Cultivation of microbial cultures at high cell density in microbioreactor fermentations to increase protein yield.

Microbioreactors have been proven to be a useful tool in high-throughput applications, such as clone screening, synthetic library testing, and media optimization. Most were designed for low cell density applications, where the optical density of the cultures typically does not exceed an OD600 of 10. In microbial applications, where protein is to be expressed, such a scale is not sufficient to produce material for extensive target molecule testing. Here, we present a method for growing high-cell density Escherichia coli cultures in milliliter-scale bioreactors, to produce milligram quantities of target protein. We used a micro-Matrix system with a starting volume of 3 ml per culture. A combination of defined medium, a fed-batch feeding strategy at low temperature, and an advanced self-adapting control algorithm achieved up to 0.7 g of wet cell weight (WCW) in a 5.7 ml final culture volume, which corresponds to 123 g/L WCW. This translates to an estimated protein yield of 1150 mg of target protein per liter final volume.

Preparation and extensive characterization of hyaluronan with narrow molecular weight distribution.

The physicochemical properties and biological functions of hyaluronan (HA) are closely related to its molecular weight (MW) and molecular weight distribution (MWD). Therefore, it is crucially important to provide a reliable characterization of these parameters for proper use of HA and its degradation products in both chemical and clinical fields. In this study, we present a novel method for the preparation of HA fragments of defined size with narrow molecular weight distribution. The HA fractionation was performed using an anion-exchange chromatography and is applicable either after enzymatic or chemical hydrolysis of polymeric HA. Isolated fractions with a molecular weight ranging from 3000-420,000gmol-1 were analyzed by size exclusion chromatography with multi-angle laser light scattering (SEC-MALLS). Hundred-milligram scale HA fragments were obtained from 5g hyaluronan starting material. Independently on weight-average molecular weight (Mw), the polydispersity index (PDI) of the HA fractions was less than 1.23. The fractionation methodology can be easily up-scaled and is applicable on any negatively charged polymers. We have also found that PDI is insufficient to characterize almost monodisperse fractions and for proper material characterization we proposed a new characteristic termed "distribution angle", calculated from the slope of the cumulative molecular weight distribution curve. Compared to PDI, the distribution angle reflects more efficiently changes in size distribution and thus is highly recommended to be used along with Mw determination of any polymer.

Characterization of Hyaluronan-Degrading Enzymes from Yeasts.

Hyaluronidases (HAases) from yeasts were characterized for the first time. The study elucidated that hyaluronate 4-glycanohydrolase and hyaluronan (HA) lyase can be produced by yeasts. Six yeasts producing HAases were found through express screening of activities. The extracellular HAases from two of the yeast isolates, Pseudozyma aphidis and Cryptococcus laurentii, were characterized among them. P. aphidis HAase hydrolyzed ß-1,4 glycosidic bonds of HA, yielding even-numbered oligosaccharides with N-acetyl-D-glucosamine at the reducing end. C. laurentii produced hyaluronan lyase, which cleaved ß-1,4 glycosidic bonds of HA in ß-elimination reaction, and the products of HA degradation were different-sized even-numbered oligosaccharides. The shortest detected HA oligomer was dimer. The enzymes' pH and temperature optima were pH 3.0 and 37-45 °C (P. aphidis) and pH 6.0 and 37 °C (C. laurentii), respectively. Both HAases showed good thermostability.

Production of hyaluronic acid by mutant strains of group C Streptococcus.

This study addresses the influence of upstream region sequence on the strength of has operon promoter in highly encapsulated S. equi subsp. zooepidemicus (SEZ). For this purpose, seven different strains were constructed. Each strain carries a point mutation in one of the following positions upstream of the has promoter: -43, -44, -49, and -50 bp. To facilitate measuring of the recombinant promoter relative strength, ß-glucuronidase gene was used as a reporter gene. Three mutations located in positions -49 and -50: AT, GT, and AG, positively impacted has promoter strength when compared to the wild type sequence GG. Conversely, two other mutations: TG and TT, exhibited a slight inhibitory effect. Further, three different strains carrying chromosomal mutations in the has promoter region were constructed. In two cases, the has operon is under the control of a stronger promoter and in the third strain the has operon is controlled by a weaker promoter. The laboratory fermenter scale cultivations confirmed the increase of hyaluronan yields for SEZPhasAG and SEZPhas2G, resulting 116 and 105 %, respectively. As expected, the yield of the hyaluronic acid of SEZPhas2B strain fell to 41 %.

High level expression of human enteropeptidase light chain in Pichia pastoris.

Human enterokinase (enteropeptidase, rhEP), a serine protease expressed in the proximal part of the small intestine, converts the inactive form of trypsinogen to active trypsin by endoproteolytic cleavage. The high specificity of the target site makes enterokinase an ideal tool for cleaving fusion proteins at defined cleavage sites. The mature active enzyme is comprised of two disulfide-linked polypeptide chains. The heavy chain anchors the enzyme in the intestinal brush border membrane, whereas the light chain represents the catalytic enzyme subunit. The synthetic gene encoding human enteropeptidase light chain with His-tag added at the C-terminus to facilitate protein purification was cloned into Pichia pastoris expression plasmids under the control of an inducible AOX1 or constitutive promoters GAP and AAC. Cultivation media and conditions were optimized as well as isolation and purification of the target protein. Up to 4 mg/L of rhEP was obtained in shake-flask experiments and the expression level of about 60-70 mg/L was achieved when cultivating in lab-scale fermentors. The constitutively expressing strains proved more efficient and less labor-demanding than the inducible ones. The rhEP was immobilized on AV 100 sorbent (Iontosorb) to allow repeated use of enterokinase, showing specific activity of 4U/mL of wet matrix.

High level expression and purification of antimicrobial human cathelicidin LL-37 in Escherichia coli.

The human antimicrobial peptide LL-37 is a cationic peptide with antimicrobial activity against both Gram-positive and Gram-negative microorganisms. This work describes the development of an expression system based on Escherichia coli capable of high production of the recombinant LL-37. The fusion protein Trx-LL-37 was expressed under control of T7 promoter. The expression of T7 polymerase in the E. coli strain constructed in this work was controlled by regulation mechanisms of the arabinose promoter. The expression plasmid was stabilized by the presence of parB locus which ensured higher homology of the culture during cultivation without antibiotic selection pressure. This system was capable of producing up to 1 g of fusion protein per 1 l of culture. The subsequent semipreparative HPLC allowed us to isolate 40 mg of pure LL-37. LL-37 showed high antimicrobial activity against both Gram-negative and Gram-positive microorganisms. Its activity against Candida albicans was practically nonexistent. Minimal Inhibition Concentration (MIC) determined for E. coli was 1.65 microM; for Staphylococcus aureus 2.31 microM, and for Enterococcus faecalis 5.54 microM. The effects of cathelicidin on E. coli included the ability to permeabilize both cell membranes, as could be observed by the increase of beta-galactosidase activity in extracellular space in time. Physiological changes were studied by scanning electron microscopy; Gram-positive microorganisms did not show any visible changes in cell shapes while the changes observed on E. coli cells were evident. The results of this work show that the herein designed expression system is capable of producing adequate quantities of active human antimicrobial peptide LL-37.