Temperature‐dependent changes in the microbial storage flora of birch and spruce sawdust

Abstract

Sawdust can be used to make pellets (biofuel) and particle boards and as a potential lignocellulose feedstock in bioethanol production. Microbial activity can affect sawdust quality; hence, we monitored the microbial population in birch- and spruce sawdust after 3 months' storage at various temperatures. Species composition was similar on both materials but was strongly influenced by temperature. Bacteria were present on all materials at all conditions: on birch, 2.8×10(8) , 1.1×10(8) , and 8.8×10(6) , and on spruce, 4.1×10(8) , 5.6×10(7) , and 1.5×10(8) CFU/g DM, at 2, 20, and 37°C, respectively. Dominant bacteria at 2, 20, and 37°C were Pseudomonas spp. (some Enterobacteriaceae spp. present), Luteibacter rhizovicinus, and Fulvimonas sp., respectively. Pseudomonas spp. were absent at ≥20°C. Among microfungi, yeasts dominated at 2°C but were absent at 37°C, whereas molds dominated at 20 and 37°C. Common yeasts included Cystofilobasidium capitatum, Cystofilobasidium infirmominiatum, Candida saitoana, Candida oregonensis, and Candida railenensis. Ophiostoma quercus was a common mold at 2 and 20°C, whereas the human pathogens Aspergillus fumigatus and Paecilomyces variotii dominated at 37°C. Attempts to influence the microflora by addition of the biocontrol yeasts, Wickerhamomyces anomalus and Scheffersomyces stipitis, were unsuccessful, as their growth in sawdust was poor to absent.