Yeast derived from lignocellulosic biomass as a sustainable feed resource for use in aquaculture

Effects of Peptidase Treatment on Properties of Yeast Protein as an Alternative Protein Source

Yeast protein, high-quality and high-content microbial protein, can serve as alternative sources of protein. This study examined the structural and functional characteristics of yeast protein through enzymatic treatment using different ratios of alcalase (endo-type) and prozyme 2000P (exo-type) including 2:1 (A2P1), 1:1 (A1P1), and 1:2 (A1P2). After enzymatic hydrolysis, a significant increase in protein solubility from less than 3.1% in untreated proteins to around 16%, particularly at pH 2 or pH 12. Furthermore, a maximum degree of hydrolysis of over 85% was achieved after enzyme treatment. Among them, the highest value of 87.73% was achieved at yeast protein treated by A1P2. Scanning electron microscopy images revealed varied surface morphologies, with exhibiting an increased surface area, particularly after treatment using A2P1. Next, yeast protein treated with A2P1 also demonstrated a superior emulsion stability index (3364.17). However, the antioxidant capacity was higher in proteins treated with A1P2 (78.30%). In addition, the elevated levels of certain amino acids, specifically leucine, lysine, phenylalanine, valine, and arginine, thereby indicating an enhanced amino acid profile was observed. Overall, yeast proteins treated with complex enzymes exhibited improved functionality and potential for diverse food applications.

Assessment of dietary yeast-based additives for cultured catfish and tilapia health

Channel catfish (Ictalurus punctatus) and Nile tilapia (Oreochromis niloticus) are two aquaculture species of great importance. Intensive production is often hindered by poor growth performance and disease mortality. The aim of this study was to evaluate the potential of a commercial fermented yeast product, DVAQUA, on channel catfish and Nile tilapia growth performance metrics and disease resistance. Channel catfish and Nile tilapia were fed practical diets supplemented with 0%, 0.1% or 0.4% of DVAQUA over approximately 2-month feeding periods in recirculation aquaculture systems. To assess the potential of the postbiotic against common aquaculture pathogens, juvenile catfish were subsequently challenged by immersion with Edwardsiella ictaluri S97-773 or virulent Aeromonas hydrophila ML09-119. Nile tilapia juveniles were challenged by injection with Streptococcus iniae ARS-98-60. Serum lysozyme activity, blood chemistry and growth metrics were measured at the end of the feeding period, but no differences were observed across the different metrics, except for survival. For the pathogen challenges, there were no differences in endpoint mortality for channel catfish with either pathogen (p > .05). In contrast, Nile tilapia survivability to S. iniae infection increased proportionally to the inclusion of DVAQUA (p = .005). Changes to sera lysozyme activity were also noted in the tilapia trial, with a reduction of activity in the fish fed the 0.4% DVAQUA diet compared to the control diet (p = .031). Expression profiles of proinflammatory genes and antibodies were also found to be modulated in channel catfish fed the postbiotic, indicating some degree of protective response. These results suggest that this postbiotic may be beneficial in protecting Nile tilapia against S. iniae infection by influencing immune parameters and additional research is needed to evaluate the potential of this DVAQUA for improving catfish health and disease control.

Substituting imported soybean meal with locally produced novel yeast protein in concentrates for Norwegian Red dairy cows: implications for rumen microbiota and fatty acid composition

This research paper addresses the hypothesis that substituting soybean meal with locally produced yeast protein from Cyberlindnera jadinii in barley-based concentrates for Norwegian Red (NR) dairy cows does not have adverse effects on milk fatty acid (FA) composition, rumen microbiota and sensory quality of milk. As soybeans also represent valuable protein sources for human consumption, alternative protein sources need to be investigated for animal feed. A total of 48 NR dairy cows were allocated into three feeding treatments, with the same basal diet of grass silage, but different concentrates. The concentrates were all based on barley, but 7% of the barley in the barley-concentrate (BAR; negative control) was replaced by either soybean meal (SBM; conventional control) or yeast microbial protein (YEA). The experiment lasted for a total of 10 weeks, including 2 weeks of adaptation with the soybean meal concentrate. Analysis of the feed revealed some differences in the FA composition of the YEA concentrate compared to the SBM and BAR concentrates. In milk, only two FAs (C17:1n-8cis9 and an unidentified isomer of C18:3) were significantly different between the YEA- and SBM-group, while six FAs differed between the BAR- and SBM-group. However, the amount of these FAs was low compared to the entire FA profile (<0.7 g/100 g). The experimental diets did not affect rumen microbiota nor the milk sensory quality. This study shows that C. jadinii can replace soybean meal as a protein source in concentrates (7% inclusion) for NR dairy cows fed a diet composed of grass silage and concentrates without any effects on rumen microbiota, and without compromising the FA composition or sensory quality of milk.

Factors Affecting Yeast Digestibility and Immunostimulation in Aquatic Animals

The aquafeed industry increasingly relies on using sustainable and appropriate protein sources to ensure the long-term sustainability and financial viability of intensive aquaculture. Yeast has emerged as a viable substitute protein source in the aquaculture sector due to its potential as a nutritional supplement. A substantial body of evidence exists to suggest that yeast has the potential to act as an effective immune-stimulating agent for a range of aquaculture fish species. Furthermore, the incorporation of yeast supplements and feed additives has the potential to bolster disease prevention, development, and production within the aquaculture sector. Except for methionine, lysine, arginine, and phenylalanine, which are typically the limiting essential amino acids in various fish species, the various yeast species exhibit amino acid profiles that are advantageous when compared to fishmeal. The present review considers the potential nutritional suitability of several yeast species for fish, with particular attention to the various applications of yeast in aquaculture nutrition. The findings of this study indicate that the inclusion of yeast in the diet resulted in the most favorable outcomes, with improvements observed in the overall health, growth performance, and nutritional condition of the fish. Digestibility, a key factor in sustainable feed development, is discussed in special detail. Additionally, this review addresses the utilization of yeast as an immunostimulating agent for fish and its digestion in fish. Furthermore, the research emphasizes the necessity of large-scale production of yeast as a substitute for fishmeal in aquaculture.

Evaluation of four novel non-grain protein sources completely replacing soybean meal on growth performance, serum biochemistry, amino acid transport and intestinal health of grass carp (Ctenopharyngodon idella) at different water temperatures

To investigate the effects of non-grain protein source and water temperature on growth and feed utilization differences of grass carp, the effects of different protein sources on the growth performance, serum biochemistry, digestive enzymes, amino acid transport and intestinal health of grass carp were studied at 24 °C, 28 °C and 32 °C. In this study, a total of 1350 grass carp (Ctenopharyngodon idella) (initial weight 5.00 ± 0.02 g) were selected, and Clostridium autoethanogenum protein (CAP), Tenebrio molitor meal (TMM), cottonseed protein concentrate (CPC) and Chlorella powder (CHP) were used as a single protein source to completely replace soybean meal for 56 days. The results showed that the final body weight (FBW), weight gain rate (WGR), specific growth rate (SGR) and protein efficiency ratio (PER) of grass carp increased significantly with the increasing temperature (P < 0.001). The CHP and SBM groups showed no significant differences in FBW, WGR, SGR and PER (P > 0.05), which were higher than the CAP, TMM and CPC groups (P < 0.001). The alanine transaminase (ALT), aspartate aminotransferase (AST), total protein (TP) and triglyceride (TG) concentrations of grass carp at 32 °C were significantly lower than those at 24 °C and 28 °C (P < 0.001). The acid phosphatase (ACP) activity decreased significantly with the increase of temperature (P = 0.001). The amylase (AMS) activity of the TMM, CPC and CHP groups was significantly lower than that of the SBM and CAP groups (P < 0.001), and the ACP and lipase (LPS) activities in the TMM group were significantly lower than those in the SBM group (P < 0.001). In addition, the interaction between temperatures and protein sources significantly affected the gene expression levels of amino acid transport including solute carrier family 1 member 3 (SLC1A3), solute carrier family 7 member 1 (SLC7A1), solute carrier family 7 member 5 (SLC7A5), solute carrier family 15 member 1b (SLC15A1b), solute carrier family 7 member 7 (SLC7A7), target of rapamycin (TOR), 4E binding protein 1 (4E-BP1) and ribosomal protein S6 kinase 1 (S6K1), intestinal inflammatory including tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), interleukin-8 (IL-8), interleukin-10 (IL-10) and tight junction proteins (occludin, claudin1, claudin3, claudin7 and claudin11) (P ≤ 0.001). Collectively, our results indicated that CHP could be a potential protein source in the case of complete replacement of soybean meal in grass carp.

Fungal Identifier (FId): An Updated Polymerase Chain Reaction-Restriction Fragment Length Polymorphism Approach to Ease Ascomycetous Yeast Isolates' Identification in Ecological Studies

Culturomics has been temporarily exceeded by the advent of omics approaches such as metabarcoding and metagenomics. However, despite improving our knowledge of microbial population composition, both metabarcoding and metagenomics are not suitable for investigating and experimental testing inferences about microbial ecological roles and evolution. This leads to a recent revival of culturomics approaches, which should be supported by improvements in the available tools for high-throughput microbial identification. This study aimed to update the classical PCR-RFLP approach in light of the currently available knowledge on yeast genomics. We generated and analyzed a database including more than 1400 ascomycetous yeast species, each characterized by PCR-RFLP profiles obtained with 143 different endonucleases. The results allowed for the in silico evaluation of the performance of the tested endonucleases in the yeast species' identification and the generation of FId (Fungal Identifier), an online freely accessible tool for the identification of yeast species according to experimentally obtained PCR-RFLP profiles.

