Abstract
Laccases can oxidize a wide range of aromatic compounds and are industrially valuable. Laccases often exist in gene families and may differ from each other in expression and function. Quantitative real-time polymerase chain reaction (qPCR) was used for transcription profiling of eight laccase genes in Cerrena sp. strain HYB07 with validated reference genes. A high laccase activity of 280.0 U/mL was obtained after submerged fermentation for 5 days. Laccase production and laccase gene transcription at different fermentation stages and in response to various environmental cues were revealed. HYB07 laccase activity correlated with transcription levels of its predominantly expressed laccase gene, Lac7. Cu2+ ions were indispensable for efficient laccase production by HYB07, mainly through Lac7 transcription induction, and no aromatic compounds were needed. HYB07 laccase synthesis and biomass accumulation were highest with non-limiting carbon and nitrogen. Glycerol and inorganic nitrogen sources adversely impacted Lac7 transcription, laccase yields, and fungal growth. The present study would further our understanding of transcription regulation of laccase genes, which may in turn facilitate laccase production as well as elucidation of their physiological roles.
Highlights
White-rot fungi secrete ligninolytic enzymes such as lignin peroxidases, manganese peroxidases, versatile peroxidases, and laccases (Wong, 2009)
The fermentation medium used in this study resulted in higher laccase yields (280.0 U/mL) than previously used PDY medium (210.8 U/mL)
MRNA abundance does not directly translate to protein abundance, dry mass-based laccase activity largely agreed with Lac7 transcript levels (Supplementary Figures S4, S5), and fluctuations in Lac7 transcription levels constituted a major cause of fluctuations in laccase yields
Summary
White-rot fungi secrete ligninolytic enzymes such as lignin peroxidases, manganese peroxidases, versatile peroxidases, and laccases (Wong, 2009). Laccases comprise a class of multi-copper containing oxidases that are environmentally friendly and industrially important. Laccases have low substrate specificity and can oxidize a wide range of substrates such as phenolic lignin compounds, recalcitrant dyestuffs, and other environment pollutants, accompanied by concomitant reduction of molecular oxygen to water. Laccases have found applications in food, bioremediation, textile, biofuel, and other industries (Giardina et al, 2010). Semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR), and quantitative real-time PCR (qPCR) have been used to determine mRNA abundance. Often at the level of Laccase Production and its Differential Transcription in Cerrena sp
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