Abstract
Laccase is widely used in several industrial applications and co-culture is a common method for enhancing laccase production in submerged fermentation. In this study, the co-culture of four yeasts with Pleurotus eryngii var. ferulae was found to enhance laccase production. An analysis of sterilization temperatures and extraction conditions revealed that the stimulatory compound in yeasts was temperature-sensitive, and that it was fat-soluble. An LC-MS analysis revealed that the possible stimulatory compound for laccase production in the four yeast extracts was β-carotene. Moreover, the addition of 4 mg β-carotene to 150 mL of P. eryngii var. ferulae culture broth improved laccase production by 2.2-fold compared with the control (i.e., a monoculture), and was similar to laccase production in co-culture. In addition, the enhanced laccase production was accompanied by an increase of lac gene transcription, which was 6.2-time higher than the control on the fifth day. Therefore, it was concluded that β-carotene from the co-cultured yeasts enhanced laccase production in P. eryngii var. ferulae, and strains that produce β-carotene could be selected to enhance fungal laccase production in a co-culture. Alternatively, β-carotene or crude extracts of β-carotene could be used to induce high laccase production in large scale.
Highlights
Laccase (EC 1.10.3.2) is a group of blue multi-copper oxidases that are widely distributed in microorganisms, plants and insects, and capable of catalyzing the reaction various organic compounds with the reduction of oxygen
Our previous study indicated that the yeast R. mucilaginosa improved the laccase production of P. eryngii var. ferulae JM301 in co-culture (Wang et al, 2015)
The results showed that three of the yeasts, Phaffia rhodozyma, S. pararoseus and R. glutinis, significantly enhanced laccase production in co-culture, and the highest laccase production (9911 U/L) by P. eryngii var. ferulae was obtained from a co-culture with S. pararoseus inoculated at 3% (Figure 1)
Summary
Laccase (EC 1.10.3.2) is a group of blue multi-copper oxidases that are widely distributed in microorganisms, plants and insects, and capable of catalyzing the reaction various organic compounds with the reduction of oxygen. Laccase is mainly produced by fungi, and co-culture is an effective method to optimize laccase production in submerged fermentation (Wang et al, 2009; Flores et al, 2010; Li et al, 2011). Different inducers enhance laccase production by various mechanisms, including the improvement of silent or poorly expressed laccase isoforms and the response to oxidative stress caused by an inducer (Hoegger et al, 2006; Wang et al, 2014). The elucidation of these mechanisms has been beneficial to the screening of more inducers that enhance laccase production
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