Characterization of Yeast Protein Hydrolysate for Potential Application as a Feed Additive

Yeast protein can be a nutritionally suitable auxiliary protein source in livestock food. The breakdown of proteins and thereby generating high-quality peptide, typically provides nutritional benefits. Enzyme hydrolysis has been effectively uesed to generate peptides; however, studies on the potential applications of different types of enzymes to produce yeast protein hydrolysates remain limited. This study investigated the effects of endo- (alcalase and neutrase) and exotype (flavourzyme and prozyme 2000P) enzyme treatments on yeast protein. Endotype enzymes facilitate a higher hydrolysis efficiency in yeast proteins than exotype enzymes. The highest degree of hydrolysis was observed for the protein treated with neutrase, which was followed by alcalase, prozyme 2000P, and flavourzyme. Furthermore, endotype enzyme treated proteins exhibited higher solubility than their exotype counterparts. Notably, the more uniform particle size distribution was observed in endotype treated yeast protein. Moreover, compared with the original yeast protein, the enzymatic protein hydrolysates possessed a higher content of β-sheets structures, indicating their higher structural stability. Regardless of enzyme type, enzyme treated protein possessed a higher total free amino acid content including essential amino acids. Therefore, this study provides significant insights into the production of protein hydrolysates as an alternative protein material.

Dietary effects of Saccharomyces cerevisiae and Allium sativum on growth, antioxidant status, hepatic and intestinal histoarchitecture, expression of growth- and immune-related genes, and resistance of Oreochromis niloticus to Aeromonas sobria

This study investigated the benefits of yeast, Saccharomyces cerevisiae and/or garlic, Allium sativum supplementation in diets of Nile tilapia with regard to growth, antioxidant status, hepatic and intestinal histoarchitecture, expression of growth- and immune-related genes, and resistance to Aeromonas sobria infection. Fish (with an initial weight of 9.43 ± 0.08 g) were allocated to twelve hapas, organized into four triplicate treatment groups defined as control (no supplementation), yeast (4 g/kg diet), garlic (30 g/kg diet), and a mixture of both. This trial continued over a 60-day feeding period. Results revealed that combined treatment (yeast + garlic) demonstrated the most promising outcomes regarding growth, with significantly higher final body weights, weight gains, and specific growth rates compared to other groups. Moreover, this combination enhanced hepatic antioxidant status, as evidenced by elevated levels of reduced glutathione and activities of catalase and superoxide dismutase enzymes, reflecting improved defense against oxidative stress. Histological assessments of the livers and intestines demonstrated structural enhancements in yeast and garlic treatments, suggesting improvements in organ health. In comparison to the control, the gene expression analyses unveiled increased expression of growth-related (igf-1 and ghr1) and immune-related (il-10, lyz, and hep) genes in the test groups, indicating a possible reinforcement of the growth and immune responses. The combined treatment also showed the highest resistance to A. sobria infection, as evidenced by improved survival rates and lower mortality compared with the other groups. These findings highlight the benefits of a combination of both yeast and garlic as a dietary supplementation regimen. In conclusion, this study suggests that the combined treatment regimen could be considered an effective strategy to promote the health and productivity of Nile tilapia under production conditions.

Cyberlindnera jadinii yeast as a functional protein source: Modulation of immunoregulatory pathways in the intestinal proteome of zebrafish (Danio rerio)

Yeasts contain bioactive components that can enhance fish immune robustness and disease resistance. Our study focused on analyzing intestinal immunoregulatory pathways in zebrafish (Danio rerio) using iTRAQ and 2D LC-MS/MS to quantify intestinal proteins. Zebrafish were fed either control diet (C) or diet supplemented with autolyzed Cyberlindnera jadinii (ACJ). KEGG analysis revealed that ACJ yeast diet induced increased abundance of proteins related to arginine and proline metabolism, phagosome, C-lectin receptor signaling, ribosome and PPAR signaling pathways, which can modulate and enhance innate immune responses. ACJ yeast diet also showed decreased abundance of proteins associated with inflammatory pathways, including apoptosis, necroptosis and ferroptosis. These findings indicate boosted innate immune response and control of inflammation-related pathways in zebrafish intestine. Our findings in the well annotated proteome of zebrafish enabled a detailed investigation of intestinal responses and provide insight into health-beneficial effects of yeast species C. jadinii, which is relevant for aquaculture species.

Polyhydroxyalkanoates for Sustainable Aquaculture: A Review of Recent Advancements, Challenges, and Future Directions

Polyhydroxyalkanoates (PHA) are biodegradable biopolymers produced by prokaryotic microbes, which, at the same time, can be applied as single-cell proteins (SCPs), growing on renewable waste-derived substrates. These PHA polymers have gained increasing attention as a sustainable alternative to conventional plastics. One promising application of PHA and PHA-rich SCPs lies within the aquaculture food industry, where they hold potential as feed additives, biocontrol agents against diseases, and immunostimulants. Nevertheless, the cost of PHA production and application remains high, partly due to expensive substrates for cultivating PHA-accumulating SCPs, costly sterilization, energy-intensive SCPs harvesting techniques, and toxic PHA extraction and purification processes. This review summarizes the current state of PHA production and its application in aquaculture. The structure and classification of PHA, microbial sources, cultivation substrates, biosynthesis pathways, and the production challenges and solutions are discussed. Next, the potential of PHA application in aquaculture is explored, focusing on aquaculture challenges, common and innovative PHA-integrated farming practices, and PHA mechanisms in inhibiting pathogens, enhancing the immune system, and improving growth and gut health of various aquatic species. Finally, challenges and future research needs for PHA production and application in aquaculture are identified. Overall, this review paper provides a comprehensive overview of the potential of PHA in aquaculture and highlights the need for further research in this area.

The effects of torula yeast as a protein source on apparent total tract digestibility, inflammatory markers, and fecal microbiota dysbiosis index in Labrador Retrievers with chronically poor stool quality

This study examined the effects of varying protein sources on apparent total tract digestibility, inflammatory markers, and fecal microbiota in Labrador Retrievers with historically poor stool quality. Thirty dogs (15 male, 15 female; aged 0.93 to 11.7 yr) with stool quality scores ≤2.5 on a 5-point scale (1 representing liquid stool and 5 representing firm stool) were randomly assigned to 1 of 3 nutritionally complete diets with differing protein sources and similar macronutrient profiles: 1) chicken meal (n = 10); 2) 10% brewer's yeast (n = 10); or 3) 10% torula yeast (n = 10). Another 10 dogs (five male, five female) with normal stool quality (scores ranging from 3 to 4) received diet 1 and served as negative control (NC). All dogs were fed diet 1 for 7 days, then provided their assigned treatment diets from days 7 to 37. Daily stool scores and weekly body weights were recorded. On days 7, 21, and 36, blood serum was analyzed for c-reactive protein (CRP), and feces for calgranulin C (S100A12), α1-proteinase inhibitor (α1-PI), calprotectin, and microbiota dysbiosis index. Apparent total tract digestibility was assessed using the indicator method with 2 g titanium dioxide administered via oral capsules. Stool scores were greater in NC (P < 0.01) as designed but not affected by treatment × time interaction (P = 0.64). Body weight was greater (P = 0.01) and CRP lower (P < 0.01) in NC dogs. Dry matter and nitrogen-free extract digestibility did not differ among groups (P ≥ 0.14). Negative controls had greater fat digestibility compared to BY (94.64 ± 1.33% vs. 91.65 ± 1.25%; P = 0.02). The overall effect of treatment was significant for protein digestibility (P = 0.03), but there were no differences in individual post hoc comparisons (P ≥ 0.07). Treatment did not affect S100A12 or α1-PI (P ≥ 0.44). Calprotectin decreased at a greater rate over time in TY (P < 0.01). The dysbiosis index score for BY and TY fluctuated less over time (P = 0.01). Blautia (P = 0.03) and Clostridium hiranonis (P = 0.05) abundances were reduced in BY and TY. Dogs with chronically poor stool quality experienced reduced body weights and increased serum CRP, but TY numerically increased protein digestibility, altered the microbiome, and reduced fecal calprotectin. Torula yeast is a suitable alternative protein source in extruded canine diets, but further research is needed to understand the long-term potential for improving the plane of nutrition and modulating gut health.

