Augmented production of alginate oligosaccharides by the Pseudomonas mendocina NK-01 mutant

Process and applications of alginate oligosaccharides with emphasis on health beneficial perspectives

Alginates are linear polymers comprising 40% of the dry weight of algae possess various applications in food and biomedical industries. Alginate oligosaccharides (AOS), a degradation product of alginate, is now gaining much attention for their beneficial role in food, pharmaceutical and agricultural industries. Hence this review was aimed to compile the information on alginate and AOS (prepared from seaweeds) during 1994-2020. As per our knowledge, this is the first review on the potential use of alginate oligosaccharides in different fields. The alginate derivatives are grouped according to their applications. They are involved in the isolation process and show antimicrobial, antioxidant, anti-inflammatory, antihypertension, anticancer, and immunostimulatory properties. AOS also have significant applications in prebiotics, nutritional supplements, plant growth development and others products.

Comparison of Biochemical Characteristics, Action Models, and Enzymatic Mechanisms of a Novel Exolytic and Two Endolytic Lyases with Mannuronate Preference

Recent explorations of tool-like alginate lyases have been focused on their oligosaccharide-yielding properties and corresponding mechanisms, whereas most were reported as endo-type with α-L-guluronate (G) preference. Less is known about the β-D-mannuronate (M) preference, whose commercial production and enzyme application is limited. In this study, we elucidated Aly6 of Flammeovirga sp. strain MY04 as a novel M-preferred exolytic bifunctional lyase and compared it with AlgLs of Pseudomonas aeruginosa (Pae-AlgL) and Azotobacter vinelandii (Avi-AlgL), two typical M-specific endolytic lyases. This study demonstrated that the AlgL and heparinase_II_III modules play indispensable roles in determining the characteristics of the recombinant exo-type enzyme rAly6, which is preferred to degrade M-enriched substrates by continuously cleaving various monosaccharide units from the nonreducing end, thus yielding various size-defined ΔG-terminated oligosaccharides as intermediate products. By contrast, the endolytic enzymes Pae-rAlgL and Avi-rAlgL varied their action modes specifically against M-enriched substrates and finally degraded associated substrate chains into various size-defined oligosaccharides with a succession rule, changing from ΔM to ΔG-terminus when the product size increased. Furthermore, site-directed mutations and further protein structure tests indicated that H¹⁹⁵NHSTW is an active, half-conserved, and essential enzyme motif. This study provided new insights into M-preferring lyases for novel resource discoveries, oligosaccharide preparations, and sequence determinations.

Alginate derived functional oligosaccharides: Recent developments, barriers, and future outlooks

Alginate is a biopolymer used extensively in the food, pharmaceutical, and chemical industries. Alginate oligosaccharides (AOS) derived from alginate exhibit superior biological activities and therapeutic potential. Alginate lyases with characteristic substrate specificity can facilitate the production of a broad array of AOS with precise structure and functionality. By adopting innovative analytical tools in conjunction with focused clinical studies, the structure-bioactivity relationship of a number of AOS has been brought to light. This review covers fundamental aspects and recent developments in AOS research. Enzymatic and microbial processes involved in AOS production from brown algae and sequential steps involved in AOS structure elucidation are outlined. Biological mechanisms underlying the health benefits of AOS and their potential industrial and therapeutic applications are elaborated. Withal, various challenges in AOS research are traced out, and future directions, specifically on recombinant systems for AOS preparation, are delineated to further widen the horizon of these exceptional oligosaccharides.

Preparation of alginate oligosaccharides and their biological activities in plants: A review

Alginate oligosaccharide (AOS) is the degradation product of alginates extracted from brown algae. As a multifunctional oligomer, it has attracted widespread attention in plant research. Different methods of preparation generate AOS possessing diverse structural properties, and result in differences in AOS activity. In this review, the methods of preparation and characterization of AOS are briefly summarized, followed by a systematic introduction to the activity and mechanisms of AOS in plants. AOS can act as a growth promoter at different growth stages of plants. AOS also enhances resistance to pathogens, drought, salt, heavy metals and other stressors by triggering plant immunity, exerting bioactivity just like a pathogen-associated molecular pattern. In addition, AOS can regulate ABA biosynthesis and metabolite to preserve fruit quality and enhance shelf life. This review provides a comprehensive summary of the biological activity of AOS in plants, which will support research and the application of AOS treatments for plants in the future.

