Cloning and characterization of a novel oligoalginate lyase from a newly isolated bacterium Sphingomonas sp. MJ-3

Screening of Alginate Lyase-Producing Bacteria and Optimization of Media Compositions for Extracellular Alginate Lyase Production

Background:

Alginate is a linear polysaccharide consisting of guluronate (polyG) and mannuronate (polyM) subunits.

Methods:

In the initial screening of alginate-degrading bacteria from soil, 10 isolates were able to grow on minimal medium containing alginate. The optimization of cell growth and alginate lyase (algL) production was carried out by the addition of 0.8% alginate and 0.2-0.3 M NaCl to the culture medium. Of 10 isolates, one was selected based on its fast growth rate on minimal 9 medium containing 0.4% sodium alginate. The selected bacterium, identified based on morphological and biochemical characteristics, as well as 16S rDNA sequence data, was confirmed to be an isolate belonging to the genus Bacillus and designated as Bacillus sp. TAG8.

Results:

The results showed the ability of Bacillus sp. TAG8 in utilizing alginate as a sole carbon source. Bacillus sp. TAG8 growth and algL production were augmented with an increase in sodium alginate concentration and also by the addition of 0.2-0.3 M NaCl. Molecular analysis of TAG8 algL gene showed 99% sequence identity with algL of Pseudomonasaeruginosa PAO1. The algL produced by Bacillus sp. TAG8 cleaved both polyM and polyG blocks in alginate molecule, as well as acetylated alginate residues, confirming the bifunctionality of the isolated lyase.

Conclusion:

The identification of novel algL genes from microbial communities constitutes a new approach for exploring lyases with specific activity against bacterial alginates and may thus contribute to the eradication of persistent biofilms from clinical samples.

Characterization of a New Cold-Adapted and Salt-Activated Polysaccharide Lyase Family 7 Alginate Lyase from Pseudoalteromonas sp. SM0524

Marine bacterial alginate lyases play a role in marine alginate degradation and carbon cycling. Although a large number of alginate lyases have been characterized, reports on alginate lyases with special characteristics are still rather less. Here, a gene alyPM encoding an alginate lyase of polysaccharide lyase family 7 (PL7) was cloned from marine Pseudoalteromonas sp. SM0524 and expressed in Escherichia coli. AlyPM shows 41% sequence identity to characterized alginate lyases, indicating that AlyPM is a new PL7 enzyme. The optimal pH for AlyPM activity was 8.5. AlyPM showed the highest activity at 30°C and remained 19% of the highest activity at 5°C. AlyPM was unstable at temperatures above 30°C and had a low T_m of 37°C. These data indicate that AlyPM is a cold-adapted enzyme. Moreover, AlyPM is a salt-activated enzyme. AlyPM activity in 0.5–1.2 M NaCl was sixfolds higher than that in 0 M NaCl, probably caused by a significant increase in substrate affinity, because the K_m of AlyPM in 0.5 M NaCl decreased more than 20-folds than that in 0 M NaCl. AlyPM preferably degraded polymannuronate and mainly released dimers and trimers. These data indicate that AlyPM is a new PL7 endo-alginate lyase with special characteristics.

Enzymatic Hydrolysis of Alginate to Produce Oligosaccharides by a New Purified Endo-Type Alginate Lyase

Enzymatic hydrolysis of sodium alginate to produce alginate oligosaccharides has drawn increasing attention due to its advantages of containing a wild reaction condition, excellent gel properties and specific products easy for purification. However, the efficient commercial enzyme tools are rarely available. A new alginate lyase with high activity (24,038 U/mg) has been purified from a newly isolated marine strain, Cellulophaga sp. NJ-1. The enzyme was most active at 50 °C and pH 8.0 and maintained stability at a broad pH range (6.0-10.0) and temperature below 40 °C. It had broad substrate specificity toward sodium alginate, heteropolymeric MG blocks (polyMG), homopolymeric M blocks (polyM) and homopolymeric G blocks (polyG), and possessed higher affinity toward polyG (15.63 mM) as well as polyMG (23.90 mM) than polyM (53.61 mM) and sodium alginate (27.21 mM). The TLC and MS spectroscopy analysis of degradation products suggested that it completely hydrolyzed sodium alginate into oligosaccharides of low degrees of polymerization (DPs). The excellent properties would make it a promising tool for full use of sodium alginate to produce oligosaccharides.

