MINIMAL CHANGES IN RHIZOBACTERIAL POPULATION STRUCTURE FOLLOWING INOCULATION WITH WILD-TYPE AND TRANSGENIC BIOCONTROL STRAINS

Authors: BANKHEAD BLOUIN, STACEY - WASHINGTON STATE UNIV; LANDA, BLANCA - INSTITUTO DE AGRICULTURA; LUTTON, E - OHIO STATE UNIVERSITY; Weller, David; MCSPADDEN GARDNER, BRIAN - OHIO STATE UNIVERSITY

Submitted to: Federation of European Microbiological Societies Microbiology Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/20/2004
Publication Date: 7/20/2004
Citation: Bankhead Blouin, S., Landa, B., Lutton, E., Weller, D.M., Mcspadden Gardner, B.B. 2004. Minimal changes in rhizobacterial population structure following inoculation with wild-type and transgenic biocontrol strains. FEMS Microbiology Ecol. 49:307-318

Interpretive Summary: Antibiotic-producing Pseudomonas fluorescens, such as 2-79, which produces phenazine carboxylic acid (PCA) and Q8r1-97, that produces 2-4 diacetylphloroglucinol (DAPG) have been shown to suppress root diseases such as take-all of wheat. These findings led to the development of the transgenic bacteria, Z-30-97, that produces both antibiotics. In this study, we characterized the impact of the transgene on both the indigenous microflora and the introduced strains' rhizosphere colonization efficiency compared to that of the wild-type strain in greenhouse trials. Using FT-ARDRA, a culture independent method, we found that although small changes occurred in the community profile with the addition of the inoculant strains, there were no consistent patterns established. The FT-ARDRA results were reinforced by the culture-based counts of heterotrophic bacteria which did not differ significantly among treatments in the majority of cycles. Additionally, the transgene did not seem to have an effect on the colonization efficiency of the bacterial strain when compared to the wild-type. Therefore, we conclude that the introduced, transgenic bacteria is similar in its effects to naturally occurring bacteria in the rhizosphere.

Technical Abstract: Rhizosphere colonization by three different bacterial biological control agents and their impact on bacterial community structure was assayed over multiple growth cycles. Prior to planting, soils were inoculated with wild-type or transgenic Pseudomonas fluorescens strains that produce the antibiotics phenazine carboxylic acid (PCA) and/or 2-4 diacetylphloroglucinol (DAPG). While only inoculated at log 4 colony forming units (CFUs) per g prior to planting, the three biocontrol strains all colonized wheat roots to levels exceeding log 6 per g (f.w.) by the end of the first growth cycle. Nonetheless, strain-specific differences in colonization potential were observed over multiple cycles of the experiment. Using culture independent and culture dependent methods, multiple differences in bacterial community structure among treatments were noted in each cycle. However, the noted effects were not consistently related to the population size nor genetic make-up of the inoculant strains. We conclude that the application of these biocontrol strains caused only small and transient disturbances in the structure of bacterial communities that colonize growing wheat roots.