Survival and Plant Growth Promotion of Detergent-Adapted Pseudomonas fluorescens ANP15 and Pseudomonas aeruginosa 7NSK2

Abstract

Four detergents were tested as selective C sources for the plant growth-promoting rhizobacteria Pseudomonas aeruginosa 7NSK2 and Pseudomonas fluorescens ANP15. CO-720 (Igepal CO-720) or DOS (dioctyl sulfosuccinate), applied at 0.2% to the soil, increased the number of detergent-adapted, inoculated strains by almost 1.5 log units after 25 days, accounting for virtually the entire increase in total bacteria. The same dose of Tween 80 or N-laurylsarcosine, on the other hand, increased the indigenous populations by almost 2.5 log units, with only minor increases in the number of detergent-adapted inoculated strains. When CO-720 or DOS was initially supplied, the number of detergent-adapted 7NSK2 organisms was about 2 log units higher after 3 months of incubation than for the detergent-unadapted strain. This better survival resulted in a significantly higher root colonization of maize in a pot experiment with soil inoculation, with a significantly (P < 0.05) higher shoot dry weight (18 to 33%). In a first field experiment with rhizosphere inoculation of 1-month-old maize plants, no effects on the height of two maize cultivars could be observed 1 month after inoculation. In a second field experiment, leaf and stem dry weights of yellow mustard and grass dry weight were increased in the treatments with seed and soil inoculation of the detergent-adapted 7NSK2 in combination with CO-720 application by, respectively, 7 to 8%, 19 to 23%, and 20 to 31%, although only the increases in grass dry weight were statistically significant at P < 0.1. To some extent, 7NSK2 and DOS application also positively affected the mineral content of yellow mustard.

Are root exudates more important than other sources of rhizodeposits in structuring rhizosphere bacterial communities?

“…Strategies that may facilitate improved control of the biomass and distribution of indigenous and introduced microorganisms can be broadly grouped into those that involve rhizodeposits and those that do not. Approaches that fall into the latter category include attempts to select for specific microbial groups by applying chemical amendments to soils (Devliegher et al , 1995), modifications to proteins in rhizodermal cell membranes involved in plant–microorganism signalling (Samaj et al , 1999), and changes to root growth and architecture. These strategies are largely beyond the scope of this review (see Ryan et al , 2009 for detailed information); however, some may be very effective.…”

Fate and activity of microorganisms introduced into soil.

“…Ecological selectivity can also be based on the use of a specific substrate which is unavailable to a majority of other soil microorganisms. Devliegher et al (41) showed the effectiveness of this principle, in the use of a combined addition of specific detergents as carbon sources and detergentdegradative Pseudomonas spp. added to soil.…”

Effect of carbon source supply and its location on competition between inoculated and established bacterial strains in sterile soil microcosm

“…In all cases the success of inoculation is greatly influenced by the number of viable cells introduced into soil [4,5]. One way to enhance the efficacy of inoculation is to improve the growth of the introduced microbial population using nutrient amendments [6,7]. Nutrient amendment can stimulate the growth of bacterial inocula but a large amount of carbon source is often required.…”