Tatsuhiko Matsuguchi

Influence of soil salinity on the populations and composition of fluorescent pseudomonads in plant rhizosphere

Abstract Effect of soil salinity associated with intensive cultivation including horticulture on microbial communities in the soil-root system was investigated in a growth chamber experiment. Spinach plants were grown on three soil samples of the same origin but with low, medium, and high levels of salinity. Microbial populations, including fluorescent pseudomonads, in three sites of the soil-root system, namely root-free soil, rhizosphere soil, and rhizoplane, of 3-week-old spinach plants were compared in relation to the levels of soil salinity. Effect of soil salinity on the microbial populations differed widely among the three sites of the soil-root system, as well as among the microbial groups. In the root-free soil, populations of total bacteria (TB) and gram-negative bacteria (GN) did not change significantly through salinity, while the populations of total fluorescent pseudomonads (FP) apparently increased. In the rhizosphere soil, however, soil salinity induced changes in the populations depending...

Application of DGGE analysis to the study of bacterial community structure in plant roots and in nonrhizosphere soil

Abstract To analyze the structure of bacterial communities in spinach roots and in the nonrhizosphere soil, we used PeR-amplified 16S rRNA gene fragments separated by denaturing gradient gel electrophoresis (DGGE). DGGE revealed a large number of band patterns, which were ascribed to various bacterial species composing each of the bacterial communities. The pattern from the roots was less complex than that from the soil. It is considered that DGGE analysis is suitable for studies of bacterial community structure in soil-plant ecosystems.

Effect of soil salinity on population structure of fluorescent pseudomonads in spinach rhizosphere

Abstract Use of PGPR (plant growth-promoting rhizobacteria) for stimulating plant growth and for the biological control of soil-borne diseases is necessary mainly in fields with intensive cropping. The intensive cultivation systems in horticulture have generally led to soil salinity due tp the high rates of fertilizer application. Therefore, the high concentration of inorganic salts accumulated in the plant rhizosphere is likely to be a factor of salinity stress affecting both roots and root-associated rhizobacteria. In a previous report (Matsuguchi and Sakai 1995), we observed that high salinity of soil had induced a significant decrease in the populations of fluorescent pseudomonads in spinach roots. Furthermore, the adverse effect of high salinity of soil was more pronounced on Pseudomonas fluorescens strains than on Pseudomonas putida strains, resulting in an alteration of the composition of fluorescent pseudomonads in the roots where vP. putida} predominated. The objective of the present study was to...

Effect of cations on the growth of fluorescent pseudomonad isolates from spinach roots grown in soils with different salinity levels

Abstract Effect of Inorganic ion concentrations in culture solution on the growth of Pseudomonas putida and P. fluorescens Isolates from spinach roots grown in soils with high-salinity (H-soil) and low-salinity (L-soil) levels was investigated. Both H- and L-soils were taken from the topsoil of a greenhouse for spinach cultivation and a nearby fallow field, respectively. In the H-soil inorganic ions had accumulated due to the high rates of application of fertilizer. Among the ions, the concentrations of Ca2+, NO3 -, and SO4 2- in the H-soil were significantly higher than those in the L-soil. Among the inorganic ions tested (K+, Na+, Ca2+, Mg2+, Cl-, NO3 -, and SO4 2-), Ca2+ was found to be the most inhibitory on the growth of isolates. In addition, the isolates from the H-soil were more Ca2+-tolerant than those from the L-soil. Consequents the growth tolerance to Ca2+ stress of the total 80 isolates, 40 each from the H-soil and L-soil, was compared at 150 mM Ca2+. Most isolates from the H-soil showed a si...

Chemotactic response to amino acids of fluorescent pseudomonads isolated from spinach roots grown in soils with different salinity levels

Abstract Chemotactic response to amino acids of fluorescent pseudomonads isolated from spinach roots grown in a low-salinity soil (LR-group) and its corresponding high-salinity soil (HR-group) was investigated. Furthermore, the amount and composition of amino acids in the root exudate under low- and high-salinity conditions were investigated. All the isolates examined showed a chemotactic response exclusively to the amino acid fraction, while most of them did not respond to the sugar and the organic acid fractions. Based on these results, the chemotactic response to 20 amino acids of randomly selected 48 isolates, of which 12 isolates each belongs to the LR- and HR-groups of both Pseudomonas putida and P. fluorescens, was investigated. The results showed that the spectrum of chemotaxis to 20 amino acids of the H-group of each species was markedly different from that of the corresponding L-group. Also, the amino acid composition of the root exudate in the high-salinity culture solution significantly differ...

