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Abstract

Pseudomonas putida WCS358r, genetically modified to have improved activity against soil-borne pathogens, was released into the rhizosphere of wheat. Two genetically modified derivatives carried the phz or the phl biosynthetic gene loci and constitutively produced either the antifungal compound phenazine-1-carboxylic acid (PCA) or the antifungal and antibacterial compound 2,4-diacetylphloroglucinol (DAPG). In 1997 and 1998, effects of single introductions of PCA producing derivatives on the indigenous microflora were studied. A transient shift in the composition of the total fungal microflora, determined by amplified ribosomal DNA restiction analysis (ARDRA), was detected. Starting in 1999, effects of repeated introduction of genetically modified microorganisms (GMMs) were studied. Wheat seeds coated with the PCA producer, the DAPG producer, a mixture of the PCA and DAPG producers, or WCS358r, were sown and the densities, composition and activities of the rhizosphere microbial populations were measured. All introduced strains decreased from 10(7) CFU per gram of rhizosphere sample to below the detection limit after harvest of the wheat plants. The phz genes were stably maintained in the PCA producers, and PCA was detected in rhizosphere extracts of plants treated with this strain or with the mixture of the PCA and DAPG producers. The phl genes were also stably maintained in the DAPG producing derivative of WCS358r. Effects of the genetically modified bacteria on the rhizosphere fungi and bacteria were analyzed by using amplified ribosomal DNA restriction analysis. Introduction of the genetically modified bacterial strains caused a transient change in the composition of the rhizosphere microflora. However, introduction of the GMMs did not affect the several soil microbial activities that were investigated in this study.

A study of different nitrogen supplements for lactating cows

“…O n the contrary, in our experiment it was soybean meal which gave a significantly higher milk production than that obtained with IBDU and urea. This is in accordance with the results of BAKKER andVEEN (1977) andTELLER et al (1979). With regard to the substitution of starea for urea, it did not significantly alter the milk productions.…”

“…Consequently, a very important ammonia flow is observed in t h e proximal d u o d e n u m of cows fed IBDU. BAKKER (1974) stated that the high ammonia flow in the d u o d e n u m could be toxic t o the cells of the intestinal wall a n d thus diminish t h e absorption of nutrients from this part.…”

Fluorescent Pseudomonas Strains with only Few Plant-Beneficial Properties Are Favored in the Maize Rhizosphere

“…Indeed, the most effective PGPR are typically multi-function strains (Rana et al, 2011; Almario et al, 2014a). In line with this, the loss of one mode of action often reduces plant-beneficial effects (Thomashow and Weller, 1988; Keel et al, 1990) while the gain of one may enhance plant-beneficial effects (Wang et al, 2000; Bakker et al, 2002; Holguin and Glick, 2003; Baudoin et al, 2010), and the combined use of PGPR strains with different modes of action can also improve the effects on the plant (Dunne et al, 1998; Combes-Meynet et al, 2011; Walker et al, 2012). Since strains with multiple plant-beneficial properties can provide higher benefits to the host, they might be more prevalent in the rhizosphere than related PGPR strains displaying a smaller number of plant-beneficial properties.…”

Impact of a Recombinant Biocontrol Bacterium, Pseudomonas fluorescens pc78, on Microbial Community in Tomato Rhizosphere

“…In the present study, we used P. fluorescens pc78 wild type strain and strain pc78-48, carrying P43- gfp in its chromosome, to estimate the potential gene transfer among microorganisms and to evaluate the effect of biocontrol strain on the microbial community in tomato rhizosphere. Several strategies are available for microbial community analysis such as temperature gradient gel electrophoresis (TGGE), denaturing gradient gel electrophoresis (DGGE), and massive sequencing of phylogenetic marker genes ( Bakker et al, 2002 ; Mühling et al, 2008 ; Sokol et al, 2006 ). In this study, we employed terminal restriction fragment length polymorphism (T-RFLP) which is similar to TGGE and DGGE in terms of amplifying 16S ribosomal RNA gene and subsequent restriction analysis.…”