Marine microbial natural products (MMNPs) have attracted increasing attention from microbiologists, taxonomists, ecologists, agronomists, chemists and evolutionary biologists during the last few decades. Numerous studies have indicated that diverse marine microbes appear to have the capacity to produce an impressive array of MMNPs exhibiting a wide variety of biological activities such as antimicrobial, anti-tumor, anti-inflammatory and anti-cardiovascular agents. Marine microorganisms represent an underexplored reservoir for the discovery of MMNPs with unique scaffolds and for exploitation in the pharmaceutical and agricultural industries. This review focuses on MMNPs discovery and development over the past decades, including innovative isolation and culture methods, strategies for discovering novel MMNPs via routine screenings, metagenomics, genomics, combinatorial biosynthesis, and synthetic biology. The potential problems and future directions for exploring MMNPs are also discussed.
The methylotrophic yeast Pichia pastoris has been used for the expression of many proteins. However, limitations such as protein degradation and aggregation became obvious when secreting heterologous protein-recombinant human consensus interferon-alpha mutant. Here, we investigate the effect of induction temperature on the yield and stability of interferon mutant expressed by P. patoris with buffered complex medium. The best results in terms of interferon mutant bioactivity and specific bioactivity were obtained when the microorganism was induced at 15 degrees C, which were 2.91 x 10(8) +/- 0.3 x 10(8) and 2.26 x 10(8 )+/- 0.23 x 10(8) IU mg(-1), respectively. At the same time, the cells grew fast owing to high AOX1-specific activity, and interferon mutant expression level reached 1.23 g l(-1), which was almost 30 times higher than that in the flask. Also, the proteolytic degradation of interferon mutant was inhibited completely because of lower protease bioactivity probably due to a reduced cell death rate at lower temperatures as well as protection of yeast extract and peptone in complex medium. In addition, interferon mutant aggregation was repressed significantly by the addition of Tween-80, and a specific bioactivity of 7.35 x 10(8) +/- 0.56 x 10(8) IU mg(-1) was obtained. These results should be applicable to other low-stability recombinant proteins expressed in P. pastoris.
Improvement of microbial strains for the high-production of industrial products has been the hallmark of all commercial fermentation processes. Strain improvement has been conventionally achieved through mutation and selection. However, most of the screenings were performed in shake flasks, which made the screening procedure very complex, time-consuming, and inefficient. Most mutant spore suspension had no chance to be screened due to the low-throughput of shake flasks and had to be sacrificed. In this paper, in order to get a Cephalosporin C (CPC) high-yield stain, traditional mutagenesis was employed to obtain the mutant library and gave them the equal screening chance by a novel mixture culture method combined with high-throughput screening method. The good correlation of fermentation results between differing-scale cultivations confirmed the feasibility of utilizing the 48-deep microtiter plates as a scale-down tool instead of shake flasks for culturing high-aerobic microbes with long cultivation period. The microbioassay based on the antibacterial activity of CPC against Alcaligenes faecalis was used to select mutants. As a result, the high-yield strain W-6 was successfully screened out and the CPC titer was nearly 50 % higher than that of the parental strain in the shake flask. The CPC production of strain W-6 was further validated in 50 l bioreactor, and the CPC production reached 32.0 g/l, twofold higher than that of the wild strain.
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