Current approaches on the roles of lactic acid bacteria in crop silage

Effects of selenium enrichment on fermentation characteristics, selenium content and microbial community of alfalfa silage

BACKGROUND

Selenium is essential for livestock and human health. The traditional way of adding selenium to livestock diets has limitations, and there is a growing trend to provide livestock with a safe and efficient source of selenium through selenium-enriched pasture. Therefore, this study was conducted to investigate the effects of selenium enrichment on fermentation characteristics, selenium content, selenium morphology, microbial community and in vitro digestion of silage alfalfa by using unenriched (CK) and selenium-enriched (Se) alfalfa as raw material for silage.

RESULTS

In this study, selenium enrichment significantly increased crude protein, soluble carbohydrate, total selenium, and organic selenium contents of alfalfa silage fresh and post-silage samples, and it significantly decreased neutral detergent fiber and acid detergent fiber contents (p < 0.05). Selenium enrichment altered the form of selenium in plants, mainly in the form of SeMet and SeMeCys, which were significantly higher than that of CK (p < 0.05). Selenium enrichment could significantly increase the lactic acid content, reduce the pH value, change the diversity of bacterial community, promote the growth of beneficial bacteria such as Lactiplantibacillus and inhibit the growth of harmful bacteria such as Pantoea, so as to improve the fermentation quality of silage. The in vitro digestibility of dry matter (IVDMD), in vitro digestibility of acid detergent fibers (IVADFD) and in vitro digestibility of acid detergent fibers (IVNDFD) of silage after selenium enrichment were significantly higher than those of CK (p < 0.05).

CONCLUSION

This study showed that the presence of selenium could regulate the structure of the alfalfa silage bacterial community and improve alfalfa silage fermentation quality. Selenium enrichment measures can change the morphology of selenium in alfalfa silage products, thus promoting the conversion of organic selenium.

Utilisation of Lactiplantibacillus plantarum and propionic acid to improve silage quality of amaranth before and after wilting: fermentation quality, microbial communities, and their metabolic pathway

Objective

The aim of this study was to investigate the effects of Lactiplantibacillus plantarum (L. plantarum) and propionic acid (PA) on fermentation characteristics and microbial community of amaranth (Amaranthus hypochondriaus) silage with different moisture contents.

Methods

Amaranth was harvested at maturity stage and prepared for ensiling. There were two moisture content gradients (80%: AhG, 70%: AhS; fresh material: FM) and three treatments (control: CK, L. plantarum: LP, propionic acid: PA) set up, and silages were opened after 60 d of ensiling.

Results

The results showed that the addition of L. plantarum and PA increased lactic acid (LA) content and decreased pH of amaranth after fermentation. In particular, the addition of PA significantly increased crude protein content (p < 0.05). LA content was higher in wilted silage than in high-moisture silage, and it was higher with the addition of L. plantarum and PA (p < 0.05). The dominant species of AhGLP, AhSCK, AhSLP and AhSPA were mainly L. plantarum, Lentilactobacillus buchneri and Levilactobacillus brevis. The dominant species in AhGCK include Enterobacter cloacae, and Xanthomonas oryzae was dominated in AhGPA, which affected fermentation quality. L. plantarum and PA acted synergistically after ensiling to accelerate the succession of dominant species from gram-negative to gram-positive bacteria, forming a symbiotic microbial network centred on lactic acid bacteria. Both wilting and additive silage preparation methods increased the degree of dominance of global and overview maps and carbohydrate metabolism, and decreased the degree of dominance of amino acid metabolism categories.

Conclusion

In conclusion, the addition of L. plantarum to silage can effectively improve the fermentation characteristics of amaranth, increase the diversity of bacterial communities, and regulate the microbial community and its functional metabolic pathways to achieve the desired fermentation effect.

Multiple strategies to improve extracellular secretion and activity of feruloyl esterase

Feruloyl esterase has a wide range of applications, but there are still problems with low enzyme yield and activity, and complex purification steps. Our previous research found Lactobacillus amylovorus feruloyl esterase could be secreted extracellular in Escherichia coli. In this study, multiple strategies were implemented to maximize the extracellular production of feruloyl esterase with improved activity in E. coli. Firstly, codon-optimized feruloyl esterase was obtained based on the preference of E. coli, resulting in 41.97 % increase in extracellular secretion. Furthermore, by cascading T7 promoters, replacing the 5' UTR, randomly mutating the N-terminal sequence, and co-expressing secretory cofactors, the extracellular secretion was increased by 36.46 %, 31.25 %, 20.66 % and 25.75 %, respectively. Moreover, the feruloyl esterase were mutated to improve the substrate affinity and activity. The catalytic efficiency of Fae-Q134T and Fae-Q198A increased by 4.62-fold and 5.42-fold. Combining above strategies, extracellular feruloyl esterase activity was increased from 2013.70 U/L to 10,349.04 U/L. These results indicated that the activity and yield of feruloyl esterase secreted by E. coli were significantly increased, which laid a foundation for its industrial application.

