Horizontal and Vertical Movement of Azospirillum brasilense Cd in the Soil and along the Rhizosphere of Wheat and Weeds in Controlled and Field Environments

Abstract

Horizontal movement of Azospirillum brasilense Cd in soil and its vertical movement in the plant rhizosphere were studied. No movement was detected in the absence of living plants. In a controlled environment the bacteria moved horizontally at least 30 cm from the inoculation point to the first growing plant. Once the first root system was colonized, all the neighbouring plants became inhabited. Horizontal movement under field conditions was at least 160 cm-, and depended on the presence of live plant roots. Several weeds that grew in the passes betweenglots acted as efficient vectors. The numbers of A . brasilense Cd decreased with increasing distance from the inoculated plot. Vertical movement in soil columns in a controlled environment was up to 40 cm. Under field conditions, bacteria were detected as deep as 50 cm in the root systems of wheat plants in various types of soil. During the growing season bacteria were mostly found on and in young roots at a depth of 20-50 cm and near the soil surface. A map of depth distribution of A. brasilense Cd showed an uneven colonization pattern within the same root system or between adjacent plants. It was concluded that A . brasilense Cd moved horizontally and vertically in various soil types and that this movement was mainly dependent on the presence of plants.

Advances in plant growth-promoting bacterial inoculant technology: formulations and practical perspectives (1998–2013)

“…Sometimes, the absence of a continuous film of water needed for their movement is an additional limiting factor. These distances, large on a microbial scale, might prove prohibitive for many PGPB, even those with a proven motility in soil like Azospirillum (Bashan and Levanony 1987).…”

Microbial dispersal in unsaturated porous media: Characteristics of motile bacterial cell motions in unsaturated angular pore networks

“…PNM, d=0.5μm PNM, d=1μm PNM, d=2.5μm Brockman et al, 2004Wang & Griffin, 1976Arora, 1986Issa et al, 1993Bashan & Levanony, 1987 (mm 2 /s) Figure 8. Effect of hydration condition on bacterial chemotactic sensitivity coefficient as a function of matric potential: comparison with experimental data available for soil bacterial species with chemotactic movement (Wong and Griffin [1976], Arora [1986], Bashan and Levanony [1987], Issa et al [1993], andBrockman et al [2004] for accusand samples with mean grain size of 0.53 mm) d denotes simulated bacterial cell size chosen from observed range of bacterial cell sizes in soil [Portillo et al, 2013]. The bacterial cell velocity is chosen to be 60 lm/ s from observed average swimming motility for many bacterial cells [McCarter, 2005].…”

Effects of Azospirillum brasilense on growth and yield compounds of maize grown at nitrogen limiting conditions

“…In this case, based on the understanding of Hallmann et al (1997) and Saubidet et al (2002) it is guessed that under the employed N fertilizer level, plants were not able to provide A. brasilense with an adequate carbon compounds supply to sustain maximal cultivar's growth and yield. As discussed in Araújo et al (2015), under limited N availability plants cannot produce sufficient root exudates, which act as signal to influence the ability of strains to colonize soil by horizontal movement or to survive in the rhizosphere (Mark et al, 2005;Bashan and Levanony, 1987).…”