Oxygen-Sensing Reporter Strain of Pseudomonas fluorescens for Monitoring the Distribution of Low-Oxygen Habitats in Soil

Abstract

The root-colonizing bacterium Pseudomonas fluorescensCHA0 was used to construct an oxygen-responsive biosensor. An anaerobically inducible promoter of Pseudomonas aeruginosa, which depends on the FNR (fumarate and nitrate reductase regulation)-like transcriptional regulator ANR (anaerobic regulation of arginine deiminase and nitrate reductase pathways), was fused to the structural lacZ gene of Escherichia coli. By inserting the reporter fusion into the chromosomalattTn7 site of P. fluorescens CHA0 by using a mini-Tn7 transposon, the reporter strain, CHA900, was obtained. Grown in glutamate-yeast extract medium in an oxystat at defined oxygen levels, the biosensor CHA900 responded to a decrease in oxygen concentration from 210 × 102 Pa to 2 × 102 Pa of O2 by a nearly 100-fold increase in β-galactosidase activity. Half-maximal induction of the reporter occurred at about 5 × 102 Pa. This dose response closely resembles that found for E. colipromoters which are activated by the FNR protein. In a carbon-free buffer or in bulk soil, the biosensor CHA900 still responded to a decrease in oxygen concentration, although here induction was about 10 times lower and the low oxygen response was gradually lost within 3 days. Introduced into a barley-soil microcosm, the biosensor could report decreasing oxygen concentrations in the rhizosphere for a 6-day period. When the water content in the microcosm was raised from 60% to 85% of field capacity, expression of the reporter gene was elevated about twofold above a basal level after 2 days of incubation, suggesting that a water content of 85% caused mild anoxia. Increased compaction of the soil was shown to have a faster and more dramatic effect on the expression of the oxygen reporter than soil water content alone, indicating that factors other than the water-filled pore space influenced the oxygen status of the soil. These experiments illustrate the utility of the biosensor for detecting low oxygen concentrations in the rhizosphere and other soil habitats.

Influence of environmental conditions on putisolvins I and II production inPseudomonas putidastrain PCL1445

“…1a and b). The latter result is of relevance as a decreasing oxygen concentration gradient occurs in biofilms (Stanley & Lazazzera, 2004) and in the rhizosphere (Hjberg et al, 1999).…”

Ecological fitness of Bacillus subtilis BGS3 regarding production of the surfactin lipopeptide in the rhizosphere

“…low oxygen status prevailing in the rhizosphere (Hojberg et al, 1999) is not detrimental to lipopeptide synthesis by BGS3 cells evolving on roots. Reduced O2 availability and slow growth were also reported to stimulate the production of the cyclic lipopeptide putisolvin by Pseudomonas putida (Dubern and Bloemberg, 2006).…”

Impact of rhizosphere factors on cyclic lipopeptide signature from the plant beneficial strain Bacillus amyloliquefaciensS499

“…Oxygen depletion is common in many soils and especially in the rhizosphere, notably due to root-and microbeassociated consumption (Højberg et al, 1999). This factor may thus potentially impact basic physiological processes, including antibiotic synthesis in aerobic Bacillus species.…”