Use of Bacterial Bioluminescence for Monitoring the Behavior of Rhizobacteria Introduced to Plant Rhizosphere

Abstract Bioluminescence (lux) genes from Vibrio harveyi were introduced into an artificial transposon vector pJFF350 as a constitutively expressing lux-genes set. The resultant recombinant plasmid pSOL2 was then transposed into the chromosome of fluorescent pseudomonad strains, in which the lux genes were stably integrated. Root colonization by the lux-marked strains was visually monitored by autophotography, and it was found that the bioluminescence intensities were highly correlated with the populations of the strains colonizing roots. A strain of Pseudomonas putida thus lux-marked was inoculated to spinach seedlings in nursery pots, and the root colonization was assayed. In sterile soil, the strain extensively colonized the entire part of the developing roots and the population densities at any sites were high. In non-sterile soil, only the inoculated site of the roots was weakly colonized. These results suggest that the presence of the indigenous microflora is an environmental constraint on root colo...

Factors regulating acetylene reduction assay for measuring heterotrophic nitrogen fixation in water-logged soils

Abstract In the C2H2-C2H4 assay for measurement of heterotrophic N2 fixation in water-logged soils, the diffusion of C2H2 into the soil and the recovery of C2H4 from it are critical factors regulating the assay result. To establish an C2H2-C2H4 assay technique suitable for waterlogged soils, the C2H2-reducing activities (ARA), assayed by varying the method of assay gas filling, the pC2H2 of the assay gas, the duration of assay incubation and of soil vibration before the gas sampling, were compared. A maximum ARA was measured when the following set of procedures were applied to the soil sample in assay flasks: 1) a 4-fold repetition of I-min evacuation under 0.01 atmospheric pressure and the subsequent I-min filling under 1 atmospheric pressure with assay gas at pC2H2 of 0.1 atm, 2) an assay incubation for 3 hr, and 3) a sampling of an aliquot of the headspace gas after strongly vibrating the flask for 1 min. The ARA measured by this technique was several times larger than those measured by the techniques ...

Effects of DD, EDB and PCP upon microorganisms and their activities in soil part I effects on microflora

Abstract The extensive use of various insecticides or herbicides makes it desirable to know what influences, if any, such chemicals may exert upon soil microorganisms. The effect of chemicals should be considered not only upon plant pathogenes, but also upon general soil micro-organisms.

STUDIES ON THE NITRIFICATION IN SOIL, WITH SPECIAL REFERENCE TO THE POPULATION OF NITRIFIER : Part 2 Nitrogenous Fertilizers and Their Effectiveness as Substrate for Nitrification

Abstract It is certain that the nitrification in soil differs from that in culture solution. But the study in culture solution is neccessary for a better understanding of nitrification. Although the perfusion technique, introduced first by Quastel and his has contributors1)2), has been a very useful tool and has conntributed much to the problem of nitrification, it must not be overlooked that it produces a specific condition. Among the information given them. the most attractive was the descrition of the state of NH4 + in soil and its nitrication3). According to their results, the nitrifier in eres to the soil particle and nitrifies NH4 +, not in the solution, but is exchangeably absorbed there. In their experiments, it was proved ht at the rate of nitrification was dependent upon the base exchange capacity of soil column and that the addition of CaCl2 to the perfusate decreased the nitrification.

Comparison of root colonization by LR- and HR-isolates of fluorescent pseudomonads in soil with high salinity

Y Successful root colonization by introduced beneficial rhizobacteria largely depends on the bacterial adaptability to the rhizosphere environment and extent of their competitive advantages over the indigenous rhizobacteria. Characteristics that may enhance the root colonization by introduced rhizobacteria include a higher growth rate than that of the indigenous population (Bowen and Rovira 1976), tolerance to adverse environmental conditions (Polonenko et al. 1981; Chen and Alexander 1983; Loper et al. 1985) or starvation (Acea et al. 1988), cell motility (de Weger et al. 1987), production of substances that promote the adherence to plant roots (Tari and Anderson 1988; van Peer et al. 1990), and the production of antibiotics (Mazzola et al. 1992).