Starvation survivability of Thermococcus strains isolated from Japanese oil reservoirs

The starvation survivability of seven Thermococcus strains isolated from four Japanese oil reservoirs was compared with that of Thermococcus strains from marine hydrothermal fields. 16S rDNA analyses showed the isolates to be closely related to Thermococcus litoralis. Growth of the isolates was dependent on amino acids, which were present at low concentrations in the oil reservoirs. At 80 degrees C in the formation water, strain CKU-1 from the oil reservoir showed a higher starvation survivability than strain KS-1 from the marine hydrothermal field. Crude oil did not affect the starvation survivability of strain CKU-1, but it reduced that of strain KS-1. These results indicate that strain CKU-1 could survive longer than stain KS-1 under the conditions of an oil reservoir. At 90 degrees C in artificial seawater without organic nutrients, the half-lives of the isolates were between 7.7 and 25.1 days. However, those of the strains from marine hydrothermal fields, except Thermococcus litoralis and Thermococcus chitonophagus, were less than 1.0 day. The higher starvation survivability is probably important for the hyperthermophiles to continue to exist in a hot subterranean oil reservoir where the supply of nutrients seems to be limited.