Down-regulation of pyruvate decarboxylase gene of white-rot fungus Phlebia sp. MG-60 modify the metabolism of sugars and productivity of extracellular peroxidase activity

Third generation biobutanol production by Clostridium beijerinckii in a medium containing mixotrophically cultivated Dunaliella salina biomass

This study aims the third generation biobutanol production in P2 medium supplemented D. salina biomass mixotrophically cultivated with marble waste (MW). The wastes derived from the marble industry contain approximately 90% of carbon-rich compounds. Microalgal growth in mixotrophic conditions was optimized in the 0.4-2 g/L of MW concentration range. The highest microalgal concentration was obtained as 0.481 g/L in the presence of 1 g/L MW. Furthermore, some important parameters for the production of biobutanol, such as microalgal cultivation conditions, initial mixotrophic microalgal biomass loading (50-300 g/L), and fermentation time (24-96 h) were optimized. The highest biobutanol, total ABE, biobutanol yield and productivity were determined as 11.88 g/L, 13.89 g/L, 0.331 g/g and 0.165 g/L/h at the end of 72 h in P2 medium including 60 g/L glucose and 200 g/L microalgal biomass cultivated in 1 g/L MW, respectively. The results show that D. salina is a suitable raw material for supporting Clostridium beijerinckii DSMZ 6422 cells on biobutanol production. To the best of our knowledge, this is the first study on the use of MW which is a promising feedstock on the mixotrophic cultivation of D. salina for biobutanol production.

Upregulation of MAP kinase HOG1 gene of white-rot fungus Phlebia sp. MG-60 inhibits the ethanol fermentation and mycelial growth

Wood biomass conversion for fossil resource replacement could result in the sustainable production of chemicals, although lignin represents an obstacle to efficient polysaccharide use. White-rot fungus Phlebia sp. MG-60 reportedly selectively and aerobically degrades lignin in hardwood, then it begins cellulose saccharification from the delignified wood to produce ethanol. Environmental conditions might change white-rot fungi-driven biomass conversion. However, how the environmental response sensor affects ethanol fermentation in white-rot fungi remains elusive. In this study, we focused on MGHOG1, the yeast Hog1 homolog in Phlebia sp. MG-60, a presumably important player in osmoresponse. We generated MGHOG1 overexpressing (OE) transformants in Phlebia sp. MG-60, exhibiting slower mycelial growth compared with the wild-type under salinity stress. MGHOG1 overexpressing liquid cultures displayed suppressed mycelial growth and ethanol fermentation. Therefore, MGHOG1 potentially influences ethanol fermentation and mycelial growth in Phlebia sp. MG-60. This study provides novel insights into the regulation of white-rot fungi-mediated biomass conversion.

Selective Homologous Expression of Recombinant Manganese Peroxidase Isozyme of Salt-Tolerant White-Rot Fungus Phlebia sp. MG-60, and Its Salt-Tolerance and Thermostability

Phlebia sp. MG-60 is the salt-tolerant, white-rot fungus which was isolated from a mangrove forest. This fungus expresses three kinds of manganese peroxidase (MGMnP) isozymes, MGMnP1, MGMnP2 and MGMnP3 in low nitrogen medium (LNM) or LNM containing NaCl. To date, there have been no reports on the biochemical salt-tolerance of these MnP isozymes due to the difficulty of purification. In present study, we established forced expression transformants of these three types of MnP isozymes. In addition, the fact that this fungus hardly produces native MnP in a high-nitrogen medium (HNM) was used to perform isozyme-selective expression and simple purification in HNM. The resulting MGMnPs showed high tolerance for NaCl compared with the MnP of Phanerochaete chrysosporium. It was worth noting that high concentration of NaCl (over 200 mM to 1200 mM) can enhance the activity of MGMnP1. Additionally, MGMnP1 showed relatively high thermo tolerance compared with other isozymes. MGMnPs may have evolved to adapt to chloride-rich environments, mangrove forest.

