Enhancement of lignocellulosic degradation in high-moisture alfalfa via anaerobic bioprocess of engineered Lactococcus lactis with the function of secreting cellulase

Adding rumen microorganisms to improve fermentation quality, enzymatic efficiency, and microbial communities of hybrid Pennisetum silage

Hybrid Pennisetum, a top biomass energy source, faces usage limitations because of its scarce lactic acid bacteria and high fiber content. This study assessed the influence of rumen fluid pretreatment on hybrid Pennisetum's silage, with focus on silage duration and rumen fluid effects on quality and fiber decomposition. Advanced third-generation sequencing was used to track microbial diversity changes and revealed that rumen fluid considerably enhanced dry matter, crude protein, and water-soluble carbohydrates, thus improving fermentation quality to satisfactory pH levels (3.40-3.67). Ideal results, including the highest fiber breakdown and enzymatic efficiency (47.23 %), were obtained with 5 % rumen fluid in 60 days. The addition of rumen fluid changed the dominant species, including Paucilactobacillus vaccinostercus (0.00 % vs. 18.21 %) and Lactiplantibacillus plantarum (21.03 % vs. 47.02 %), and no Enterobacter was detected in the high-concentration treatments. Moreover, strong correlations were found between specific lactic acid bacteria and fermentation indicators, revealing the potential of achieving efficient and economically beneficial hybrid Pennisetum production.

Expression of β-Glucosidases from the Yak Rumen in Lactic Acid Bacteria: A Genetic Engineering Approach

β-glucosidase derived from microorganisms has wide industrial applications. In order to generate genetically engineered bacteria with high-efficiency β-glucosidase, in this study two subunits (bglA and bglB) of β-glucosidase obtained from the yak rumen were expressed as independent proteins and fused proteins in lactic acid bacteria (Lactobacillus lactis NZ9000). The engineered strains L. lactis NZ9000/pMG36e-usp45-bglA, L. lactis NZ9000/pMG36e-usp45-bglB, and L. lactis NZ9000/pMG36e-usp45-bglA-usp45-bglB were successfully constructed. These bacteria showed the secretory expression of BglA, BglB, and Bgl, respectively. The molecular weights of BglA, BglB, and Bgl were about 55 kDa, 55 kDa, and 75 kDa, respectively. The enzyme activity of Bgl was significantly higher (p < 0.05) than that of BglA and BglB for substrates such as regenerated amorphous cellulose (RAC), sodium carboxymethyl cellulose (CMC-Na), desiccated cotton, microcrystalline cellulose, filter paper, and 1% salicin. Moreover, 1% salicin appeared to be the most suitable substrate for these three recombinant proteins. The optimum reaction temperatures and pH values for these three recombinant enzymes were 50 °C and 7.0, respectively. In subsequent studies using 1% salicin as the substrate, the enzymatic activities of BglA, BglB, and Bgl were found to be 2.09 U/mL, 2.36 U/mL, and 9.4 U/mL, respectively. The enzyme kinetic parameters (Vmax, Km, Kcat, and Kcat/Km) of the three recombinant strains were analyzed using 1% salicin as the substrate at 50 °C and pH 7.0, respectively. Under conditions of increased K⁺ and Fe²⁺ concentrations, the Bgl enzyme activity was significantly higher (p < 0.05) than the BglA and BglB enzyme activity. However, under conditions of increased Zn²⁺, Hg²⁺, and Tween20 concentrations, the Bgl enzyme activity was significantly lower (p < 0.05) than the BglA and BglB enzyme activity. Overall, the engineered lactic acid bacteria strains generated in this study could efficiently hydrolyze cellulose, laying the foundation for the industrial application of β-glucosidase.

