To the average person, desert soils can appear to be dry, lifeless
environments. Research conducted by Fred Rainey and his colleagues
on microbial biodiversity dispels this myth and offers insight into
characteristics of some bacteria found in arid environments.
 Rainey’s
lab at Louisiana State University analyzed the ionizing-radiation
fractions of soil bacterial communities in a soil sample taken from
the CAP LTER study area. Previous research had suggested that ionizing-radiation
resistance is not simply an adaptation to environmental radiation.
Rainey and his colleagues hypothesized that DNA repair mechanisms
have evolved to compensate for desiccation, a stress producing a
pattern of DNA damage similar to that of ionizing radiation.
To test
this hypothesis, researchers compared the ionizing-radiation
fractions of soil bacterial communities in samples taken from the
Sonoran Desert and a Louisiana forest. They recovered bacterial isolates
surviving doses of 30 kGy from the Sonoran Desert soil, whereas no
bacteria in the Louisiana forest soil survived doses greater than
13 kGy. The study results were consistent with the hypothesis that
organisms with heightened DNA repair capacity are among the species
that have a selective advantage in arid environments.
Analysis of
the Sonoran Desert sample revealed that strains related to
the taxonomic groups Bosea, Chelatococcus, Corbulabacter, and Geodermatophilus,
Planococcus (species of the family Sphingomonadaceae) and
Spirosoma were resistant to gamma radiation, a new finding. Researchers
also recovered a high number of Deinococcus isolates from a soil
sample exposed to high ionizing-radiation levels, which confirmed
that species of this genus are very ionizing-radiation resistant.
Through genetic sequencing, the researchers established that nine
new species of the genus Deinococcus were present in the soil taken
from the Sonoran Desert: D. hohokamensis, D. navajonensis, D. hopiensis,
D. apachensis, D. maricopensis, D. pimensis, D. yavapaiensis, D.
papagonensis, and D. sonorensis.
Little is known about the microbial
diversity in arid environments, and there are few data about
the abundance or diversity of ionizing-radiation resistant bacteria
in these environments. Work by Rainey and his colleagues contributes
greatly to knowledge about bacterial communities in arid
environments and indicates direction for additional research on ionizing-radiation
resistant bacteria.
References
Rainey, F.A., K. Ray, M.
Ferreira, B. Gatz, M.F. Nobre, D. Bagaley, B. Rash, M.-J.
Park, A. Earl, N. Shank, A. Small, M. Henk, J. Battista,
P. Kämpfer,
and M. da Costa. 2005. Extensive diversity of ionizing-radiation-resistant
bacteria recovered from Sonoran Desert soil and description
of nine new species of the genus Deinococcus obtained from a single
soil sample. Applied and Environmental Microbiology 71(9):5225-5235.
CAP LTER Microbial Observatory at the Rainey Lab http://www.biology.lsu.edu/webfac/frainey/raineylab/capltermo/caplter.htm |
