Ammonia nitrogen recovery from biogas slurry by SCP production using Candida utilis

A data fusion system based on attenuated total reflectance mid-infrared spectroscopy and colorimetry combined with chemometrics for monitoring the fermentation process of Candida utilis

The fermentation of Candida utilis has become a cost-effective and high-yield process, characterized by its high nutritional value, high productivity, and short fermentation time. To efficiently and comprehensively monitor the fermentation process of Candida utilis, this study employed an integrated data fusion system, based on attenuated total reflectance mid-infrared (ATR-MIR) spectroscopy and colorimetry, combined with chemometrics to achieve efficient and comprehensive monitoring of the Candida utilis fermentation process. By analyzing the trends in key physicochemical indicators during fermentation, the fermentation process could be divided into four stages: 0-3 h, 3-9 h, 9-24 h, and 24-33 h. Principal component analysis (PCA) was employed to reduce the dimensionality of the highly collinear infrared spectral data to 1-10 principal components. Through the evaluation of four distinct machine learning algorithms, the optimal data fusion method and the best-performing machine learning model (random forest, with a classification accuracy of 95.30 %) were identified. PCA and linear discriminant analysis (LDA) revealed that samples from different fermentation times exhibited distinct clustering trends, although full differentiation was not achieved. To enhance classification accuracy, supervised learning models based on class labels were introduced. A comparison of classification accuracy between single signal and fusion signal approaches revealed that the optimal model achieved superior performance on the fusion dataset, with a 4-stage classification accuracy of 0.978, which was higher than that of the 11-stage classification. Quantitative prediction of key physicochemical parameters during the fermentation process was conducted using partial least squares regression (PLSR) and support vector regression (SVR) based on colorimeter dataset, ATR-MIR dataset, and fusion dataset. The data fusion strategy demonstrated excellent predictive performance for physicochemical indicators, particularly in predicting pH (R2p = 0.940, RMSEP = 0.210) and cell concentration (R2p = 0.946, RMSEP = 0.236). The color difference dataset exhibited the highest accuracy in predicting reducing sugar (R2p = 0.987, RMSEP = 0.988). The results demonstrated that, compared to PLSR, SVR demonstrated superior performance in these quantitative analysis tasks, enabling more accurate prediction of the physicochemical parameters in the Candida utilis fermentation process.

Solid-state fermentation of corn wet distiller grains and wheat bran with Trichoderma reesei and Candida utilis for improving feed value

BACKGROUND

Solid-state fermentation is one of the most effective methods for the high-value utilization of agro-industrial by-products. Co-fermentation of wet distiller grains and agricultural waste is an effective way to mitigate the feed shortage caused by corn consumption for bioethanol. It is still challenging to convert wet distiller grains and wheat bran to easily accessible carbon sources and adjust the balanced proportion of amino acids together by fermentation.

RESULTS

Fermentation time, strain ratio, and the addition of ammonium sulfate have been verified to be the important factors influencing the symbiosis of Trichoderma reesei (T. reesei) and Candida utilis (C. utilis) in a mixed system of wet distiller grains and wheat bran. The optimum conditions were fermentation for 8 days, 2:1 (T. reesei: C. utilis) strain ratio, and addition of 4% ammonium sulfate. After fermentation, the cellulose degradation proportion reached 39.1%, and the hemicellulose degradation proportion was 13.1%. The protein content improved by 29.6%. The lysine content increased by 126%, reaching 11.3 g·kg-1. The threonine content increased from 6.10 to 10.3 g·kg-1. The phytate content was decreased to 3.97 g·kg-1. The in vitro digestibility of dry matter and protein increased to 62.8% and 76.1%, respectively.

CONCLUSIONS

These results indicated the feasibility of improving the feeding value of wet distiller grains and wheat bran by the symbiosis of T. reesei and C. utilis. © 2024 Society of Chemical Industry.