Falsirhodobacter sp. alg1 Harbors Single Homologs of Endo and Exo-Type Alginate Lyases Efficient for Alginate Depolymerization

Alginate-degrading bacteria play an important role in alginate degradation by harboring highly efficient and unique alginolytic genes. Although the general mechanism for alginate degradation by these bacteria is fairly understood, much is still required to fully exploit them. Here, we report the isolation of a novel strain, Falsirhodobacter sp. alg1, the first report for an alginate-degrading bacterium from the family Rhodobacteraceae. Genome sequencing reveals that strain alg1 harbors a primary alginate degradation pathway with only single homologs of an endo- and exo-type alginate lyase, AlyFRA and AlyFRB, which is uncommon among such bacteria. Subsequent functional analysis showed that both enzymes were extremely efficient to depolymerize alginate suggesting evolutionary interests in the acquirement of these enzymes. The exo-type alginate lyase, AlyFRB in particular could depolymerize alginate without producing intermediate products making it a highly efficient enzyme for the production of 4-deoxy-L-erythro-5-hexoseulose uronic acid (DEH). Based on our findings, we believe that the discovery of Falsirhodobacter sp. alg1 and its alginolytic genes hints at the potentiality of a more diverse and unique population of alginate-degrading bacteria.

Cloning and characterization of two thermo- and salt-tolerant oligoalginate lyases from marine bacterium Halomonas sp

Two new alginate lyase genes, oalY1 and oalY2, have been cloned from the newly isolated marine bacterium Halomonas sp. QY114 and expressed in Escherichia coli The deduced alginate lyases, OalY1 and OalY2, belonged to polysaccharide lyase (PL) family 17 and showed less than 45% amino acid identity with all of the characterized oligoalginate lyases. OalY1 and OalY2 exhibited the highest activities at 45°C and 50°C, respectively. Both of them showed more than 50% of the highest activity at 60°C, and 20% at 80°C. In addition, they were salt-dependent and salt-tolerant since both of them showed the highest activity in the presence of 0.5 M NaCl and preserved 63% and 68% of activity in the presence of 3 M NaCl. Significantly, OalY1 and OalY2 could degrade both polyM and polyG blocks into alginate monosaccharides in an exo-lytic type, indicating that they are bifunctional alginate lyases. In conclusion, our study indicated that OalY1 and OalY2 are good candidates for alginate saccharification application, and the salt-tolerance may present an exciting new concept for biofuel production from native brown seaweeds.

Defluviitalea phaphyphila sp. nov., a Novel Thermophilic Bacterium That Degrades Brown Algae

Brown algae are one of the largest groups of oceanic primary producers for CO2 removal and carbon sinks for coastal regions. However, the mechanism for brown alga assimilation remains largely unknown in thermophilic microorganisms. In this work, a thermophilic alginolytic community was enriched from coastal sediment, from which an obligate anaerobic and thermophilic bacterial strain, designated Alg1, was isolated. Alg1 shared a 16S rRNA gene identity of 94.6% with Defluviitalea saccharophila LIND6LT2(T). Phenotypic, chemotaxonomic, and phylogenetic studies suggested strain Alg1 represented a novel species of the genus Defluviitalea, for which the name Defluviitalea phaphyphila sp. nov. is proposed. Alg1 exhibited an intriguing ability to convert carbohydrates of brown algae, including alginate, laminarin, and mannitol, to ethanol and acetic acid. Three gene clusters participating in this process were predicted to be in the genome, and candidate enzymes were successfully expressed, purified, and characterized. Six alginate lyases were demonstrated to synergistically deconstruct alginate into unsaturated monosaccharide, followed by one uronic acid reductase and two 2-keto-3-deoxy-d-gluconate (KDG) kinases to produce pyruvate. A nonclassical mannitol 1-phosphate dehydrogenase, catalyzing D-mannitol 1-phosphate to fructose 1-phosphate in the presence of NAD(+), and one laminarase also were disclosed. This work revealed that a thermophilic brown alga-decomposing system containing numerous novel thermophilic alginate lyases and a unique mannitol 1-phosphate dehydrogenase was adopted by the natural ethanologenic strain Alg1 during the process of evolution in hostile habitats.

Engineering broad-spectrum digestion of polyuronides from an exolytic polysaccharide lyase

BACKGROUND

Macroalgae represents a promising source of fermentable carbohydrates for use in the production of energy efficient biofuel. The primary carbohydrate in brown algae is the uronic acid-containing alginate, whereas green algae contains a significant amount of glucuronan. A necessary step in the conversion of these polyuronides to bioethanol is saccharification, which can be achieved by enzymatic or chemical degradation.