Nucleic acid-extracted torula yeast from the paper industry as a protein feed for ruminants: A comparison with soybean meal

We compared nucleic acid-extracted torula yeast (NTY) with soybean meal (SBM) to evaluate NTY as a potential protein feed for ruminants in a metabolic trial using four castrated male goats. NTY was replaced isonitrogenously with SBM at a 25% crude protein (CP) level on a dry matter (DM) basis. NTY has 55% CP and 74% total digestive nutrients on DM. Absorbed N was lower on the NTY diet, but since the urinary N excretion was lower on the NTY diet, no significant between-diet difference in retained N was observed. The efficiency of N utilization (retained N/absorbed N) was significantly higher on the NTY diet. The Lys and Met contents (presumed limiting amino acids for dairy cattle) were higher in NTY than SBM, which may be why N utilization efficiency was higher for the NTY diet. Ruminal ammonia-N and blood serum N were lower on the NTY diet, suggesting that NTY has more rumen undegradable protein than SBM. There was no significant between-diet difference in the visceral disorder indicators or antioxidant activities. Our results indicate that NTY is a safe protein feed with a high CP ratio and high-quality amino acid profile for ruminants that is equivalent to SBM.

Engineered yeasts and lignocellulosic biomaterials: shaping a new dimension for biorefinery and global bioeconomy

The next milestone of synthetic biology research relies on the development of customized microbes for specific industrial purposes. Metabolic pathways of an organism, for example, depict its chemical repertoire and its genetic makeup. If genes controlling such pathways can be identified, scientists can decide to enhance or rewrite them for different purposes depending on the organism and the desired metabolites. The lignocellulosic biorefinery has achieved good progress over the past few years with potential impact on global bioeconomy. This principle aims to produce different bio-based products like biochemical(s) or biofuel(s) from plant biomass under microbial actions. Meanwhile, yeasts have proven very useful for different biotechnological applications. Hence, their potentials in genetic/metabolic engineering can be fully explored for lignocellulosic biorefineries. For instance, the secretion of enzymes above the natural limit (aided by genetic engineering) would speed-up the down-line processes in lignocellulosic biorefineries and the cost. Thus, the next milestone would greatly require the development of synthetic yeasts with much more efficient metabolic capacities to achieve basic requirements for particular biorefinery. This review gave comprehensive overview of lignocellulosic biomaterials and their importance in bioeconomy. Many researchers have demonstrated the engineering of several ligninolytic enzymes in heterologous yeast hosts. However, there are still many factors needing to be well understood like the secretion time, titter value, thermal stability, pH tolerance, and reactivity of the recombinant enzymes. Here, we give a detailed account of the potentials of engineered yeasts being discussed, as well as the constraints associated with their development and applications.

Effect of Cyberlindnera jadinii yeast on growth performance, nutrient digestibility, and gut health of broiler chickens from 1 to 34 d of age

The effect of dietary graded levels of Cyberlindnera jadinii yeast (C. jadinii) on growth performance, nutrient digestibility, and gut health of broilers was evaluated from 1 to 34 d of age. A total of 360 male broiler chicks were randomly allocated to 1 of 4 dietary treatments (6 replicate pens each) consisting of a wheat-soybean meal-based pelleted diet (Control or CJ0), and 3 diets in which 10% (CJ10), 20% (CJ20), and 30% (CJ30) of the crude protein were supplied by C. jadinii, by gradually replacing protein-rich ingredients. Body weight and feed intake were measured at d 1, 11, 22, and 32. Pellet temperature, durability, and hardness increased linearly (P < 0.05) with C. jadinii inclusion, with highest (P < 0.05) values for CJ30. Up until d 22, feed conversion ratio (FCR) was similar between treatments (P = 0.169). Overall, increasing C. jadinii inclusion linearly increased (P = 0.047) feed intake but had no effect on weight gain or mortality. FCR increased (P < 0.05) linearly with increasing C. jadinii inclusion but only birds fed CJ30 had a significantly poorer FCR compared to the Control. Ileal digestibility was not affected by C. jadinii inclusion, however, there was a significant linear decrease in crude protein and phosphorus, and a tendency for a decrease in fat digestibility. Apparent metabolizable energy (AME) decreased (P < 0.001) quadratically with increasing C. jadinii and was significantly lower in CJ30 compared to the Control. Ileal concentrations of volatile fatty acids (VFAs) were not affected by C. jadinii inclusion, but butyric acid and total VFAs were linearly and quadratically increased and were significantly higher in cecal digesta of birds fed CJ20 and CJ30. Increasing C. jadinii inclusion was associated with an increase (P < 0.05) in the relative abundance of lactobacillus in the ileum and cecum. In conclusion, C. jadinii yeast can supply up to 20% of the total dietary protein without negatively affecting performance, digestibility, or gut health of broilers. The potential confounding role of feed processing and C. jadinii cell wall components on broiler performance is discussed.

Amino Acid Digestibility of Different Formulations of Torula Yeast in an In Vitro Porcine Gastrointestinal Digestion Model and Their Protective Effects on Barrier Function and Inflammation in a Caco-2/THP1Co-Culture Model

Single-cell protein from torula yeast (Cyberlindnera jadinii) grown on lignocellulosic biomass has been proven to be an excellent alternative protein source for animal feed. This study aimed to evaluate the amino acid (AA) digestibility by estimating intestinal absorption from three yeast-based ingredients, produced by cultivating C. jadinii on hydrolysate, using either mixed woody species (drum- (WDI) or spray-dried (WSI)) or corn dextrose (drum-dried (DDI)) as the carbon source. Further, the protective effect of intestinal digests on activated THP1-Blue™-induced epithelial damage and cytokine profile was evaluated. Total protein content from these three ingredients ranged from 34 to 45%, while the AA dialysis showed an estimated bioaccessibility between 41 and 58%, indicating good digestibility of all test products. A protective effect against epithelial-induced damage was observed for two of the three tested products. Torula yeast cultivated on wood and drum-dried (WDI) and torula yeast cultivated on wood and spray-dried (WSI) significantly increased transepithelial electrical resistance (TEER) values (111-147%, p < 0.05), recovering the epithelial barrier from the inflammation-induced damage in a dose-dependent manner. Further, WSI digests significantly reduced IL8 (250.8 ± 28.1 ng/mL), IL6 (237.9 ± 1.8 pg/mL) and TNF (2797.9 ± 216.3 pg/mL) compared to the blank control (IL8 = 485.7 ± 74.4 ng/mL, IL6 = 478.7 ± 58.9 pg/mL; TNF = 4273.5 ± 20.9 pg/mL) (p < 0.05). These results align with previous in vivo studies, supporting torula yeast-based ingredients as a high-quality protein source for pigs, protecting the intestinal barrier from inflammatory damage, and reducing the pro-inflammatory response. We provided novel insights into the mechanisms behind the health improvement of pigs fed on torula yeast-based ingredients, with potential applications for designing nutritional interventions to recover intestinal homeostasis during critical production periods, such as weaning.

Cyberlindnera jadinii yeast as a functional protein source for Atlantic salmon (Salmo salar L.): Early response of intestinal mucosal compartments in the distal intestine

The interplay between nutrition and the immune system is well recognized, and several studies show that experimental diets elicit local morphological changes and alteration of gene and protein expression in the intestinal mucosa of Atlantic salmon. In this study the pathophysiological effects of experimental diets on mucosal responses in the distal intestine of Atlantic salmon were investigated. Atlantic salmon were fed diets with inclusion of soybean meal (SBM) and Cyberlindnera jadinii (CJ) yeast for 7 days. A standard fish meal (FM) diet was used as a control. Morphological, immunohistochemical and gene expression analyses were used to evaluate the presence of immune cells, proliferating cells, and stem cell populations in mucosal compartments of the simple folds in the distal intestine. Fish fed SBM developed morphological changes consistent with SBM induced enteritis. Immunohistochemistry showed an increased presence of apoptotic cells, CD3ϵ and CD8α labelled cells in the simple fold epithelium of SBM group compared with the CJ group. For the investigated genes, expression levels in all three groups were mostly higher in the epithelial compartment of the simple fold than in the compartment beneath the folds. Most changes within the epithelial compartment were observed in fish fed SBM, where expression of CD3ζ, CD8α, MHC I and MHC II were lower than the FM control group. The CJ group had an increased expression of the stem cell marker Lgr5 in the epithelial compartment compared with SBM group. The division of the simple fold into an apical and basal compartment showed that the increase in Lgr5 was evident along the whole length of the simple folds and not confined to the base of the folds. Similarly, proliferation (PCNA, MCM2) and apoptosis (Caspase-3) gene expression was present in the entire length of the simple folds, suggesting that intestinal epithelial cell turnover is not confined to the basal or apical part of the fold. This study shows that the epithelial compartment is active in the early immunoregulatory response towards dietary stimuli and that the level of an intestinal stem cell marker in salmon was influenced by a diet containing CJ yeast.

