Surfactin-family lipopeptides are green biosurfactants with substantial industrial potential. The major problem prohibiting surfactin use is the low titer of the wild producer, Bacillus subtilis. Using transcriptomic analysis, four strong promoters, PgroE, Pcdd, PrplK, and PsspE, were identified and cloned from the genome of B. subtilis THY-7, a novel surfactin producer that has been identified from soil with a 0.55 g/L surfactin titer. An optimal promoter, PgroE, was selected to replace the native THY-7 surfactin synthase (SrfA) promoter through single-cross homologous recombination; however, the resulting engineered strain containing the PgroE substitution did not synthesize surfactin. The sucrose-inducible promoters PsacB and PsacP were then substituted in place of PsrfA, and the resulting engineered strains produced 1.09 and 0.22 g/L surfactin, respectively. An artificial, sucrose-inducible Pg1 promoter was produced through fusion of the PgroE and PsacB ribonucleic antiterminator (RAT), and the engineered strain containing the Pg1-substitution produced a surfactin titer of 1.44 g/L. An artificial IPTG-inducible promoter, Pg2, was constructed from a PgroE-lacO fusion and then substituted for the chromosomal PsrfA locus, and the surfactin titer of the resulting THY-7/Pg2-srfA increased to 5.98 g/L. The driving capacity of Pg2 was further improved by the inclusion of two point mutations in the -35 and -10 regions to produce the novel promoter Pg3. Pg3 exhibited super-strong activity as measured by lacZ reporter gene overexpression (approximately 3000 U). The Pg3-substitution strain THY-7/Pg3-srfA produced up to 9.74 g/L surfactin in a 5 L fermentor. The maximum productivity was 0.30 g/L/h, and the greatest yield reached 0.14 g surfactin/g sucrose. Biotechnol. Bioeng. 2017;114: 832-842. © 2016 Wiley Periodicals, Inc.
This study aims to investigate the effects of epigallocatechin gallate (EGCG) on the growth performance and serum metabolic characteristics of heat-stressed broilers. A total of 192 14-day-old Arbor Acres broilers were divided into 4 groups with 6 replicates per group (8 chickens/cage). Thermoneutral group (Group TN) was fed the basal diet and maintained at 28°C for 24 h/d. The heat-stressed groups were housed at 35°C for 12 h/d and 28°C for 12 h/d and fed the basal diet supplemented with EGCG at 0, 300, and 600 mg/kg diet (Groups HS0, HS300, and HS600, respectively). The production performance and serum metabolic characteristics were analyzed at d 21, 28, and 35, respectively. At d 35 of age, heat stress reduced (P < 0.05) the body weight (BW), feed intake (FI) and the contents of serum total protein (TP) and glucose (GLU); inhibited (P < 0.05) alkaline phosphatase (ALP) activity; But increased (P < 0.05) the contents of uric acid (UA), cholesterol (CHOL), triglyceride (TG), and the activities of creatine kinase (CK), lactate dehydrogenase (LDH), aspartate aminotransferase (AST). Heat-stressed chickens fed EGCG exhibited a linear increase (P < 0.05) in BW, FI, the levels of serum TP, GLU, and ALP activity; and linear decrease (P < 0.05) in the contents of serum UA, CHOL, and TG, as well as the activities of LDH, CK, and AST. Heat stress also reduced (P < 0.05) the activities of serum glutathione peroxidase (GSH-Px), superoxide dismutase (SOD) and catalase (CAT) on d 35 and increased (P < 0.05) the GSH-Px and SOD activity on d 21 and malondialdehyde (MDA) contents. There was a linear increase (P < 0.05) in activities of GSH-Px, SOD and CAT at 35 d of age, and linear decreased (P < 0.05) in MDA contents. In conclusion, EGCG can improve the growth performance of broilers by enhancing antioxidant property and alleviating oxidant damage caused by heat stress.
Muscle development and growth influences the efficiency of poultry meat production, and is closely related to deposition of intramuscular fat (IMF), which is crucial in meat quality. To clarify the molecular mechanisms underlying muscle development and IMF deposition in chickens, protein expression profiles were examined in the breast muscle of Beijing-You chickens at ages 1, 56, 98 and 140 days, using isobaric tags for relative and absolute quantification (iTRAQ). Two hundred and four of 494 proteins were expressed differentially. The expression profile at day 1 differed greatly from those at day 56, 98 and 140. KEGG pathway analysis of differential protein expression from pair-wise comparisons (day 1 vs. 56; 56 vs. 98; 98 vs. 140), showed that the fatty acid degradation pathway was more active during the stage from day 1 to 56 than at other periods. This was consistent with the change in IMF content, which was highest at day 1 and declined dramatically thereafter. When muscle growth was most rapid (days 56–98), pathways involved in muscle development were dominant, including hypertrophic cardiomyopathy, dilated cardiomyopathy, cardiac muscle contraction, tight junctions and focal adhesion. In contrast with hatchlings, the fatty acid degradation pathway was downregulated from day 98 to 140, which was consistent with the period for IMF deposition following rapid muscle growth. Changes in some key specific proteins, including fast skeletal muscle troponin T isoform, aldehyde dehydrogenase 1A1 and apolipoprotein A1, were verified by Western blotting, and could be potential biomarkers for IMF deposition in chickens. Protein–protein interaction networks showed that ribosome-related functional modules were clustered in all three stages. However, the functional module involved in the metabolic pathway was only clustered in the first stage (day 1 vs. 56). This study improves our understanding of the molecular mechanisms underlying muscle development and IMF deposition in chickens.
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