Bacterial diversity of stingless bee honey in Yunnan, China: isolation and genome sequencing of a novel acid-resistant Lactobacillus pentosus (SYBC-MI) with probiotic and L. tryptophan producing potential via millet fermentation.

Stingless bee (Hymenoptera, Apidae, and Trigona) honey is a remarkable "miracle liquid" with a wide range of medical benefits for conditions including gastroenteritis, cataracts, and wound healing. Our study aimed to isolate, identify, and characterize acid-resistant Lactobacillus spp. from sour honey distributed in Yunnan, China. To assess the safety of an entirely novel Lactobacillus pentosus strain, S4 (OM618128), based on probiotic property evaluation and whole-genome sequencing analysis. A 16S rRNA gene high-throughput sequencing analysis showed that Lactobacillus was abundant at the genus level in sour honey. Seven Lactobacillus strains (viz. S1-7) were isolated from sour honey using a multiple-anaerobic culture enrichment method. One potential acid-resistant isolate, Lactobacillus sp. S4, was obtained after screening the seven Lactobacillus isolates, and it had the highest lactic acid production (17.62 g/L), followed by Lactobacillus sp. S3 (17.07 g/L). Phylogenetic and comparative analyses of conserved sequence regions have shown that all seven strains are phylogenetically located in the Lactobacillus pentosus sub-cluster. In L. pentosus SYBC-MI, there is a circular chromosome (3288615 bps) and 11,466 bps plasmids. GC content is 44.03%. The number of predicted genes is 3,129, with 16 rRNAs and 74 tRNAs present. During the fermentation of foxtail millet by seven Lactobacillus pentosus (S1-7) strains isolated from sour honey, a potential tryptophan accumulating isolate, Lactobacillus pentosus S4, was obtained, which could reach a maximum tryptophan content of 238.43 mgL-1 that is 1.80 times the initial tryptophan content in the fermentation broth. This strain has strong acid tolerance, salt tolerance, and fermentation acid production abilities. This strain degrades nitrite at a rate of over 99%, and it has high probiotic potential as well. This project has established a solid foundation for further exploring the excellent lactic acid bacteria in sour honey. It is also investigating the key taxa and their role in the environment. According to the results of our studies, these LAB isolates provide a lot of potential for use in the future, as a source of probiotics for human, animals, and starter cultures for food applications.

Bacterial metabolic engineering for the production of second-generation (2 G) bioethanol and biobutanol; a review.

The second generation (2 G) biofuels were introduced to solve the issues associated with first-generation biofuel (dependency on food materials) and fossil fuels, such as reservoirs diminution, high demand, price fluctuation, and lethal greenhouse gases emission. Butanol and ethanol are the main 2 G biofuels. They are used as a disinfectant, antiseptic, and chemical solvent in the pharmaceutical, plastic, textiles, cosmetics, and fuel industries. Currently, their bacterial biological production from lignocellulosic material at the industrial level with primitive microorganisms is under development and not economical and qualitative compatible as compared to that of fossil origin, due to the slow growth rate, low titer, recalcitrant nature of lignocellulose, strain intolerance to a higher amount of butanol and ethanol, and strain inability to tolerate inhibitors accumulated during pretreatment of lignocellulosic materials. Therefore, metabolic engineering strategies such as redirection of carbon flux, knocking out competing pathways, enhancing strain robustness and wide range of substrate utilization ability, and overexpression of enzymes involved in their biological synthesis have been applied to bacteria for enhancing their ability for 2 G ethanol and butanol production in a highly cost-effective amount from lignocellulosic materials. Herein, we summarized and reviewed the progress in metabolic engineering of bacterial species such as Clostridium spp,Escherichia coli, and Zymomonas mobilis for the synthesis of 2 G butanol and ethanol, especially from lignocellulosic materials.

A Review on Recent Advancement in Expression Strategies Used in Bacillus subtilis.

Bacillus subtilis is a Gram-positive bacterium that has gained an unprecedented reputation as an expression system at the industrial scale due to characteristics, such as GRAS (Generally recognized as safe), ease of genetic manipulation, high growth rate on the cheap substrate, and short fermentation cycle. This expression system has been widely accepted for the production of various chemicals, pharmaceutical products, food products, proteins, and enzymes. However, there are various hurdles to optimizing the production of heterologous protein in this expression system due to a lack of understanding regarding metabolic pathways and expression elements. In this review, we have emphasized strategies that can enhance the expression level of heterologous proteins in B. subtilis. These strategies include optimization of B. Subtilis strain, expression elements, such as promotors, UTR (Untranslated region), RBS (Ribosome binding site), signal peptide, and metabolic pathways. Finally, contemporary challenges and future perspectives of B. subtilis as an industrial-scale expression system are discussed.

Nanoencapsulation of Mandarin Essential Oil: Fabrication, Characterization, and Storage Stability.

This study evaluates the combined efficiency of whey protein isolate (WPI) with maltodextrin (MD) and gum arabic (GA), as a delivery system for encapsulating Citrus reticulata essential oil (CEO). The wall materials blended at different rates were produced to obtain seven formulations of nanocapsules (NCEO), namely NCEO-GA, NCEO-MD, NCEO-WPI, NCEO-GA/MD, NCEO-GA/WPI, NCEO-MD/WPI, and NCEO-GA/MD/WPI. The interaction between CEO and WPI was simulated by molecular docking. Findings showed that the physicochemical characteristics and storage stability of formulations containing WPI were considerably improved. The NCEO-GA/MD/WPI formulation demonstrated the optimum values of encapsulation efficiency (92.08%), highest glass transition temperature (79.11 °C), high crystallinity (45.58%), high thermal stability (mass loss at 100 °C < 5%), and also had the highest antioxidant activity and lowest peroxide value after storage. This study demonstrated that combining WPI with MD and GA, as wall material encapsulation, can produce nanocapsules with superior properties to those created using polysaccharides individually.