Biotechnology and bioengineering of pullulanase: state of the art and perspectives

Engineering hyperthermophilic pullulanase to efficiently utilize corn starch for production of maltooligosaccharides and glucose

Pullulanase is a starch-debranching enzyme that hydrolyzes side chain of starch, oligosaccharides and pullulan. Nevertheless, the limited activities of pullulanases constrain their practical application. Herein, the hyperthermophilic type II pullulanase from Pyrococcus yayanosii CH1 (PulPY2) was evolved by synergistically engineering the substrate-binding pocket and active-site lids. The resulting mutant PulPY2-M2 exhibited 5-fold improvement in catalytic efficiency (kcat/Km) compared to that of PulPY2. PulPY2-M2 was utilized to develop a one-pot reaction system for efficient production of maltooligosaccharides. The maltooligosaccharides conversion rate of PulPY2-M2 reached 96.1%, which was increased by 5.4% compared to that of PulPY2. Furthermore, when employed for glucose production, the glucose productivity of PulPY2-M2 was 25.4% and 43.5% higher than that of PulPY2 and the traditional method, respectively. These significant improvements in maltooligosaccharides and glucose production and the efficient utilization of corn starch demonstrated the potential of the engineered PulPY2-M2 in starch sugar industry.

Characteristic analysis and fermentation optimization of a novel Aureobasidium pullulans RM1603 with high pullulan yield

A high-yielding microbial polysaccharide-producing strain, named RM1603, was isolated from rhizosphere soil and identified by morphological and phylogenetic analysis. The extracellular polysaccharides (EPS) were identified by thin-layer chromatography and infrared spectroscopy. The fermentation conditions were optimized by single factor experiments in shake flasks and a 5-L fermentor. The results of morphological and phylogenetic tree analysis showed that RM1603 was a strain of Aureobasidium pullulans. Its microbial polysaccharide was identified as pullulan, and the EPS production capacity reached 33.07 ± 1.03 g L-1 in shake flasks. The fermentation conditions were optimized in a 5-L fermentor, and were found to encompass an initial pH of 6.5, aeration rate of 2 vvm, rotor speed of 600 rpm, and inoculum size of 2 %. Under these conditions, the pullulan yield of RM1603 reached 62.52 ± 0.24 g L-1. Thus, this study contributes RM1603 as a new isolation with high-yielding pullulan and potential application value in biotechnology.

Simulated gastrointestinal digestion of polylactic acid (PLA) biodegradable microplastics and their interaction with the gut microbiota

The accumulation of microplastics (MPs) in the environment as well as their presence in foods and humans highlight the urgent need for studies on the effects of these particles on humans. Polylactic acid (PLA) is the most widely used bioplastic in the food industry and medical field. Despite its biodegradability, biocompatibility, and "Generally Recognized As Safe" (GRAS) status, recent animal model studies have shown that PLA MPs can alter the intestinal microbiota; however, to date, no studies have been reported on the possible gut and health consequences of its intake by humans. This work simulates the ingestion of a realistic daily amount of PLA MPs and their pass through the gastrointestinal tract by combining the INFOGEST method and the gastrointestinal simgi® model to evaluate possible effects on the human colonic microbiota composition (16S rRNA gene sequencing analysis) and metabolic functionality (lactic acid and short-chain fatty acids (SCFA) production). Although PLA MPs did not clearly alter the microbial community homeostasis, increased Bifidobacterium levels tended to increase in presence of millimetric PLA particles. Furthermore, shifts detected at the functional level suggest an alteration of microbial metabolism, and a possible biotransformation of PLA by the human microbial colonic community. Raman spectroscopy and field emission scanning electron microscopy (FESEM) characterization revealed morphological changes on the PLA MPs after the gastric phase of the digestion, and the adhesion of organic matter as well as a microbial biofilm, with surface biodegradation, after the intestinal and colonic phases. With this evidence and the emerging use of bioplastics, understanding their impact on humans and potential biodegradation through gastrointestinal digestion and the human microbiota merits critical investigation.

Pullulanase: unleashing the power of enzyme with a promising future in the food industry

Pullulanases are the most important industrial group of enzymes in family 13 glycosyl hydrolases. They hydrolyze either α-1,6 and α-1,4 or both glycosidic bonds in pullulan as well as other carbohydrates to produce glucose, maltose, and maltotriose syrups, which have important uses in food and other related sectors. However, very less reports are available on pullulanase production from native strains because of low yield issues. In line with the increasing demands for pullulanase, it has become important to search for novel pullulanase-producing microorganisms with high yields. Moreover, high production costs and low yield are major limitations in the industrial production of pullulanase enzymes. The production cost of pullulanase by using the solid-state fermentation (SSF) process can be minimized by selecting agro-industrial waste. This review summarizes the types, sources, production strategies, and potential applications of pullulanase in different food and other related industries. Researchers should focus on fungal strains producing pullulanase for better yield and low production costs by using agro-waste. It will prove a better enzyme in different food processing industries and will surely reduce the cost of products.

