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

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.