Mixed yeasts inocula for simultaneous production of SCP and treatment of vinasse to reduce soil and fresh water pollution

Current trends and possibilities of typical microbial protein production approaches: a review

Global population growth and demographic restructuring are driving the food and agriculture sectors to provide greater quantities and varieties of food, of which protein resources are particularly important. Traditional animal-source proteins are becoming increasingly difficult to meet the demand of the current consumer market, and the search for alternative protein sources is urgent. Microbial proteins are biomass obtained from nonpathogenic single-celled organisms, such as bacteria, fungi, and microalgae. They contain large amounts of proteins and essential amino acids as well as a variety of other nutritive substances, which are considered to be promising sustainable alternatives to traditional proteins. In this review, typical approaches to microbial protein synthesis processes were highlighted and the characteristics and applications of different types of microbial proteins were described. Bacteria, fungi, and microalgae can be individually or co-cultured to obtain protein-rich biomass using starch-based raw materials, organic wastes, and one-carbon compounds as fermentation substrates. Microbial proteins have been gradually used in practical applications as foods, nutritional supplements, flavor modifiers, and animal feeds. However, further development and application of microbial proteins require more advanced biotechnological support, screening of good strains, and safety considerations. This review contributes to accelerating the practical application of microbial proteins as a promising alternative protein resource and provides a sustainable solution to the food crisis facing the world.

Impact of some amendments on kinetics of leaching dissolved organic carbon and ammonium in calcareous sandy soil under vinasse addition

The access of vinasse leachates to water bodies and groundwater exacerbates environmental problems, especially eutrophication. Therefore, a column experiment was performed to examine the effect of adding zeolite (ZL), bone char (BC), and wood chips biochar (WCB) in the presence of vinasse on carbon dioxide (CO2) emission, leaching dissolved organic carbon (DOC) and ammonium (NH4+) in calcareous sandy soil, as well as studying the kinetics of leaching dissolved organic carbon and ammonium. This column experiment contains four treatments: soil alone (CK), soil + zeolite (SZL), soil + bone char (SBC), and soil + wood chips biochar (SWCB). These amendments were applied to the soil at a level of 4%. Vinasse was added to all treatments at a level of 13 mL per column. The leached total cumulative DOC and total cumulative soluble ammonium amounts decreased significantly with applying ZL, BC, and WCB compared with the soil alone. The effectiveness of these amendments in lowering the total cumulative DOC leaching is in the order of SBC > SWCB > SZL > CK. However, the effectiveness of these amendments in decreasing the total cumulative NH4+ leaching is in the order of SZL > SWCB > SBC > CK. The rate constant (k) of DOC leaching decreased significantly with the application of bone char compared to soil alone treatment. In the presence of vinasse, the apparent half-life of leached DOC from the soil was 8.1, 12.9, 36.7, and 15.5 days for soil CK, SZL, SBC, and SWCB treatments, respectively. Half-life values of leached soluble ammonium from the soil in the presence of vinasse addition were 10.1, 39.5, 28.5, and 37.9 days for CK, SZL, SBC, and SWCB treatments, respectively. Amending soil with BC increased significantly the phosphorus availability, however, applying ZL and BC caused a significant increase in the available potassium in calcareous sandy soil compared to the control treatment. According to these results, it is recommended not to add vinasse alone to sandy soils, but it is preferred to be co-applied with BC amendment at the level of 4% better than ZL and WCB. This would decrease leaching DOC and ammonium to the water table and groundwater as well as enhance nutrient retention in the soil, which in turn, plays a vital role in reducing the harmful effect of vinasse and improving soil fertility.