A molecular study on recombinant pullulanase type I from Metabacillus indicus

Despite the great potential of cold-adapted pullulanase type I in tremendous industrial applications, the majority of commercialized pullulnases type I are of mesophilic and thermophilic origin so far. Hence, the present study underlines cloning, heterologous expression in Escherichia coli, characterization, and in silico structural modeling of Metabacillus indicus open reading frame of cold-adapted pullulanase type I (Pull_Met: 2133 bp & 710 a.a) for the first time ever. The predicted Pull_Met tertiary structure by I-TASSER, was structurally similar to PDB 2E9B pullulanase of Bacillus subtilis. Purified to homogeneity Pull_Met showed specific activity (667.6 U/mg), fold purification (31.7), molecular mass (79.1 kDa), monomeric subunit and Km (2.63 mg/mL) on pullulan. Pull_Met had optimal pH (6.0) and temperature (40 ^oC). After 10 h pre-incubation at pH 2.6-6.0, Pull_Met maintained 47.12 ± 0.0-35.28 ± 1.64% of its activity. After 120 min pre-incubation at 30 ^oC, the retained activity was 51.11 ± 0.29%. At 10 mM Mn²⁺, Na²⁺, Ca²⁺, Mg²⁺, and Cu²⁺ after 30 min preincubation, retained activity was 155.89 ± 8.97, 134.71 ± 1.82, 97.64 ± 7.06, 92.25 ± 4.18, and 71.28 ± 1.10%, respectively. After 30 min pre-incubation with Tween-80, Tween-20, Triton X-100, and commercially laundry detergents at 0.1% (v/v), the retained activity was 141.15 ± 3.50, 145.45 ± 0.20, 118.12 ± 11.00, and 90%, respectively. Maltotriose was the only end product of pullulan hydrolysis. Synergistic action of CA-AM21 (α-amylase) and Pull_Met on starch liberated 16.51 g reducing sugars /g starch after 1 h at 40 ^oC. Present data (cold-adeptness, detergent stability, and ability to exhibit starch saccharification of Pull_Met) underpins it as a promising pullulanase type I for industrial exploitation.

Reinvention of starch for oral drug delivery system design

Starch is a polysaccharide with varying amylose-to-amylopectin ratios as a function of its biological sources. It is characterized by low shear stress resistance, poor aqueous/organic solubility and gastrointestinal digestibility which limit its ease of processing and functionality display as an oral drug delivery vehicle. Modulation of starch composition through genetic engineering primarily alters amylose-to-amylopectin ratio. Greater molecular properties changes require chemical and enzymatic modifications of starch. Acetylation reduces water solubility and enzymatic digestibility of starch. Carboxymethylation turns starch acid-insoluble and aggregative at low pHs. The summative effects are sustaining drug release in the upper gut. Acid-insoluble carboxymethylated starch can be aminated to provide an ionic character essential for hydrogel formation which further reduces its drug release. Ionic starch can coacervate with oppositely charged starch, non-starch polyelectrolyte or drug into insoluble, controlled-release complexes. Enzymatically debranched and resistant starch has a small molecular size which confers chain aggregation into a helical hydrogel network that traps the drug molecules, protecting them from biodegradation. The modified starch has been used to modulate the intestinal/colon-specific or controlled systemic delivery of oral small molecule drugs and macromolecular therapeutics. This review highlights synthesis aspects of starch and starch derivatives, and their outcomes and challenges of applications in oral drug delivery.

Improved Stability and Hydrolysates of Hyperthermophilic GH57 Type II Pullulanase from the Deep-Sea Archaeon Thermococcus siculi HJ21 by Truncation

Pullulanase (EC 3.2.1.41) belongs to the amylase family and is often used alone or in combination with other amylases in the industrial production of starch-based products. This enzyme is often required in industrial production because of its better stability. We here truncated the pullulanase gene from the deep-sea hydrothermal anaerobic archaeon Thermococcus siculi HJ21 and obtained Pul-HJΔ782, which is a member of the α-amylase family GH57. The results revealed that the optimum temperature for Pul-HJΔ782 was 100 °C, and its thermostability at 100 °C improved after truncation. Less than 15% of its enzyme activity was lost after 1 h of incubation at 100 °C, and 57% activity remained after 5 h of treatment. Truncation significantly improved the overall pH tolerance range of Pul-HJΔ782, and its stability in the pH range 4–8 was over 80% relative activity from an average of 60%. The sequence and structural model of Pul-HJΔ782 was analyzed, and its instability index was reduced significantly. Furthermore, the hydrolysates of the truncated and wild-type pullulanase were analyzed, and the enzymatic digestion efficiency of the truncated Pul-HJΔ782 was higher.

