Efficient extracellular production of κ-carrageenase in Escherichia coli: effects of wild-type signal sequence and process conditions on extracellular secretion

Optimization of Fermentation Conditions for Carrageenase Production by Cellulophaga Species: A Comparative Study

Simple Summary

Cellulophaga species are rarely studied marine bacteria with the potential for carrageenase production. We examined the carrageenase secretion ability of six bacterial species from the Cellulophaga genus. Among them, C. algicola produced the maximum amount of ι-carrageenase. Most of the bacteria produced their highest quantity of enzymes at 25 °C after 48 h of incubation time. The maximum enzyme production was achieved with the fermentation medium composition of 30 g/L sea salt, 1.4 g/L furcellaran and 3 g/L yeast extract. In addition, the properties of the ultrafiltered ι-carrageenase extracted from C. algicola were studied.

Abstract

Carrageenases appear in various species of marine bacteria and are widely used for the degradation of carrageenans, the commercially significant sulphated polysaccharides. The carrageenase production ability of six different Cellulophaga species was identified, with ι-carrageenase being the most abundant carrageenolytic enzyme. C. algicola was the most potent strain, followed by C. fucicola and C. geojensis, whereas C. pacifica was the least effective carrageenase producer among the studied strains. The enzyme production was maximized using the one-factor-at-a-time optimization method. The optimal incubation temperature was identified as 25 °C and the incubation time was set as 48 h for all tested species. The optimal medium composition for Cellulophaga strains was determined as 30 g/L sea salt, 1.4 g/L furcellaran, and 3 g/L yeast extract. An ultrafiltered enzyme extracted from C. algicola had the highest activity at around 40 °C. The optimal pH for enzymatic degradation was determined as 7.8, and the enzyme was fairly stable at temperatures up to 40 °C.

Fermentation optimization, purification and biochemical characterization of ι-carrageenase from marine bacterium Cellulophaga baltica

The ι-carrageenan degrading marine bacterium, Cellulophaga baltica, was isolated from the surface of a filamentous red alga Vertebrata fucoides. Maximum ι-carrageenase production was optimized by single-factor experiments. Optimal fermentation conditions were 1.6 g/L furcellaran, 4 g/L yeast extract as carbon sources, 5 g/L sea salt, and 48 h of incubation time at 20 °C. Extracellular ι-carrageenase from the culture supernatant was purified by ultrafiltration, ammonium sulfate precipitation, and finally by anion-exchange chromatography, showed a 26-fold increase in specific activity as compared to that in the crude enzyme. According to the results from SDS-PAGE and HPLC-SEC, the molecular weight of the purified enzyme was estimated to be 31 kDa. The purified enzyme showed the maximum specific activity of 571 U/mg at 40 °C and pH 7.5-8.0. It maintained 73% of the total activity below 40 °C and 90% of its total activity at pH 7.2. Notably, the enzyme is a cold-adapted ι-carrageenase, which showed 33.4% of the maximum activity at 10 °C. The enzyme was stimulated by Na⁺, K⁺, and NH₄⁺, whereas Ca²⁺, Mg²⁺, Fe³⁺, sea salt, and EDTA acted as enzyme inhibitors.

Production of a thermo-tolerant κ-carrageenase via a food-grade host and anti-oxidant activity of its enzymatic hydrolysate

κ-Carrageenase cleaves the β-(1-4) linkages of κ-carrageenan into κ-carrageenan oligosaccharides (κ-COS), which exhibit various biological activities. In this study, a glycoside hydrolase (GH) family 16 κ-carrageenase gene, cgkA, was cloned from the marine bacterium Vibrio sp. SY01 and secretory expressed in a food-grade host, Yarrowia lipolytica. The specific activity of the purified CgkA was 12.5 U/mg. Determination of biochemical properties showed that CgkA was a thermo-tolerant enzyme, and 59.9% of the initial enzyme activity was recovered by immediately placing the sample at 20 °C for 30 min after enzymatic inactivation by boiling for 5 min. The recombinant CgkA was an endo-type enzyme, the main enzymatic product was κ-carradiaose (accounting for 87.6% of total products), and κ-carratetraose was the minimum substrate. Additionally, in vitro and in vivo analyses indicated that enzymatic κ-carradiaose possesses anti-oxidant activity. These features make CgkA as a promising candidate for biotechnological applications in the production of anti-oxidant κ-COS.

Synechocystis sp. PCC 6803 overexpressing genes involved in CBB cycle and free fatty acid cycling enhances the significant levels of intracellular lipids and secreted free fatty acids

The integrative aspect on carbon fixation and lipid production is firstly implemented in cyanobacterium Synechocystis sp. PCC 6803 using metabolic engineering approach. Genes related to Calvin–Benson–Bassham (CBB) cycle including rbcLXS and glpD and free fatty acid recycling including aas encoding acyl-ACP synthetase were practically manipulated in single, double and triple overexpressions via single homologous recombination. The significantly increased growth rate and intracellular pigment contents were evident in glpD-overexpressing (OG) strain among all strains studied under normal growth condition. The triple aas_glpD_rbcLXS-overexpressing (OAGR) strain notably gave the highest contents of both intracellular lipids and extracellular free fatty acids (FFAs) of about 35.9 and 9.6% w/DCW, respectively, when compared to other strains at day 5 of cultivation. However, the highest intracellular lipid titer and production rate were observed in OA strain at day 5 (228.7 mg/L and 45.7 mg/L/day, respectively) and OG strain at day 10 (358.3 mg/L and 35.8 mg/L/day, respectively) due to their higher growth. For fatty acid (FA) compositions, the main saturated fatty acid of palmitic acid (C16:0) was dominantly found in both intracellular lipid and secreted FFAs fractions. Notably, intracellular FA proportion of myristic acid (C14:0) was induced in all engineered strains whereas the increase of stearic acid (C18:0) composition was found in extracellular FFAs fraction. Altogether, these overexpressing strains efficiently produced higher lipid production via homeostasis balance on both its lipid synthesis and FFAs secretion.