The Effect of Lactiplantibacillus plantarum ZZU203, Cellulase-Producing Bacillus methylotrophicus, and Their Combinations on Alfalfa Silage Quality and Bacterial Community

This study assessed the effects of Lactiplantibacillus plantarum (ZZU203), cellulase-producing Bacillus methylotrophicus (CB), or their combination (ZZU203_CB) on the fermentation parameters of alfalfa after 10 and 60 days of ensiling. Additionally, the bacterial community compositions were analyzed using absolute quantification 16S-seq (AQS). The results showed that CB silage displayed a higher lactic acid (LA) concentration at 10 d, a higher abundance of Lactobacillus, and lower abundance of Pediococcus, Enterococcus, and Weissella than those in the control (CK) silage. Compared with CK silage, the ZZU203 silage increased LA concentration, fructose and rhamnose concentrations, and the abundance of Lactobacillus, and decreased pH value, ammoniacal nitrogen, acetic acid, neutral detergent fiber and acid detergent fiber concentrations, and the abundance of Pediococcus, Enterococcus, Weissella, Hafnia, and Garciella after 60 days of ensiling. In addition, ZZU203 and ZZU203_CB silage had a similar silage quality and bacterial community, while the inoculation of ZZU203_CB significantly promoted LA accumulation and the numbers of Lactobacillus at 10 d compared with ZZU203 silage. Therefore, ZZU203 or a combination of ZZU203 and CB can be used as potential silage additives to improve the silage quality of alfalfa.

Effects of Konjac Flour and Lactiplantibacillus plantarum on Fermentation Quality, Aerobic Stability, and Microbial Community of High-Moisture Forage Rape Silages

To obtain high-quality silage and better understand the mechanism underlying silage fermentation, a study was conducted to investigate the effects of konjac flour (KF), Lactiplantibacillus plantarum (LP) and their combination on fermentation quality, aerobic stability, and microbial community of high-moisture forage rape after 60 days of ensiling. Results showed that the KF and LP treatments increased the lactic acid content, decreased the pH value, and inhibited the production of butyric acid in ensiled forage rape (p < 0.05). The additives also altered the bacterial community of forage rape silages, showing reduced Shannon and Simpson indexes (p < 0.05), while the abundance of desirable Lactobacillus was increased, and the abundance of undesirable bacteria, such as enterobacteria and clostridia, was decreased (p < 0.05). In addition, their combination significantly improved the aerobic stability (96 h vs. 28 h, p < 0.05) and exhibited notable influence on the bacterial community, with the highest abundance of Lactobacillus. These results indicated that KF and LP improved the silage quality of high-moisture forage rape, and their combination displayed a beneficial synergistic effect.

The Effect of Different Lactic Acid Bacteria Inoculants on Silage Quality, Phenolic Acid Profiles, Bacterial Community and In Vitro Rumen Fermentation Characteristic of Whole Corn Silage

Corn silage is an important source of forage, but whether or not bacterial inoculants should be applied is somewhat controversial in ruminant feeding practice. In the present study, chopped whole corn plants treated with a single inoculant of Lactobacillus buchneri (LB), Lactobacillus plantarum (LP), Pediococcus pentosaceus (PP) served as either homofermentation (e.g., lactate only) or heterofermentation (e.g., lactate and acetate) controls and compared with those treated with either a mixture of the lactic acid bacteria (QA: 60% LP, 10%PP, 30% LB) or a mixture of the lactic acid bacteria (QB: 60% LP, 15% PP, 25% LB), to investigate their effects on the fermentation quality, ester-linked phenolic acids, and in vitro digestibility. After 60 day ensiling, the addition of QA exhibited the lowest pH (3.51) with greater lactic acid (LA) production. The ester-linked ferulic acid (FAest) and p-coumaric acid (pCAest) concentrations were significantly decreased during 60 days ensiling. And among all these groups, the LB and QA treated group showed a lower concentration of FAest and pCAest than other groups. After 60 days ensiling, Lactobacillus was the dominant genus in all LAB treated groups. Meanwhile, negative correlations of Bacillus, Bacteroides, Bifidobacterium, Blautia, Prevotella, Ruminococcus, and Roseburia with FAest content after 60 days ensiling occurred in the present study. Komagataeibacter was mainly found in LB and PP addition silages, and presented a significant negative effect with the level of acid detergent fiber (ADF). To explore whether the addition of LABs can improve digestibility of whole corn silage, an in vitro rumen fermentation was conducted using the 60 day ensiled whole corn silages as substrates. The QA addition group exhibited a greater 48 h and 96 h in vitro dry matter and ADF disappearance, greater 48 h gas production and less methane emissions. Even though there were the same neutral NDF levels in corn silages treated with LB and QA after 60 days ensiling, the QA treated silages with lower FAest and pCAest presented higher IVDMD after 96 h and 48 h in vitro fermentation. In brief, the addition of mixed inoculants of 60% LB,10% PP, 30% LB compared with the addition of whichever single HoLAB or HeLAB inoculants, facilitated the release of ester-linked phenolic acids (e.g., ferulic and p-coumaric acids) and remarkably, improved silage quality in terms of sharp pH decline and greater lactate production. Taken together with the improvement in rumen microbial fermentation, the results obtained in the present study provided concrete evidence for the role of mixed LAB application in corn silage preparation for ruminant feeding practices.

