Effects of Megasphaera elsdinii SC8-1 and Cutibacterium acnes SC8-2W supplementation on in vitro ruminal fermentation, methane emission, and their genomic attributes
摘要
This study aimed to isolate, characterize, and evaluate co-cultures of potential bacteria as direct-fed microbials for dairy goats and to examine their effect on ruminal fermentation using the in vitro gas production method. Phase I: Isolation and screening of putative LUBs included bacterial isolation from ruminal fluid and both quantitative and qualitative screening of lactate utilization. The quantitative screening of LUBs involved inoculating LUBs in glucose broth, sodium lactate broth, and DL-lactic acid broth and measuring propionic acid production. Subsequently, the isolates that exhibited the greatest propionic acid production were chosen for in vitro testing. Phase II: Evaluation of the effect of co-culture LUBs supplementation on rumen fermentation comprised a co-culture study and in vitro ruminal fermentation analysis. A co-culture study examined propionic acid production and lactate consumption between the individual strains SC8-1 and SC8-2W, along with their co-culture. The in vitro fermentation consisted of 10 groups of co-culture supplementation: one control group and nine treatment groups. Co-culture treatment groups include different concentrations of SC8-1 and SC8-2W, ranging from 1 × 109 to 1 × 1011 cfu/mL. The concentrations of volatile fatty acids, gas production, methane emissions, and digestibility were analyzed. Fourteen LUBs were isolated from the crossbred dairy goat rumen. The two highest propionate-producing bacteria were identified as Megasphaera elsdenii SC8-1 and Cutibacterium acnes SC8-2W. Genomic features, the dominant propionate-producing pathways of both LUBs were the acrylate pathway (arcC, pct) and succinate pathway (oadA). The pH, lactic acid concentration, bacterial cell growth, and propionic acid concentration of the co-cultures of M. elsdenii SC8-1 (ME group) and C. acnes SC8-2W (CU group) were compared to those of the individual cultures. The results demonstrated that lactate utilization was greatest in the co-culture group (MECU group) (p < 0.01). Bacterial cell growth was greater in the co-culture group and SC8-1 group than in the SC8-2W group (p < 0.01). However, the pH differed significantly between the SC8-1 group and the other groups (p < 0.05). The synergistic effect of co-culture was confirmed in this study. Moreover, the cryoprotectant formula for freeze dried product of LUBs was 10% skim milk with 10% trehalose. The suitable supplementation dose was determined in phase II. Supplementation with SC8-1 at 1 × 109 cfu/mL and SC8-2W at 1 × 109 cfu/mL (T1, pH 7.79 ± 0.05) significantly maintained the pH stability throughout 48 h of fermentation when compared to Control group (pH 7.49 ± 0.04) (p < 0.01). Additionally, this combination enhanced the digestibility of dry matter (p < 0.01), crude protein (p < 0.01), neutral detergent fiber (p < 0.01), and acid detergent fiber (p < 0.01) compared to control group. The proportion of butyric acid in the control group was significantly greater than that in all treatment groups (p < 0.01). Further, the total gas production in the control group was significantly lower than in the treatment groups (p < 0.01). LUB supplementation had no impact on methane production (p > 0.05). Therefore, M. elsdenii SC8-1 and C. acnes SC8-2W are considered potential LUBs for direct-fed microbial in dairy goat and the proper dosage of supplementation is 1 × 109 cfu/mL for M. elsdenii SC8-1 and 1 × 109 cfu/mL for C. acnes SC8-2W to enhance digestibility and rumen stability without adverse effects.