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.