Effects of hydrolyzed fish protein and autolyzed yeast as substitutes of fishmeal in the gilthead sea bream (Sparus aurata) diet, on fish intestinal microbiome.

BACKGROUND: This study evaluated the effects of partial substitution of dietary fishmeal (FM) with either fish protein hydrolysate (FPH) or autolysed dried yeast (HiCell®, Biorigin, Brazil) on intestinal microbiota of gilthead sea bream (Sparus aurata). A total number of 720 fish of 122.18 ± 6.22 g were fed for 92 days with three different diets in triplicate (3 tanks/diet). A diet based on FM/vegetable meal was used as control. The other two diets were formulated by replacing FM with 5% of either FPH or HiCell®. To analyze the gut microbiota associated to autochthonous and allochthonous microbial communities, the Illumina MiSeq platform for sequencing of 16S rRNA gene and QIIME pipeline were used. RESULTS: A total number of 102 OTUs (operational taxonomic units) at 97% identity were identified in fish gut samples collected at the end of feeding trial. Fourteen OTUs constituted the core gut microbiota, i.e. those OTUs found in at least nine out of fifteen samples per group and shared regardless of the diet. Eight OTUs were assigned to Firmicutes represented by Lactobacillus, Staphylococcus, and Bacillus genera, and six to Proteobacteria phylum. Dietary dried yeast autolysate modulated the intestinal microbiota by promoting the growth of some beneficial bacteria. At order level, fish fed yeast showed an enrichment in Bacillales and Clostridiales as compared to the control group, whereas fish fed FPH showed a significantly lower amount of bacteria belonging to Alteromonadales and Enterobacteriales than the other two feeding groups. Although we did not observe any effect of 5% FM replacement with alternative nitrogen sources at phylum level, at lower taxonomical levels, the composition of gut microbiota, in terms of relative abundance of specific taxa, was significantly influenced by the dietary treatment. CONCLUSIONS: The metabarcoding analysis revealed a clearly intestinal microbiota modulation in response to dietary autolyzed yeast. The abundance of some beneficial bacteria, i.e. indigestible carbohydrate degrading- and SCFA producing bacteria, was positively affected. Autolysed dried yeast obtained by the fermentation of a strain of Saccharomyces cerevisiae could be a valid alternative protein source to FM as well as a valid functional ingredient for aquafeed production [corrected].

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.

Microbial chitinases and their relevance in various industries.

Chitin, the second most abundant biopolymer on earth after cellulose, is composed of ß-1,4-N-acetylglucosamine (GlcNAc) units. It is widely distributed in nature, especially as a structural polysaccharide in the cell walls of fungi, the exoskeletons of crustaceans, insects, and nematodes. However, the principal commercial source of chitin is the shells of marine or freshwater invertebrates. Microbial chitinases are largely responsible for chitin breakdown in nature, and they play an important role in the ecosystem's carbon and nitrogen balance. Several microbial chitinases have been characterized and are gaining prominence for their applications in various sectors. The current review focuses on chitinases of microbial origin, their diversity, and their characteristics. The applications of chitinases in several industries such as agriculture, food, the environment, and pharmaceutical sectors are also highlighted.

Single Cell Proteins production from food processing effluents and digestate.

The increase in human population determines a higher proteins request to sustain the feed demand for animals and aquaculture. Single Cell Proteins (SCPs) consist of mixed protein from pure and mixed culture of bacteria, fungi, algae, and yeast, which are grown and harvested to accomplish the food requirement of human and animals. This work investigated the production of Saccharomyces cerevisiae to be used as SCPs for animal feeding. The effluent of candies production process, rich in sugars, about 40 g/L, and agricultural digestate rich in nitrogen and other macro and micronutrients, were used for the yeast's growth. Preliminary batch tests demonstrated that aerobic conditions optimized the biomass growth. Then, continuous aerobic tests were conducted at different dilution rates. The dilution rate of 0.50 d-1, corresponding to a hydraulic retention time of 2 days, optimized both the biomass productivity of 0.25 g/L per day and the protein content of 28% w/w. The analysis of the aminoacidic profile demonstrated that obtained SCPs could be used as an integrator of feed for fish and monogastric animals. On the contrary, they were not suitable for pet feed as all the amino acids concentrations were lower than required standards. These results suggested that anaerobic digesters in the agricultural sector can be transformed into small biorefineries for microbial protein production.

Synthetic biology-driven customization of functional feed resources.

To constantly supply functional feed resources (FFRs) toward meeting the rapidly growing meat demand, an efficient process alternative to traditional farming is required. Fermentation of synthetic microorganisms serves as an emerging solution, necessitating the coordination of (i) microorganism customization, (ii) product processing, and (iii) effect evaluation using animal experiments.

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.

Protein Sources Alternative to Meat: State of the Art and Involvement of Fermentation.

Meat represents an important protein source, even in developing countries, but its production is scarcely sustainable, and its excessive consumption poses health issues. An increasing number of Western consumers would replace, at least partially, meat with alternative protein sources. This review aims at: (i) depicting nutritional, functional, sensory traits, and critical issues of single-cell proteins (SCP), filamentous fungi, microalgae, vegetables (alone or mixed with milk), and insects and (ii) displaying how fermentation could improve their quality, to facilitate their use as food items/ingredients/supplements. Production of SCP (yeasts, filamentous fungi, microalgae) does not need arable land and potable water and can run continuously, also using wastes and byproducts. Some filamentous fungi are also consumed as edible mushrooms, and others are involved in the fermentation of traditional vegetable-based foods. Cereals, pseudocereals, and legumes may be combined to offer an almost complete amino acid profile. Fermentation of such vegetables, even in combination with milk-based products (e.g., tarhana), could increase nutrient concentrations, including essential amino acids, and improve sensory traits. Different insects could be used, as such or, to increase their acceptability, as ingredient of foods (e.g., pasta). However, insects as a protein source face with safety concerns, cultural constraints, and a lack of international regulatory framework.

An overview of anoxygenic phototrophic bacteria and their applications in environmental biotechnology for sustainable Resource recovery.

Anoxygenic phototrophic bacteria (APB) are a phylogenetically diverse group of organisms that can harness solar energy for their growth and metabolism. These bacteria vary broadly in terms of their metabolism as well as the composition of their photosynthetic apparatus. Unlike oxygenic phototrophic bacteria such as algae and cyanobacteria, APB can use both organic and inorganic electron donors for light-dependent fixation of carbon dioxide without generating oxygen. Their versatile metabolism, ability to adapt in extreme conditions, low maintenance cost and high biomass yield make APB ideal for wastewater treatment, resource recovery and in the production of high value substances. This review highlights the advantages of APB over algae and cyanobacteria, and their applications in photo-bioelectrochemical systems, production of poly-ß-hydroxyalkanoates, single-cell protein, biofertilizers and pigments. The ecology of ABP, their distinguishing factors, various physiochemical parameters governing the production of high-value substances and future directions of APB utilization are also discussed.