title: Does a DNA-less cellular organism exist on Earth?
abstract: All the self-reproducing cellular organisms so far examined have DNA as the genome. However, a DNA-less organism carrying an RNA genome is suggested by the fact that many RNA viruses exist and the widespread view that an RNA world existed before the present DNA world. Such a possibility is most plausible in the microbial world where biological diversity is enormous and most organisms have not been identified. We have developed experimental methodology to search DNA-less microorganisms, which is based on cultivation with drugs that inhibit replication or expression of DNA, detection of DNA in colonies with a fluorescent dye and double staining for DNA and RNA at a cellular level. These methods have been applied for about 100 microbial samples from various waters including hot springs, soils including deep sea sediments, and organisms. We found many colonies and cells which apparently looked DNA-less and examined them further. So far, all such colonies that reformed colonies on isolation were identified to be DNA-positive. However, considering the difficulty in cultivation, we think it possible for DNA-less microorganisms to live around us. We believe that our ideas and results will be of interest and useful to discover one in the future.
authors.affiliation: Department of Applied Life Science, Sojo University, Ikeda, Kumamoto city, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Hiyoshi
authors.forename: Kohji
authors.initials: K
authors.lastname: Miyahara
authors.forename: Chiaki
authors.initials: C
authors.lastname: Kato
authors.forename: Yasumi
authors.initials: Y
authors.lastname: Ohshima
mesh_terms: D000332:Aerobiosis; D000693:Anaerobiosis; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001105:Archaea / Q000235:genetics* / Q000302:isolation & purification; D001419:Bacteria / Q000235:genetics* / Q000302:isolation & purification; D015373:Bacterial Typing Techniques; D001562:Benzimidazoles / Q000032:analysis / Q000494:pharmacology; D002939:Ciprofloxacin / Q000494:pharmacology; D015169:Colony Count, Microbial; D004247:DNA / Q000235:genetics*; D004261:DNA Replication / Q000187:drug effects*; D018534:Earth, Planet; D005456:Fluorescent Dyes / Q000032:analysis; D045482:Hot Springs; D008853:Microscopy; D012313:RNA / Q000235:genetics*; D012293:Rifampin / Q000494:pharmacology; D012623:Seawater; D012988:Soil Microbiology; D013194:Staining and Labeling / Q000379:methods*; D014871:Water Microbiology
chemical_list: D000900:Anti-Bacterial Agents; D001562:Benzimidazoles; D005456:Fluorescent Dyes; D002939:Ciprofloxacin; D012313:RNA; D004247:DNA; C017807:bisbenzimide ethoxide trihydrochloride; D012293:Rifampin