BackgroundWe previously cloned a 1,3-specific lipase gene from the fungus Rhizomucor miehei and expressed it in methylotrophic yeast Pichia pastoris strain GS115. The enzyme produced (termed RML) was able to catalyze methanolysis of soybean oil and showed strong position specificity. However, the enzyme activity and amount of enzyme produced were not adequate for industrial application. Our goal in the present study was to improve the enzyme properties of RML in order to apply it for the conversion of microalgae oil to biofuel.ResultsSeveral new expression plasmids were constructed by adding the propeptide of the target gene, optimizing the signal peptide, and varying the number of target gene copies. Each plasmid was transformed separately into P. pastoris strain X-33. Screening by flask culture showed maximal (21.4-fold increased) enzyme activity for the recombinant strain with two copies of the target gene; the enzyme was termed Lipase GH2. The expressed protein with the propeptide (pRML) was a stable glycosylated protein, because of glycosylation sites in the propeptide. Quantitative real-time RT-PCR analysis revealed two major reasons for the increase in enzyme activity: (1) the modified recombinant expression system gave an increased transcription level of the target gene (rml), and (2) the enzyme was suitable for expression in host cells without causing endoplasmic reticulum (ER) stress. The modified enzyme had improved thermostability and methanol or ethanol tolerance, and was applicable directly as free lipase (fermentation supernatant) in the catalytic esterification and transesterification reaction. After reaction for 24 hours at 30°C, the conversion rate of microalgae oil to biofuel was above 90%.ConclusionsOur experimental results show that signal peptide optimization in the expression plasmid, addition of the gene propeptide, and proper gene dosage significantly increased RML expression level and enhanced the enzymatic properties. The target enzyme was the major component of fermentation supernatant and was stable for over six months at 4°C. The modified free lipase is potentially applicable for industrial-scale conversion of microalgae oil to biodiesel.Electronic supplementary materialThe online version of this article (doi:10.1186/1754-6834-7-111) contains supplementary material, which is available to authorized users.

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Objectives This study was conducted to investigate the effects of dietary supplementation of Perilla frutescens seed (PFS) on growth performance, blood profiles, meat quality and meat nutrient characteristics in finishing castrated male Songliao black pigs. Methods A total of 80 castrated male Songliao black pigs with an average initial body weight (BW) of 84.1 ± 2.1 kg were used in a 75 days feeding trial. All pigs were randomly assigned into four dietary treatments: CON, basal diet; PFS3.0, basal diet + 3.0% of PFS; PFS6.0, basal diet + 6.0% of PFS and PFS9.0, basal diet + 9.0% of PFS. Results As a result of this experiment, dietary supplementation of PFS improved the growth performance parameters, blood albumin and blood lipid parameters. Whereas, on FBW, average daily feed intake and average daily gain there showed a non‐dose‐dependent manner that pigs in PFS9.0 had lowest performance compared with other two PFS treatments. Furthermore, meat colour of yellowness, pH, cook meat rate, moisture, crude protein and crude fat were increased by PFS addition. However, lower growth performance was observed in PFS9.0 group. As well as, dietary inclusion of PFS also alters the meat amino acid composition and meat fatty acids composition. Particularly, umami amino acid contents and polyunsaturated fatty acid were all enhanced by PFS addition. Conclusions In summary, dietary supplementation of PFS have beneficial effects on the performance and meat quality and nutritional values in Songliao black pigs.

In‐depth studies of carcass characters and meat quality could provide insight both for breeding improvement and food development in pigs. Breed and gender are two main factors affected the carcass and meat altitude, which plays important roles in pork industry. The aim of this study was to evaluate the sex effects on carcass characteristics and meat quality traits in a novel Duroc strain pig crossbred from French line, American line and Canadian line pigs. A total of 30 pigs (15 surgical‐castrated males and 15 females) with similar birthweight (1.8 ± 0.13 kg) was used in experiment. During the experiment period, all pigs were fed same commercial diets. Overall, female pigs observed higher (p < 0.05) carcass weight, slaughter backfat, loin muscle area, loin muscle depth, carcass yield, pH on 45 min, meat histidine and essential amino acid (AA) compositions, and eicosenoic, unsaturation and free fatty acids (FA) compositions compared with meat from castrated males. Whereas, castrated males’ meat showed better altitude (p < 0.05) on meat lightness, meat moisture content percentage, total umami AA and stearic acid and saturated FA compositions than those from female ones. In conclusion, the results of this study provide evidence on the sex effects on meat quality and carcass parameters in Duroc strain pigs. Furthermore, this study also give a reference on the relationship between sex and carcass and meat characteristics in Durco strain pigs.