Deciphering cell wall sensors enabling the construction of robust P. pastoris for single-cell protein production

Single-cell protein (SCP) production in the methylotrophic yeast Pichia pastoris has the potential to achieve a sustainable protein supply. However, improving the methanol fermentation efficiency and reducing carbon loss has been a long-standing challenge with far-reaching scientific and practical implications. Here, comparative transcriptomics revealed that PAS_0305, a gene directly associated with cell wall thickness under methanol stress, can be used as a target for unlocking cell wall sensors. Intracellular trehalose accumulation confirmed that cell wall sensors were activated after knocking out PAS_0305, which resulted in increased cell wall permeability. Genome-wide signal perturbations were transduced through the HOG module and the CWI pathway, which was confirmed to connected by Pbs2-Mkk. As a consequence of CWI pathway activation, ΔPAS_0305 elicited a rescue response of cell wall remodeling by increasing the β-1,3-glucan content and decreasing the chitin/mannose content. Remarkably, perturbations in global stress signals led to a fine-tuning of the metabolic network of ΔPAS_0305, resulting in a superior phenotype with highest crude protein and methanol conversion rate of 67.21% and 0.46 gDCW/g. Further genome-scale metabolic models were constructed to validate the experimental results, confirming that unlocking cell wall sensors resulted in maximized flux from methanol towards SCP and effectively addressing the issue of carbon loss in methanol fermentation. This work sheds new light on the potential of manipulating cellular signaling pathways to optimize metabolic networks and achieve exceptional phenotypic characteristics, providing new strategies for constructing versatile cell factories in P. pastoris.

Economical production of Pichia pastoris single cell protein from methanol at industrial pilot scale

BACKGROUND

Methanol, synthesized from CO2, is a potentially sustainable one-carbon (C1) resource for biomanufacturing. The use of methanol as a feedstock to produce single cell protein (SCP) has been investigated for decades as an alternative to alleviate the high global demand for animal-derived proteins. The methylotrophic yeast Pichia pastoris is an ideal host for methanol-based SCP synthesis due to its natural methanol assimilation ability. However, improving methanol utilization, tolerance to higher temperature, and the protein content of P. pastoris are also current challenges, which are of great significance to the economical industrial application using methanol as a feedstock for SCP production.

RESULTS

In the present work, adaptive laboratory evolution (ALE) has been employed to overcome the low methanol utilization efficiency and intolerance to a higher temperature of 33 °C in P. pastoris, associated with reduced carbon loss due to the lessened detoxification of intracellular formaldehyde through the dissimilation pathway and cell wall rearrangement to temperature stress resistance following long-term evolution as revealed by transcriptomic and phenotypic analysis. By strengthening nitrogen metabolism and impairing cell wall synthesis, metabolic engineering further increased protein content. Finally, the engineered strain via multi-strategy produced high levels of SCP from methanol in a pilot-scale fed-batch culture at 33 °C with a biomass of 63.37 g DCW/L, methanol conversion rate of 0.43 g DCW/g, and protein content of 0.506 g/g DCW. SCP obtained from P. pastoris contains a higher percentage of protein compared to conventional foods like soy, fish, meat, whole milk, and is a source of essential amino acids, including methionine, lysine, and branched-chain amino acids (BCAAs: valine, isoleucine, leucine).

CONCLUSIONS

This study clarified the unique mechanism of P. pastoris for efficient methanol utilization, higher temperature resistance, and high protein synthesis, providing a P. pastoris cell factory for SCP production with environmental, economic, and nutritional benefits.

Yeast-driven valorization of agro-industrial wastewater: an overview

The intensive industrial and agricultural activities currently on-going worldwide to feed the growing human population have led to significant increase in the amount of wastewater produced. These effluents are high in phosphorus (P), nitrogen (N), chemical oxygen demand (COD), biochemical oxygen demand (BOD), and heavy metals. These compounds can provoke imbalance in the ecosystem with grievous consequences to both the environment and humans. Adequate treatment of these wastewaters is therefore of utmost importance to humanity. This can be achieved through valorization of these waste streams, which is based on biorefinery idea and concept of reduce, reuse, and recycle for sustainable circular economy. This concept uses innovative processes to produce value-added products from waste such as wastewater. Yeast-based wastewater treatment is currently on the rise given to the many characteristics of yeast cells. Yeasts are generally fast growing, and they are robust in terms of tolerance to stress and inhibitory compounds, in addition to their ability to metabolize a diverse range of substrates and create a diverse range of metabolites. Therefore, yeast cells possess the capacity to recover and transform agro-industrial wastewater nutrients into highly valuable metabolites. In addition to remediating the wastewater, numerous value-added products such as single cell oil (SCO), single cell proteins (SCPs), biofuels, organic acid, and aromatic compounds amongst others can be produced through fermentation of wastewater by yeast cells. This work thus brings to limelight the potential roles of yeast cells in reducing, reusing, and recycling of agro-industrial wastewaters while proffering solutions to some of the factors that limit yeast-mediated wastewater valorization.