The potential role of yeasts in the mitigation of health issues related to beer consumption

Food consumption of healthier products has become an essential trend in the food sector. This is also the case in beer, a biochemical process of transformation performed by yeast cells. More and more studies proclaim the need to reduce ethanol content in alcoholic drinks, certainly the most important health issue of beer consumption. In this review we gather key health issues related to beer consumption and the last advances regarding the use of yeast to attenuate those health problems. Furthermore, we have included the latest findings about the general positive impact of yeast in health as a consequence of its ability to biotransform polyphenolic compounds present in the wort, producing healthy compounds as hydroxytyrosol or melatonin, and its ability to perform as a probiotic driver. Besides, a group of population with chronic diseases as diabetes or celiac disease could take advantage of low carbohydrate or gluten-free beers, respectively. The role of yeast in beer production has been traditionally associated to its fermentative power. But here we have found a change in this dogma in the last years toward yeasts being a main driver to enhance healthy aspects of beer. The key findings are discussed and possible future directions are proposed.

In-Depth Characterization of Debranching Type I Pullulanase from Priestia koreensis HL12 as Potential Biocatalyst for Starch Saccharification and Modification

Pullulanase is an effective starch debranching enzyme widely used in starch saccharification and modification. In this work, the biochemical characteristics and potential application of a new type I pullulanase from Priestia koreensis HL12 (HL12Pul) were evaluated and reported for the first time. Through in-depth evolutionary analysis, HL12Pul was classified as type I pullulanase belonging to glycoside hydrolase family 13, subfamily 14 (GH13_14). HL12Pul comprises multi-domains architecture, including two carbohydrate-binding domains, CBM68 and CBM48, at the N-terminus, the TIM barrel structure of glycoside hydrolase family 13 (GH13) and C-domain. Based on sequence analysis and experimental cleavage profile, HL12Pul specifically hydrolyzes only α-1,6 glycosidic linkage-rich substrates. The enzyme optimally works at 40 °C, pH 6.0, with the maximum specific activity of 181.14 ± 3.55 U/mg protein and catalytic efficiency (kcat/Km) of 49.39 mL/mg·s toward pullulan. In addition, HL12Pul worked in synergy with raw starch-degrading α-amylase, promoting raw cassava starch hydrolysis and increasing the sugar yield by 2.9-fold in comparison to the α-amylase alone in a short reaction time. Furthermore, HL12Pul effectively produces type III-resistant starch (RSIII) from cassava starch with a production yield of 70%. These indicate that HL12Pul has the potential as a biocatalyst for starch saccharification and modification.

A Bibliometric Analysis and Review of Pullulan-Degrading Enzymes—Past and Current Trends

Starch and pullulan degrading enzymes are essential industrial biocatalysts. Pullulan-degrading enzymes are grouped into pullulanases (types I and type II) and pullulan hydrolase (types I, II and III). Generally, these enzymes hydrolyse the α-1,6 glucosidic bonds (and α-1,4 for certain enzyme groups) of substrates and form reducing sugars such as glucose, maltose, maltotriose, panose or isopanose. This review covers two main aspects: (i) bibliometric analysis of publications and patents related to pullulan-degrading enzymes and (ii) biological aspects of free and immobilised pullulan-degrading enzymes and protein engineering. The collective data suggest that most publications involved researchers within the same institution or country in the past and current practice. Multi-national interaction shall be improved, especially in tapping the enzymes from unculturable prokaryotes. While the understanding of pullulanases may reach a certain extend of saturation, the discovery of pullulan hydrolases is still limited. In this report, we suggest readers consider using the next-generation sequencing technique to fill the gaps of finding more new sequences encoding pullulan-degrading enzymes to expand the knowledge body of this topic.

Regulate the hydrophobic motif to enhance the non-classical secretory expression of Pullulanase PulA in Bacillus subtilis

Bacillus subtilis has been widely used as a prokaryotic host for the secretory expression of heterologous proteins. In this study, a pullulanase (PulA) from Anoxybacillus sp. LM18-11 was firstly identified to be expressed in Bacillus subtilis 1A751 through non-classical secretion pathway. Results showed that both the N- and C-terminal regions of PulA were essential for its soluble expression. To explore its specific structural basis of secretion in B. subtilis, we revealed a hydrophobic motif A501-H507 which is vital for the secretion of the whole protein of PulA. Through a series of site-specific mutagenesis, the triple-sites mutants R503E/I506E/H507E and R503E/I506Y/H507E showed the highest extracellular activity (160.07 U/mL) and total activity (243.37 U/mL) which was 1.71 times and 1.55 times higher than those of PulA. The highest secretion rate of mutant I506E/H507E was more than 50% which was 34.72% higher comparing with that of PulA. The glutamic acid substitution on these three key surface sites which decreased the surface hydrophobicity of that region was confirmed to be beneficial to improve the secretory expression of PulA. This novel discovery for the secretory expression of PulA in B. subtilis would make a new perspective on regulating a kind of non-classical secretion in B. subtilis.