Exploring the Potential of Candida sp. SW4-6 as a Probiotic for Enhancing Water Quality in Aquaculture

Aquaculture, a vital industry supplying a significant portion of the world's seafood, faces challenges such as the deterioration of the aquaculture environment. The objective of this study was to isolate and identify microorganisms with the capacity to eliminate nitrite in water from shrimp ponds and evaluate their potential as probiotics to improve water quality. Additionally, the study also determines the ideal conditions for the probiotic to effectively reduce nitrite-N and ammonia-N. Water samples were collected from four shrimp ponds (SW1, SW2, SW3, SW4) and isolates were obtained. Among all the samples, SW4 was the most effective in reducing the concentration of nitrite-N. Upon further isolation of SW4, the strain SW4-W6 showed significant nitrite-N reduction capabilities compared to the 19 other isolates tested. Through morphological, genetic (ITS sequence), and phylogenetic analyses, strain SW4-6 was identified as Candida sp. The isolation of Candida sp. SW4-6 showed superior nitrite-N and ammonia-N reduction capabilities, with sucrose as the carbon source and complete reduction observed at a C/N ratio of 15-20. Gene expression analysis revealed the up-regulation of nitrite reductase in SW4-6 after inoculation, with significantly higher expression observed with sucrose as the carbon source. Salinity and temperature significantly influenced nitrite-N and ammonia-N reduction by SW4-6, with higher temperatures (30 °C) and 0% NaCl favoring faster reduction rates. Candida sp. SW4-6 emerges as a promising probiotic candidate for aquaculture water quality management due to its efficient nitrite-N and ammonia-N reduction capabilities under optimal conditions. Its virulence profile and ability to thrive across various salinity and temperature conditions further support its potential applicability in aquaculture.

A novelty strategy for AMD prevention by biogas slurry: Acetate acid inhibition effect on chalcopyrite biooxidation and leachate

With the widespread application of anaerobic digestion technology, biogas slurry become the main source of organic amendments in practice. Comprehensive studies into the inhibitory effects of low molecular weight (LMW) organic acids, essential components in biogas slurry, on the sulfide minerals biooxidation and its bioleaching (AMD) have been lacking. In this study, acetic acid (AA) served as a representative of LMW organic acids in biogas slurry to investigate its impact on the inhibition of chalcopyrite biooxidation by Acidithiobacillus ferrooxidans (A. ferrooxidans). It was shown that AA could slow down the chalcopyrite biooxidation and inhibit the jarosite formation on the mineral surface. Compared with the control group (0 ppm AA), the sulfate increment in the leachate of the 50 ppm, 100 ppm, and 200 ppm AA-treated groups decreased by 36.4%, 66.8%, and 69.0%, respectively. AA treatment (≥50 ppm) could reduce the oxidation of ferrous ions in the leachate by one order of magnitude. At the same time, the bacterial concentration of the leachate in the 50 ppm, 100 ppm, and 200 ppm AA-treated groups decreased by 70%, 93%, and 94%, respectively. These findings provide a scientific basis for new strategies to utilize biogas slurry for mine remediation and contribute to an enhanced comprehension of organic amendments to prevent AMD in situ in mining soil remediation.

Enhanced Microbial Protein Production from CO2 and Air by a MoS2 Catalyzed Bioelectrochemical System

Carbon dioxide can be relatively easily reduced to organic matter in a bioelectrochemical system (BES). However, due to insufficient reduction force from in-situ hydrogen evolution, it is difficult for nitrogen reduction. In this study, MoS2 was firstly used as an electrocatalyst for the simultaneous reduction of CO2 and N2 to produce microbial protein (MP) in a BES. Cell dry weight (CDW) could reach 0.81±0.04 g/L after 14 d operation at -0.7 V (vs. RHE), which was 108±3 % higher than that from non-catalyst control group (0.39±0.01 g/L). The produced protein had a better amino acid profile in the BES than that in a direct hydrogen system (DHS), particularly for proline (Pro). Besides, MoS2 promoted the growth of bacterial cell on an electrode and improved the biofilm extracellular electron transfer (EET) by microscopic observation and electrochemical characterization of MoS2 biocathode. The composition of the microbial community and the relative abundance of functional enzymes revealed that MoS2 as an electrocatalyst was beneficial for enriching Xanthobacter and enhancing CO2 and N2 reduction by electrical energy. These results demonstrated that an efficient strategy to improve MP production of BES is to use MoS2 as an electrocatalyst to shift amino acid profile and microbial community.