RESULTS

Polysaccharide lyases are a class of enzymes which cleave uronic acid-containing glycans via a β-elimination mechanism, acting both endo- and exolytically on their substrates. In the present work, we characterize a putative alginate lyase from Stenotrophomonas maltophilia K279a (Smlt2602) and describe a H208F mutant that, in addition to cleaving alginate-based substrates, displays significant, exolytic glucuronan activity.

CONCLUSIONS

To our knowledge this is the first polysaccharide lyase to act exolytically on glucuronan and is an attractive candidate for the broad-spectrum digestion of polyuronides into fermentable monomers.

Impact of different alginate lyases on combined cellulase–lyase saccharification of brown seaweed

Alginate attack characteristics and impact on cellulase–lyase catalyzed saccharification of brown seaweed were compared for three microbial PL7 alginate lyases (EC 4.2.2.-) two of them heterologously expressed in Escherichia coli as part of the work.

Site-Directed Mutagenesis-Based Functional Analysis and Characterization of Endolytic Lyase Activity of N- and C-Terminal Domains of a Novel Oligoalginate Lyase from Sphingomonas sp. MJ-3 Possessing Exolytic Lyase Activity in the Intact Enzyme

A novel oligoalginate lyase from a marine bacterium, Sphingomonas sp. strain MJ-3, exhibited a unique alginate degradation activity that completely depolymerizes alginate to monomers through the formation of oligomers. In order to reveal the reason why MJ-3 oligoalginate can exhibit both endolytic and exolytic alginate lyase activities, ten mutants were developed and characterized on the basis of homology modeling. When the recombinant cell lysates containing the mutated proteins of MJ-3 oligoalginate lyase were allowed to react with alginate, the Asn177Ala, His178Ala, Tyr234Phe, His389Ala, and Tyr426Phe mutants showed reduced oligoalginate lyase activity, whereas the Arg236Ala mutant exhibited endolytic activity. Interestingly, the overexpressed Arg236Ala protein (79.6 kDa) was proteolytically cleaved into two fragments, i.e., the N-terminal 32.0-kDa and the C-terminal 47.6-kDa fragments. Both the purified N-terminal and C-terminal fragments showed endolytic lyase activity. They preferentially degraded a heteropolymeric (polyMG) block than poly-β-D-mannuronate (polyM) or poly-α-L-guluronate (polyG) blocks. These results suggest that the oligoalginate lyase activity of MJ-3 enzyme is derived from the cooperative interaction between the N- and C-terminal endolytic alginate lyase domains in the intact enzyme.

Cloning and characterization of the first polysaccharide lyase family 6 oligoalginate lyase from marine Shewanella sp. Kz7

Alginate, the most abundant carbohydrate in brown macroalgae, is widely used in the food and pharmaceutical industries. Recently, alginate has attracted increasing attention, as it may serve as an alternative biomass for the production of biofuel. The degradation of alginate into monomeric units is the prerequisite for bioethanol production. All known oligoalginate lyases belong to the polysaccharide lyase (PL) family 7, 14, 15 and 17, and most of them preferred to degrade the polyM blocks to yield 4-deoxy-l-erythro-5-hexoseulose uronic acid as the primary product. In this study, we cloned an oligoalginate lyase gene, oalS6, from Shewanella sp. Kz7 and expressed it in Escherichia coli. The PL family 6 oligoalginate lyase (OalS6) has no significant sequence similarity with other known oligoalginate lyases. OalS6 contains a chondroitinase-like domain and was assigned to the PL family 6. This lyase is an exo-type oligoalginate lyase and prefer to depolymerize polyG block into 2, 4, 5, 6-tetrahydroxytetrahydro-2H-pyran-2-carboxylic acid. All of these results indicate that OalS6 is a novel oligoalginate lyase that is structurally and functionally different from other known oligoalginate lyases. This finding provides new insights into the development of biofuel processing biotechnologies from seaweed.

Alginate lyase: Review of major sources and classification, properties, structure-function analysis and applications

Alginate lyases catalyze the degradation of alginate, a complex copolymer of α-L-guluronate and its C5 epimer β-D-mannuronate. The enzymes have been isolated from various kinds of organisms with different substrate specificities, including algae, marine mollusks, marine and terrestrial bacteria, and some viruses and fungi. With the progress of structural biology, many kinds of alginate lyases of different polysaccharide lyases families have been characterized by obtaining crystal structures, and the catalytic mechanism has also been elucidated. Combined with various studies, we summarized the source, classification and properties of the alginate lyases from different polysaccharide lyases families. The relationship between substrate specificity and protein sequence was also investigated.