Life-cycle assessment of yeast-based single-cell protein production with oat processing side-stream

Production of fish meal and plant-based feed proteins continues to increase to meet the growing demand for seafood, leading to impacts on marine and terrestrial ecosystems. Microbial proteins such as single-cell proteins (SCPs) have been introduced as feed alternatives since they can replace current fish feed ingredients, e.g., soybean, which are associated with negative environmental impacts. Microbial protein production also enables utilization of grain processing side-streams as feedstock sources. This study assesses the environmental impacts of yeast-based SCP using oat side-stream as feedstock (OS-SCP). Life-cycle assessment with a cradle-to-gate approach was used to quantify global warming, freshwater eutrophication, marine eutrophication, terrestrial acidification, land use, and water consumption of OS-SCP production in Finland. Dried and wet side-streams of oat were compared with each other to identify differences in energy consumption and transportation effects. Sensitivity analysis was performed to examine the difference in impacts at various locations and fermentation times. Benchmarking was used to evaluate the environmental impacts of OS-SCP and other feed products, including both conventional and novel protein products. Results highlight the importance of energy sources in quantifying the environmental performance of OS-SCP production. OS-SCP produced with dried side-streams resulted in higher global warming (16.3 %) and water consumption (7.5 %) than OS-SCP produced from wet side-streams, reflecting the energy and water requirements for the drying process. Compared with conventional products, such as soy protein concentrates, OS-SCP resulted in 61 % less land use, while exacerbating the environmental impacts in all the other categories. OS-SCP had more impact on global warming (205-754 %), water consumption (166-1401 %), freshwater eutrophication (118-333 %), and terrestrial acidification (85-340 %) than other novel products, including yeast protein concentrate, methanotrophic bacterial SCP, and insect meal, while lowering global warming (11 %) and freshwater eutrophication (20 %) compared with dry microalgae biomass.

Torula yeast may improve intestinal health and immune function of weanling pigs

An experiment was conducted to test the hypothesis that inclusion of a conventional torula yeast or a torula yeast produced from forestry byproducts (i.e., woody torula yeast) in diets for weanling pigs instead of fish meal and plasma protein improves growth performance and intestinal health of pigs. A total of 120 weanling pigs (6.53 ± 0.78 kg) were allotted to three treatments with ten replicate pens per diet. Pigs were fed one of three diets from days 1 to 14 post-weaning (phase 1), whereas all pigs were fed a common diet in phase 2 (days 15 to 28). The three treatments in phase 1 included a control diet with 5% fish meal, 3.5% plasma protein, and no torula yeast. The second diet contained 1.5% fish meal, 14% woody torula yeast, and no plasma protein, whereas the third diet contained 1.5% fish meal, 14% conventional torula yeast, and no plasma protein. Fecal scores were assessed every other day. On day 7, one pig per pen was euthanized to collect ileal tissue and mucosa for determination of morphology and for ribonucleic acid (RNA) sequencing analysis. At the end of phases 1 and 2, blood samples were collected and concentrations of cytokines, plasma urea nitrogen (PUN), peptide YY, immunoglobulin G, total protein, and albumin were analyzed. Results indicated that both torula yeast sources could replace fish meal and plasma protein without affecting growth performance, intestinal morphology, or blood characteristics of pigs. Pigs fed a diet containing torula yeast had improved (P < 0.05) fecal scores during phase 1. Pigs fed the conventional torula yeast diet had greater (P < 0.05) concentration of interleukin-2 compared with pigs fed the control diet. On day 14, greater (P < 0.05) concentrations of interleukin-4 and interleukin-10 were observed in pigs fed the diet containing the woody torula yeast or conventional torula yeast compared with pigs fed the control diet. Results from the RNA sequencing indicated that 19 of 24 analyzed genes involved in digestion and absorption of protein and vitamins were downregulated in pigs fed the diet containing woody torula yeast compared with pigs fed the control diet. However, only two genes (i.e., ANKS4B and FAM54A) were downregulated in pigs fed the woody torula yeast diet compared with the conventional torula yeast diet. In conclusion, using woody or conventional torula yeast instead of fish meal and plasma protein in the phase 1 diet for weanling pigs may improve intestinal health without influencing growth performance of pigs.

Valorization of agro-industrial wastes into polyhydroxyalkanoates-rich single-cell proteins to enable a circular waste-to-feed economy

Recovering and converting carbon and nutrients from waste streams into healthy single-cell proteins (SCPs) can be an effective strategy to address costly waste management and support the increasing animal feed demand for the global food supply. Recently, SCPs rich in polyhydroxybutyrate (PHB) have been identified as an effective biocontrol healthy feed to replace conventional antibiotics-supplemented aquaculture feed. PHB, an intercellular polymer of short-chain-length (SCL) hydroxy-fatty acids, is a common type of polyhydroxyalkanoates (PHA) that can be microbially produced from various organics, including agro-industrial wastes. The complex chemical properties of agro-industrial wastes might produce SCPs containing PHA with SCL and/or medium chain-length (MCL) hydroxy-fatty acids. However, the effects of MCL-PHA-containing SCPs on aqua species' health and disease-fighting ability remains poorly understood. This study investigated the feasibility of producing various PHA-containing SCPs from renewable agro-industrial wastes/wastewaters, the effectiveness of SCL- and MCL-PHA as biocontrol agents, and the effects of these PHA-rich SCPs on the growth and disease resistance of an aquaculture animal model, brine shrimp Artemia. Zobellella denitrificans ZD1 and Pseudomonas oleovorans were able to grow on different pure substrates and agro-industrial wastes/wastewaters to produce various SCL- and/or MCL-PHA-rich SCPs. Low doses of MCL-fatty acids (i.e., PHA intermediates) efficiently suppressed the growth of aquaculture pathogens. Moreover, MCL-PHA-rich SCPs served as great food/energy sources for Artemia and improved Artemia's ability to fight pathogens. This study offers a win-win approach to address the challenges of wastes/wastewater management and feed supply faced by the aquaculture industry.

Clostridium autoethanogenum protein inclusion in the diet for broiler: Enhancement of growth performance, lipid metabolism, and gut microbiota

This study aimed to investigate the effects of dietary supplementation of the new single-cell protein Clostridium autoethanogenum protein (CAP) on growth performance, plasma biochemical indexes, liver histology, lipid metabolism, and gut microbiota in Cobb broilers. According to the randomized block experimental design, 960 Cobb broilers (1d old) were divided into six treatments with eight replicates of 20 birds each. Six isonitrogenous and isoenergetic diets were formulated with different contents of CAP (0, 1, 2, 3, 4, and 5%) to replace soybean meal (SBM). The results showed that the addition of CAP did not influence liver health when it exceeded 2%. The protein metabolism markers and feed conversion rate increased (P < 0.05), significantly improving the growth performance. When the content of CAP was greater than 4%, it could promote lipolysis without affecting lipogenesis, decreasing the abdominal fat rate. There was no significant difference in MDA between these groups (P = 0.948). The increase of SOD and GSH-Px indicated the enhancement of antioxidant response. Alpha diversity did not significantly differ between groups (P > 0.05). Inclusion of 4% or less CAP led to the increase in beneficial microbiota, the concentration of short-chain fatty acids (SCFAs) such as acetic acid, propionic acid, and butyric acid (P < 0.05), and the concentration of primary bile acids such as cholic acid and goose deoxycholic acid (P < 0.05). While the concentration of secondary bile acids such as taurocholic acid and taurine goose deoxycholic acid was decreased (P < 0.05). These results illustrated that the CAP had a high potential for application in poultry nutrition. In terms of improving growth performance and antioxidant capacity and reducing fat deposition rate, 4% CAP content is recommended.

Use of Microorganisms as Nutritional and Functional Feedstuffs for Nursery Pigs and Broilers

The objectives of this review paper are to introduce the structures and composition of various microorganisms, to show some applications of single cells as alternative protein supplements or energy feeds in swine and poultry diets, and to discuss the functional effects of microorganisms as feed additives on the growth performance and intestinal health of nursery pigs and broilers. Microorganisms, including bacteria, yeasts, and microalgae, have been commonly supplemented in animal diets because they are cost-effective, stable, and have quantitative production that provides nutritional and functional benefits to pigs and broilers. Microorganisms could be alternative antibiotics to enhance intestinal health due to bioactive components from cell wall components, which interact with receptors on epithelial and immune cells. In addition, bioactive components could be digested by intestinal microbiota to produce short-chain fatty acids and enhance energy utilization. Otherwise, microorganisms such as single-cell protein (SCP) and single-cell oils (SCOs) are sustainable and economic choices to replace conventional protein supplements and energy feeds. Supplementing microorganisms as feedstuffs and feed additives improved the average daily gain by 1.83%, the daily feed intake by 0.24%, and the feed efficiency by 1.46% in pigs and broilers. Based on the properties of each microorganism, traditional protein supplements, energy feeds, and functional feed additives could be replaced by microorganisms, which have shown benefits to animal's growth and health. Therefore, specific microorganisms could be promising alternatives as nutritional and functional feedstuffs in animal diets.