Sustainable utilization of residual grass: effect of anaerobic storage days on chemical composition, fermentation performance, microbial community, and functional profiles of Pennisetum giganteum

The seasonal surplus and putrefactive property of moist forages inevitably increase the pressure on environmental protection and residual grass disposal. In the current work, the anaerobic fermentation approach was adopted to assist the sustainable recycling of leftover Pennisetum giganteum (LP), and its chemical composition, fermentation performance, bacterial community and functional profiles during anaerobic fermentation were studied. Fresh LP was spontaneously fermented for up to 60 d. At the end of anaerobic fermentation, fermented LP (FLP) displayed homolactic fermentation with low pH value, ethanol, and ammonia nitrogen concentrations but high lactic acid concentration. Weissella was dominant in 3-day FLP, yet Lactobacillus was the overwhelming genus (92.6%) in 60-day FLP. The anaerobic fermentation process promoted (P < 0.05) the metabolism of carbohydrate and nucleotide while suppressing (P < 0.05) that of lipid, cofactors, vitamins, energy, and amino acid. The results showed that the residual grass with LP as an example could be successfully fermented even if no additives were added, without signs of clostridial and fungal contamination.

Role of Lactic Acid Bacteria in Insecticide Residue Degradation

Lactic acid bacteria are gaining global attention, especially due to their role as a probiotic. They are increasingly being used as a flavoring agent and food preservative. Besides their role in food processing, lactic acid bacteria also have a significant role in degrading insecticide residues in the environment. This review paper highlights the importance of lactic acid bacteria in degrading insecticide residues of various types, such as organochlorines, organophosphorus, synthetic pyrethroids, neonicotinoids, and diamides. The paper discusses the mechanisms employed by lactic acid bacteria to degrade these insecticides, as well as their potential applications in bioremediation. The key enzymes produced by lactic acid bacteria, such as phosphatase and esterase, play a vital role in breaking down insecticide molecules. Furthermore, the paper discusses the challenges and future directions in this field. However, more research is needed to optimize the utilization of lactic acid bacteria in insecticide residue degradation and to develop practical strategies for their implementation in real-world scenarios.

Investigating the efficacy of an exopolysaccharide (EPS)-producing strain Lactiplantibacillus plantarum L75 on oat silage fermentation at different temperatures

This study investigates the effectiveness of an exopolysaccharide (EPS)-producing strain (Lactiplantibacillus plantarum L75) alone or in combination with Saccharomyces cerevisiae on the fermentation characteristics, antioxidant capacities and microbial community successions of oat silage stored at various temperatures. A rapid decrease in pH and lactic acid accumulation was observed in silages treated with L. plantarum and S. cerevisiae (LS) as early as 3 days of ensiling (p < 0.05). Over the ensiling period of 7-60 days, L. plantarum (L)-inoculated groups showed the lowest pH, lowest ammonia nitrogen and the highest amount of lactic acid regardless of the storage temperatures. When the oat silage was stored at 15°C, LS-inoculated group exhibited a higher superoxide dismutase (SOD) activity than control and L-inoculated group. Furthermore, the proportion of Lactiplantibacillus in the combined inoculation group increased by 65.42% compared to the L-inoculated group (33.26%). Fungal community data revealed abundant Penicillium carneum in the control and L-inoculated groups stored at 15°C. Conclusively, these results showed that combined inoculation of L. plantarum L75 and S. cerevisiae improved the fermentation quality of oat silage at 15°C, thus proposing a technique for enhancing the fermentation quality of silage in regions with low temperatures during harvest season.

How are microbes helping end hunger?

This article explores the potential of microbiology to positively impact all aspects of the food supply chain, improving the quantity, quality, safety, and nutritional value of food products by providing innovative ways of growing, processing, and preserving food and thus contributing to Zero Hunger, one of the Sustainable Development Goals (SDGs) of the United Nations.

