| White-rot fungi in recent times are being explored for their potential to valorize agrocrop residue and also induced to produce cellulase enzymes which have various industrial applications.Agro-crop residue,including rice straw waste generation,continues to increase due to the increase in rice production,which is one of the stable food of the growing Chinese population.This has made rice straw residue ubiquitous,and its disposal raises serious environmental concerns for which better alternatives are constantly been investigated.One of such better alternatives is to utilize rice straw as a ruminant feed material since ruminants are known to be efficient in converting agro-waste into valuable products.Its utilization is much more limited due to the high degree of lignification and low digestibility.White-rot fungi are known to have the potential to improve or valorize agro-wastes via delignification,leaving a protein-enriched biomass which has the potential of serving as a ruminant feed material.Furthermore,white-rot fungi cellulase enzyme and its mycelium biomass which have several industrial applications,are known to be inducible.Three studies were therefore designed to evaluate the potential of two(2)white-rot fungi species in their effective valorization of rice straw and to evaluate cellulase production and mycelium biomass yield of the fungi species in response to different inducer sources.Experiment 1:Effect of ligninolytic axenic and coculture white-rot fungi on rice straw chemical composition and in vitro rumen digestibility and fermentation parametersThe study sought to investigate the potentials of axenic cultures of Pleurotus ostreatus,Phanerochaete chrysosporium and their coculture(P.chrysosporium and P.ostreatus)to break down lignin and to enhance the rumen fermentability of rice straw.Rice straw was fermented by two lignin-degrading fungi,namely,P.ostreatus,P.chrysosporium and its coculture(P.ostreatus and P.chrysosporium)with uninoculated straw as control under solidstate fermentation employing a completely randomized research design.The coculture exhibited a mutual intermingling plus inhibition interaction.The fungi treatment increased the crude protein from(5.1%)in control to(6.5%,6.6%,and 6.7%)in P.ostreatus,P.chrysosporium and coculture,respectively(P<0.05).The coculture-treated straw had a lower lignin content(5.3%)compared to the P.chrysosporium(6.2%),with the P.ostreatus recording the least(3.3%)lignin fraction(P<0.05).Treatment of rice straw with coculture improved the in vitro dry matter digestibility(68.1%),ammonia-nitrogen(12.55 mg/dL),total volatile fatty acids(35.3 mM),and total gas(57.4 ml/200 mg)compared to P.chrysosporium(45.1%,10.24 mg/dL,32.2 mM,44.4 ml/200 mg)(P<0.05)but was second to P.ostreatus(75.3%,13.32 mg/dL,38.3 mM,65.6 ml/200 mg)(P<0.05).Cellulolytic bacteria(R.albus,R.flavefaciens,F.succinogens,P.ruminicola)population proliferated(P<0.05)whilst methanogen,rumen protozoa and rumen fungi declined in P.ostreatus-treated rice straw compared to the untreated straw(P<0.05).In general,instead of an anticipated synergistic effect from the coculture,a competitive antagonistic effect was instead observed at the end of the study,a condition that can be attributed to the coculture behaviour.Experiment 2:Effect of ammoniated and/or basidiomycete white-rot fungi treatment on rice straw chemical composition,in vitro rumen digestibility and fermentation parametersVarious pretreatments are employed to increase the utilization of rice straw as a ruminant feed ingredient to minimize its negative environmental impact.However,an efficient alternative is still needed.The purpose of the study was to evaluate the ability of ammonia and/or white-rot fungi(Pleurotus ostreatus)to degrade lignin,increase the nutritional value,and enhance the rumen fermentability of rice straw.Rice straw was treated with ammonia and/or basidiomycete white-rot fungi(P:ostreatus)with untreated straw as a control under solid-state fermentation employing a completely randomized design.The crude protein increased from 