Screening of Selenium/Glutathione-Enriched Candida utilis and Its Anti-inflammatory and Antioxidant Activities in Mice

This study aimed to screen a mutant of Candida utilis SE-172 with high selenite tolerance and glutathione (GSH) biosynthesis capability via 60Co γ-radiation mutagenesis to prepare selenium (Se)-enriched yeast. The maximal intracellular contents of GSH and organic Se of 22.94 mg/g and 1308.1 μg/g were obtained, respectively, under a batch culture of SE-172. The physiological mechanism underlying increased GSH and organic Se contents in Se/GSH-enriched C. utilis SE-172 was revealed based on assaying activities of γ-glutamylcysteine synthase (γ-GCS) involved in GSH biosynthesis and selenophosphate synthase (SPS) related to organic Se bioconversion, and by determining intracellular ATP and NADH contents and ATP/ADP and NADH/NAD+ ratios associated with energy supply and regeneration. Moreover, the effect of this selenized yeast on anti-inflammatory and antioxidant activities in mice with colitis was investigated. The supplementation of Se/GSH-enriched yeast decreased the dextran sodium sulfate-induced damage to colon tissues, reduced the expression of pro-inflammatory factors [interleukin (IL)-6, IL-1β, and tumor necrosis factor-α (TNF-α)] in serum, increased the antioxidant-related enzyme [superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px)] activities, and decreased the malondialdehyde content in colon. The Se/GSH-enriched C. utilis SE-172 showed potent anti-inflammatory and antioxidant activities in mice with colitis.

Production of single cell protein rich in potassium by Nectaromyces rattus using biogas slurry and molasses

Single-cell protein (SCP) is a vital supplement for animal protein feed. This study utilized biogas slurry and sugarcane molasses to ferment Nectaromyces rattus for the production of SCP. The optimal batch fermentation conditions were obtained in a 5L jar with a tank pressure of 0.1 MPa, an initial speed of 300 rpm, and an inoculum volume of 30%. The highest cell dry weight concentrations of the fed-batch fermentation without reflux and the fed-batch fermentation with reflux were 46.33 g/L and 29.71 g/L, respectively. The nitrogen conversion rates (47.05% and 44.12%) and the cell yields of total organic carbon (1 g/g and 1.17 g/g) of both fermentation modes were compared. The SCP contained 42.32% amino acids. Its high concentrations of potassium (19859.96 mg/kg) and phosphorus (7310.44 mg/kg) present a novel approach for the extraction of these essential nutrients from biogas slurry. The enrichment of K was related to the H+ efflux and sugar transport.

Valorization of Food Waste into Single-Cell Protein: An Innovative Technological Strategy for Sustainable Protein Production

The rapidly increasing population and climate change pose a great threat to our current food systems. Moreover, the high usage of animal-based and plant-based protein has its drawbacks, as these nutritional sources require many hectares of land and water, are affected by seasonal variations, are costly, and contribute to environmental pollution. Single-cell proteins (SCPs) are gaining a lot of research interest due to their remarkable properties, such as their high protein content that is comparable with other protein sources; low requirements for land and water; low carbon footprint; and short production period. This review explores the use of food waste as a sustainable feedstock for the advancement of SCP processes. It discusses SCP studies that exploit food waste as a substrate, alongside the biocatalysts (bacteria, fungi, yeast, and microalgae) that are used. The operational setpoint conditions governing SCP yields and SCP fermentation routes are elucidated as well. This review also demonstrates how the biorefinery concept is implemented in the literature to improve the economic potential of "waste-to-protein" innovations, as this leads to the establishment of multiproduct value chains. A short section that discusses the South African SCP scenario is also included. The technical and economic hurdles facing second-generation SCP processes are also discussed, together with future perspectives. Therefore, SCP technologies could play a crucial role in the acceleration of a "sustainable protein market", and in tackling the global hunger crisis.

Using the inherent elements in yeast biomass to produce Ni2P/N-doped biocarbon composites for efficient hexavalent chromium reduction

The heterogeneous catalytic reduction of Cr(VI) to Cr(III) is an effective strategy for aqueous Cr(VI) contamination abatement, which requires the development of highly efficient, low-cost, and recyclable catalysts. Herein, Ni2P/N-doped biocarbon composites (Ni2P/N-BC) were fabricated through an anoxic pyrolysis process using NaCl and KCl as activators. A precursor of yeast biomass provided the essential C, N, and P elements for Ni2P/N-BC formation. When adopted for Cr(VI) reduction in the presence of oxalic acid as a reductant, the fabricated Ni2P/N-BC performed superior catalytic activity with a 100% Cr(VI) reduction efficiency within 10 min (Ni2P/N-BC-5 = 0.2 g L-1, oxalic acid = 0.4 g L-1, Cr(VI) = 20 mg L-1). Typical affecting parameters, e.g., catalyst dosage, oxalic acid loading, reaction temperature, initial solution pH, and water matrix, were investigated. Ni2P/N-BC exhibited good applicability in a broad pH range from 3.0 to 9.0 and in actual aquatic systems. Cr(VI) reduction efficiency remained 92.7% after five recycle runs. Such promising catalytic activity may originate from the well-crystallized Ni2P, N-doped biocarbon framework and high specific surface area of the materials. Preliminary reaction mechanism analysis indicated that the favorable charge state of Ni2P, fast hydrogen transfer, affinity of oxalic acid to Cr(VI), and inherent electron transfer in the biocarbon matrix contributed to effective Cr(VI) reduction. This work not only provides a facile and low-cost strategy to construct Ni2P/N-doped biocarbon nanosheet composite using environmentally benign biomass but also brings new insights for the remediation of Cr(VI) contamination.