Single-Cell Protein Production as a Strategy to Reincorporate Food Waste and Agro By-Products Back into the Processing Chain

Food waste is a serious problem with negative environmental and economic consequences. Unused food (either as waste or by-products and referred to as food residues in the present work) is a source of carbohydrates, lipids, proteins, vitamins, minerals and bioactive compounds that could be used in an alternate or secondary life cycle to avoid discarding it. The present work reviews the potential use of food residues for the bioengineering of single-cell protein (SCP), addressing aspects of production, nutrition and safety, as well as the main challenges and perspectives. SCP is obtained from various microorganisms, including fungi, bacteria, yeasts and algae, in pure or mixed form. SCP generally contains a higher percentage of protein (30-80%) compared to soy (38.6%), fish (17.8%), meat (21.2%) and whole milk (3.28%). SCP is a source of essential amino acids, including methionine, threonine and lysine. The use of food residues as substrates for the production of SCP would reduce production costs (35-75%); however, optimization and industrial scaling are some of the main challenges to its sustainable production. The use food waste and agro by-products from the food industry could be a promising alternative to obtain protein according to a circular production scheme.

Two-stage fermentation enhanced single-cell protein production by Yarrowia lipolytica from food waste

The resource utilization of food waste is crucial, and single-cell protein (SCP) is attracting much attention due to its high value. This study aimed to convert food waste to SCP by Yarrowia lipolytica. It was found the chemical oxygen demand (COD) removal rate 77 ± 1.70% was achieved at 30 g COD/L with the protein content of biomass only 24.1 ± 0.4% w/w biomass dry weight (BDW) in one-stage fermentation system. However, the protein content was significantly increased to 38.8 ± 0.2% w/w BDW with the COD removal rate 85.5 ± 0.7% by a two-stage fermentation process, where the food waste was firstly anaerobically fermented to volatile fatty acids and then converted to SCP with Yarrowia lipolytica. Transcriptomic analysis showed that the expression of SCP-producing genes including ATP citrate (pro-S)-lyase and fumarate hydratase class II were up-regulated in the two-stage transformation, resulting in more organic degradation for SCP synthesis.

Single Cell Protein for Foods and Feeds: A Review of Trends

Introduction:

Predictions on the world’s population in the next few decades suggest that the global demand for animal-derived proteins may not be met if current conventional agriculture approaches are used. One promising solution to this complex crisis lies in the use of single-cell proteins (SCP). SCP refers to the edible biomass of unicellular microorganisms and can be developed as animal feeds or human foods. This paper provides a detailed overview on research towards the production and utilisation of SCPs and trends within the field.

Study Design:

A bibliometric based study was conducted on 425 SCP research articles collected from the Web of Science database, analysing the most cited papers using VOSviewer software, and contributing authors, affiliations and country of origin. Research publications on SCP started in 1961 and has grown steadily over the years.

Discussion:

Emerging research topics within SCP production focused on the use of improved fungal strains, the composition and characteristics of SCPs based on the type of substrates used, industrial production processes and the use of waste for SCP production, which serves the dual purpose of mitigating the cost associated with waste disposal and production of a valuable product.

Regulation of Hydrogen Peroxide Dosage in a Heterogeneous Photo-Fenton Process

In this work, a classical linear control approach for the peroxide (H2O2) dosage in a photo-Fenton process is presented as a suitable solution for improving the efficiency in the treatment of recalcitrant organic compounds that cannot be degraded by classical wastewater treatment processes like anaerobic digestion. Experiments were carried out to degrade Lignin, Melanoidin, and Gallic acid, which are typical recalcitrant organic compounds present in some kinds of effluents such as vinasses from the Tequila and Cachaça industries. Experiments were carried in Open-Loop mode for obtaining the degradation model for the three compounds in the form of a Transfer Function, and in Closed-Loop mode for controlling the concentration of each compound. First-order Transfer Functions were obtained using the reaction curve method, and then, based on these models, the parameters of Proportional Integral controllers were calculated using the direct synthesis method. In the Closed-Loop experiments, the Total Organic Carbon removal was 39% for lignin, 7% for melanoidin, and 29% for Gallic acid, which were greater than those obtained in the Open-Loop experiments.