Structure of a PL17 family alginate lyase demonstrates functional similarities among exotype depolymerases

Brown macroalgae represent an ideal source for complex polysaccharides that can be utilized as precursors for cellulosic biofuels. The lack of recalcitrant lignin components in macroalgae polysaccharide reserves provides a facile route for depolymerization of constituent polysaccharides into simple monosaccharides. The most abundant sugars in macroalgae are alginate, mannitol, and glucan, and although several classes of enzymes that can catabolize the latter two have been characterized, studies of alginate-depolymerizing enzymes have lagged. Here, we present several crystal structures of Alg17c from marine bacterium Saccharophagus degradans along with structure-function characterization of active site residues that are suggested to be involved in the exolytic mechanism of alginate depolymerization. This represents the first structural and biochemical characterization of a family 17 polysaccharide lyase enzyme. Despite the lack of appreciable sequence conservation, the structure and β-elimination mechanism for glycolytic bond cleavage by Alg17c are similar to those observed for family 15 polysaccharide lyases and other lyases. This work illuminates the evolutionary relationships among enzymes within this unexplored class of polysaccharide lyases and reinforces the notion of a structure-based hierarchy in the classification of these enzymes.

cDNA cloning and bacterial expression of a PL-14 alginate lyase from a herbivorous marine snail Littorina brevicula

Herbivorous marine snails like Littorina species are known to possess alginate lyases in their digestive tracts. The Littorina enzymes have been identified as endolytic polymannuronate (poly(M)) lyases (EC 4.2.2.3); however, it is still unclear which polysaccharide-lyase family (PL) the Littorina enzymes belong to, since no complete primary structure of Littorina enzymes has been determined. Thus, in the present study, we analyzed the primary structure of LbAly28, a 28kDa alginate lyase isozyme of Littorina brevicula, by the cDNA method. LbAly28 cDNAs were amplified by PCR followed by 5'- and 3'-RACE PCRs from the L. brevicula hepatopancreas cDNA. A cDNA covering entire coding region of LbAly28 consisted of 1129bp and encoded an amino-acid sequence of 291 residues. The deduced amino-acid sequence comprised an initiation methionine, a putative signal peptide of 14 residues, a propeptide-like region of 16 residues, and a mature LbAly28 domain of 260 residues. The mature LbAly28 domain showed 43-53% amino-acid identities with other molluscan PL-14 enzymes. The catalytically important residues in PL-14 enzymes, which were identified in the Chlorella virus glucuronate-specific lyase vAL-1 and Aplysia poly(M) lyase AkAly30, were also conserved in LbAly28. Site-directed mutagenesis regarding these residues, that is, replacements of Lys94, Lys97, Thr121, Arg 123, Tyr135, and Tyr137 to Ala, decreased the activity of recombinant LbAly28 to various degrees. From these results we concluded that LbAly28 is a member of PL-14 alginate lyases. Besides the effects of above mutations, we noticed that the replacement of T121 by Ala changed the substrate preference of LbAly28. Namely, the activities toward sodium alginate and poly(MG)-block substrate increased and became comparable with the activity toward poly(M)-block substrate. This suggests that the region including T121 of LbAly28 closely relates to the recognition of poly(MG) region of alginate.

Molecular identification of a polyM-specific alginate lyase from Pseudomonas sp. strain KS-408 for degradation of glycosidic linkages between two mannuronates or mannuronate and guluronate in alginate

An alginate lyase gene of a newly isolated Pseudomonas sp. strain KS-408 was cloned by using PCR with the specific primers designed from homologous nucleotide sequences. A partial protein sequence of KS-408 alginate lyase was homology-modeled on the basis of the crystal structure of A1-III alginate lyase from Sphingomonas sp. strain A1. The proposed 3-D structure of KS-408 alginate lyase shows that Asn-198, His-199, Arg-246, and Tyr-253 residues are conserved for the catalytic active site. The recombinant KS-408-1F (with signal peptide) and KS-408-2F (without signal peptide) alginate lyases with the (His)6 tag consist of 393 (44.5 kDa) and 372 (42.4 kDa) amino acids with isoelectric points of 8.64 and 8.46, respectively. The purified recombinant KS-408 alginate lyase was very stable when it was incubated at 40 °C for 30 min. Alginate oligosaccharides produced by the KS-408-2F alginate lyase were purified on a Bio-Gel P2 column and analyzed by thin-layer chromatography, fast-protein liquid chromatography, and electrospray ionization mass spectrometry. 1H NMR data showed that the KS-408-2F alginate lyase cleaved the glycosidic linkages between two mannuronates (mannuronate-β(1–4)-mannuronate) or mannuronate and guluronate (mannuronate-β(1–4)-guluronate), indicating that the KS-408 alginate lyase is a polyM-specific lyase.