Two novel screened microbial consortia and their application in combination with Lactobacillus plantarum for improving fermentation quality of high-moisture alfalfa

AIMS

To enrich lignocellulolytic microbial consortia and evaluate whether a combination of these consortia and Lactobacillus plantarum can facilitate degradation of structural carbohydrates and improve fermentation quality of high-moisture alfalfa silage.

METHODS AND RESULTS

Two novel microbial consortia (CL and YL) with high lignocellulolytic potential were enriched, and had higher enzyme activities at slightly acidic conditions (pH 3.5-6.5). Two consortia were inoculated with and without combined L. plantarum (LP) to alfalfa for up to 120 days of ensiling. The two consortia alone or combined with LP significantly (p < 0.05) increased lactic-to-acetic acid ratios and decreased contents of volatile organic acids and NH₃ -N as compared to the control. Treatments that combining microbial consortia and LP further resulted in the higher contents of lactic acid (LA), water soluble carbohydrates (WSC) and crude protein, dry matter (DM) recovery, and lower neutral detergent fibre, acid detergent lignin and cellulose contents, with YLP silage showing the lowest pH (4.41) and highest LA content (76.72 g kg^-1  DM) and the conversion of WSC into LA (184.03%).

CONCLUSIONS

The addition of lignocellulolytic microbial consortia (CL or YL) to alfalfa silages as attractive silage inoculants could improve fermentation quality, and that their combination with L. plantarum appeared more effective on the degradation of structural carbohydrates and conversion of soluble carbohydrates into LA.

SIGNIFICANCE AND IMPACT OF THE STUDY

High-moisture alfalfa is difficult to ensile due to its high buffering capacity and low readily fermentable carbohydrate contents. Microbial consortia (CL and YL) can encode a broad selection of multi-functional CAZymes, and their combination with LP could be promising for the degradation of structural carbohydrates simultaneously with improvement fermentation quality, with high performance in LA production.

Effect of lactic acid bacteria, molasses, and their combination on the fermentation quality and bacterial community of cassava foliage silage

This study investigated the effects of LAB inoculants (L) and molasses (M) on the microbial community and fermentation quality of cassava foliage (CF). The small segments (about 2-3 cm) CF were ensiled in plastic bags and incubated at normal temperature (25°C). Four treatments were carried out as follows: control (no additives, CK), LAB inoculants (Lactobacillus plantarum, L), molasses (M), and LAB in combination with molasses (LM). The LAB and molasses obviously altered the bacterial community structure of the CF silage and enhanced the fermentation quality. The combination addition could increase the abundance of Lactobacillus and reduce the Pseudomonas. The LAB and molasses also significantly elevated the lactic acid concentration (P < 0.001) and decreased the pH (P < 0.001), as well as the concentrations of acetic acid, propionic acid, butyric acid, and ammonia-N (P < 0.05). In addition, the combination treatment displayed more effective results on silage fermentation. The LAB and molasses improved the fermentation quality of the CF silage by altering the bacterial community structure. Furthermore, the bacterial community was significantly correlated with fermentation indexes.

