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Microbiology 150 (2004), 1661-1669; DOI  10.1099/mic.0.26657-0
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Microbiology 150 (2004), 1661-1669; DOI  10.1099/mic.0.26657-0
© 2004 Society for General Microbiology

Characterization of Pseudomonas putida genes responsive to nutrient limitation

Chris K. C. Syn1,{dagger}, Jon K. Magnuson2, Mark T. Kingsley2 and Sanjay Swarup1

1 Department of Biological Sciences, National University of Singapore, 14 Science Drive 4, Singapore 117 543
2 Pacific Northwest National Laboratory, Richland, WA, USA

Correspondence
Sanjay Swarup
dbsss{at}nus.edu.sg

The low bioavailability of nutrients and oxygen in the soil environment has hampered successful expression of biodegradation and biocontrol genes that are driven by promoters highly active during routine laboratory conditions of high availability of nutrients and oxygen. Hence, in the present study, expression of the gus-tagged genes in 12 Tn5-gus mutants of the soil microbe Pseudomonas putida PNL-MK25 were examined under various conditions chosen to mimic the soil environment: low carbon, phosphate, nitrate or oxygen, and in the rhizosphere. Based on their expression profiles, three nutrient-responsive mutant (NRM) strains, NRM5, NRM7 and NRM17, were selected for identification of the tagged genes. In strain NRM5, expression of the glutamate dehydrogenase (gdhA) gene was increased 4·9–26·4-fold under various low-nutrient conditions. In NRM7, expression of the novel NADPH : quinone oxidoreductase-like (nql) gene was consistently amongst the highest and was synergistically upregulated by low-nutrient and anoxic conditions. The cyoD gene in NRM17, which encodes the fourth subunit of the cytochrome o ubiquinol oxidase complex, had decreased expression in low-nutrient conditions but its absolute expression level was still amongst the highest. Additionally, it was independent of oxygen availability, in contrast to that in Escherichia coli.

Abbreviations: ADH, alcohol dehydrogenase; CCR, carbon catabolite repression; GUS, {beta}-glucuronidase; NRM, nutrient-responsive mutant; QOR, quinone oxidoreductase; RE, root exudate

The GenBank accession numbers for the P. putida PNL-MK25 gdhA, nql and cyoD genes reported in this paper are AF321093, AF321092, and AF321090, respectively.

{dagger}Present address: Centre for Forensic Science, Health Sciences Authority, 11 Outram Road, 169078, Singapore.






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