Current trends for distillery wastewater management and its emerging applications for sustainable environment

Ethanol distillation generates a huge volume of unwanted chemical liquid known as distillery wastewater. Distillery wastewater is acidic, dark brown having high biological oxygen demand, chemical oxygen demand, contains various salt contents, and heavy metals. Inadequate and indiscriminate disposal of distillery wastewater deteriorates the quality of the soil, water, and ultimately groundwater. Its direct exposure via food web shows toxic, carcinogenic, and mutagenic effects on aquatic-terrestrial organisms including humans. So, there is an urgent need for its proper management. For this purpose, a group of researchers applied distillery wastewater for fertigation while others focused on its physico-chemical, biological treatment approaches. But until now no cutting-edge technology has been proposed for its effective management. So, it becomes imperative to comprehend its toxicity, treatment methods, and implication for environmental sustainability. This paper reviews the last decade's research data on advanced physico-chemical, biological, and combined (physico-chemical and biological) methods to treat distillery wastewater and its reuse aspects. Finally, it revealed that the combined methods along with the production of value-added products are one of the best options for distillery wastewater management.

Bio-hydrolysis of used soybean oil: environmental-friendly technology using microbial consortium

In this work, strains of Bacillus subtilis were inoculated in consortium with Rhodotorula mucilaginosa into spent soy oil as aiming to biological treatment and low-cost reuse. The microorganisms were previously isolated and selected for the lipolytic capacity of the alperujo residue generated during the processing of olive oil. For fermentation, bioassays containing Rhodotorula mucilaginosa isolated from alperujo and Candida rugosa CCMA 00371, both co-inoculated with Bacillus subtilis CCMA 0085 in medium containing (% w/v) 0.075 glucose and 0.375 (NH₄)₃ PO₄ in 75 mL of water and 75 mL of spent soy oil. Despite the low biomass productivity, it has favorable characteristics to be used in animal feed supplementation. Spent soy oil was used as a carbon source proven by Bartha respirometer. The strains of R. mucilaginosa UFLA RAS 144 and B. subtilis CCMA 0085 are promising inoculants for oil degradation and can be applied in a waste treatment system.

Bioconversion of yellow wine wastes into microbial protein via mixed yeast-fungus cultures

The potential for microbial protein production in the mixture of yellow wine lees and rice soaking wastewater was examined. Strong symbiotic effect was observed in fermentation with yeast-fungus mixed culture of Candida utilis and Geochichum candidum at a ratio of 1:1 (v/v). The maximum specific biomass yield of 4.91 ± 0.48 g _{final biomass}/g _{initial biomass} with a protein content of 68.5 ± 1.0% was achieved at inoculum-to-substrate ratio of 10% (v/v) and aeration rate of 1.0 volume_air/volume_liquid/min. The essential amino acids contents of the derived protein were comparable to commercial protein sources with high amounts of methionine (2.87%, based on total protein). The reduction in soluble chemical oxygen demand of 79.4 ± 0.4% was mainly due to uptake of carbohydrate, soluble protein, volatile fatty acids, amino acids, etc. The application of mixed yeast-fungus technology provides a new opportunity for microbial protein production from these low-value organic residue streams.

2-Phenylethanol and 2-phenylethylacetate production by nonconventional yeasts using tequila vinasses as a substrate

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Yeast species influenced the de novo synthesis of 2-phenylethylacetate.

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Inhibitory compounds showed a strong influence on cell growth and 2-phenylethylacetate production for the evaluated yeasts.

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More than a 50 % reduction in the chemical and biochemical oxygen demand was achieved by yeast fermentation.

