Penicillium subrubescens, a new species efficiently producing inulinase

Abstract

Inulin is a reserve carbohydrate in about 15 % of the flowering plants and is accumulated in underground tubers of e.g. chicory, dahlia and Jerusalem artichoke. This carbohydrate consists of linear chains of β-(2,1)-linked fructose attached to a sucrose molecule. Inulinases hydrolyse inulin into fructose and glucose. To find efficient inulin degrading fungi, 126 fungal strains from the Fungal Biotechnology Culture Collection (FBCC) at University of Helsinki and 74 freshly isolated strains from soil around Jerusalem artichoke tubers were screened in liquid cultures with inulin as a sole source of carbon or ground Jerusalem artichoke tubers, which contains up to 19 % (fresh weight) inulin. Inulinase and invertase activities were assayed by the dinitrosalicylic acid (DNS) method and a freshly isolated Penicillium strain originating from agricultural soil (FBCC 1632) was the most efficient inulinase producer. When it was cultivated at pH 6 and 28 °C in 2 litre bioreactors using inulin and Jerusalem artichoke as a carbon source, inulinase and invertase activities were on day 4 7.7 and 3.1 U mL(-1), respectively. The released sugars analysed by TLC and HPLC showed that considerable amounts of fructose were released while the levels of oligofructans were low, indicating an exoinulinase type of activity. Taxonomic study of the inulinase producing strain showed that this isolate represents a new species belonging in Penicillium section Lanata-divaricata. This new species produces a unique combination of extrolites and is phenotypically and phylogenetically closely related to Penicillium pulvillorum. We propose the name Penicillium subrubescens sp. nov. (CBS 132785(T) = FBCC 1632(T)) for this new species.