Sodium meta bisulfite and ph tolerance ofPleurotus sajor caju under submerged cultivation

To develop a procedure for submerged cultivation of the edible fungusPleurotus sajor caju, we investigated the organism’s tolerance to sodium meta bisulfite and acidic pH levels. These factors were evaluated as means of controlling bacterial and/or fungal contamination. Trials were conducted in 500 mL Erlenmeyer flasks that contained 200–300 mL of a 3% glucose, 0.5% yeast extract medium, and either 0-0.225% SMB (wt/wt) added, or initially adjusted to pH levels between 1.8–6.5. Inoculated flasks were incubated 7–10 d at 30°C and 200 rpm in an environmental shaker, with samples removed daily to determine mycelial dry weights. Results showed that SMB levels up to 0.05% significantly lengthened the lag phase (from 27 to 79 h) but had no effect on productivity. Maximal productivity varied between 0.054–0.057 g/L/h, whereas overall productivity was 0.042–0.045 g/L/h. Biomass concentrations ranged from 7.1–8.4 g/L. Higher SMB levels rapidly reduced productivities and yields, eventually inactivating the inoculum above 0.1% SMB. In one instance the SMB tolerance of P.sajor caju was increased to 0.075% by repeatedly exposing the organism to sublethal levels of the chemical; however, this trait was not maintained in later trials. Bacterial contaminants were detected at SMB concentrations of 0.02–0.07%, while fungal contaminants were found up to 0.125% SMB. Thus it appears that SMB might be useful in controlling bacterial contamination, but may not be as effective against fungal contaminants. The optimum pH range in terms of lag phase length, biomass yield, and productivity was 4.5–5.5, however, in certain trialsP. sajor caju still exhibited good growth parameters at pH levels as low as 3.8–4.0. pH levels below 3.8 and above 5.8 greatly reduced both growth rates and yields. Acidic pH levels (3.8–4.5) were also effective in controlling the majority of bacterial and fungal contaminants encountered. Therefore low pH or perhaps a combination of low pH and SMB should be useful in developing a large scale system for submerged cultivation ofP. sajor caju.