Evaluation of Torula yeast as a protein source in extruded feline diets

The objective of this work was to evaluate the use of a Torula yeast (TY) on diet processing, palatability, and total tract nutrient digestibility in extruded feline diets. Four dietary treatments were compared, differing by protein source: TY, pea protein concentrate (PP), soybean meal (SM), and chicken meal (CM). Diets were produced using a single-screw extruder under similar processing conditions. Palatability assessment was conducted as a split plate design where both first choice and intake ratio (IR) were determined. Apparent total tract digestibility (ATTD) of nutrients was estimated using Titanium dioxide as an indigestible marker. During diet production, specific mechanical energy of TY and SM (average of 187 kJ/kg) was greater (P < 0.05) than for PP (138 kJ/kg); however, CM was similar to all treatments (167 kJ/kg). Kibble diameter, piece volume, and sectional expansion ratio were greatest for TY (P < 0.05). Additionally, both bulk and piece density were lowest (P < 0.05) for TY. Kibble hardness was lower for TY and SM (P < 0.05; average of 2.10 Newtons) compared to CM and PP (average of 2.90 Newtons). During the palatability trial, TY was chosen first a greater number of times than CM (P < 0.05; 36 vs. 4, respectively), but differences were not found between TY and PP (25 vs. 15, respectively) or TY and SM (24 vs. 16, respectively). Cats had a greater IR (P < 0.05) of TY compared to CM and PP (0.88 and 0.73, respectively). However, there was no difference in preference between TY and SM. ATTD of dry matter (DM) and organic matter (OM) was greater (P < 0.05) for CM (87.43% and 91.34%, respectively) than other treatments. Both DM and OM ATTD of TY were similar (P < 0.05) to PP and SM (average of 86.20% and average of 89.76%, respectively). Ash ATTD was greater (P < 0.05) for cats fed TY and SM (average of 37.42%), intermediate for PP (32.79%), and lowest for CM (23.97%). Crude protein (CP) ATTD of TY was similar to all other treatments (average of 89.97%), but fat ATTD was lower (P < 0.05; 92.52%) than other treatments (93.76% to 94.82%). Gross energy ATTD was greater (P < 0.05) for CM than TY (90.97% vs. 90.18%, respectively); however, TY was similar to PP and SM (average of 90.22%). Total dietary fiber ATTD was similar between TY and CM (average of 66.20%) and greater (P < 0.05) than PP and SM (average of 58.70%). The TY used in this study facilitated diet formation, increased diet preference, and was highly digestible when fed to cats.

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.

Valorization of food waste fermentation liquid into single cell protein by photosynthetic bacteria via stimulating carbon metabolic pathway and environmental behaviour

Single cell protein (SCP) production by photosynthetic bacteria (PSB) is dependent on the bioavailability of carbon source, while sufficient volatile fatty acids (VFAs) in food waste fermentation liquid might be a potential alternative. It is unclear how the fermentation liquid affects the SCP biosynthesis and the related metabolic mechanism. This work demonstrated that the SCP production could be improved effectively (2088.4 mg/L) with high conversion capacity of carbon source (0.99 mg-biomass/mg-COD) by regulating carbon source level. PSB preferred to utilize the VFAs in food waste fermentation liquid. The carbon metabolic pathways (e.g., the transformation of VFAs to acetyl-CoA, and tricarboxylic acid cycle) involved in the SCP production were enhanced under optimal condition. Moreover, optimal carbon source regulation could significantly stimulate the environmental behaviour of PSB (e.g., two-component system, quorum sensing, and ATP-binding cassette transporter) involved in adaptation to external stimulus and maintaining high bacterial activity, resulting in SCP yield promotion.

Effect of Autolyzed Yarrowia lipolytica on the Growth Performance, Antioxidant Capacity, Intestinal Histology, Microbiota, and Transcriptome Profile of Juvenile Largemouth Bass (Micropterus salmoides)

The improper components of formulated feed can cause the intestinal dysbiosis of juvenile largemouth bass and further affect fish health. A 28 day feeding trial was conducted to investigate the effect of partially replacing fish meal (FM) with autolyzed Yarrowia lipolytica (YL) on juvenile largemouth bass (Micropterus salmoides). We considered four diets—control, YL25, YL50, and YL75—in which 0%, 25%, 50%, and 75% of the FM content, respectively, was replaced with YL. According to results, the weight gain rate (WGR) and specific growth rate (SGR) of the fish with the YL25 and YL50 diets were significantly higher than the WGR and SGR with the control diet, while the YL75 diet significantly reduced fish growth and antioxidant enzymes activities, and shortened the villus height in the intestinal mucosa. The 16S rRNA analysis of the intestinal microbiota showed that the relative abundance of Mycoplasma was significantly increased with the YL25 and YL50 diets, while the Enterobacteriacea content was increased with the YL75 diet. Moreover, our transcriptome analysis revealed that certain differentially expressed genes (DEGs) that are associated with growth, metabolism, and immunity were modulated by YL inclusion treatment. Dietary YL25 and YL50 significantly reduced the mRNA level of ERBB receptor feedback inhibitor 1 (errfi1) and dual-specificity phosphatases (dusp), while the expression of the suppressor of cytokine signaling 1 (socs1), the transporter associated with antigen processing 2 subunit type a (tap2a), and the major histocompatibility complex class I-related gene (MHC-I-l) were sharply increased with YL75 treatment. We determined that the optimum dose of dietary YL required for maximum growth without any adverse influence on intestinal health was 189.82 g/kg (with 31.63% of the fishmeal replaced by YL), while an excessive substitution of YL for fishmeal led to suppressed growth and antioxidant capacity, as well as intestinal damage for juvenile largemouth bass.

A new single-cell protein from Clostridium autoethanogenum as a functional protein for largemouth bass (Micropterus salmoides)

Clostridium autoethanogenum protein (CAP) is a new single-cell protein source originating from inactivated bacteria. An in vitro digestion experiment and an 8-wk growth experiment were conducted to evaluate the molecular weight distribution of the CAP hydrolysate, and the effects of dietary CAP levels on the growth performance, plasma parameters, hepatic and intestinal health, and the diversity of gut-adherent microbiota of largemouth bass (Micropterus salmoides). The fish (initial body weight of 47.99 ± 0.01 g) were fed diets where CAP gradually replaced 0% (CAP0), 12.5% (CAP12.5), 25% (CAP25), 37.5% (CAP37.5) and 50% (CAP50) of low-temperature steam dried anchovy fish meal (LTFM) in the diet. Results showed that the content of peptides below 1,000 Da in the CAP hydrolysate (0.56 mg/mL) was higher than that of the LTFM hydrolysate (0.48 mg/mL). Dietary CAP inclusion had no negative effect on growth performance, while whole-body lipid content significantly reduced in the CAP25 and CAP50 groups (P < 0.05). The plasma alanine aminotransferase activities and triglyceride concentrations in the CAP inclusion groups were significantly lower than those in the CAP0 group (P < 0.05). The plasma aspartate aminotransferase activity was significantly reduced in the CAP37.5 group (P < 0.05). The richness and diversity of the gut-adhesive microbiota and the proportion of Clostridium sensu stricto 12 in the CAP50 group were significantly higher than those in the CAP0 group (P < 0.05). Dietary CAP inclusion inhibited inflammatory responses by down-regulating the mRNA levels of interleukin 1β (IL1β), IL10 and transforming growth factor β1 (P < 0.05) in the liver. The mRNA levels of acetyl-CoA carboxylase 1 were significantly down-regulated in the CAP12.5, CAP25 and CAP37.5 groups (P < 0.05), while that of fatty acid synthase was significantly down-regulated in the CAP50 group (P < 0.05). These results demonstrate that dietary CAP inclusion could improve the hepatic and intestinal health of largemouth bass, and can be helpful to further develop CAP as a functional feed ingredient.

Yeast β-Glucans as Fish Immunomodulators: A Review

Simple Summary

The β-glucan obtained from yeast—a very important molecule for fish production—activates the immune system of fish by different mechanisms and induces protection against pathogens. However, most previous related studies have focused on the use of commercial β-glucan from the yeast Saccharomyces cerevisiae to understand the activation pathways. Experimental β-glucans extracted from other yeasts show other interesting biological activities even at lower doses. This review article analyzes the current information and suggests perspectives on yeast β-glucans.

Abstract

Administration of immunostimulants in fish is a preventive method to combat infections. A wide variety of these biological molecules exist, among which one of the yeast wall compounds stands out for its different biological activities. The β-glucan that forms the structural part of yeast is capable of generating immune activity in fish by cell receptor recognition. The most frequently used β-glucans for the study of mechanisms of action are those of commercial origin, with doses recommended by the manufacturer. Nevertheless, their immune activity is inefficient in some fish species, and increasing the dose may show adverse effects, including immunosuppression. Conversely, experimental β-glucans from other yeast species show different activities, such as antibacterial, antioxidant, healing, and stress tolerance properties. Therefore, this review analyses the most recent scientific reports on the use of yeast β-glucans in freshwater and marine fish.

Oleaginous yeast Rhodotorula toruloides biomass effect on the metabolism of Arctic char (Salvelinus alpinus)

Sustainability issues arise when using fish oil and vegetable oils in fish feed production for aquaculture purposes. Microbial production of single cell oil is a potential alternative as a lipid ingredient in the production of fish feed. In this study, we replaced the vegetable oils with the oleaginous yeast R. toruloides biomass in the diet of Arctic char (S. alpinus) and investigated the effects on health and composition. Measurement of fish growth parameters showed a higher liver weight and hepatosomatic index in the experimental group of fish fed partly with yeast biomass compared to a control group fed a diet with vegetable oils. No significant differences in the lipid content of muscle and liver tissues were found. The fatty acid profiles in the muscle of both fish groups were similar while the experimental fish group had a higher amount of monounsaturated fatty acids in the liver. Histology of livers showed no significant difference in the number of lipid droplets. The size of hepatic lipid droplets seemed to be related to liver fat content. Quantification of metabolites in the liver revealed no differences between the fish groups while plasma metabolites involved in energy pathways such as alanine, 3-hydroxybutyrate, creatinine, serine, betaine, and choline were significantly higher in the experimental fish group.

