The influence of moisture on microbial transport, survival and 2,4-D biodegradation with a genetically marked Burkholderia cepacia in unsaturated soil columns

The influence of moisture on the survival, movement and degradation activity of a 2,4-D degrading bacterium, Burkholderia cepacia strain BRI6001L, genetically engineered to contain bioluminescent and lactose utilization genes, was studied in unsaturated soil columns. The distance traveled by BRI6001L was dependent on the clay content of the soil, higher clay contents being responsible for higher filtration coefficients. Long term survival, in excess of one year, was attributed to strain BRI6001L's ability to survive dry conditions. Changes in the 2,4-D biodegradation rate showed a better correlation with the BRI6001L population density than with the total viable bacterial population. At moisture levels between field capacity and 40% moisture (-33 kPa to -100 kPa) 2,4-D degradation was attributed mainly to BRI6001L. At moisture levels between 6 and 15%, 2,4-D disappearance was attributed to the indigenous microbial population, with no degradation occurring at moisture levels below 6%. Returning the moisture to above 40% led to an increase of 4 orders of magnitude in the BRI6001L population density and to a 10-fold increase in the 2,4-D degradation rate. The ability to monitor a specific microbial population using reporter genes has demonstrated the importance of controlling moisture levels for maximizing biodegradation rates in unsaturated soil environments.