Modeling of phenoxy acid herbicide mineralization and growth of microbial degraders in 15 soils monitored by quantitative real-time PCR of the functional tfdA gene.
Mineralization potentials, rates, and kinetics of the three phenoxy acid (PA) herbicides, 2,4-dichlorophenoxyacetic acid (2,4-D), 4-chloro-2-methylphenoxyacetic acid (MCPA), and 2-(4-chloro-2-methylphenoxy)propanoic acid (MCPP), were investigated and compared in 15 soils collected from five continents. The mineralization patterns were fitted by zero/linear or exponential growth forms of the three-half-order models and by logarithmic (log), first-order, or zero-order kinetic models. Prior and subsequent to the mineralization event, tfdA genes were quantified using real-time PCR to estimate the genetic potential for degrading PA in the soils. In 25 of the 45 mineralization scenarios, ∼60% mineralization was observed within 118 days. Elevated concentrations of tfdA in the range 1 × 10(5) to 5 × 10(7) gene copies g(-1) of soil were observed in soils where mineralization could be described by using growth-linked kinetic models. A clear trend was observed that the mineralization rates of the three PAs occurred in the order 2,4-D > MCPA > MCPP, and a correlation was observed between rapid mineralization and soils exposed to PA previously. Finally, for 2,4-D mineralization, all seven mineralization patterns which were best fitted by the exponential model yielded a higher tfdA gene potential after mineralization had occurred than the three mineralization patterns best fitted by the Lin model.
Geological Survey of Denmark and Greenland, Department of Geochemistry, Copenhagen, Denmark.
Jacob
J
Bælum
Emmanuel
E
Prestat
Maude M
MM
David
Bjarne W
BW
Strobel
Carsten S
CS
Jacobsen
D015084:2,4-Dichlorophenoxyacetic Acid / Q000378:metabolism*; D008456:2-Methyl-4-chlorophenoxyacetic Acid / Q000031:analogs & derivatives* / Q000378:metabolism*; D017931:DNA Primers / Q000235:genetics; D049308:Dioxygenases / Q000235:genetics*; D005798:Genes, Bacterial / Q000235:genetics*; D006540:Herbicides / Q000378:metabolism*; D007700:Kinetics; D008903:Minerals / Q000378:metabolism; D008954:Models, Biological; D060888:Real-Time Polymerase Chain Reaction; D012988:Soil Microbiology
D017931:DNA Primers; D006540:Herbicides; D008903:Minerals; D015084:2,4-Dichlorophenoxyacetic Acid; C008340:mecoprop; D008456:2-Methyl-4-chlorophenoxyacetic Acid; D049308:Dioxygenases