Response to carbon-starvation in Pseudomonas aeruginosa strain IE-6S+: analysis of general cross protection,production of some nematocidal compounds in vitro,and the biological control of Meloidogyne javanica in tomato |
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Authors: | Siddiqui Imran A. Shaukat S. Shahid |
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Affiliation: | (1) Soil Biology and Ecology Laboratory, Department of Botany, University of Karachi, Karachi, 75270, Pakistan |
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Abstract: | Adaptation to nutrient-limited conditions by repeated culture on soil agar media was found to induce resistance to osmotic, oxidation, thermal and pH stress as well as carbon-limited culture conditions in Pseudomonas aeruginosa strain IE-6S+. Culture filtrate of the resistant strains obtained from 10% strength King's medium B (KMB) caused greater (32–54%) mortality of Meloidogyne javanica juveniles compared with their parental strain. When 10% strength KMB was amended with 1% (w/v) glucose, the ability to cause nematode mortality was substantially enhanced by adapted strains, while activity of the parental strain was repressed. Two of the four starved bacteria IE-6S+PBK1 and IE-6S+KUC2 grown in KMB liquid medium amended with glucose synthesized salicylic acid (5.1 and 5.8 g ml–1, respectively) and hydrogen cyanide (picrate paper turned yellow to brownish red for both strains) in greater quantities compared to wild type strain (SA = 4.4 g ml–1, picrate paper turned orange-yellow). Neither wild type strain IE-6S+ nor its adapted strains were capable of utilizing tomato root exudates as a sole carbon source. Strains adapted to carbon-limiting conditions exhibited enhanced colonization in the rhizosphere and inner root tissues of tomato compared to their exponentially growing counterpart. Pre-adapted bacterial inoculants applied in the soil also caused greater (15%) reduction in nematode penetration compared to the parental strain or controls. |
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Keywords: | Biological control endophytes nutrient starvation Pseudomonas root-knot nematode |
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