Aerobic fermentation prior to pasteurization produces a selective substrate for cultivation of the mushroom Pleurotus pulmonarius

Description of the subject. Pleurotus species are cultivated on lignocellulosic substrates, in which contaminant fungi such as Trichoderma spp. are common. A selective substrate for Pleurotus provides the necessary conditions for protection against contaminants. Studies show that Paenibacillus polymyxa and other thermophilic bacteria benefit from the selectivity of Pleurotus cultivation substrate, however, little is known regarding these bacterial communities. Objectives. To evaluate the effect of substrate inoculation with Paenibacillus polymyxa on the productivity of Pleurotus pulmonarius and its protection against Trichoderma. Method. Barley straw inoculated with P. polymyxa and non-inoculated straw (control) was used following 0, 3 or 5 days of fermentation prior to heat treatment in order to produce the cultivation substrate. The microbiological content before and after the heat treatment, the mycelial colonization by P. pulmonarius and Trichoderma viride in competition and the yield of P. pulmonarius were all evaluated. Results. We observed that inoculation with P. polymyxa increased the number of cultivable bacteria and changed the composition of the community. The inoculation decreased the colonization ability of T. viride and favored the mycelial growth, although the yield of mushrooms was affected. Higher yields of P. pulmomarius were obtained in the control substrate where no contamination of Trichoderma spp. was observed. Conclusions. Addition of P. polymyxa modified the natural microbiological succession in a fermentation of barley straw for 5 days, favoring the competitiveness of P. pulmonarius against T. viride. Fermentation of barley straw for 3 days, followed by heat treatment, benefits the yield and protection of P. pulmonarius against Trichoderma viride.