Dietary Inclusion of Hydrolyzed Debaryomyces hansenii Yeasts Modulates Physiological Responses in Plasma and Immune Organs of Atlantic Salmon (Salmo salar) Parr Exposed to Acute Hypoxia Stress

Stress related to salmon aquaculture practices (handling, sub-optimal nutrition, diseases, and environmental problems) may compromise fish welfare. This study describes the effects of two hydrolyzed Debaryomyces hansenii yeast-based products (LAN4 and LAN6) on physiological and immune responses of Atlantic salmon (Salmo salar) parr exposed to short hypoxia stress. A commercial-like diet (control diet: CD) and two experimental diets (CD supplemented with 0.1% of either component LAN4 or LAN6) were fed to fish for 8 weeks. At the end of the feeding experiment, fish were exposed to 1-min hypoxia and samples were collected at 0, 1, 3, 6, 12, and 24 h post-stress. Results showed that plasma cortisol reached a peak at 1 h post-stress in CD and LAN6 groups, whereas no significant increase in cortisol levels was detected in the LAN4 group. Moreover, the LAN6 group enhanced IL-10 responses to hypoxia, when compared to the control and LAN4 group. This suggests a regulation of immunosuppressive profiles in fish fed LAN4. Hypoxia stress increased TNFα in all groups, which indicates that fish may compensate for the short-term stress response, by modulating innate immune molecules. The apparent suppression of hypoxia responses in the LAN4 group coincided with the detection of differences in goblet cells size and Muc-like proteins production in DI; and upregulation (1 h post-stress) of pathways related to oxygen transport, hemoglobin complex, and glutathione transferase activity and the downregulation of fatty acid metabolism (6 h post-stress) in gills. To conclude, a 1-min hypoxia stress exposure affects the response to stress and immunity; and D. hansenii-based yeast products are promising components in functional aquafeeds for salmon due to their ability to counteract possible consequences of hypoxic stress.

Specific importance of low level dietary supplementation of Lypomyces starkeyi CB1807 yeast strain in red sea bream (Pagrus major)

Most probiotic yeast supplement in fish exhibit beneficial effect at ≤1% of the dietary proportion. This study aimed at evaluating the specific effects of Lypomyces starkeyi CB1807 yeast strain supplemented at ≤1% of dietary proportion on the performance of juvenile red sea bream (Pagrus major, 1.9 ± 0.04 g). Five diets were supplemented with yeast at graded levels of 0% (Control diet ‘CD1’), 0.05% (D2), 0.1% (D3), 0.5% (D4), and 1.0% (D5). After 45-days of feeding trial, significant (P<0.05) improvement was detected on final body weight (FBW) and body weight gain (BWG) in fish fed D3 and D5 compared to control. Low values of total cholesterol (T-Cho) and aspartate aminotransferase (AST) were recorded in fish groups fed on D2, D4, and D5, respectively. Fish fed on D3, D4 and D5 diets showed high (P<0.05) values of serum, mucus and liver lysozyme compared to control. Fish fed on D5 showed high values of Total immunoglobulin (Ig) compared to control. Fish fed on D2 showed strong correlation with biological antioxidant activity (BAP), superoxide dismutase (SOD) and catalase activity (CAT). The biological antioxidant potential (BAP) activity in fish fed on D2 was significantly higher compared to control (P<0.05). The reactive oxygen metabolites (d-ROM) were significantly lower in fish fed on D2 and D3 compared to CD1 (P<0.05). Peroxidase activity was improved significantly (P<0.05) in fish fed on D3, D4 and D5 compared to control. The tolerance ability (LT50) of fish fed on D5 against low salinity stress were significantly higher compared to control (P<0.05). It was concluded that dietary benefits of spent L. starkeyi yeast at ≤1% showed considerable improvement in antioxidant capacity in red sea bream, P. major.

Effects of Yeast Species and Processing on Intestinal Health and Transcriptomic Profiles of Atlantic Salmon (Salmo salar) Fed Soybean Meal-Based Diets in Seawater

The objective of the current study was to examine the effects of yeasts on intestinal health and transcriptomic profiles from the distal intestine and spleen tissue of Atlantic salmon fed SBM-based diets in seawater. Cyberlindnera jadinii (CJ) and Wickerhamomyces anomalus (WA) yeasts were heat-inactivated with spray-drying (ICJ and IWA) or autolyzed at 50 °C for 16 h (ACJ and AWA), followed by spray-drying. Six diets were formulated, one based on fishmeal (FM), a challenging diet with 30% soybean meal (SBM) and four other diets containing 30% SBM and 10% of each of the four yeast fractions (i.e., ICJ, ACJ, IWA and AWA). The inclusion of CJ yeasts reduced the loss of enterocyte supranuclear vacuolization and reduced the population of CD8α labeled cells present in the lamina propria of fish fed the SBM diet. The CJ yeasts controlled the inflammatory responses of fish fed SBM through up-regulation of pathways related to wound healing and taurine metabolism. The WA yeasts dampened the inflammatory profile of fish fed SBM through down-regulation of pathways related to toll-like receptor signaling, C-lectin receptor, cytokine receptor and signal transduction. This study suggests that the yeast species, Cyberlindnera jadinii and Wickerhamomyces anomalus are novel high-quality protein sources with health-beneficial effects in terms of reducing inflammation associated with feeding plant-based diets to Atlantic salmon.

Torula yeast in the diet of Atlantic salmon Salmo salar and the impact on growth performance and gut microbiome

Atlantic salmon aquaculture is expanding, and with it, the need to find suitable replacements for conventional protein sources used in formulated feeds. Torula yeast (Cyberlindnera jadinii), has been identified as a promising alternative protein for feed and can be sustainably cultivated on lignocellulosic biomasses. The present study investigated the impact of torula yeast on the growth performance and gut microbiome of freshwater Atlantic salmon. A marine protein base diet and a mixed marine and plant protein base diet were tested, where conventional proteins were replaced with increasing inclusion levels of torula yeast, (0%, 10%, 20%). This study demonstrated that 20% torula yeast can replace fish meal without alteration to growth performance while leading to potential benefits for the gut microbiome by increasing the presence of bacteria positively associated with the host. However, when torula yeast replaced plant meal in a mixed protein diet, results suggested that 10% inclusion of yeast produced the best growth performance results but at the 20% inclusion level of yeast, potentially negative changes were observed in the gut microbial community, such as a decrease in lactic acid bacteria. This study supports the continued investigation of torula yeast for Atlantic salmon as a partial replacement for conventional proteins.

Fishmeal Dietary Replacement Up to 50%: A Comparative Study of Two Insect Meals for Rainbow Trout (Oncorhynchus mykiss)

The demand of optimal protein for human consumption is growing. The Food and Agriculture Organization (FAO) has highlighted aquaculture as one of the most promising alternatives for this protein supply gap due to the high efficiency of fish growth. However, aquaculture has been facing its own sustainability problem, because its high demand for protein has been traditionally satisfied with the use of fishmeal (FM) as the main source. Some of the most promising and sustainable protein substitutes for FM come from insects. The present manuscript provides insight into an experiment carried out on rainbow trout (Oncorhynchus mykiss) with a 50% replacement of FM with different larvae insect meals: Hermetia illucens (HI), and Tenebrio molitor (TM). TM showed better results for growth, protein utilization and more active digestive function, supported by intestinal histological changes. Liver histology and intermediary metabolism did not show relevant changes between insect meals, while other parameters such as antioxidant enzyme activities and tissue damage indicators showed the potential of insect meals as functional ingredients.

Yeast Protein as an Easily Accessible Food Source

In recent years, the awareness and willingness of consumers to consume healthy food has grown significantly. In order to meet these needs, scientists are looking for innovative methods of food production, which is a source of easily digestible protein with a balanced amino acid composition. Yeast protein biomass (single cell protein, SCP) is a bioavailable product which is obtained when primarily using as a culture medium inexpensive various waste substrates including agricultural and industrial wastes. With the growing population, yeast protein seems to be an attractive alternative to traditional protein sources such as plants and meat. Moreover, yeast protein biomass also contains trace minerals and vitamins including B-group. Thus, using yeast in the production of protein provides both valuable nutrients and enhances purification of wastes. In conclusion, nutritional yeast protein biomass may be the best option for human and animal nutrition with a low environmental footprint. The rapidly evolving SCP production technology and discoveries from the world of biotechnology can make a huge difference in the future for the key improvement of hunger problems and the possibility of improving world food security. On the market of growing demand for cheap and environmentally clean SCP protein with practically unlimited scale of production, it may soon become one of the ingredients of our food. The review article presents the possibilities of protein production by yeast groups with the use of various substrates as well as the safety of yeast protein used as food.

