This study aimed to investigate the changes of lipid-related gene and serum metabolites in broiler chickens fed with fermented cottonseed meal (FCSM) diet, through quantitative real-time PCR and metabolomics analysis. Totally, 180 1-day-old Cobb broilers were randomly assigned to two groups with six replicates of 15 birds in each. The two diets consisted of a control diet supplemented with 0% FCSM (CON group) and an experimental diet with 6% FCSM (fermented by Candida tropicalis) replacing the soybean meal (FCSM group). The results showed that both abdominal fat content and subcutaneous fat thickness significantly reduced (p < 0.05) in response to dietary FCSM supplementation at the age of 21 d. Serum concentrations of glucose, triglyceride, and low-density lipoprotein cholesterol decreased (p < 0.05) in FCSM fed broilers compared with CON fed broilers, while the levels of epinephrine and growth hormone in serum, liver and abdominal fat tissue were higher (p < 0.05) in FCSM than in CON fed broilers. The activity of hormone-sensitive esterase and lipoprotein lipase (LPL) in the liver and abdominal fat were higher (p < 0.05) in FCSM than CON group. Additionally, compared with the CON group (p < 0.05), the expression of peroxisome proliferator-activated receptor alpha and LPL genes were upregulated in the livers of FCSM group broilers. Gene expressions of hormone-sensitive lipase and LPL in the abdominal fat tissue were also upregulated (p < 0.05) with the broilers fed with FCSM diets. A total of 20 significantly different metabolites were obtained in the serum of different dietary FCSM supplemented fed broilers. The mainly altered pathways were clustered into organic acid metabolism, fatty acid metabolism, and amino acid metabolism. These results not only provide a better understanding of broilers’ lipid metabolism with FCSM but also can be helpful in further improvement of the broilers’ healthy production and utilization of FCSM.

Skatole is a harmful, odorous pollutant in livestock manure. Skatole-degrading strains are mostly harmful Gram-negative bacteria, whereas safe Gram-positive strains demonstrate poor degradation performance, limiting bioremediation applications. To solve this problem, this study was conducted to enhance the skatole degradation capacity of the food-grade strain Lactococcus lactis NZ9000 via heterologous expression of the skatole-degrading Ska enzyme from Acinetobacter piscicola p38. Three gene sequences, designated Ska-Y (original sequence from A. piscicola p38), Ska-D (E. coli codon-optimized), and Ska-R (L. lactis codon-optimized), were separately expressed using constitutive pMG36e and nisin-inducible pNZ8148 plasmids. The constitutive system only transcribed mRNA but produced misfolded, nonfunctional inclusion bodies. By contrast, the codon-optimized pNZ8148-Ska-R strain exhibited prominent skatole degradation ability, even under non-inductive conditions. Under optimal conditions (30 ℃, ultra-low nisin induction), the engineered strain increased the 24 h degradation rate of 50 mg/L skatole from 20% to 88% and completely degraded 25 mg/L skatole. Field tests verified that the strain effectively reduced skatole accumulation in manure compost and lagoon manure. This study achieved efficient functional heterologous expression in Gram-positive bacteria, provides new insights into ultra-low-dose induction and codon optimization, and offers a safe and efficient microbial agent for livestock manure odor remediation.