Water flow induced transport of Pseudomonas fluorescens cells through soil columns as affected by inoculant treatment

Abstract

Water flow induced transport of Pseudomonas fluorescens cells through soil columns was measured as affected by the inoculant treatment. Bacterial cells were introduced into the topsoil of columns, either encapsulated in alginate beads of different types or mixed with bentonite clay in concentrations ranging from 0.5 to 5.0% (w/v). Survival of bacterial cells was improved with the use of alginate or bentonite. Transport, as determined by destructive sampling of the columns, was reduced with the use of alginate encapsulation. Drying of the beads had no influence on transport. The presence of bentonite in the topsoil, either pre-mixed through the soil, or applied as a slurry together with the bacteria, also reduced transport, except when 0.5% was pre-mixed through the soil. P. fluorescens cells encapsulated in alginate beads prepared with water and supplemented with skim milk powder and bentonite showed the best survival during the time of the experiment and the most reduced transport compared to the control. Therefore, cells encapsulated in this way are suitable, due to their optimal survival and reduced spread, for use in a field experiment with genetically manipulated bacteria.

Percolation and Survival of Escherichia coli O157:H7 and Salmonella enterica Serovar Typhimurium in Soil Amended with Contaminated Dairy Manure or Slurry

“…However, for organic substrates such as manure and slurry, the adsorption and desorption behavior of bacteria are due not only to differences in physical characteristics of the substrate but also to biophysical properties of the organic matter (22). Experiments on the percolation of Pseudomonas fluorescens also showed that application of an adsorption substrate (such as bentonite clay) to the soil may increase survival of P. fluorescens and reduce transport to deeper layers (13). In our experiments, it is likely that some of the organic matter in the slurry moved down the soil profile while manure particles moved less readily.…”

“…However, we were more interested in determining the influence of the manure or slurry application method on the distribution and survival of E. coli O157:H7 and Salmonella serovar Typhimurium in soil columns. Another limitation was that relatively small soil columns were used, which may not be representative of field conditions due to the influence of soil cracks and wall effects on water flow (13). However, only in such controlled experiments is it possible to distinguish the exact influence of certain factors.…”

“…When microorganisms are introduced on or in soil, their movement is mainly determined by the flow of percolating water (13). Water flow and the ultimate distribution of bacteria in soil are affected by soil texture, pH, temperature, and the structure of the root system in soil (17).…”

“…While it was shown that water is the most important dispersal factor for percolation of bacteria in different types of soil (13,36) as well as for percolation of enteropathogens under various management practices (11), the movement and distribution of E. coli O157:H7 and Salmonella serovar Typhimurium in soil after application of manure and slurry are still unclear. It is also not clear if and how survival of enteric pathogens is influenced by the depth of the soil where they end up after transport through the soil.…”

The role of bacterial motility in the survival and spread of Pseudomonas fluorescens in soil and in the attachment and colonisation of wheat roots

“…Spread of bacteria through soil has implications for the persistence of genetically modi¢ed organisms [7,8] and contamination of groundwater supplies by microorganisms present in sewage from soil-based waste disposal systems [9]. Understanding bacterial movement in soil is also important for manipu-lating colonisation of plant roots [10,11] and for optimising the dispersal of inoculants used in biocontrol and bioremediation strategies [12,13]. Previous studies have investigated the numerous factors a¡ecting movement of bacteria in soil [7,10,14^16] but few have attempted to di¡erentiate between passive spread of bacteria and active motility involving £agella [11,17,18].…”