An integrated transcriptomic and metabolic phenotype analysis to uncover the metabolic characteristics of a genetically engineered Candida utilis strain expressing δ-zein gene

Introduction

Candida utilis (C. utilis) has been extensively utilized as human food or animal feed additives. With its ability to support heterologous gene expression, C. utilis proves to be a valuable platform for the synthesis of proteins and metabolites that possess both high nutritional and economic value. However, there remains a dearth of research focused on the characteristics of C. utilis through genomic, transcriptomic and metabolic approaches.

Methods

With the aim of unraveling the molecular mechanism and genetic basis governing the biological process of C. utilis, we embarked on a de novo sequencing endeavor to acquire comprehensive sequence data. In addition, an integrated transcriptomic and metabolic phenotype analysis was performed to compare the wild-type C. utilis (WT) with a genetically engineered strain of C. utilis that harbors the heterologous δ-zein gene (RCT).

Results

δ-zein is a protein rich in methionine found in the endosperm of maize. The integrated analysis of transcriptomic and metabolic phenotypes uncovered significant metabolic diversity between the WT and RCT C. utilis. A total of 252 differentially expressed genes were identified, primarily associated with ribosome function, peroxisome activity, arginine and proline metabolism, carbon metabolism, and fatty acid degradation. In the experimental setup using PM1, PM2, and PM4 plates, a total of 284 growth conditions were tested. A comparison between the WT and RCT C. utilis demonstrated significant increases in the utilization of certain carbon source substrates by RCT. Gelatin and glycogen were found to be significantly utilized to a greater extent by RCT compared to WT. Additionally, in terms of sulfur source substrates, RCT exhibited significantly increased utilization of O-Phospho-L-Tyrosine and L-Methionine Sulfone when compared to WT.

Discussion

The introduction of δ-zein gene into C. utilis may lead to significant changes in the metabolic substrates and metabolic pathways, but does not weaken the activity of the strain. Our study provides new insights into the transcriptomic and metabolic characteristics of the genetically engineered C. utilis strain harboring δ-zein gene, which has the potential to advance the utilization of C. utilis as an efficient protein feed in agricultural applications.

Nitrogen recovery from low-value biogenic feedstocks via steam gasification to methylotrophic yeast biomass

Carbon and nitrogen are crucial elements for life and must be efficiently regenerated in a circular economy. Biomass streams at the end of their useful life, such as sewage sludge, are difficult to recycle even though they contain organic carbon and nitrogen components. Gasification is an emerging technology to utilize such challenging waste streams and produce syngas that can be further processed into, e.g., Fischer-Tropsch fuels, methane, or methanol. Here, the objective is to investigate if nitrogen can be recovered from product gas cleaning in a dual fluidized bed (DFB) after gasification of softwood pellets to form yeast biomass. Yeast biomass is a protein-rich product, which can be used for food and feed applications. An aqueous solution containing ammonium at a concentration of 66 mM was obtained and by adding other nutrients it enables the growth of the methylotrophic yeast Komagataella phaffii to form 6.2 g.L^-1 dry yeast biomass in 3 days. To further integrate the process, it is discussed how methanol can be obtained from syngas by chemical catalysis, which is used as a carbon source for the yeast culture. Furthermore, different gas compositions derived from the gasification of biogenic feedstocks including sewage sludge, bark, and chicken manure are evaluated for their ability to yield methanol and yeast biomass. The different feedstocks are compared based on their potential to yield methanol and ammonia, which are required for the generation of yeast biomass. It was found that the gasification of bark and chicken manure yields a balanced carbon and nitrogen source for the formation of yeast biomass. Overall, a novel integrated process concept based on renewable, biogenic feedstocks is proposed connecting gasification with methanol synthesis to enable the formation of protein-rich yeast biomass.