Effects of Different Lactic Acid Bacteria in Single or Mixed Form on the Fermentative Parameters and Nutrient Contents of Early Heading Triticale Silage for Livestock

Lactic acid bacteria (LAB) are excellent anaerobic fermenters that produce highly valuable grass-based animal feed containing essential nutrients. In the present study, an ensiling process was used to improve anaerobic fermentation in triticale silage under different moisture conditions with LAB. The triticale was treated with either a single bacterium or combined LAB and then vacuum-sealed. After 180 and 360 days of storage, the silage's fermentation characteristics, microbial changes and nutrient contents were analyzed. The pH of the silage was significantly lower than the control silage. There was a significant difference in the pH values between the silages treated with single or mixed LAB. The LAB treatment led to a substantial increase in lactic acid (LA), a decrease in butyric acid (BA), and marginal levels of acetic acid (AA). The LA content after the mixed LAB treatment was significantly higher than that after the single culture LAB treatment. After single or combined inoculant treatments, the LAB population in the silage increased, while the yeast and mold levels decreased. These findings suggest that the addition of LAB to silage during ensiling could enhance the nutritional quality and reduce unwanted microbial growth. The mixed LAB treatments produced silage with a significantly higher nutritional value than the single LAB treatments.

Microbiota and Nutrient Portraits of European Roe Deer (Capreolus capreolus) Rumen Contents in Characteristic Southern German Habitats

Roe deer (Capreolus capreolus) are found in various habitats, from pure forest cultures to agricultural areas and mountains. In adapting to the geographically and seasonally differentiating food supply, they depend, above all, on an adapted microbiome. However, knowledge about the microbiome of wild ruminants still needs to be improved. There are only a few publications for individual species with a low number of samples. This study aims to identify a core microbiota for Bavarian roe deer and present nutrient and microbiota portraits of the individual habitat types. This study investigated the roe deer's rumen (reticulorumen) content from seven different characteristic Bavarian habitat types. The focus was on the composition of nutrients, fermentation products, and the rumen bacterial community. A total of 311 roe deer samples were analysed, with the most even possible distribution per habitat, season, age class, and gender. Significant differences in nutrient concentrations and microbial composition were identified for the factors habitat, season, and age class. The highest crude protein content (plant protein and microbial) in the rumen was determined in the purely agricultural habitat (AG), the highest value of non-fibre carbohydrates in the alpine mountain forest, and the highest fibre content (neutral detergent fibre, NDF) in the pine forest habitat. Maximum values for fibre content go up to 70% NDF. The proportion of metabolites (ammonia, lactate, total volatile fatty acids) was highest in the Agriculture-Beech-Forest habitat (ABF). Correlations can be identified between adaptations in the microbiota and specific nutrient concentrations, as well as in strong fluctuations in ingested forage. In addition, a core bacterial community comprising five genera could be identified across all habitats, up to 44% of total relative abundance. As with all wild ruminants, many microbial genera remain largely unclassified at various taxonomic levels. This study provides a more in-depth insight into the diversity and complexity of the roe deer rumen microbiota. It highlights the key microorganisms responsible for converting naturally available nutrients of different botanical origins.

Inoculation with Lentilactobacillus buchneri alone or in combination with Lentilactobacillus hilgardii modifies gene expression, fermentation profile, and starch digestibility in high-moisture corn

Inoculants combining Lentilactobacillus buchneri and Lentilactobacillus hilgardii have been shown to improve the aerobic stability of high-moisture corn (HMC) and whole-plant corn silage, but the mode of action of this co-inoculation remains to be elucidated. This study used metatranscriptomics to evaluate the effects of inoculation with L. buchneri alone or combined with L. hilgardii on the bacterial community, gene expression, fermentation profile, and starch digestibility in HMC. High-moisture corn not inoculated (Control) or inoculated with L. buchneri NCIMB 40788 (LB) or L. buchneri NCIMB 40788 combined with L. hilgardii CNCM-I-4785 (Combo) was ensiled in mini silo bags for 30, 60, 120, and 180 days. The fermentation profile was evaluated at all time points. Metatranscriptomics was performed on samples collected on day 120. Combo had a greater alpha diversity richness index of contigs than LB and Control, and inoculation with Combo and LB modified the beta-diversity of contigs compared to Control. Out of 69 genes of interest, 20 were differentially expressed in LB compared to Control and 25 in Combo compared to Control. Of those differently expressed genes, 16 (10 of which were associated with carbohydrate metabolism and six with amino acid metabolism) were differently expressed in both LB and Combo compared to Control, and all those genes were upregulated in the inoculated silages. When we compared Combo and LB, we found seven genes expressed differently, four associated with carbohydrate metabolism and downregulated in Combo, and three associated with amino acid metabolism and upregulated in Combo. At day 120, the inoculated silages had more culturable lactic acid bacteria, higher Lactobacillus relative abundance, and lower Leuconostoc relative abundance than Control. The concentration of acetic acid remained low throughout ensiling in Control, but in LB and Combo, it increased up to day 60 and remained stable from day 60 to 180. The 1,2-propanediol was only detected in LB and Combo. Inoculation did not affect the concentration of starch, but starch digestibility was greater in Combo than in Control. Inoculation of HMC with Combo modified the gene expression and fermentation profile compared to Control and LB, improving starch digestibility compared to uninoculated HMC.

