Optimization of consolidated bioprocessing by response surface methodology in the conversion of corn stover to bioethanol by thermophilic Geobacillus thermoglucosidasius

Formation of a Novel Antagonistic Bacterial Combination to Enhance Biocontrol for Cucumber Fusarium Wilt

Paenibacillus polymyxa strain PJH16, isolated and tested by our team, suppresses cucumber Fusarium wilt as an efficient biocontrol agent. For further investigation, the strain has been combined with two other Bacillus strains (Bacillus velezensis VJH504 and Bacillus subtilis JNF2) to enhance biocontrol ability, which formed high-efficiency microbial agents in the current study. The methodological target taken is based on achieving the optimal growth conditions of the combined microbial agents; hence, the medium composition and culture conditions were optimized through a single-factor test, orthogonal test and response surface methodology. Following this, the effectiveness of the microbial combination was assessed through pot experiments, which provided a theoretical foundation for the synthesis of microbial flora to significantly control cucumber Fusarium wilt. The results showed excellent compatibility, proving suitable for the proliferation and growth of Paenibacillus polymyxa PJH16, Bacillus velezensis VJH504, and Bacillus subtilis JNF2 strains together, specifically, when the inoculation amounts were adjusted to 4% of each. Using the single-factor test and orthogonal test analysis, the optimum composition of culture medium for the composite strain was identified as 3% glucose as the optimal carbon source, 2% yeast extract powder as the preferred nitrogen source, and 1% dipotassium hydrogen phosphate as the most suitable inorganic salt. Furthermore, the optical density (OD600) of the composite strain solution reached its highest level at 3.16 under the following culture conditions: inoculation volume of 200 µL, 171 rpm culture speed, 21.6 h culture time, 30 °C cultural temperature, and an initial pH of 7.0. The pot experiment demonstrated that the mixed bacterial solution achieved a relative control efficacy of 93.4% against cucumber Fusarium wilt, which was significantly superior to that of single- strain or pesticide treatment, and also promoted cucumber growth. In summary, the microbial flora synthesized by the three Bacillus strains displayed a high bacterial concentration, following the optimization of culture conditions, and exerted remarkable control and growth-promoting effects on cucumber Fusarium wilt. This finding holds great significance for future developments of composite microbial agents.

Biofuel production from lignocellulose via thermophile-based consolidated bioprocessing

The depletion of fossil fuels and their impact on the environment have led to efforts to develop alternative sustainable fuels. While biofuel derived from lignocellulose is considered a sustainable, renewable, and green energy source, enhancing biofuel production and achieving a cost-effective bioconversion of lignocellulose at existing bio-refineries remains a challenge. Consolidated bioprocessing (CBP) using thermophiles can simplify this operation by integrating multiple processes, such as hydrolytic enzyme production, lignocellulose degradation, biofuel fermentation, and product distillation. This paper reviews recent developments in the conversion of lignocellulose to biofuel using thermophile-based CBP. First, advances in thermostable enzyme and thermophilic lignocellulolytic microorganism discovery and development for lignocellulosic biorefinery use are outlined. Then, several thermophilic CBP candidates and thermophilic microbes engineered to drive CBP of lignocellulose are reviewed. CRISPR/Cas-based genome editing tools developed for thermophiles are also highlighted. The potential applications of the Design-Build-Test-Learn (DBTL) synthetic biology strategy for designing and constructing thermophilic CBP hosts are also discussed in detail. Overall, this review illustrates how to develop highly sophisticated thermophilic CBP hosts for use in lignocellulosic biorefinery applications.

Selective recovery of esterase from Trichoderma harzianum through adsorption: Insights on enzymatic catalysis, adsorption isotherms and kinetics

In recent years, numerous attempts have been made to develop a low-cost adsorbent for selectively recovering industrially important products from fermentation broth or complex mixtures. The current study is a novel attempt to selectively adsorb esterase from Trichoderma harzianum using cheap adsorbents like bentonite (BT), activated charcoal (AC), silicon dioxide (SiO2), and titanium dioxide (TiO2). AC had the highest esterase adsorption of 97.58% due to its larger surface area of 594.45 m3/g. SiO2 was found to have the highest selectivity over esterase, with an estimated purification fold of 7.2. Interestingly, the purification fold of 5.5 was found in the BT-extracted fermentation broth. The functional (FT-IR) and morphological analysis (SEM-EDX) were used to characterize the adsorption of esterase. Esterase adsorption on AC, SiO2, and TiO2 was well fitted by Freundlich isotherm, demonstrating multilayer adsorption of esterase. A pseudo-second-order kinetic model was developed for esterase adsorption in various adsorbents. Thermodynamic analysis revealed that adsorption is an endothermic process. AC has the lowest Gibbs free energy of -10.96 kJ/mol, which supports the spontaneous maximum adsorption of both esterase and protein. In the desorption study, the maximum recovery of esterase from TiO2 using sodium chloride was 41.34 %. Unlike other adsorbents, the AC-adsorbed esterase maintained its catalytic activity and stability, implying that it could be used as an immobilization system for commercial applications. According to the kinetic analysis, the overall rate of the reaction was controlled by reaction kinetics rather than external mass transfer resistance, as indicated by the Damkohler number.