Dynamics of Fermentation Parameters and Bacterial Community in High-Moisture Alfalfa Silage with or without Lactic Acid Bacteria

The aim of this study was to gain deeper insights into the dynamics of fermentation parameters and the bacterial community during the ensiling of high-moisture alfalfa. A commercial lactic acid bacteria (YX) inoculant was used as an additive. After 15 and 30 days of ensiling, the control silage (CK) exhibited a high pH and a high concentration of ammoniacal nitrogen (NH₃-N); Enterobacter and Hafnia-Obesumbacterium were the dominant genera. At 60 d, the pH value and the concentration of NH₃-N in CK silage increased compared with 15 and 30 d, propionic acid and butyric acid (BA) were detected, and Garciella had the highest abundance in the bacterial community. Compared with CK silage, inoculation of YX significantly promoted lactic acid and acetic acid accumulation and reduced pH and BA formation, did not significantly reduce the concentration of NH₃-N except at 60 d, and significantly promoted the abundance of Lactobacillus and decreased the abundance of Garciella and Anaerosporobacter, but did not significantly inhibit the growth of Enterobacter and Hafnia-Obesumbacterium. In conclusion, high-moisture alfalfa naturally ensiled is prone to rot. Adding YX can delay the process of silage spoilage by inhibiting the growth of undesirable microorganisms to a certain extent.

Low-Carbohydrate Tolerant LAB Strains Identified from Rumen Fluid: Investigation of Probiotic Activity and Legume Silage Fermentation

The objective of this study was to isolate and characterize lactic acid bacteria (LAB) with low carbohydrate tolerance from rumen fluid and to elucidate their probiotic properties and the quality of fermentation of Medicago sativa L. and Trifolium incarnatum L. silage in vitro. We isolated 39 LAB strains and screened for growth in MRS broth and a low-carbohydrate supplemented medium; among them, two strains, Lactiplantibacillus plantarum (Lactobacillus plantarum) RJ1 and Pediococcus pentosaceus S22, were able to grow faster in the low-carbohydrate medium. Both strains have promising probiotic characteristics including antagonistic activity against P. aeruginosa, E. coli, S. aureus, and E. faecalis; the ability to survive in simulated gastric-intestinal fluid; tolerance to bile salts; and proteolytic activity. Furthermore, an in vitro silage fermentation study revealed that alfalfa and crimson clover silage inoculated with RJ1 and S22 showed significantly decreased pH and an increased LAB population at the end of fermentation. Also, the highest lactic acid production was noted (p < 0.05) in LAB-inoculated silage vs. non-inoculated legume silage at high moisture. Overall, the data suggest that RJ1 and S22 could be effective strains for fermentation of legume silage.

Pretreatment of Pennisetum sinese silages with ferulic acid esterase-producing lactic acid bacteria and cellulase at two dry matter contents: Fermentation characteristics, carbohydrates composition and enzymatic saccharification

The impact of Lactobacillus plantarum A1 producing ferulic acid esterase and Acremonium cellulase on Pennisetum sinese silages was investigated at two dry matter contents by studying the ensiling characteristics, lignocellulosic degradation and enzymatic saccharification properties. The P. sinese was treated with nothing (control), Acremonium cellulase (AC), L. plantarum A1 (Lp) and AC + Lp and ensiled for 60 d. All additive treatments effectively preserved P. sinese and promoted the degradation of lignocellulose in comparison with control. Pretreatment with AC exhibited better effects in degradation of lignocellulose and enhancing enzymatic saccharification of P. sinese silage with low dry matter content (L-DM), while AC + Lp performed better in lignocellulose degradation in silages with high dry matter content (H-DM). Application of Lp exhibited a better performance in reducing the concentration of acid detergent lignin in treated silages. In addition, Lp enhanced enzymatic saccharification at 72 h in H-DM silage relative to other treatments.