Process for culturing microorganisms on a selected substrate

1. A process for culturing acetogenic bacteria on syngas, the process comprising:

culturing the acetogenic bacteria on a first substrate to provide a cell density of at least about 0.005 g/L, wherein the first substrate includes a carbon source selected from the group consisting of yeast extract, carbohydrates, alcohol, amino acids, peptone, peptides, protein, fatty acids, lipid and mixtures thereof;

sporulating the acetogenic bacteria by replacing at least a portion of the first substrate with syngas having at least about 10 mole % CO and replacing at least a portion of a first medium with a production medium to convert at least a portion of the bacteria to spores, wherein the sporulating provides a spore number to cell number ratio of about 0.05 or more; and

germinating the spores in the production medium at a pH of about 4.1 to about 5 with syngas having at least about 10 mole % CO to provide a specific CO uptake of at least about 0.25 mmole/min/gram of cells and a space time yield (STY) of about 1 g or more ethanol/(L·day gram cells).

2. The process of claim 1 wherein the syngas has a CO/CO 2 molar ratio of at least about 0.75.

3. The process of claim 1 wherein the acetogenic bacterium is selected from the group consisting of Acetogenium kivui, Acetoanaerobium noterae, Acetobacterium woodii, Alkalibaculum bacchi CP11 (ATCC BAA-1772), Blautia producta, Butyribacterium methylotrophicum, Caldanaerobacter subterraneous, Caldanaerobacter subterraneous pacificus, Carboxydothermus hydrogenoformans, Clostridium aceticum, Clostridium acetobutylicum, Clostridium acetobutylicum P262 (DSM 19630 of DSMZ Germany), Clostridium autoethanogenum (DSM 19630 of DSMZ Germany), Clostridium autoethanogenum (DSM 10061 of DSMZ Germany), Clostridium autoethanogenum (DSM 23693 of DSMZ Germany), Clostridium autoethanogenum (DSM 24138 of DSMZ Germany), Clostridium carboxidivorans P7 (ATCC PTA-7827), Clostridium coskatii (ATCC PTA-10522), Clostridium drakei, Clostridium ljungdahlii PETC (ATCC 49587), Clostridium ljungdahlii ERI2 (ATCC 55380), Clostridium ljungdahlii C-01 (ATCC 55988), Clostridium ljungdahlii O-52 (ATCC 55889), Clostridium magnum, Clostridium pasteurianum (DSM 525 of DSMZ Germany), Clostridium ragsdali P11 (ATCC BAA-622), Clostridium scatologenes, Clostridium thermoaceticum, Clostridium ultunense, Desulfotomaculum kuznetsovii, Eubacterium limosum, Geobacter sulfurreducens, Methanosarcina acetivorans, Methanosarcina barkeri, Morrella thermoacetica, Morrella thermoautotrophica, Oxobacter pfennigii, Peptostreptococcus productus, Ruminococcus productus, Thermoanaerobacter kivui , and mixtures thereof.

4. The process of claim 1 wherein germinating is effective for providing a spore number to cell number ratio of about 0.04 or less.

5. The process of claim 1 wherein the production medium comprises at least one or more of:

at least about 112 mg of nitrogen per gram of cells,

at least about 10.5 mg of phosphorous per gram of cells, or

at least about 26 mg of potassium per gram of cells.