Efficient production of aggregation prone 4-α-glucanotransferase by combined use of molecular chaperones and chemical chaperones in Escherichia coli

In this study, a combined optimization strategy, based on co-expression of molecular chaperones and supplementation of osmolytes, was used to reduce the formation of inclusion bodies and enhance the expression of the soluble form of 4-α-glucanotransferase. The 4-α-glucanotransferase yield was enhanced by co-expression with pGro7 and supplementation of trimetlylamine oxide. Subsequently, the effects of process conditions (temperature, inducer concentration, and arabinose concentration) on cell growth and 4-α-glucanotransferase production were also investigated in shake flasks. In addition, a modified high-cell-density fermentation approach was proposed and applied in 3-L fermentor supplied with l-arabinose and trimetlylamine oxide, which achieved a dry cell weight of 65.92 g·L^-1. Through this cultivation approach at 28 °C, the activity of 4-α-glucanotransferase reached 332.5 U·g^-1 dry cell weight, which was 24.6-fold greater than the initial activity in shake flask cultivation. This combined strategy is expected to provide an efficient and economical approach to overproduction of aggregation prone proteins on a large scale.

Secretion of recombinant proteins from E. coli

The microorganism Escherichia coli is commonly used for recombinant protein production. Despite several advantageous characteristics like fast growth and high protein yields, its inability to easily secrete recombinant proteins into the extracellular medium remains a drawback for industrial production processes. To overcome this limitation, a multitude of approaches to enhance the extracellular yield and the secretion efficiency of recombinant proteins have been developed in recent years. Here, a comprehensive overview of secretion mechanisms for recombinant proteins from E. coli is given and divided into three main sections. First, the structure of the E. coli cell envelope and the known natural secretion systems are described. Second, the use and optimization of different one- or two-step secretion systems for recombinant protein production, as well as further permeabilization methods are discussed. Finally, the often-overlooked role of cell lysis in secretion studies and its analysis are addressed. So far, effective approaches for increasing the extracellular protein concentration to more than 10 g/L and almost 100% secretion efficiency exist, however, the large range of optimization methods and their combinations suggests that the potential for secretory protein production from E. coli has not yet been fully realized.

Extracellular expression of a novel β-agarase from Microbulbifer sp. Q7, isolated from the gut of sea cucumber

A novel endo-type β-agarase was cloned from an agar-degrading bacterium, Microbulbifer sp. Q7 (CGMCC No. 14061), that was isolated from sea cucumber gut. The agarase-encoding gene, ID2563, consisted of 1800 bp that encoded a 599-residue protein with a signal peptide of 19 amino acids. Sequence analysis suggested that the agarase belongs to the GH16 family. The agarase was expressed in Escherichia coli with a total activity of 4.99 U/mL in fermentation medium. The extracellular enzyme activity accounted for 65.73% of the total activity, which indicated that the agarase can be extracellularly secreted using the wild-type signal peptide from Microbulbifer sp. Q7. The agarase exhibited maximal activity at approximately 40 °C and pH 6.0. It was stable between pH 6.0 and pH 9.0, which was a much wider range than most of the reported agarases. The agarase was sensitive to some metal ions (Cu²⁺, Zn²⁺ and Fe³⁺), but was resistant to urea and SDS. The agarase hydrolyzed β-1,4-glycosidic linkages of agarose, primarily yielding neoagarotetraose and neoagarohexaose as the final products. These indicate that this recombinant agarase can be an effective tool for the preparing functional neoagaro-oligosaccharides.

Bacterial carrageenases: an overview of production and biotechnological applications

Carrageenan, one of the phycocolloids is a sulfated galactan made up of linear chains of galactose and 3,6-anhydrogalactose with alternating α-(1 → 3) and β-(1 → 4) linkages and further classified based on the number and the position of sulfated ester(s); κ-, ι- and λ-carrageenan. Enzymes which degrade carrageenans are called k-, ι-, and λ-carrageenases. They all are endohydrolases that cleave the internal β-(1-4) linkages of carrageenans yielding products of the oligo-carrageenans. These enzymes are produced only by bacteria specifically gram negative bacteria. Majority of the marine bacteria produce these enzymes extracellularly and their activity is in wide range of temperature. They have found potential applications in biomedical field, bioethanol production, textile industry, as a detergent additive and for isolation of protoplast of algae etc. A comprehensive information shall be helpful for the effective understanding and application of these enzymes. In this review exhaustive information of bacterial carrageenases reported till date has been done. All the aspects like sources, production conditions, characterization, cloning and- biotechnological applications are summarized.