Experimental Results and Integrated Modeling of Bacterial Growth on an Insoluble Hydrophobic Substrate (Phenanthrene)

Metabolism of a low-solubility substrate is limited by dissolution and availability and can hardly be determined. We developed a numerical model for simultaneously calculating dissolution kinetics of such substrates and their metabolism and microbial growth (Monod kinetics with decay) and tested it with three aerobic phenanthrene (PHE) degraders: Novosphingobium pentaromativorans US6-1, Sphingomonas sp. EPA505, and Sphingobium yanoikuyae B1. PHE was present as microcrystals, providing non-limiting conditions for growth. Total PHE and protein concentration were tracked over 6-12 days. The model was fitted to the test results for the rates of dissolution, metabolism, and growth. The strains showed similar efficiency, with v(max) values of 12-18 g dw g(-1) d(-1), yields of 0.21 g g(-1), maximum growth rates of 2.5-3.8 d(-1), and decay rates of 0.04-0.05 d(-1). Sensitivity analysis with the model shows that (i) retention in crystals or NAPLs or by sequestration competes with biodegradation, (ii) bacterial growth conditions (dissolution flux and resulting chemical activity of substrate) are more relevant for the final state of the system than the initial biomass, and (iii) the desorption flux regulates the turnover in the presence of solid-state, sequestered (aged), or NAPL substrate sources

Fungal bioremediation of creosote-contaminated soil: A laboratory scale bioremediation study using indigenous soil fungi

The aim of the study is to determine the efficacy of indigenous soil fungi in removing (PAHs) from creosote-contaminated soil with a view to developing a bioremediation strategy for creosote-contaminated soil. Five fungal isolates, Cladosporium, Fusarium, Penicillium, Aspergillus and Pleurotus, were separately inoculated onto sterile barley grains and incubated in the dark. The colonized barley was inoculated onto creosote-contaminated (250 000 mg kg(-1)) soil in 18 duplicate treatments and incubated at 25 degrees C for seventy days. The soil was amended with nutrient supplements to give a C:N:P ratio of 25:5:1 and tilled weekly. Creosote removal was higher (between 78 and 94%) in nutrient supplemented treatments than in the un-supplemented ones (between 65 and 88%). A mixed population of fungi was more effective (94.1% in the nutrient amended treatment) in creosote removal than single populations wit a maximum of 88%. Barley supported better fungal growth and PAH removal. Pleurotus sp. removed the creosote more than the other isolates. Two and three-ring PAHs were more susceptible to removal than the 4- and 5-ring PAHs, which continued to remain in small amounts to the end of the treatment. Reduction of creosote in the present study was higher than was observed in an earlier experiment using a consortium of microorganisms, mainly bacteria, on the same contaminated soil (Atagana, 2003)