Effect of peat components on microorganisms, with special reference to humic acids

Muthukumarasamy, Sivagurunathan (2000) Effect of peat components on microorganisms, with special reference to humic acids. Masters thesis, Memorial University of Newfoundland.

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Abstract

Research was carried out to study the effect of humic substances, which are compounds that control or affect important environmental processes, on the metabolic activities of selected microorganisms. A yeast and a bacterium with potential economic importance were selected as test organisms. Given the potential of peat in pollution control applications and in other processes, humic substances from this material were employed in this study. Phaffia rhodozyma, a carotenoid producing yeast, was used as a test organism. The effect of different peat extracts on the growth and astaxanthin pigment production by P. rhodozyma was studied. Response Surface Methodology (RSM) was used to optimize the main operating conditions, fermentation time, temperature, and pH of media, for the experiments. At optimized growth conditions a maximum biomass productivity of 9.52 g.L⁻¹ was observed in peat hydrolysate (PH, non- modified peat hydrolysate), which was significantly higher over other peat hydrolysates tested (modified peat hydrolysates). The modified peat hydrolysates studied were: debituminised peat hydrolysate (DPH), peat hydrolysate with humic substances removed (PHR) and debituminised peat hydrolysate with humic substances removed (DPHR). The biomass productivity attained with non- modified peat hydrolysate was also significantly higher than that produced with yeast extract-malt extract (YM) broth. YM broth, the medium employed as control, produced biomass with the maximum astaxanthin content (487 μg.g⁻¹). Among the different peat hydrolysates, PHR produced a maximum astaxanthin content of 474 μg.g⁻¹, which was significantly higher than that produced in the other peat hydrolysates. The removal of humics contributed to increased pigment content. Also, the results indicated that peat bitumens promote the pigment production. When humic acids were added at different concentrations to YM broth, they affected the biomass concentration and yield significantly, compared to control experiments with no humic acids. -- Studies were conducted with four strains of Pseudomonas fluorescens, a bacterium isolated from petroleum contaminated soils, to find the effect of humic acids on the biodegradation potential of polycyclic aromatic hydrocarbons (PAHs). These strains had been shown to degrade toluene and naphthalene. The optimum growth parameters temperature, pH of medium and agitation, were determined by applying RSM, and degradation studies were conducted at the optimized conditions. Humic acids, the main component of humic substances, from two sources (one isolated from peat and the other supplied by Aldrich Chemicals) were employed at concentrations between 0.02 to 0.1 %. Higher concentrations were inhibitory to all the four organisms and no degradation was observed. At lower concentrations, degradation was observed, though some inhibition of the degradation was also present. -- This research indicates that humic substances have a definitive effect on the metabolism of the microbial species studied. The findings have implications for the use of humic substances-containing materials such as peat and soil in biodegradation / bioremediation operations. Peat and soil are commonly employed as support medium for biofilm development. It appears that the removal of humic substances or humic acids from these materials could result in better microbial degradation action.

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