Growth substrates

For those pesticides that are cometabolized, ie, not utilized as a growth substrate, the assumption of first-order kinetics is appropriate. The more accurate kinetic expression is actually pseudo-first-order kinetics, where the rate is dependent on both the pesticide concentration and the numbers of pesticide-degrading microorganisms. However, because of the difficulties in enumerating pesticide-transforming microorganisms, first-order rate constants, or half-hves, are typically reported. Based on kinetic constants, it is possible to rank the relative persistence of pesticides. Pesticides with half-hves of <10 days are considered to be relatively nonpersistent pesticides with half-hves of >100 days are considered to be relatively persistent. 

For those pesticides which are utilized as microbial growth substrates, sigmoidal rates of biodegradation are frequentiy observed (see Fig. 2). Sigmoidal data are more difficult to summarize than exponential (first-order) data because of their inherent nonlinearity. Sigmoidal rates of pesticide metabohsm can be described using microbial growth kinetics (Monod) however, four kinetics constants are required. Consequentiy, it is more difficult to predict the persistence of these pesticides in the environment. 

Monod kinetics Kinetics of microbial cell growth as a function of substrate concentration proposed by Jacques Monod and widely used to understand growth-substrate relationships. 

Growth, substrate utilisation and product formation time courses exhibit coincident maxima. 

Formaldehyde is highly toxic and reactive and not suitable as a growth substrate. Methanol is more soluble in water than methane and would seem a suitable substrate. 

Engesser KH, E Schmidt, H-J Knackmuss (1980) Adaptation of Alcaligenes eutrophus B9 and Pseudomonas sp. B13 to 2-fluorobenzoate as growth substrate. Appl Environ Microbiol 39 68-73. 

Mauersberger S, RN Matyashova, H-G Muller, AB Losinov (1980) Influence of the growth substrate and the oxygen concentration in the medium on the cytochrome P-450 content in Candida guilliermondii. Eur J Appl Microbiol Biotechnol 9 285-294. 

Patterson JA, RB Hespell (1979) Trimethylamine and methylamine as growth substrates for rumen bacteria ind Methanosarcina barkeri. Curr Microbiol 3 79-83. 

Denef VJ, MA Patrauchan, C Florizone, J Park, TV Tsoi, W Verstraete, JM Tiedje, LD Eltis (2005) Growth substrate- and phase-specific expression of biphenyl, benzoate, and Cl metabolic pathways in Burkhold-eria xenovorans LB400. J Bacterial 187 7996-8005. 

Derivatives of 1,3,5-triazine are important herbicides so that attention has been directed to their persistence particularly in the terrestrial environment. In some experiments when a growth substrate was supplied, they have been used as sources of nitrogen or sulfur ... 

Walter, M., Boul, L., Chong, R., and Ford, C., Growth substrate selection and biodegradation of PCP by New Zealand white-rot fungi, J. Environ. Manage., 71, 361-369, 2004. 

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