Application of white-rot fungi for the biodegradation of natural organic matter from potable water
Creators: name: Solarska, Sylwia
Publisher: name: RMIT University
Year: 2024

description: Drinking water quality and its treatment are negatively impacted by the presence of coloured natural organic matter (NOM). Ligninolytic white rot fungi (WRF) secrete non-specific oxidative enzymes that can oxidise a wide range of recalcitrant organic compounds. The potential of a selection of these organisms to degrade concentrated aquatic NOM and fresh NOM from Beaconsfield Reservoir was investigated without the addition of nutrients. <br><br>Preliminary work involved the screening of twenty-one isolates from diverse fungal genera using NOM and cellulose plate assays. Five WRF strains: B. adusta, Trametes sp., Polyporus sp., Trametes versicolor ATCC 7731 and Pycnoporus cinnabarinus VIC, which displayed good NOM decolourisation on solid medium were further investigated in shake-flask culture using concentrated NOM (in distilled and tap water) and fresh NOM from Beaconsfield Reservoir. For most fungi, higher levels of colour removal which correlated well with the reduction in UV-absorbing compounds (A254) were obtained in the NOM-tap water preparation and this was attributed to the increased concentrations of mineral nutrients. The decolourisation (in percentage terms) of NOM concentrate by Trametes sp. decreased with increasing initial NOM content; however, the degradation of the equivalent amount of NOM (mg C L-1) measured as colour increased. <br><br>The decolourisation of aquatic NOM concentrate and fresh NOM coincided with the onset of extracellular enzyme activity, in particular that of Lac and MnP, which varied with fungal strain, NOM preparation and concentration. LiP activity was detected only for T. versicolor, B. adusta and P. cinnabarinus. For most fungi, NOM decolourisation in tap water occurred in conjunction with increasing activity of Lac and MnP, whilst in distilled water and fresh NOM the late onset of enzyme activities indicated the initial removal of NOM to be predominantly via adsorption. B. adusta, which had markedly lower enzyme activity, gave the greatest reduction in colour and this may be attributed to the action of a versatile peroxidase. <br><br>Fungal treatment of NOM concentrate and Beaconsfield NOM led to increased A254 and DOC, and the proportional increases (which were attributed to cell lysis), were greater for lower NOM concentrations. When the fungal-treated NOM samples were subjected to a consortium of microbes, considerable reduction in the colour, UV absorbance and fungal-generated DOC was observed.<br><br>The decolourisation of NOM concentrate and Beaconsfield NOM by the WRF was accompanied by a decrease in the average molecular weight (MW) along with the formation of lower MW intermediates which subsequent bacterial treatment preferentially removed. Fractionation of the fungal-treated NOM-tap water preparation demonstrated the extensive breakdown of the very hydrophobic acids which contributed most of the colour of NOM, and less of the slightly hydrophobic acids. <br><br>In vitro decolourisation of NOM concentrate by commercial preparations of Lac, MnP and LiP was accompanied by a decrease in the average MW of both the coloured and UV-absorbing species, for which Lac gave the greatest reduction. <br>