Cyberlindnera jadinii yeast as a protein source in early- to mid-lactation dairy cow diets: Effects on feed intake, ruminal fermentation, and milk production

We examined the effects of substituting soybean meal with either yeast protein from Cyberlindnera jadinii or barley in concentrate feeds on feed intake, ruminal fermentation products, milk production, and milk composition in Norwegian Red (NRF) dairy cows. The concentrate feeds were prepared in pellet form as soy-based (SBM; where soybean meal is included as a protein ingredient), yeast-based (YEA; soybean meal replaced with yeast protein), or barley-based (BAR; soybean meal replaced with barley). The SBM contained 7.0% soybean meal on a dry matter (DM) basis. This was replaced with yeast protein and barley in the YEA and BAR concentrate feeds, respectively. A total of 48 early- to mid-lactation [days in milk ± standard deviation (SD): 103 ± 33.5 d] NRF cows in their first to fourth parity and with initial milk yield of 32.6 kg (SD = 7.7) were allocated into 3 groups, using a randomized block design, after feeding a common diet [SBM and good-quality grass silage: crude protein (CP) and neutral detergent fiber (NDF) content of 181 and 532 g/kg of DM, respectively] for 14 d (i.e., covariate period). The groups (n = 16) were then fed one of the dietary treatments (SBM, YEA, or BAR) for a period of 56 d (i.e., experimental period). The concentrate feeds were offered in split portions from 3 automatic feeders using electronic identification, with ad libitum access to the same grass silage. Dietary treatments had no effect on daily silage intake, total DM intake, or total NDF intake. Dietary CP intake was lower and starch intake was higher in the BAR group compared with the other groups. Ruminal fluid pH, short-chain volatile fatty acid (VFA) concentrations, acetate-to-propionate ratio, and non-glucogenic to glucogenic VFA ratio were not affected by dietary treatments. No effects of the dietary treatments were observed on body weight change, body condition score change, milk yield, energy-corrected milk yield, milk lactose and fat percentages, or their yields. In conclusion, yeast protein can substitute conventional soybean meal in dairy cow diets without adverse effect on milk production and milk composition, given free access to good-quality grass silage.

Understanding metabolic phenomena accompanying high levels of yeast in broiler chicken diets and resulting carcass weight and meat quality changes

The use of yeast as a protein source was investigated in broiler chicken diets on carcass quality, storage stability, and metabolite changes in leg meat. Male Ross 308 chickens (n = 100) were fed with one of 5 diets: control, control added 0.6% formic acid, or 3 diets where soybean meal was substituted with 10, 20, and 30% crude protein from inactivated yeast Cyberlindnera jadinii (CJ10, CJ20, CJ30, respectively). The yeast-containing diets reduced carcass weight, linoleic acid, and warm-over flavor in chicken leg meat. Protein degradation-related metabolite biomarkers were upregulated in the leg of chickens that were fed yeast-containing diets, indicating an adaptive response to the loss of appetite. Chill-stored leg meat of birds fed yeast diets showed increased browning and metallic taste compared with those fed the control diet. The use of formic acid in the diet reduced cooking loss and had a positive effect on vitamin B content.

Antimicrobial and prebiotic activity of mannoproteins isolated from conventional and nonconventional yeast species-the study on selected microorganisms

Yeast mannoproteins are proposed as a paraprobiotics with antimicrobial and prebiotic properties. They can be used as biopreservatives in food and in diseases therapies. The knowledge about the specificity and/or capability of their influence on the growth of different microorganism is limited. The study determined the effect of mannoprotein preparations of Saccharomyces cerevisiae (S. cerevisiae) ATCC 7090 and nonconventional yeast origin [Metschnikowia reukaufii (M. reukaufii) WLP 4650 and Wickerhamomyces anomalus (W. anomalus) CCY 38-1-13] on the growth of selected bacteria of the genera: Lactobacilllus, Limosilatobacillus, Limosilatobacillus, Bifidobacterium, Staphylococcus, Enterococcus, Pseudomonas, Escherichia, Proteus and Salmonella. The degree of stimulation or growth inhibition of tested bacteria depended on the type and dose of the mannoprotein and the bacterial strain. The addition of the tested preparations in the entire range of applied concentrations had a positive effect especially on the growth of Lactobacillus arabinosus ATCC 8014 and Bifidobacterium animalis subsp. lactis B12. Mannoproteins isolated from S. cerevisiae limited the growth of the Escherichia coli (E. coli) ATCC 25922, Pseudomonas aureoginosa (P. aureoginosa) ATCC 27853, Proteus mirabilis ATCC 35659 and Salmonella Enteritidis ATCC 13076 to the greatest extent, while preparations of M. reukaufii and W. anomalus origin most effectively limited the growth of Staphylococcus aureus strains, E. coli and P. aureoginosa. The growth of Enterococcus faecalis was stimulated by the presence of all studied preparations in most of the concentrations used. Further research will determine how the purification process of studied mannoproteins or oligosaccharide fractions, its structure and composition influence on the growth of selected bacteria and what is the mechanism of its activity.

Bioprocesses with Reduced Ecological Footprint by Marine Debaryomyces hansenii Strain for Potential Applications in Circular Economy

The possibility to perform bioprocesses with reduced ecological footprint to produce natural compounds and catalyzers of industrial interest is pushing the research for salt tolerant microorganisms able to grow on seawater-based media and able to use a wide range of nutrients coming from waste. In this study we focused our attention on a Debaryomyces hansenii marine strain (Mo40). We optimized cultivation in a bioreactor at low pH on seawater-based media containing a mixture of sugars (glucose and xylose) and urea. Under these conditions the strain exhibited high growth rate and biomass yield. In addition, we characterized potential applications of this yeast biomass in food/feed industry. We show that Mo40 can produce a biomass containing 45% proteins and 20% lipids. This strain is also able to degrade phytic acid by a cell-bound phytase activity. These features represent an appealing starting point for obtaining D. hansenii biomass in a cheap and environmentally friendly way, and for potential use as an additive or to replace unsustainable ingredients in the feed or food industries, as this species is included in the QPS EFSA list (Quality Presumption as Safe-European Food Safety Authority).

Bioconversion of Apple Pomace into Microbial Protein Feed Based on Extrusion Pretreatment

Apple pomace (AP) is often used directly as animal feed, while the value of feeding is limited by its low protein content. In this study, extrusion pretreatment was performed for AP, and further fermentation was carried out to improve its nutrition value. Strains suitable for extruded apple pomace (EAP) to produce high-quality microbial protein (MP) feed were screened from 12 different strains. Results showed that Aspergillus niger 3.324 (Asn), Candida utilis1314 (Cau), Geotrichum candidum 1315 (Gec), Bacillus subtilis A308 (Bas1), and Lactic acid bacteria (Lac) were screened as the dominant strains, which exhibited higher feeding value. Strong symbiotic effect was observed in fermentation with mixed strains of Asn, Cau, Gec, and Lac at the ratio of 1:1:1:1. Compared with AP, the pure protein content in the optimized fermented EAP (FEAP) was increased by 138% accompanying with a pleasant flavor and taste. And its pure protein content was increased by 19.20% in comparison to that of the fermented apple pomace. The nutrition value of FEAP was characterized by amino acid profiles; it found that FEAP was comparable to other commercial proteins with higher contents of histidine, phenylalanine, threonine, and valine. Combination of fermentation and extrusion technology significantly enhanced pure protein content and nutritional composition of apple pomace, which was revalorized as a nutritive animal feed rich in microbial protein.

Effects of Multi-Bacteria Solid-State Fermented Diets with Different Crude Fiber Levels on Growth Performance, Nutrient Digestibility, and Microbial Flora of Finishing Pigs

Simple Summary

Dietary cellulase was found to be an important nutrient, and solid-state fermentation could improve the nutritional value of feed. To study the effects of multi-bacteria solid-state fermented diets and dietary crude fiber levels on finishing pigs, a total of 36 pigs were divided into four treatments: (1) pigs fed a basal diet containing 7.00% CF (HF), (2) pigs fed a basal multi-bacteria fermentation diet containing 7.00% CF (HFM), (3) pigs fed a basal diet containing 2.52% CF (LF), and (4) piglets fed a basal multi-bacteria fermentation diet containing 2.52% CF (LFM). The growth performance, nutrient digestibility and digestion amount, serum biochemical index, and fecal microflora were evaluated. Multi-bacteria solid-state fermentation had a positive effect on the nutrient digestion and serum biochemical indicators, which was contrary to high-fiber diets. Both high-fiber diets and multi-bacteria solid-state fermentation could optimize intestinal flora in finishing pigs.

