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Involvement of gacS and rpoS in enhancement of the plant growth-promoting capabilities of Enterobacter cloacae CAL2 and UW4

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The plant growth-promoting bacteria Enterobacter cloacae CAL2 and UW4 were genetically transformed with a multicopy plasmid containing an rpoS or gacS gene from Pseudomonas fluorescens. The transformed strains were compared with the nontransformed strains for growth, indoleacetic acid (IAA) production, antibiotic production, 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase activity, siderophore production, cell morphology, and the ability to promote canola root elongation. All transformed strains had a longer lag phase, were slower in reaching stationary phase, and attained a higher cell density than the nontransformed strains. Transformation resulted in cells that were significantly shorter than the nontransformed cells. The transformed strains also produced significantly more IAA than the nontransformed strains. Introduction of rpoS or gacS from Pseudomonas fluorescens was associated with a reduction in the production of both antibiotics, 2,4-diacetylphloroglucinol and mono-acetylphloroglucinol, produced by Enterobacter cloacae CAL2. With Enterobacter cloacae CAL2, plasmid-borne rpoS, but not gacS, increased the level of ACC deaminase activity, while introduction of rpoS in Enterobacter cloacae UW4 caused a decrease in ACC deaminase activity. Neither gacS nor rpoS significantly affected the level of siderophores synthesized by either bacterial strain. Overproduction of either GacA or RpoS in Enterobacter cloacae CAL2 resulted in a significant increase in the root lengths of canola seedlings when seeds were treated with the bacteria, and overproduction of RpoS caused an increase in canola shoot as well as root lengths.Key words: plant growth-promoting bacteria, canola, ethylene, ACC deaminase, GacS, RpoS, indoleacetic acid, siderophores, antibiotics.

Les bactéries favorisant la croissance végétale Enterobacter cloacae CAL2 et UW4 ont été génétiquement transformées avec un plasmide mutli-copie contenant un gène rpoS ou gacS de Psuedomonas fluorescens. La croissance, la production d'acide indoleacétique (IAA), la production d'antibiotiques, l'activité acide 1-aminocyclopropane-1-carboxylique (ACC) désaminase, la production de sidérophores, la morphologie cellulaire et la capacité de favoriser l'élongation des racines de canola des souches transformées ont été comparées aux souches non transformées. Toutes les souches transformées avaient une phase de latence prolongée, sont arrivées à la phase stationnaire plus lentement et ont atteint des densités cellulaires supérieures aux cellules non transformées. La transformation a engendré des cellules qui étaient significativement plus courtes que les cellules non transformées. Les souches transformées ont également produit significativement plus de IAA que les souches non transformées. L'introduction des gènes rpoS or gacS de Pseudomonas fluorescens a été associée avec une diminution de la production des deux antibiotiques, le 2,4-diacétylphloroglucinol et le mono-acétylphloroglucinol, produits par Enterobacter cloacae CAL2. Chez Enterobacter cloacae CAL2, le rpoS plasmidique, mais non le gacS, a augmenté le niveau d'activité ACC désaminase, alors que l'introduction de rpoS chez Enterobacter cloacae UW4 a entraîné une diminution de l'activité ACC désaminase. Ni gacS, ni rpoS n'ont affecté significativement les taux de sidérophores synthétisés par l'une ou l'autre des souches bactériennes. La surproduction de GacA ou de RpoS dans Enterobacter cloacae CAL2 a entraîné une augmentation de la longueur des racines de plantules de canola lorsque les semis avaient été traités avec les bactéries, et la surproduction de RpoS a causé une accroissement de la longueur des pousses et des racines de canola.Mots clés : bactéries favorisant la croissance des plantes, canola, éthylène, ACC désaminase, GacS, RpoS, acide indoleacétique, sidérophores, antibiotiques.[Traduit par la Rédaction]

Keywords: ACC deaminase; ACC désaminase; GacS; RpoS; acide indoleacétique; antibiotics; antibiotiques; bactéries favorisant la croissance des plantes; canola; ethylene; indoleacetic acid; plant growth-promoting bacteria; siderophores; sidérophores; éthylène

Document Type: Research Article

Publication date: 2001-08-01

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  • Published since 1954, this monthly journal contains new research in the field of microbiology including applied microbiology and biotechnology; microbial structure and function; fungi and other eucaryotic protists; infection and immunity; microbial ecology; physiology, metabolism and enzymology; and virology, genetics, and molecular biology. It also publishes review articles and notes on an occasional basis, contributed by recognized scientists worldwide.
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