Investigating Pseudomonas putida-Candida humicola interactions as affected by chelate Fe(III) in soil.

Microcalorimetric technique was applied to assess the toxic effect of EDTA-chelated trivalent iron on Pseudomonas putida (P. putida) (bacterium), Candida humicola (C. humicola) (fungus) and their mixture in sterilized soil. Microbial growth rate constant k, total heat evolution Q T, metabolic enthalpy ∆H met, mass specific heat rate J Q/S, microbial biomass C and inhibitory ratio I were calculated. Results showed that microcalorimetric indexes decreased with the increasing Fe(III)-EDTA complex concentration. Comparing the single and mixed strains, the effect of Fe(III) on bacterium-fungus interaction was dominant at lower dose, whereas, the metal toxicity at high dose of Fe was the main factor affecting P. putida and C. humicola activity. Thus, the mixture had moderate tolerance to the iron overload, and exhibit synergistic interaction in exponential growth phase (0-0.3 mg g(-1)). The results of glucose degradation showed that glucose was consumed totally at the end of exponential phase of microbial growth.