We screened soil samples for CO2-requiring extreme oligotrophs similar to Rhodococcus erythropolis N9T-4, which can grow on a basal salt agar medium without an organic carbon source. From 387 soil samples, three isolates were obtained and identified as Streptomyces spp. by 16S rDNA analysis. The isolates required gaseous CO2 for growth and grew on a basal salt medium solidified by silica gel. These results suggest that such CO2-requiring oligotrophs occur widely in nature.
