Rice straw hydrolysis using in-situ produced enzymes: Feedstock influences fungal enzyme composition and hydrolytic efficiency

Trichoderma reesei RUT-C30 was cultivated on differentially pretreated rice straw and pure cellulose as a carbon source/inducer for cellulase production, and the enzymes were evaluated for hydrolysis of sequential acid and alkali pretreated rice straw. Growth on pretreated rice straw enhanced protein secretion and cellulase activities compared to pure cellulose as a carbon source. The yield of cellulolytic enzymes was higher for alkali pretreated rice straw (ALP-RS), while H2O2-treated (HP-RS) could not induce cellulases to a larger level compared to pure cellulose. Protein concentration was 3.5-fold higher on ALP-RS as compared to pure cellulose, with a maximum filter-paper cellulase (FPase) activity of 1.76 IU/ml and carboxy-methyl cellulase (CMCase) activity of 40.16 IU/ml (2.18 fold higher). Beta-glucosidase (BGL) activity was more or less the same with the different substrates and supplementation of heterologous BGL could result in a quantum jump in hydrolytic efficiencies, which in the case of ALP-RS induced enzymes was 34% (increased from 69.26% to 92.51%). The use of lignocellulosic biomass (LCB) itself as a substrate for the production of cellulase is advantageous not only in terms of raw material costs but also for obtaining a more suitable enzyme profile for biomass hydrolysis.

Harnessing lignocellulosic biomass for butanol production through clostridia for sustainable waste management: recent advances and perspectives

The escalating waste generation rates, driven by population growth, urbanization, and consumption patterns, have made waste management a critical global concern with significant environmental, social, and economic repercussions. Among the various waste sources, lignocellulosic biomass represents a significant proportion of agricultural, agro-industrial, and municipal wastes. Biofuels are gaining attention as a promising substitute to fossil fuels, and butanol is one such biofuel that has been identified as a potential candidate due to its compatibility with existing fuel infrastructure, lower volatility, and higher energy density. Sustainable management of lignocellulosic biomass waste and its utilization in fermentation are viable alternatives to produce butanol via the promising microbial catalyst clostridia. This review provides an overview of lignocellulosic biomass waste management, focusing on recent advances in strain development for butanol production from renewable biomass with an emphasis on future perspectives.

Bioupgrading of the aqueous phase of pyrolysis oil from lignocellulosic biomass: a platform for renewable chemicals and fuels from the whole fraction of biomass

Pyrolysis, a thermal decomposition without oxygen, is a promising technology for transportable liquids from whole fractions of lignocellulosic biomass. However, due to the hydrophilic products of pyrolysis, the liquid oils have undesirable physicochemical characteristics, thus requiring an additional upgrading process. Biological upgrading methods could address the drawbacks of pyrolysis by utilizing various hydrophilic compounds as carbon sources under mild conditions with low carbon footprints. Versatile chemicals, such as lipids, ethanol, and organic acids, could be produced through microbial assimilation of anhydrous sugars, organic acids, aldehydes, and phenolics in the hydrophilic fractions. The presence of various toxic compounds and the complex composition of the aqueous phase are the main challenges. In this review, the potential of bioconversion routes for upgrading the aqueous phase of pyrolysis oil is investigated with critical challenges and perspectives.

Polyhydroxybutyrate Production from Methane and Carbon Dioxide by a Syntrophic Consortium of Methanotrophs with Oxygenic Photogranules without an External Oxygen Supply

Here, a syntrophic process was developed to produce polyhydroxy-β-butyrate (PHB) from a gas stream containing CH₄ and CO₂ without an external oxygen supply using a combination of methanotrophs with the community of oxygenic photogranules (OPGs). The co-culture features of Methylomonas sp. DH-1 and Methylosinus trichosporium OB3b were evaluated under carbon-rich and carbon-lean conditions. The critical role of O₂ in the syntrophy was confirmed through the sequencing of 16S rRNA gene fragments. Based on their carbon consumption rates and the adaptation to a poor environment, M. trichosporium OB3b with OPGs was selected for methane conversion and PHB production. Nitrogen limitation stimulated PHB accumulation in the methanotroph but hindered the growth of the syntrophic consortium. At 2.9 mM of the nitrogen source, 1.13 g/L of biomass and 83.0 mg/L of PHB could be obtained from simulated biogas. These results demonstrate that syntrophy has the potential to convert greenhouse gases into valuable products efficiently.

Sequential mild acid and alkali pretreatment of rice straw to improve enzymatic saccharification for bioethanol production

Sequential pretreatment using different NaOH concentrations (0.5%, 1.0%, 1.5%, w/w) and 1% H₂SO₄ (w/w) was evaluated as a strategy for effective hydrolysis of rice straw. The efficiency of sequential NaOH and H₂SO₄ (SNA) pretreatment against sequential H₂SO₄ and NaOH (SH) was assessed. SH pretreated biomass attained more sugar yield compared to SNA pretreated biomass. The sugar yields from pretreated biomass improved with increasing NaOH concentration in both SH and SNA treatments. The maximum sugar release of 40.6 mg/ml (83.2% efficiency) was obtained from SH pretreated biomass when the stage 2 alkali treatment was performed at 1.5% w/w NaOH. The non-detoxified hydrolysate from this biomass was fermented with 96.8% efficiency.

Mild alkaline pretreatment can achieve high hydrolytic and fermentation efficiencies for rice straw conversion to bioethanol

Mild alkaline pretreatment was evaluated as a strategy for effective lignin removal and hydrolysis of rice straw. The pretreatment efficiency of different NaOH concentrations (0.5, 1.0, 1.5 or 2.0% w/w) was assessed. Rice straw (RS) pretreated with 1.5% NaOH achieved better sugar yield compared to other concentrations used. A cellulose conversion efficiency of 91% (45.84 mg/ml glucose release) was attained from 1.5% NaOH pretreated rice straw (PRS), whereas 1% NaOH pretreated rice straw yielded 35.10 mg/ml of glucose corresponding to a cellulose conversion efficiency of 73.81%. The ethanol production from 1% and 1.5% NaOH pretreated RS hydrolysates was similar at ∼3.3% (w/v), corresponding to a fermentation efficiency of 86%. The non-detoxified hydrolysate was fermented using the novel yeast strain Saccharomyces cerevisiae RPP-03O without any additional supplementation of nutrients.

Effect of inoculated azotobacteria and Phanerochaete chrysosporium on the composting of olive pomace: Microbial community dynamics and phenols evolution

The effect of inoculated azotobacteria and basidiomycetes white-rot fungi on the population dynamics of bacteria and eumycetes during the co-composting of olive mill pomace and wheat straw was evaluated by Polymerase Chain Reaction-Denaturing Gradient Gel Electrophoresis (PCR-DGGE) analysis combined with sequencing of rRNA gene amplicons from selected DGGE bands. The evolution of pH, temperature, phytotoxicity and water-soluble phenol content during co-composting was also monitored. In general, a similar evolution of microbial biodiversity was seen in both the inoculated and uninoculated (control) piles, which was in keeping with a similar evolution of phytotoxicity and water-soluble phenol content. Overall, under the conditions applied, data suggest a marginal influence of the inoculated starters on the physical, chemical and microbiological properties of compost piles, with the resident microbiota playing a major role.