacturer the pH of the medium by CO2 gas, no growth was observed, even with a longer incubation period. Growth of the strain was observed only when CO2 gas was used as a headspace gas (Fig. 1a) or when the medium was supplemented with sodium bicarbonate even under N2 gas atmosphere

(Fig. 1b). Co-atmosphere culture vessels were designed (Fig. 2a) to test the effects of gases produced by metabolic activities of indigenous microbiota on the growth of S. hippei YIT 12066T. As shown in Figure 2b, co-atmosphere culture with fecal microbiota from three healthy subjects, A, B, and C, supported the growth of S. hippei YIT 12066T in a CO2-depleted environment. This result strongly suggests that CO2 generated by the metabolic activity of Idoxuridine indigenous microbiota induced the proliferation of S. hippei YIT 12066T. The requirement for an atmosphere containing high CO2 levels for growth is not unique among bacterial species. In 1971, Dehority (13) reported that an absolute requirement for CO2 was observed for some species of rumen bacteria, although the underlying reason was not clear. Recent studies have revealed that mutants for carbonic anhydrase (CA) of Ralstonia europha (14) and Escherichia coli (15,16) show an absolute growth dependence on CO2. In addition, recent completion of genomic sequencing of Symbiobacterium thermophilum, a CO2-requiring thermophilic bacterium isolated from compost, has revealed that the genome of this organism lacks the genes for CA (17). Carbonic anhydrases are ubiquitous zinc metalloenzymes that catalyze the interconversion of CO2 and bicarbonate anion (HCO3−), and have an extensive and fundamental role in prokaryotic biology (18).