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PRODUCTION OF PLANT GROWTH PROMOTING SUBSTANCES IN BACTERIAL ISOLATES FROM THE SEAGRASS RHIZOSPHERE
Citation:
Kurtz, J C., M. A. Savka, L. A. Brown, D F. Yates, AND R D. Devereux. PRODUCTION OF PLANT GROWTH PROMOTING SUBSTANCES IN BACTERIAL ISOLATES FROM THE SEAGRASS RHIZOSPHERE. Presented at 1999 Annual Meeting of the American Society for Microbiology, Chicago, IL, 5/30-6/3/99.
Description:
Plants and rhizosphere bacteria have evolved chemical signals that enable their mutual growth. These relationships have been well investigated with agriculturally important plants, but not in seagrasses, which are important to the stability of estuaries. Seagrasses are rooted in anoxic sediments, where sulfate reduction often serves as the dominant terminal electron accepting process. Among the chemicals produced by rhizosphere bacteria are plant growth-promoting substances, including the auxin indole-3- acetic acid (IAA). In addition, rhizobacteria produce acylated homoserine lactones (AHLs) that serve as autoinducers of bacterial population activities, and interactions of the bacteria with the environment and host plant. The objective of this study was to evaluate the frequency of chemical signaling compounds produced by isolates obtained from the rhizosphere of the seagrass Vallisneria americana. Of 57 heterotrophic, aerobic isolates, representing twelve different genera, 24 produced IAA and/or IAA analogs, as determined by a modified method using the Salkowski reagent and thin layer chromatography. IAA producers included Aeromonas hydrophilia (1 isolate), Aeromonas veronii (11 of 12 isolates), Edwardsiella tarda (1), Listonella anguillarum (1), Pantoea ananas (3), Vibrio fluvialis (3), and Vibrio furnissii (4 of 5 isolates). The incidence of phytohormone-producing strains (42%) is lower than that reported for some fertile soils (86%) but is consistent with other reported terrestrial incidences (24-42%). AHLs have been assayed in these isolates using an Agrobacterium tumefaciens indicator strain harboring lacZ fused to traG in the presence of traR. Strains that produce AHLs induce the indicator strain producing a colorimetric response, as observed in 8 of these isolates. The presence of bacteria in the seagrass rhizosphere that produce IAA and AHLs suggest that these traits are important to the biology of seagrasses and to associated plant-microbe interactions in