Isolation, identification and characterization of soil microbes which degrade phenolic allelochemicals

To isolate and characterize microbes in the soils containing high contents of phenolics and to dissolve the allelopathic inhibition of plants through microbial degradation.

Four microbes were isolated from plant soils using a screening medium containing p-coumaric acid as sole carbon source. The isolates were identified by biochemical analysis and sequences of their 16S or 18S rDNA, and designated as Pseudomonas putida 4CD1 from rice (Oryza sativa) soil, Ps. putida 4CD3 from pine (Pinus massoniana) soil, Pseudomonas nitroreducens 4CD2 and Rhodotorula glutinis 4CD4 from bamboo (Bambusa chungii) soil. All isolates degraded 1 g l(-1) of p-coumaric acid by 70-93% in inorganic and by 99% in Luria-Bertani solutions within 48 h. They also effectively degraded ferulic acid, p-hydroxybenzoic acid and p-hydroxybenzaldehyde. The microbes can degrade p-coumaric acid and reverse its inhibition on seed germination and seedling growth in culture solutions and soils. Low pHs inhibited the growth and phenolic degradation of the three bacteria. High temperature inhibited the R. glutinis. Co(2+) completely inhibited the three bacteria, but not the R. glutinis. Cu(2+), Al(3+), Zn(2+), Fe(3+), Mn(2+), Mg(2+) and Ca(2+) had varying degrees of inhibition for each of the bacteria.

Phenolics in plant culture solutions and soils can be decomposed through application of soil microbes in laboratory or controlled conditions. However, modification of growth conditions is more important for acidic and ions-contaminated media.

The four microbes were first isolated and characterized from the soils of bamboo, rice or pine. This study provides some evidence and methods for microbial control of phenolic allelochemicals.