Enrichment and Isolation of Microorganisms. Carbonmonoxide-utilizing microorganisms were selectively isolated from anaerobic enrichment cultures. About 50 ml of reduced liquid medium (described below) was prepared, but without adding trypticase, and inoculated with a 1 g sample of anaerobic, black sediment from Crystal Lake, Urbana, Ill. or from a duck pond located outside Champaign, Ill. Enrichment cultures were incubated at 340 under a stream of sterile, oxygenfreeH2-CO gas (80:20 mixture). When turbid growth developed, a sample of cells was obtained from the enrichment culture by means of a platinum inoculation loop and transferred into 50 ml of sterile reduced liquid medium prepared as before. After cells had been subcultured under the H2-CO gas atmosphere at least three times, a loopful of cells was spread onto sterile solid medium prepared in an anaerobic bottle (19). Using routine techniques, three strains of a Rhodopseudomonas species were isolated from different enrichment cultures that grew in strictly dark conditions (19) under pure CO gas.
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