Abstract

This study aimed to investigate the effects of multi-bacteria solid-state fermented diets with different crude fiber (CF) levels on growth performance, nutrient digestibility, and microbial flora of finishing pigs. The multi-bacteria solid-state fermented diets were made up of Lactobacillus amylovorus, Enterococcus faecalis, Bacillus subtilis, and Candida utilis. According to a 2 (factors) × 2 (levels) design, with the two factors being multi-bacteria solid-state fermentation (fed non-fermented diet or multi-bacteria fermentation) or CF levels (fed a basal diet containing 2.52% CF or 7.00% CF), a total of 36 finishing pigs (70.80 ± 5.75 kg) were divided into 4 treatments with 9 barrows per group: (1) pigs fed a diet containing 7.00% CF (HF), (2) pigs fed a multi-bacteria fermentation diet containing 7.00% CF (HFM), (3) pigs fed a diet containing 2.52% CF (LF), and (4) piglets fed a multi-bacteria fermentation diet containing 2.52% CF (LFM). This experiment lasted 28 days. The multi-bacteria solid-state fermented diet increased the backfat thickness (p < 0.05) and apparent total tract nutrient digestibility (ATTD) of CF, neutral detergent fiber (NDF), acid detergent fiber (ADF), crude protein (CP), 8 amino acids (Trp, Asp, Gly, Cys, Val, Met, Ile, and Leu), total essential amino acids (EAA), total non-essential amino acids (NEEA), and total amino acids (TAA) (p < 0.05). Multi-bacteria solid-state fermented diet increased serum concentrations of HDL-c, ABL, TP, and GLU, the serum enzyme activities of GSH-Px, T-AOC, SOD, and CAT (p < 0.05), the relative abundance of Lactobacillus, Oscillospira, and Coprococcus (p < 0.05), and the abundance of YAMINSYN3-PWY, PWY-7013, GOLPDLCAT-PWY, ARGORNPROST-PWY, and PWY-5022 pathways (p < 0.05). The multi-bacteria solid-state fermented diet reduced the digestion amount of CF, NDF, and ADF (p < 0.05), the serum concentrations of TC, TG, LDL-c, BUN, and MDA (p < 0.05), the relative abundance of Streptococcaceae (p < 0.05), and the abundance of PWY-6470, PWY0-862, HSERMETANA-PWY, LACTOSECAT-PWY, MET-SAM-PWY, PWY-6700, PWY-5347, PWY0-1061, and LACTOSECAT-PWY pathways (p < 0.05). The high-fiber diet increased average daily feed intake (p < 0.05), the serum concentrations of TC, TG, LDL-c, BUN, and MDA (p < 0.05), the relative abundance of Clostridiaceae_Clostridium and Coprococcus (p < 0.05), and the abundance of TCA-GLYOX-BYPASS, GLYCOLYSIS-TCA-GLYOX-BYPASS, and PWY-6906 pathways (p < 0.05). The high-fiber diet reduced chest circumference (p < 0.05) and ATTD of ether extract (EE), CF, NDF, ADF, Ca, CP, 18 amino acids (Trp, Thr, Val, Met, Ile, Leu, Phe, Lys, His, Arg Asp, Ser, Glu, Gly, Ala, Cys, Tyr, and Pro), EAA, NEAA, and TAA (p < 0.05). The high-fiber diet also reduced the serum concentrations of HDL-c, TP, ABL, and GLU, the serum enzyme activities of T-AOC, GSH-Px, SOD, and CAT (p < 0.05), and the relative abundance of Akkermansia and Oscillospira (p < 0.05). There was no significant effect of the interaction between multi-bacteria fermentation and dietary CF levels, except on the digestion amount of CF (p < 0.05). The 7.00% CF had a negative effect on the digestion of nutrients, but multi-bacteria solid-state fermentation diets could relieve this negative effect and increase backfat thickness. High-fiber diets and multi-bacteria solid-state fermentation improved the diversity and abundance of fecal microorganisms in finishing pigs.

The Spleen as a Target to Characterize Immunomodulatory Effects of Down-Stream Processed Cyberlindnera jadinii Yeasts in Atlantic Salmon Exposed to a Dietary Soybean Meal Challenge

Aquaculture feeds have changed dramatically from being largely based on fishmeal (FM) towards increased use of plant protein sources, which could impact the fish's immune response. In order to characterize immunomodulatory properties of novel functional ingredients, this study used four diets, one based on FM, a challenging diet with 40% soybean meal (SBM), and two diets containing 40% SBM with 5% of Cyberlindnera jadinii yeast exposed to different down-stream processing conditions: heat-inactivated (ICJ) or autolysation (ACJ). The immunomodulatory effects of the diets were analyzed in the spleen of Atlantic salmon after 37 days of feeding, using a transcriptomic evaluation by RNA sequencing (RNA-seq) and the detection of specific immunological markers at the protein level through indirect Enzyme-linked Immunosorbent Assay (indirect ELISA). The results showed that SBM (compared to FM) induced a down-regulation of pathways related to ion binding and transport, along with an increase at the protein level of pro-inflammatory cytokines such as tumor necrosis factor alpha (TNFα) and interferon gamma (IFNγ). On the other hand, while ICJ (compared to FM-group) maintain the inflammatory response associated with SBM, with higher levels of TNFα and IFNγ, and with an upregulation of creatine kinase activity and phosphagen metabolic process, the inclusion of ACJ was able to modulate the response of Atlantic salmon compared to fish fed the SBM-diet by the activation of biological pathways related to endocytosis, Pattern recognition receptor (PPRs)-signal transduction and transporter activity. In addition, ACJ was also able to control the pro-inflammatory profile of SBM, increasing Interleukin 10 (IL-10) levels and decreasing TNFα production, triggering an immune response similar to that of fish fed an FM-based diet. Finally, we suggest that the spleen is a good candidate to characterize the immunomodulatory effects of functional ingredients in Atlantic salmon. Moreover, the inclusion of ACJ in fish diets, with the ability to control inflammatory processes, could be considered in the formulation of sustainable salmon feed.

Fecal Excretion and Whole-Body Retention of Macro and Micro Minerals in Atlantic Salmon Fed Torula Yeast Grown on Sugar Kelp Hydrolysate

Yeast is a microbial feed ingredient that can be produced from non-food biomasses. Brown seaweed contains high levels of complex carbohydrates that are not digested to any extent by monogastric animals but can be used as carbon sources for yeast production. The objective of this study was to investigate how minerals originating from brown macroalgae (Saccharina latissima) are incorporated in Cyberlindnera jadinii yeast and to assess the bioavailability of these different minerals as well as their accumulation into different organs of Atlantic salmon. The yeast C. jadinii was produced on a seaweed hydrolysate mixed with a sugar-rich wood hydrolysate in a 9:1 volume ratio and fed to Atlantic salmon (Salmo salar) in two different experiments: a digestibility experiment with 30% dietary inclusion of yeast and a retention experiment with increasing inclusion of yeast (5, 10, and 20%). Seaweed minerals such as zinc (Zn), copper (Cu), iodine (I), manganese (Mn), and cobalt (Co) were incorporated to a high degree in the yeast. The apparent fecal excretion of minerals was similar in both experiments, in general, with low excretion of, I, bromine (Br), and arsenic (As) (ranging from 18.0% to 63.5%) and high excretion of iron (Fe), Cu, Mn, aluminum (Al), cadmium (Cd) and lead (Pb) (ranging from 56.9% to <100%), despite the different fish size and fecal sampling method. High levels of Cu, I, Br, and Co in the yeast resulted in a linear decrease (p < 0.05) in retention of these minerals in salmon fed increasing levels of yeast. Despite increasing amounts of these minerals in the feed, whole-body levels of Cu and Mn remained stable, whereas whole-body levels of Co, somewhat unexpectedly, decreased with increased dietary yeast inclusion. The Cd from the yeast had low bioavailability but was concentrated more in the kidney (0.038 mg kg^-1) and liver (0.025 mg kg^-1) than in muscle (0.0009 mg kg^-1). The given Cd level in fish strengthens the indication that it is safe to feed salmon with up to 20% inclusion of seaweed yeast without exceeding the maximum limit for Cd of 0.05 mg kg^-1 w.w. in fish meat. The level and retention (p < 0.05) of As were lower in the yeast compared to fishmeal. The high level of iodine in S. latissima (3900 mg kg^-1) was partly transferred to the yeast, and salmon fed increasing levels of yeast displayed a linear increase in whole-body I content (p < 0.05). There is, however, a need for a growth experiment with larger fish to draw any firm conclusions regarding food safety. Overall, this study shows that yeast grown on hydrolyzed seaweed can be a suitable mineral source for Atlantic salmon, especially when diets are low in fishmeal.

Sustainable plant-based diets promote rainbow trout gut microbiota richness and do not alter resistance to bacterial infection

Background

Farmed fish food with reduced fish-derived products are gaining growing interest due to the ecological impact of fish-derived protein utilization and the necessity to increase aquaculture sustainability. Although different terrestrial plant proteins could replace fishmeal proteins, their use is associated with adverse effects. Here, we investigated how diets composed of terrestrial vegetal sources supplemented with proteins originating from insect, yeast or terrestrial animal by-products affect rainbow trout (Onchorynchus mykiss) gut microbiota composition, growth performance and resistance to bacterial infection by the fish pathogen Flavobacterium psychrophilum responsible for frequent outbreaks in aquaculture settings.

Results

We showed that the tested regimes significantly increased gut bacterial richness compared to full vegetal or commercial-like diets, and that vegetal diet supplemented with insect and yeast proteins improves growth performance compared to full vegetal diet without altering rainbow trout susceptibility to F. psychrophilum infection.

Conclusion

Our results demonstrate that the use of insect and yeast protein complements to vegetal fish feeds maintain microbiota functions, growth performance and fish health, therefore identifying promising alternative diets to improve aquaculture’s sustainability.

Supplementary Information

The online version contains supplementary material available at 10.1186/s42523-021-00107-2.