Distribution of metabolic activity and phosphate starvation response of lux-tagged Pseudomonas fluorescens reporter bacteria in the barley rhizosphere

• Published in: Applied and Environmental Microbiology 1997-12, Vol.63 (12), p.4920-4928
• Main Authors: Kragelund, L, Hosbond, C, Nybroe, O
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; Amino Acid Sequence; Bacteriology; Base Sequence; Biochemistry and biology; Biological and medical sciences; Chemical, physicochemical, biochemical and biological properties; DNA Primers - genetics; DNA Transposable Elements - genetics; DNA, Bacterial - genetics; Escherichia coli - genetics; Fundamental and applied biological sciences. Psychology; GENBANK/U59930; Genes, Bacterial; Genes, Reporter; Genetics; Hordeum - microbiology; HORDEUM VULGARE; Luciferases - genetics; Luminescence; Metabolism; Microbiology; MOLECULAR SEQUENCE DATA; NUCLEOTIDE SEQUENCE; Phosphates; Phosphates - metabolism; Physics, chemistry, biochemistry and biology of agricultural and forest soils; PSEUDOMONAS FLUORESCENS; Pseudomonas fluorescens - genetics; Pseudomonas fluorescens - metabolism; RHIZOSPHERE; RIZOSFERA; SECUENCIA NUCLEOTIDICA; SEQUENCE NUCLEOTIDIQUE; Soil science; Symbiosis
• ISSN: 0099-2240; 1098-5336
• DOI: 10.1128/aem.63.12.4920-4928.1997

The purpose of this study was to determine the metabolic activity of Pseudomonas fluorescens DF57 in the barley rhizosphere and to assess whether sufficient phosphate was available to the bacterium. Hence, two DF57 reporter strains carrying chromosomal luxAB gene fusions were introduced into the rhizosphere. Strain DF57-40E7 expressed luxAB constitutively, making bioluminescence dependent upon the metabolic activity of the cells under defined assay conditions. The DF57-P2 reporter strain responded to phosphate limitation and the luxAB gene fusion was controlled by a promoter containing regulatory sequences characteristic of members of the phosphate (Pho) regulon. DFS7 generally had higher metabolic activity in a gnotobiotic rhizosphere than in the corresponding bulk soil. Within the rhizosphere the distribution of metabolic activity along the root differed between the rhizosphere soil and the rhizoplane, suggesting that growth conditions may differ between these two habitats. The DF57-P2 reporter strain encountered phosphate limitation in a gnotobiotic rhizosphere but not in a natural rhizosphere. This difference in phosphate availability seemed to be due to the indigenous microbial population, as DF57-P2 did not report phosphate limitation when established in the rhizosphere of plants in sterilized soil amended with indigenous microorganisms