Metagenomic insights into the microbiota involved in lactate and butyrate production and manipulating their synthesis in alfalfa silage

AIMS

Lactate and butyrate are important indicators of silage quality. However, the microorganisms and mechanisms responsible for lactate and butyrate production in silage are not well documented.

METHODS AND RESULTS

whole-metagenomic sequencing was used to analyse metabolic pathways, microbiota composition, functional genes, and their contributions to lactate and butyrate production in alfalfa silage with (SA) and without (CK) sucrose addition. Carbon metabolism was the most abundant metabolic pathway. We identified 11 and 2 functional genes associated with lactate and butyrate metabolism, respectively. Among them, D-lactate dehydrogenase (ldhA) and L-lactate dehydrogenase (ldhB) were most important for the transition between D/L-lactate and pyruvate and were primarily related to Lactobacillus in the SA group. The genes encoding L-lactate dehydrogenase (lldD), which decomposes lactate, were the most abundant and primarily associated with Enterobacter cloacae. Butyrate-related genes, mainly encoding butyryl-CoA: acetate CoA-transferase (but), were predominantly associated with Klebsiella oxytoca and Escherichia coli in the CK group.

CONCLUSIONS

Enterobacteriaceae and Lactobacillaceae were mainly responsible for butyrate and lactate formation, respectively.

Effects of Condensed Tannins on Bacterial and Fungal Communities during Aerobic Exposure of Sainfoin Silage

BACKGROUND

Sainfoin is a forage legume that is widely distributed around the world and is beneficial for animals owing to the characteristics of its condensed tannins (CTs), which, from certain plants, can prolong the aerobic stability of silage.

METHODS

The present study investigated whether sainfoin CTs can prolong aerobic stability by adding polyethylene glycol (PEG) to inactivate CT activity in the silage system.

RESULTS

The results showed that aerobic stability increased under the PEG treatment (p < 0.05). Ammonia nitrogen (0.71 g/kg DM vs. 0.94 g/kg DM; p < 0.05) was higher in the PEG-treated group compared with the control after 3 d of aerobic exposure. BA was detected only in the PEG-treated group upon aerobic exposure. Yeasts were more abundant in the control compared with the PEG-treated group after 7 d of aerobic exposure, after which the relative abundance of Lactobacillus was lower in the PEG-treated group (65.01% vs. 75.01% in the control; p < 0.05), while the relative abundance of Pediococcus was higher in the PEG-treated group compared with the control (10.9% vs. 4.49%, respectively; p < 0.05).The relative abundances of Apiotrichum and Aspergillus were lower in the control than in the PEG-treated group after 7 d of aerobic exposure.

CONCLUSIONS

The results suggested that sainfoin CTs decreased aerobic stability, but could inhibit certain bacteria and fungi, such as Pediococcus and Apiotrichum, and preserve the protein content during the aerobic exposure of silage.

Improving cold-adaptability of mesophilic cellulase complex with a novel mushroom cellobiohydrolase for efficient low-temperature ensiling

Low ambient temperature poses a challenge for rice straw-silage processing in cold climate regions, as cold limits enzyme and microbial activity in silages. Here, a novel cold-active cellobiohydrolase (VvCBHI-I) was isolated from Volvariella volvacea, which exhibited outstanding cellobiohydrolase activity at 10-30 °C. The crude cellulase complex in the VvCBHI-I-expressing transformant T1 retained 50% relative activity at 10 °C, while the wildtype Trichoderma reesei showed <5% of the activity. VvCBHI-I greatly improved the saccharification efficiency of the cellulase complex with pretreated rice straw as substrate at 10 °C. In rice straw silage, pH (<4.5) and lactic acid content (>4.6%) remained stable after 15-day ensiling with the cellulase complex from T1 and Lactobacillus plantarum. Moreover, the proportions of cellulose and hemicellulose decreased to 29.84% ± 0.15% and 21.25% ± 0.26% of the dried material. This demonstrates the crucial potential of mushroom-derived cold-active cellobiohydrolases in successful ensiling in cold regions.