Screening and identification of urease producing microorganisms from New Zealand pasture soils

Abstract

Urea is the most commonly used fertiliser in agricultural systems because of its relatively low price, high nitrogen (N) content and wide availability. However, urea N can be quickly lost from the system via ammonia volatilization or nitrate leaching following urea hydrolysis by urease producing soil microorganisms (UPSMs). N availability to the plant is therefore reduced, and the production of nitrous oxide and leaching of soil nitrate would contribute to environmental damage. Soils from under dairy pastures across New Zealand were collected and UPSMs, including fungi and bacteria, isolated using ureacontaining medium and then identified using polymerase chain reaction (PCR)-based molecular methods. Fungal species identified included Absidia sp., Chaetomium sp., Cladosporium cladosporioides, Cordyceps sp., Fusarium culmorum, Fusarium graminearum, Fusarium oxysporum, Fusarium solani, Geomyces sp., Gliomastix murorum, Humicola grisea, Lewia infectoria, Mariannaea sp., Mucor hiemalis, Nectria sp., Paecilomyces carneus, Paecilomyces lilacinus, Paecilomyces marquandii, Penicillium spinulosum, Phoma exigua, Phoma paspali, Pochonia bulbillosa, Thelonectria veuillotiana (Cylindrocarpon candidulum) and Trichosporon sp., all of which have a role in urea degradation in soil. Pasture soil-resident urease producing bacteria were also identified as: Citrobacter freundii, Cupriavidus sp., Enterobacter ludwigii, Pseudomonas chlororaphis, Rahnella aquatilis, Serratia proteamaculans and Yersinia kristensenii. Cupriavidus sp. and Mucor hiemalis showed strong urease activity when cultured on urease medium. Biological suppression of UPSMs is being investigated as a method to reduce soil urease.