Enhanced synthesis of alginate oligosaccharides in Pseudomonas mendocina NK-01 by overexpressing MreB

This study aimed to investigate the effects of cytoskeleton protein MreB on bacterial cell morphology and the synthesis of alginate oligosaccharides (AO) and polyhydroxyalkanoate (PHA) by Pseudomonas mendocina NK-01. To overexpress the mreB gene, an expression vector encoding MreB-GFP fusion protein was constructed. The scanning electron microscope (SEM) showed that cells expressing MreB were longer than the wild ones, which agrees with MreB's relationship with the synthesis of peptidoglycan. Cells expressing the MreB-GFP fusion protein emitted green fluorescence under a fluorescence microscope, suggesting that MreB was functionally expressed in strain NK-01. Under a confocal laser scanning microscope, MreB was observed as located around the cell membrane. Furthermore, the recombinant strain could synthesize 0.961 g/L AO, which was 5.86-fold higher than wild-type strain. Through the medium optimization test, we finally selected the addition of 20 g/L glucose as the optimal glycogen addition for AO fermentation based on a high AO yield and high substrate transformation efficiency. The results indicated that overexpression of MreB affected the cell morphology, the activity of AO polymerase, and the efficiency of AO secretion. However, the synthesis of PHA for recombinant strain was slightly reduced. The results suggested that the overexpression of this cytoskeleton protein affected the yield of specific intracellular and extracellular products.

Production of a novel medium chain length poly(3-hydroxyalkanoate) using unprocessed biodiesel waste and its evaluation as a tissue engineering scaffold

This study demonstrated the utilization of unprocessed biodiesel waste as a carbon feedstock for Pseudomonas mendocinaCH50, for the production of PHAs. A PHA yield of 39.5% CDM was obtained using 5% (v/v) biodiesel waste substrate. Chemical analysis confirmed that the polymer produced was poly(3‐hydroxyhexanoate‐co‐3‐hydroxyoctanoate‐co‐3‐hydroxydecanoate‐co‐3‐hydroxydodecanoate) or P(3HHx‐3HO‐3HD‐3HDD). P(3HHx‐3HO‐3HD‐3HDD) was further characterized and evaluated for its use as a tissue engineering scaffold (TES). This study demonstrated that P(3HHx‐3HO‐3HD‐3HDD) was biocompatible with the C2C12 (myoblast) cell line. In fact, the % cell proliferation of C2C12 on the P(3HHx‐3HO‐3HD‐3HDD) scaffold was 72% higher than the standard tissue culture plastic confirming that this novel PHA was indeed a promising new material for soft tissue engineering.

Efficient production of polyhydroxyalkanoates (PHAs) from Pseudomonas mendocina PSU using a biodiesel liquid waste (BLW) as the sole carbon source

Conditions for the optimal production of polyhydroxyalkanoate (PHA) by Pseudomonas mendocina PSU using a biodiesel liquid waste (BLW) were determined by response surface methodology. These were an initial carbon to nitrogen ratio (C/N) of 40 (mole/mole), an initial pH of 7.0, and a temperature of 35 °C. A biomass and PHA concentration of 3.65 g/L and about 2.6 g/L (77% DCW), respectively, were achieved in a growth associated process using 20 g/L glycerol in the BLW after 36 h of exponential growth. The PHA monomer compositions were 3HB (3-hydroxybutyrate), a short-chain-length-PHA, and the medium-chain-length-PHA e.g. 3-hydroxyoctanoate and 3-hydroxydecanoate. Both the phbC and phaC genes were characterized. The phbC enzyme had not been previously detected in a Pseudomonas mendocina species. A 2.15 g/L of an exopolysaccharide, alginate, was also produced with a similar composition to that of other Pseudomonas species.

Nitric oxide removal by wastewater bacteria in a biotrickling filter

Nitric oxide (NO) is one of the most important air pollutants in atmosphere mainly emitted from combustion source. A biotrickling filter was designed and operated to remove NO from an air stream using bacteria extracted from the sewage sludge of a municipal sewage treatment plant. To obtain the best operation conditions for the biotrickling filter, orthogonal experiments (L9(3(4))) were designed. Inlet oxygen concentration was found to be the most significant factor of the biotrickling filter and has a significant negative effect on the system. The optimal conditions of the biotrickling filter occurred at a temperature of 40°C, a pH of 8.0 and a chemical oxygen demand of 165 mg/L in the recycled water with no oxygen in the system. The bacteria sample was detected by DNA sequencing technology and showed 93%-98% similarity to Pseudomonas mendocina. Moreover, a full gene sequencing results indicated the bacterium was a brand new strain and named as P. mendocina DLHK. This strain can transfer nitrate to organic nitrogen. The result suggested the assimilation nitrogen process in this system. Through the isotope experimental analysis, two intermediate products ((15)NO and (15)N2O) were found. The results indicated the denitrification function and capability of the biotrickling filter in removing NO.