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, 2.8x10(8), 1.1x10(8), and 8.8x10(6), and on spruce, 4.1x10(8), 5.6x10(7), and 1.5x10(8)CFU/g DM, at 2, 20, and 37 degrees C, respectively. Dominant bacteria at 2, 20, and 37 degrees C were Pseudomonas spp. (some Enterobacteriaceae spp. present), Luteibacter rhizovicinus, and Fulvimonas sp., respectively. Pseudomonas spp. were absent at 20 degrees C. Among microfungi, yeasts dominated at 2 degrees C but were absent at 37 degrees C, whereas molds dominated at 20 and 37 degrees 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 degrees C, whereas the human pathogens Aspergillus fumigatus and Paecilomyces variotii dominated at 37 degrees 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.