Vinasses from the tequila industry are wastewaters with highly elevated organic loads. Therefore, to obtain value-added products by yeast fermentations, such as 2-phenylethanol (2-PE) and 2-phenylethylacetate (2-PEA), could be interesting for industrial applications from tequila vinasses. In this study, four yeasts species (Wickerhamomyces anomalus, Candida glabrata, Candida utilis, and Candida parapsilosis) were evaluated with two different chemically defined media and tequila vinasses. Differences in the aroma compounds production were observed depending on the medium and yeast species used. In tequila vinasses, the highest concentration (65 mg/L) of 2-PEA was reached by C. glabrata, the inhibitory compounds decreased biomass production and synthesis of 2-PEA, and biochemical and chemical oxygen demands were reduced by more than 50 %. Tequila vinasses were suitable for the production of 2-phenylethylacetate by the shikimate pathway. A metabolic network was developed to obtain a guideline to improve 2-PE and 2-PEA production using flux balance analysis (FBA).

Assessing the efficiency in assisted depuration of coffee processing wastewater from mixed wild microbial selected inoculum

This work evaluated the efficiency of bacterial bio-augmentation to the biological treatment of coffee processing wastewater (CPWW) in a pilot wastewater treatment plant (WTP). Biochemical oxygen demand (BOD) and chemical oxygen demand (COD) values were the basis for the treatment efficiency. Serratia marcescens CCMA 1010 and CCMA 1013, Corynebacterium flavescens CCMA 1006 and Acetobacter indonesiensis CCMA 1002 were previously selected. The microbial cocktail was inoculated and persisted in CPWW during all treatments. The richness of wild species was a little altered over time and up to nine species were found in each sampled season. The microbiota composition presented variation of a total of 13 species, despite the inoculation of the microbial inoculum. The biodegradability index of effluent, close to 0.5, was favourable to biological treatment. The pollution parameters of CPWW were decreased in function of the variation of community composition and microbial activity. The greatest reduction of BOD (~ 33%) and COD (~ 25%) was observed between 72 h and 8 days of the biological treatment. The CPWW toxicity in Allium cepa seeds was lower by up to 60%, and the germination index (GI) exceeded 100% in the treated CPWW. The results of the CPWW biological treatment by bio-augmentation from native micro-organisms in the pilot-scale WTP indicated the greatest efficiency relating to the spontaneous biological treatment of CPWW. After this treatment, the discharge of effluent in the environment would not have toxic effects on the plants.

The potential application of an autochthonous fungus from the northwest of Argentina for treatment of sugarcane vinasse

Vinasse is a waste material from distillery industries, which causes major environmental problems around the world. Argentina alone produces about 4 billion liters of vinasse annually; consequently, diverse biological eco-friendly treatments are evaluated for their ability to reduce the detrimental effects. The present study reports on the degradation of a 50% (v/v) local vinasse sample by an autochthonous fungus identified as Aspergillus sp. V1. The Bioprocess was conducted for 15 d at 30 °C after inoculation of spores at an end concentration of 1 × 10⁶ CFU/mL. Effluent neutralization was detected after 6 d of treatment, with maximum COD and BOD removal after 12 d (49% and 59%, respectively). Effects of vinasse before and after treatment were predicted using Caco-2 cells and Triticum aestivum L. (wheat) seeds as toxicological indicators. Only 13% viability was observed for Caco-2 cells exposed to untreated vinasse, but this percentage increased more than 3-fold for cells exposed to the treated effluent. While vinasse without treatment completely inhibited germination of seeds, exposure to treated effluent demonstrated a germination percentage of 60%. The present study highlights the use of a dual-purpose biotechnological process that aimed at reducing the detrimental effects of vinasse, enhancing its quality for agricultural practices.

