The physicochemical conditions of isolation source determine the occurrence of Pseudomonas fluorescens group species

Abstract

Pseudomonas fluorescens group species are indigenous bacteria in many different environments. The physicochemical conditions related to their selection to different surface and subsurface environments are poorly understood. We isolated 35 P. fluorescens group strains under the pesticide stress from mesocosms of surface soils and groundwater-monitoring pipe deposit slurries, and from a few of their initially sterilized counterparts, which were colonized during 599–625 days of laboratory incubation. In addition, strains were isolated from mesocosms of drilling sediment slurries. Based on the 16S rDNA analysis, strains belonged to five species. The statistical analysis of relationships between the isolates and physicochemical conditions in their isolation mesocosms revealed the typical habitats of five species. Pseudomonas IC038 and Pseudomonas LAB-23-like strains were common in mesocosms of deposit/sediment slurries low in growth substrates. Pseudomonas marginalis-like isolates preferred surface soil mesocosms rich in nutrients. Pseudomonas veronii and Pseudomonas mandelii-like strains grew in mesocosms of surface soils and subsurface deposit/sediment slurries, which indicated that they either had a versatile metabolism to adapt to different environments, or differed in substrate specificities. The initially sterilized mesocosms were mainly colonized with the same species as their non-sterilized counterparts, while all P. fluorescens group species tolerated atrazine and/or terbutryn. Our results on habitats were in agreement with the isolation sources of strains with identical 16S rDNA sequences in databases. The observed differences in the distribution patterns of the P. fluorescens group species indicate that species selection should be carefully done for man-made ecosystem applications, such as stable bioremediation.