TY - JOUR

T1 - Kinetics of malate transport and decomposition in acid soils and isolated bacterial populations: The effect of microorganisms on root exudation of malate under Al stress

AU - Jones, Davey L.

AU - Prabowo, Abdul M.

AU - Kochian, L.V.

PY - 1996/5

Y1 - 1996/5

N2 - The kinetics and characteristics of malate degradation were studied in four acid soils ranging in both pH (4.30 to 5.00) and vegetation type. The breakdown of malate was rapid in all soils with a half life of approximately 1.7 h, Km of 1.7 mM and Vmax of 70 nmol g−1 soil h−1. No relationship was observed between malate decomposition rate and pH. Co-metabolism studies with other C and N substrates (glucose, glycine, glutamate, citrate and succinate) indicated that the microorganisms were not N limited and competitive inhibition of malate breakdown was only observed in the presence of succinate. Studies with isolated mixed bacterial cultures indicated that the bacterial malate uptake was mediated by an energy dependent, dicarboxylate transporter which can be inhibited by succinate and is independent of pH between pH 5.0 and 7.0. The Km and Vmax parameters ranged from 279–955 μM and 0.1–17 μmol mg−1 protein h−1 for the mixed bacterial cultures depending on the bacteria's previous C source. The results indicate that in acid topsoils where microbial populations are high, the microbes may provide a considerable sink for organic acids. If organic acids are being released by roots in response to an environmental stress (e.g. Al toxicity, P deficiency) it can be expected that the efficiency of these root mediated metal resistance mechanisms will be markedly reduced by rapid microbial degradation.

AB - The kinetics and characteristics of malate degradation were studied in four acid soils ranging in both pH (4.30 to 5.00) and vegetation type. The breakdown of malate was rapid in all soils with a half life of approximately 1.7 h, Km of 1.7 mM and Vmax of 70 nmol g−1 soil h−1. No relationship was observed between malate decomposition rate and pH. Co-metabolism studies with other C and N substrates (glucose, glycine, glutamate, citrate and succinate) indicated that the microorganisms were not N limited and competitive inhibition of malate breakdown was only observed in the presence of succinate. Studies with isolated mixed bacterial cultures indicated that the bacterial malate uptake was mediated by an energy dependent, dicarboxylate transporter which can be inhibited by succinate and is independent of pH between pH 5.0 and 7.0. The Km and Vmax parameters ranged from 279–955 μM and 0.1–17 μmol mg−1 protein h−1 for the mixed bacterial cultures depending on the bacteria's previous C source. The results indicate that in acid topsoils where microbial populations are high, the microbes may provide a considerable sink for organic acids. If organic acids are being released by roots in response to an environmental stress (e.g. Al toxicity, P deficiency) it can be expected that the efficiency of these root mediated metal resistance mechanisms will be markedly reduced by rapid microbial degradation.

KW - aluminium

KW - bacteria

KW - breakdown

KW - malate

KW - microbial biomass

KW - rhizosphere

U2 - 10.1007/BF00029055

DO - 10.1007/BF00029055

M3 - Article

VL - 182

SP - 239

EP - 247

JO - Plant and Soil

JF - Plant and Soil

SN - 0032-079X

IS - 2

ER -