Influence of root exudates on the bacterial degradation of chlorobenzoic acids

Abstract

Degradation of chlorobenzoic acids (e.g., products of microbial degradation of PCB) by strains of microorganisms isolated from PCB contaminated soils was assessed. From seven bulk-soil isolates two strains unique in ability to degrade a wider range of chlorobenzoic acids than others were selected, individually and even in a complex mixture of 11 different chlorobenzoic acids. Such a feature is lacking in most tested degraders. To investigate the influence of vegetation on chlorobenzoic acids degraders, root exudates of two plant species known for supporting PCB degradation in soil were tested. While with individual chlorobenzoic acids the presence of plant exudates leads to a decrease of degradation yield, in case of a mixture of chlorobenzoic acids either a change in bacterial degradation specificity, associated with 3- and 4-chlorobenzoic acid, or an extension of the spectrum of degraded chlorobenzoic acids was observed.

Figure 1

Degradation of single CBA ((a), (c)) and mixture of CBA ((b), (d)) by strains A7 (Pseudomonas fluorescens) ((a), (b)) and A8 (Pseudomonas fluorescens) ((c), (d)). Black bar in minimal medium, stripped bar in minimal medium with exudates of black nightshade (Solanum nigrum), and grey bar in minimal medium with exudates of tobacco (Nicotiana tabacum). Stars indicate the statistically significant CBA removal (ANOVA).

Figure 2

Degradation of single CBA ((a), (c)) and mixture of CBA ((b), (d)) by strains A18 (Pseudomonas pseudoalcaligenes) ((a), (b)) and A19 (Pseudomonas stutzeri) ((c), (d)), Black bar in minimal medium, stripped bar in minimal medium with exudates of black nightshade (Solanum nigrum), and grey bar in minimal medium with exudates of tobacco (Nicotiana tabacum). Stars indicate the statistically significant CBA removal (ANOVA).

Figure 3

Degradation of single CBA ((a), (c)) and mixture of CBA ((b), (d)) by strains UH82 (Arthrobacter sp.) ((a), (b)) and UH133 (Pandoraea sp.) ((c), (d)). Black bar in minimal medium, stripped bar in minimal medium with exudates of black nightshade (Solanum nigrum), and grey bar in minimal medium with exudates of tobacco (Nicotiana tabacum). Stars indicate the statistically significant CBA removal (ANOVA).

Figure 4

Degradation of single CBA ((a), (c)) and mixture of CBA ((b), (d)) by strains UH222 (Pandoraea sp.) ((a), (b)) and control ((c), (d)). Black bar in minimal medium, stripped bar in minimal medium with exudates of black nightshade (Solanum nigrum), and grey bar in minimal medium with exudates of tobacco (Nicotiana tabacum). Stars indicate the statistically significant CBA removal (ANOVA).