2.05%in control to 3.47%in ammoniated rice straw,5.24%in basidiomycete white-rot fungi(P.ostreatus),and 6.58%in ammoniated-basidiomycete white-rot fungi(P.ostreatus)treated rice straw(P<0.05).The ammoniated-basidiomycete white-rot fungi(P.ostreatus)treated rice straw had the least lignin content(3.76%)(P<0.05)compared to untreated rice straw(8.75%),ammoniated rice straw(6.66%),and white-rot fungi(P.ostreatus)treated rice straw(5.96%)(P<0.05).Ammoniated-basidiomycete white-rot fungi(P.ostreatus)treated rice straw had improved in vitro dry matter digestibility(65.52%),ammonia-nitrogen(19.86 mg/dL),total volatile fatty acid(76.56 mM),and total gas production(56.78 mL/g)compared to ammoniated rice straw(56.16%,15.72 mg/dL,67.71 mM,44.30 mL/g)or basidiomycete white-rot fungi(P.ostreatus)treated rice straw(61.12%,17.14 mg/dL,75.36 mM,49.31 mL/g)respectively(P<0.05).The ammoniated-basidiomycete white-rot fungi(P.ostreatus)treatment improved rice straw’s nutritional value,in vitro dry matter digestibility,ammonia-nitrogen,volatile fatty acids,and gas production.Cellulolytic bacteria(R.albus,R.flavefaciens,F.succinogens,S.ruminatium)population improved(P<0.05)whilst methanogen,rumen protozoa and rumen fungi non-pro liferated in ammoniated-basidiomycete white-rot fungi(P.ostreatus)treated rice straw compared to the untreated straw(P<0.05).Experiment 3:Effect of different carbon and nitrogen on cellulase enzyme and mycelium biomass production by white-rot basidiomycetes Pleurotus ostreatus and Phanerochaete chrysosporium under submerged fermentationCellulase enzymes and mycelium biomass attract a lot of research due to their industrial application.Diverse cellulase-producing organisms and substances that induce cellulase and mycelium biomass are highly sought-after.This study aimed to evaluate the effect of different inducer sources on cellulase and mycelium biomass production by white rot fungi P.ostreatus CGMCC 3.7292 and P.chrysosporium CGMCC 3,7212 under submerged fermentation employing a one-variable-at-a-time experimental design.The different inducer sources tested were nitrogen(yeast,potassium nitrate,sodium nitrate,ammonium sulphate,aqueous ammonia and urea),carbon(malt extract,glucose,fructose,carboxymethylcellulose,starch and xylose)and agro-biomass(stevia straw,wheat straw,oat straw,alfalfa straw,corn cobs and corn stover).These inducer sources strongly impacted enzyme activities and mycelium biomass by P.ostreatus CGMCC 3.7292 and P.chrysosporium CGMCC 3.7212.The suitable nitro gen and carbon inducer sources for cellulase activity by P.ostreatus and P.chrysosporium were yeast(1.354 U/mL and 1.154 U/mL)and carboxymethylcellulose(0.976 U/mL and 0.776 U/mL)(P<0.05)while the suitable agro-biomass were wheat straw(6.880 U/mL)and corn stover(6.525 U/mL),respectively(P<0.05).The least inducer sources in terms of nitrogen,carbon and agro-biomass for cellulase activity by P.ostreatus and P.chrysosporium were urea(0.213 U/mL and 0.081 U/mL),glucose(0.042 U/mL and 0.035 U/mL),xylose(0.042 U/mL and 0.035 U/mL)and stevia straw(1.555 U/mL and 0.960 U/mL)(P<0.05),Mycelium biomass yields from P.ostreatus and P.chrysosporium were best in glucose(286.24 mg;299.24 mg)and yeast extract(332.33 mg;349.50 mg)medium(P<0.05)but worse in a carboxymethylcellulose(123.15 mg;129.75)and urea medium(118.50 mg;163.51 mg)(P<0.05).In submerged fermentation,the cellulase enzyme activity of P.ostreatus in response to various inducer sources was relatively higher than P.chrysosporium,which was vice versa in terms of mycelium biomass production.In summary,although the coculture exhibited a mutual intermingling plus inhibition interaction which outperformed P.chrysosporium with regards to the parameters assessed,it was not superior to P.ostreatus,and combining ammoniation with P.ostreatus for rice straw treatment resulted in better outcomes than ammoniation or P.ostreatus treatment.Finally,P.ostreatus generally produced greater cellulase in response to different inducer sources than P.chrysosporium. |
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