Genomic Studies of White-Rot Fungus Cerrena unicolor SP02 Provide Insights into Food Safety Value-Added Utilization of Non-Food Lignocellulosic Biomass

Cerrena unicolor is an ecologically and biotechnologically important wood-degrading basidiomycete with high lignocellulose degrading ability. Biological and genetic investigations are limited in the Cerrena genus and, thus, hinder genetic modification and commercial use. The aim of the present study was to provide a global understanding through genomic and experimental research about lignocellulosic biomass utilization by Cerrena unicolor. In this study, we reported the genome sequence of C. unicolor SP02 by using the Illumina and PacBio 20 platforms to obtain trustworthy assembly and annotation. This is the combinational 2nd and 3rd genome sequencing and assembly of C. unicolor species. The generated genome was 42.79 Mb in size with an N50 contig size of 2.48 Mb, a G + C content of 47.43%, and encoding of 12,277 predicted genes. The genes encoding various lignocellulolytic enzymes including laccase, lignin peroxidase, manganese peroxidase, cytochromes P450, cellulase, xylanase, α-amylase, and pectinase involved in the degradation of lignin, cellulose, xylan, starch, pectin, and chitin that showed the C. unicolor SP02 potentially have a wide range of applications in lignocellulosic biomass conversion. Genome-scale metabolic analysis opened up a valuable resource for a better understanding of carbohydrate-active enzymes (CAZymes) and oxidoreductases that provide insights into the genetic basis and molecular mechanisms for lignocellulosic degradation. The C. unicolor SP02 model can be used for the development of efficient microbial cell factories in lignocellulosic industries. The understanding of the genetic material of C. unicolor SP02 coding for the lignocellulolytic enzymes will significantly benefit us in genetic manipulation, site-directed mutagenesis, and industrial biotechnology.

Conservation of Xylose Fermentability in Phlebia Species and Direct Fermentation of Xylan by Selected Fungi

In efforts to lower the cost of total conversion of lignocellulosic materials, utilization of hemicellulose must be considered. White-rot fungus Phlebia sp. MG-60 can produce ethanol directly from cellulose and has fermentation ability for glucose, cellulose, and xylose. Therefore, white-rot fungi can be considered a good candidate for consolidated bioprocessing to give bioethanol from lignocellulosic biomass, although little information is available on the direct fermentation of xylan. In the present study, some Phlebia species were selected as candidates because of their ability to ferment xylose to ethanol more efficiently than Phlebia sp. MG-60. This process indicated that the basidiomycetes that can produce ethanol from xylose are closely related genetically within the Phlebia genus. The selected Phlebia species showed higher ethanol productivity from corn core and beechwood xylans than Phlebia sp. MG-60. The ethanol yields from corn core xylan in culture with Phlebia acerina HHB11146, Phlebia ludoviciana HHB9640, and Phlebia subochracea HHB8494 were 46.2%, 46.7%, and 39.7% of theoretical maximum, and those from beechwood xylan were 19.09%, 17.7%, and 21.4% of the theoretical maximum, respectively.

Butanol production from cellulosic material by anaerobic co-culture of white-rot fungus Phlebia and bacterium Clostridium in consolidated bioprocessing

Butanol production from lignocelluloses is desirable. Unfortunately, the known wild-types of butanol fermenting Clostridium bacteria are not capable of delignification and saccharification. Here we analyzed butanol production from cellulosic material using anaerobic co-culture of C. saccharoperbutylacetonicum with the white-rot fungus Phlebia sp. MG-60-P2. In consolidated bioprocessing, the co-culture synergistically produced butanol and enhanced saccharification. Knockout of the pyruvate decarboxylase gene from MG-60-P2 to produce transformant line KO77 led to inhibition of ethanol fermentation and high accumulation of saccharified cellobiose and glucose from cellulose. In co-culture of KO77 with C. saccharoperbutylacetonicum, enhanced butanol production was observed (3.2 g/L, compared with 2.5 g/L in co-culture of MG-60-P2 and C. saccharoperbutylacetonicum). We believe this is the first application of co-culture between white-rot fungus and Clostridium to produce butanol from cellulose; butanol production from lignocellulose by co-culture of C. saccharoperbutylacetonicum with Phlebia sp. MG-60-P2 and its transformant should be pursued.