Genetic diversity among Arthrobacter species collected across a heterogeneous series of terrestrial deep-subsurface sediments as determined on the basis of 16S rRNA and recA gene sequences

This study was undertaken in an effort to understand how the population str ucture of bacteria within terrestrial deep-subsurface environments correlat es with the physical and chemical structure of their environment, Phylogene tic analysis was performed on strains of Arthrobacter that were collected f rom various depths, which included a number of different sedimentary units from the Yakima Barricade borehole at the U.S, Department of Energy's Hanfo rd site, Washington, in August 1992, At the same time that bacteria mere is olated, detailed information on the physical, chemical, and microbiological characteristics of the sediments was collected, Phylogenetic trees were pr epared from the 39 deep-subsurface Arthrobacter isolates las well as 17 rel ated type strains) based on 16S rRNA and recA gene sequences. Analyses base d an each gene independently were in general agreement. These analyses show ed that, for all but one of the strata (sedimentary layers characterized by their own unifying lithologic composition), the deep-subsurface isolates f rom the same stratum are largely monophyletic. Notably, the layers for whic h this is true were composed of impermeable sediments, This suggests that t he populations within each of these strata have remained isolated under con stant, uniform conditions, which have selected for a particular dominant ge notype in each stratum, Conversely, the few strains isolated from a gravel- rich Layer appeared along several lineages. This suggests that the higher-p ermeability gravel decreases the degree of isolation of this population (th rough greater groundwater how), creating fluctuations in environmental cond itions or allowing migration, such that a dominant population has not been established. No correlation was seen between the relationship of the strain s and any particular chemical or physical characteristics of the sediments. Thus, this work suggests that within sedimentary deep-subsurface environme nts, permeability of the deposits plays a major role in determining the gen etic structure of resident bacterial populations.