Microbial alkaline proteases: From a bioindustrial viewpoint

Gelation of gellan – A review

Microbial polysaccharides are multifunctional and can be divided into intracellular polysaccharides, structural polysaccharides and extracellular polysaccharides or exopolysaccharides (EPS). Extracellular polymeric substances (EPS), produced by both prokaryotes (eubacteria and archaebacteria) and eukaryotes (phytoplankton, fungi, and algae), have been of topical research interest. Newer approaches are carried out today to replace the traditionally used plant gums by their bacterial counterparts. The bacterial exopolysaccharides represent a wide range of chemical structures, but have not yet acquired appreciable significance. Chemically, EPS are rich in high molecular weight polysaccharides (10 to 30 kDa) and have heteropolymeric composition. They have new-fangled applications due to the unique properties they possess. Owing to this, exopolysaccharides have found multifarious applications in the food, pharmaceutical and other industries. Hence, the present article converges on bacterial exopolysaccharides.

Bacterial exopolysaccharides – a perception

Bacteria produce a wide range of exopolysaccharides which are synthesized via different biosynthesis pathways. The genes responsible for synthesis are often clustered within the genome of the respective production organism. A better understanding of the fundamental processes involved in exopolysaccharide biosynthesis and the regulation of these processes is critical toward genetic, metabolic and protein-engineering approaches to produce tailor-made polymers. These designer polymers will exhibit superior material properties targeting medical and industrial applications. Exploiting the natural design space for production of a variety of biopolymer will open up a range of new applications. Here, we summarize the key aspects of microbial exopolysaccharide biosynthesis and highlight the latest engineering approaches toward the production of tailor-made variants with the potential to be used as valuable renewable and high-performance products for medical and industrial applications.

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Bacterial exopolysaccharides: biosynthesis pathways and engineering strategies

The genus Sphingomonas: physiology and ecology.

GELRITE, a new gelling agent with good thermal stability and clarity, was evaluated in media for culturing selected thermophilic microorganisms. It was also evaluated for performing counts of thermophilic bacteria from soil samples. In most cases, GELRITE was shown to be superior to agar for these applications.

GELRITE as a Gelling Agent in Media for the Growth of Thermophilic Microorganisms.

Curdlan is a water-insoluble β-(1,3)-glucan produced by Agrobacterium species under nitrogen-limited condition. Its heat-induced gelling properties render curdlan to be very useful in the food industry initially. Recent advances in the understanding of the role curdlan plays in both innate and adaptive immunity lead to its growing applications in biomedicine. Our review focuses on the recent advances on curdlan biosynthesis and the improvements of curdlan fermentation production both from our laboratory and many others as well as the latest advances on the new applications of curdlan and its derivatives particularly in their immunological functions in biomedicine.

Recent advances in curdlan biosynthesis, biotechnological production, and applications

A novel osmotic pressure control fed-batch fermentation strategy for improvement of erythritol production by Yarrowia lipolytica from glycerol.

The production of porcine interferon-α (pIFN-α) by Pichia pastoris was largely enhanced when adopting sorbitol/methanol co-feeding induction strategy at 30 °C in a 10-L fermentor. Analysis of energy regeneration pattern and carbon metabolism revealed that major energy metabolism energizing pIFN-α synthesis shifted from formaldehyde dissimilatory energy metabolism pathway to TCA cycle under the methanol/sorbitol co-feeding induction strategy. The sorbitol/methanol co-feeding induction strategy weakened formaldehyde dissimilatory pathway and repressed the accumulation of toxic metabolite-formaldehyde, reduced theoretical oxygen consumption rate and oxygen supply requirement, and increased energy/methanol utilization efficiency so that more methanol could be effectively used for pIFN-α synthesis. As a result, pIFN-α antiviral activity reached a highest level of 1.8 × 107 IU/mL which was about 10- to 200-folds of those obtained under pure methanol induction at 20 and 30 °C, respectively.

Methanol/sorbitol co-feeding induction enhanced porcine interferon-α production by P. pastoris associated with energy metabolism shift.

Osmotic pressure is a critical factor for erythritol production with osmophilic yeast. Protein expression patterns of an erythritol-producing yeast, Yarrowia lipolytica, were analyzed to identify differentially-expressed proteins in response to osmotic pressure. In order to analyze intracellular protein levels quantitatively, two-dimensional gel electrophoresis was performed to separate and visualize the differential expression of the intracellular proteins extracted from Y. lipolytica cultured under low (3.17 osmol/kg) and high (4.21 osmol/kg) osmotic pressures. Proteomic analyses allowed identification of 54 differentially-expressed proteins among the proteins distributed in the range of pI 3-10 and 14.4-97.4 kDa molecular mass between the osmotic stress conditions. Remarkably, the main proteins were involved in the pathway of energy, metabolism, cell rescue, and stress response. The expression of such enzymes related to protein and nucleotide biosynthesis was inhibited drastically, reflecting the growth arrest of Y. lipolytica under hyperosmotic stress. The improvement of erythritol production under high osmotic stress was due to the significant induction of a range of crucial enzymes related to polyols biosynthesis, such as transketolase and triosephosphate isomerase, and the osmotic stress responsive proteins like pyridoxine-4-dehydrogenase and the AKRs family. The polyols biosynthesis was really related to an osmotic response and a protection mechanism against hyperosmotic stress in Y. lipolytica. Additionally, the high osmotic stress could also induce other cell stress responses as with heat shock and oxidation stress responses, and these responsive proteins, such as the HSPs family, catalase T, and superoxide dismutase, also had drastically increased expression levels under hyperosmotic pressure.

Chi-Chung Lin

Papers

GELRITE as a Gelling Agent in Media for the Growth of Thermophilic Microorganisms.

Recent advances in curdlan biosynthesis, biotechnological production, and applications

A novel osmotic pressure control fed-batch fermentation strategy for improvement of erythritol production by Yarrowia lipolytica from glycerol.

Methanol/sorbitol co-feeding induction enhanced porcine interferon-α production by P. pastoris associated with energy metabolism shift.

Proteomic Analysis of Erythritol-Producing Yarrowia lipolytica from Glycerol in Response to Osmotic Pressure.