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

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

Understanding the mechanism of interaction of candidate soil stabilizing prototypes by using microscopy and spectroscopy techniques

Globally, there is a high demand for bio-based soil stabilizers required for improving the strength properties of weak in situ soil. Microbes and microbial components such as Bacillus spp. have gained interest as soil stabilizers due to their production of spores, bio-enzymes, and bio-polymers. However, the current approach for any microlevel assessment of bio-additives and in situ soil improvement is limited. This paper provides data for microstructural evaluation of stabilized soil material for the postulation of the mode of action. In this study, the microbonding effect (i.e., bio-based cementation, bio-clogging, and soil particle bio-coating) is successfully observed within the various stabilizing prototypes, obtained from a novel Bacillus spp. using advanced methods, namely field emission gun-scanning electron microscopy and Fourier transform-infrared spectroscopy. The results show that treated soil versus untreated soil properties are altered by the bio-additive/s stabilizing effect. These indicator tests provide data for further bio-stabilizer product prototype development and processes (i.e., improved products in terms of strength and moisture susceptibility). The use of microscopy and spectroscopy was sufficient for the preliminary selection of suitable candidates for soil stabilization.

Establishing miniaturised structural testing techniques to enable high-throughput screening of microorganisms and microbial components for unpaved road stabilisation application

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Development of miniaturised techniques to assess the structural properties of in-situ material.

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Structural criterion includes: abrasion, erosion, water absorption & compression load tests.

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Designed models consistent with industry, on a smaller scale using 3D printing technology.

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Development of methods for high-throughput screening of novel bio-based samples from Bacillus.

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Proof of Concept established on the use of bio-based stabilisers.

Roads are expensive to develop particularly in challenging environmental conditions, and a lack of understanding of the properties of soil can lead to poor design and premature failures contributing to costly maintenance. The construction industry is exploring new opportunities involving biological processes and products to modify the structural properties of the in situ material, in terms of strength, volume stability, durability and permeability. Through an integrative interdisciplinary approach several microorganisms and other existing bio-enzymatic products such as secondary metabolites, enzymes, endospores, and extracellular polymeric substances have been considered as possible alternatives to conventional methods for the development of sustainable road infrastructure. Limitations in the current state of technology to developing bio-based solutions include microorganism selection and the ability to evaluate derivative components in rapid structural tests that enhance the time to development of proper commercial products. This study focused on the testing of fermentation derived components of biological materials in a high-throughput manner, using miniaturised structural tests to validate screening and selection methodology. The methods tested included resistance to abrasion, resistance to erosion, water absorption and resistance to compression load. Unique miniaturised test equipment was successfully developed using computer-aided design (CAD) and 3D printing technologies. Effects were measured to enable the rapid evaluation of a target microorganism and for screening of biological components or fractions. Results obtained using a Bacillus isolate reported in the current study exhibit strength characteristics and can potentially be formulated as a product for soil stabilisation. This work forms the basis for in vitro selection methodology to enhance development of bio-based structural materials for application in the road sector.

Competitive exclusion as a mode of action of a novel Bacillus cereus aquaculture biological agent

AIMS

To determine the contribution of potential modes of action of a Bacillus cereus aquaculture biological control agent in inhibition of the fish pathogen, Aeromonas hydrophila.

METHODS AND RESULTS

When B. cereus was tested in plate well inhibition studies, no production of antimicrobial compounds was detected. Bacillus cereus had a high growth rate (0.96 h(-1)), whereas Aer. hydrophila concentration decreased by c. 70% in co-culture experiments. In nutrient limitation studies, B. cereus had a significantly higher growth rate when cultured under glucose (P < 0.05) and iron (P < 0.01) limitation in comparison with Aer. hydrophila. Bacillus cereus glucose (0.30 g l(-1) h(-1)) and iron (0.60 mg l(-1) h(-1)) uptake rates were also significantly higher (P < 0.01) than the Aer. hydrophila glucose (0.14 g l(-1) h(-1)) and iron (0.43 mg l(-1) h(-1)) uptake rates. Iron uptake was facilitated by siderophore production shown in time profile studies where relative siderophore production was c. 60% through the late exponential and sporulation phases.

CONCLUSIONS

Competitive exclusion by higher growth rate, competition for organic carbon and iron, facilitated by siderophore production, could be identified as mechanisms of pathogen growth inhibition by B. cereus.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study is the first elucidation of the mechanism of action of our novel B. cereus biological agent in growth attenuation of pathogenic Aer. hydrophila. This study enhances the application knowledge and attractiveness for adoption of B. cereus NRRL 100132 for exploitation in aquaculture.

The modular xylanase Xyn10A fromRhodothermus marinusis cell-attached, and its C-terminal domain has several putative homologues among cell-attached proteins within the phylum Bacteroidetes

Until recently, the function of the fifth domain of the thermostable modular xylanase Xyn10A from Rhodothermus marinus was unresolved. A putative homologue to this domain was however identified in a mannanase (Man26A) from the same microorganism which raised questions regarding a common function. An extensive search of all accessible data-bases as well as the partially sequenced genomes of R. marinus and Cytophaga hutchinsonii showed that homologues of this domain were encoded by multiple genes in microorganisms in the phylum Bacteroidetes. Moreover, the domain occurred invariably at the C-termini of proteins that were predominantly extra-cellular/cell attached. A primary structure motif of three conserved regions including structurally important glycines and a proline was also identified suggesting a conserved 3D fold. This bioinformatic evidence suggested a possible role of this domain in mediating cell attachment. To confirm this theory, R. marinus was grown, and activity assays showed that the major part of the xylanase activity was connected to whole cells. Moreover, immunocytochemical detection using a Xyn10A-specific antibody proved presence of Xyn10A on the R. marinus cell surface. In the light of this, a revision of experimental data present on both Xyn10A and Man26A was performed, and the results all indicate a cell-anchoring role of the domain, suggesting that this domain represents a novel type of module that mediates cell attachment in proteins originating from members of the phylum Bacteroidetes.