Parageobacillus thermoglucosidasius as an emerging thermophilic cell factory

Parageobacillus thermoglucosidasius is a thermophilic and facultatively anaerobic microbe, which is emerging as one of the most promising thermophilic model organisms for metabolic engineering. The use of thermophilic microorganisms for industrial bioprocesses provides the advantages of increased reaction rates and reduced cooling costs for bioreactors compared to their mesophilic counterparts. Moreover, it enables starch or lignocellulose degradation and fermentation to occur at the same temperature in a Simultaneous Saccharification and Fermentation (SSF) or Consolidated Bioprocessing (CBP) approach. Its natural hemicellulolytic capabilities and its ability to convert CO to metabolic energy make P. thermoglucosidasius a potentially attractive host for bio-based processes. It can effectively degrade hemicellulose due to a number of hydrolytic enzymes, carbohydrate transporters, and regulatory elements coded from a genomic cluster named Hemicellulose Utilization (HUS) locus. The growing availability of effective genetic engineering tools in P. thermoglucosidasius further starts to open up its potential as a versatile thermophilic cell factory. A number of strain engineering examples showcasing the potential of P. thermoglucosidasius as a microbial chassis for the production of bulk and fine chemicals are presented along with current research bottlenecks. Ultimately, this review provides a holistic overview of the distinct metabolic characteristics of P. thermoglucosidasius and discusses research focused on expanding the native metabolic boundaries for the development of industrially relevant strains.

Similarities of Geobacillus bacteria based on their profiles of antimicrobial susceptibility in milk samples

The genus Geobacillus is composed of thermophilic bacteria that exhibit diverse biotechnological potentialities. Specifically, Geobacillus stearothermophilus is included as a test bacterium in commercial microbiological inhibition methods, although it exhibits limited sensitivity to aminoglycosides, macrolides, and quinolones. Therefore, this article evaluates the antibiotic susceptibility profiles of five test bacteria (G. stearothermophilus subsp. calidolactis C953, Geobacillus thermocatenulatus LMG 19007, Geobacillus thermoleovorans LMG 9823, Geobacillus kaustophilus DSM 7263 and Geobacillus vulcani 13174). For that purpose, the minimum inhibitory concentrations (MICs) of 21 antibiotics were determined in milk samples for five test bacteria using the radial diffusion microbiological inhibition method. Subsequently, the similarities between bacteria and antibiotics were analyzed using cluster analysis. The dendrogram of this multivariate analysis shows an association between a group formed by G. thermocatenulatus and G. stearothermophilus and another by G. thermoleovorans, G. kaustophilus and G. vulcani. Finally, future microbiological methods could be developed in microtiter plates using G. thermocatenulatus as test bacterium, as it exhibits similar sensitivities to G. stearothermophilus. Conversely, G. vulcani, G. thermoleovorans and G. kaustophilus show higher MICs than G. thermocatenulatus.

A comprehensive analysis of bioethanol and ethyl lactate joint production in second-generation biorefinery: Simulation, techno-economic, and profitability assessments

Second-generation biorefineries (2GBR) represent an innovative application of bioresources technologies to produce bioenergy and valuable products. This paper aims to introduce and analyze the joint production of bioethanol and ethyl lactate in a 2GBR. Techno-economic and profitability perspectives are considered in the analysis which is conducted via simulation considering corn stover as raw material. A key aspect in the analysis is a joint production parameter named α, whose values can dictate either the sole production of bioethanol (α = 0), joint production (0 < α < 1), or the unique production of ethyl lactate (α = 1). In other words, the proposed joint production scheme provides versatility in production. Simulations show that the lowest Total Capital Investment, Unit Production Cost, and Operating Cost values were associated with low values of α. Furthermore, when α ≥ 0.4, the 2GBR under study can achieve internal rates of return above 30%, which implies that the project offers a potentially high profitability.