Evaluation of a mixed simultaneous vinasse degradation treatment using Komagataeibacter kakiaceti GM5 and Trametes versicolor DSM 3086

In the bioethanol industry and its derivative processes, 9-14 l of vinasse per liter of ethanol are obtained as residue, depending on whether or not a recirculation process is used. If the vinasse is discharged directly into water bodies without proper treatment it can produce negative effects on existing biota and on human health. The main objective of this study was to evaluate the capacity of a mixed treatment with Komagataeibacter kakiaceti GM5 and Trametes versicolor DSM 3086 to degrade and reduce the toxicity of this by-product. In order to carry out the tests, an experimental culture media of vinasse at 60% (v/v) was used. This culture was compared to a standard medium of glucose at 2% and, simultaneously, a mixed culture (bacterium-fungus) was used through a batch process in an orbital shaker. When compared to the treatments evaluated with individually grown microorganisms, the mixed treatment proposed produced the best COD results in vinasse degradation. However, better results were obtained when using the treatment with T. versicolor DSM 3086 for color removal and treatment with K. kakiaceti GM5 produced better results in terms of turbidity and toxicity. Although the simultaneous mixed treatment did not improve all the variables studied, it never showed the lowest performance. Therefore, this proposal can be considered as an innovative biological alternative in degradation processes of great organic pollutants such as vinasse.

Seasonal characterization of sugarcane vinasse: Assessing environmental impacts from fertirrigation and the bioenergy recovery potential through biodigestion

Sugarcane vinasse has been widely used as a soil fertilizer in the Brazilian sucro-alcohol industry for recycling potassium and water. However, the potential negative effects from long-term soil fertirrigation represent a major drawback regarding this practice, whereas the application of biodigestion represents an efficient method for reducing the polluting organic load and recovering bioenergy from vinasse. Regardless of the predicted use for vinasse, an understanding of the potential of each option is imperative, as the seasonal alterations in the inorganic/organic fractions of vinasse directly affect its management. In this context, this study presents a detailed compositional characterization of sugarcane vinasse from a large-scale Brazilian biorefinery throughout the 2014/2015 harvest to assess the environmental effects (due to fertirrigation) and to estimate the biogas energetic potential. Calculated inputs of organic matter into soils due to vinasse land application were equivalent to the polluting load of populations (117-257inhabha^-1) at least 2-fold greater than the largest Brazilian capital cities (78-70inhabha^-1). Two-phase biodigestion could efficiently reduce the polluting load of vinasse (23-52inhabha^-1) and eliminate the negative effects from direct sulfide emissions in the environment. However, a high risk of soil sodification could result from using high doses of Na-based alkalizing compounds in biodigestion plants. Finally, the optimized recovery of bioenergy through biogas (13.3-26.7MW as electricity) could supply populations as large as 305 thousand inhabitants, so that over 30% of the surplus electricity produced by the studied biorefinery could be obtained from biogas. Overall, applying biodigestion in the treatment of vinasse provides important environmental and energetic gains. However, the benefits of reducing the polluting organic load of vinasse through bioenergy recovery may lose their effect depending on the alkalizing strategy, indicating that the proper use of chemicals in full-scale biodigestion plants is imperative to attain process sustainability.

Concept for Recycling Waste Biomass from the Sugar Industry for Chemical and Biotechnological Purposes

The objective of this study was to develop a method for the thermally-assisted acidic hydrolysis of waste biomass from the sugar industry (sugar beet pulp and leaves) for chemical and biotechnological purposes. The distillates, containing furfural, can be catalytically reduced directly into furfurayl alcohol or tetrahydrofurfuryl alcohol. The sugars present in the hydrolysates can be converted by lactic bacteria into lactic acid, which, by catalytic reduction, leads to propylene glycol. The sugars may also be utilized by microorganisms in the process of cell proliferation, and the biomass obtained used as a protein supplement in animal feed. Our study also considered the effects of the mode and length of preservation (fresh, ensilage, and drying) on the yields of furfural and monosaccharides. The yield of furfural in the distillates was measured using gas chromatography with flame ionization detector (GC-FID). The content of monosaccharides in the hydrolysates was measured spectrophotometrically using enzymatic kits. Biomass preserved under all tested conditions produced high yields of furfural, comparable to those for fresh material. Long-term storage of ensiled waste biomass did not result in loss of furfural productivity. However, there were significant reductions in the amounts of monosaccharides in the hydrolysates.