Cloning and Characterization of a Novel Agarase from a Newly Isolated Bacterium Simiduia sp. Strain TM-2 Able to Degrade Various Seaweeds

Comparative Genomic and Secretomic Analysis Provide Insights Into Unique Agar Degradation Function of Marine Bacterium Vibrio fluvialis A8 Through Horizontal Gene Transfer

Agarose-oligosaccharide production from agar degradation by agarase exhibits lots of advantages and good application prospects. In this study, a novel agar-degrading bacterium Vibrio sp. A8 was isolated from a red algae in the South China Sea. The whole genome sequencing with comparative genomic and secretomic analysis were used to better understand its genetic components about agar degradation. This strain exhibited good agarase production in artificial seawater after culture optimization. The complete genome (4.88 Mb) of this strain comprised two circular chromosomes (3.19 and 1.69 Mb) containing 4,572 protein-coding genes, 108 tRNA genes and 31 rRNA genes. This strain was identified as Vibrio fluvialis A8 by comparative genomic analysis based on genome phylogenetic tree and average nucleotide identity (ANI) similarity. Different from other 20 similar strains including three strains of the same species, V. fluvialis A8 possessed unique agar degradation ability with four β-agarases (GH50) and one α-1,3-L-NA2 hydrolase (GH117) due to the horizontal gene transfer. Secretomic analysis showed that only β-agarase (gene 3152) was abundantly expressed in the secretome of V. fluvialis A8. This agarase had a good substrate specificity and wide work conditions in complex environments, suggesting its potential application for agarose-oligosaccharide production.

Recombinant β-agarases: insights into molecular, biochemical, and physiochemical characteristics

Agarases (agarose 4-glycanohydrolase; EC 3.2.1.81) are class of enzymes that belong to glycoside hydrolase (GH) family capable of hydrolyzing agar. Their classification depends on hydrolysis pattern and product formation. Among all the agarases, β-agarases and the oligosaccharides formed by its action have fascinated quite a lot of industries. Ample of β-agarase genes have been endowed from marine sources such as algae, sea water, and marine sediments, and the expression of these genes into suitable host gives rise to recombinant β-agarases. These recombinant β-agarases have wide range of industrial applications due to its improved catalytic efficiency and stability in tough environments with ease of production on large scale. In this review, we have perused different types of recombinant β-agarases in consort with their molecular, physiochemical, and kinetic properties in detail and the significant features of those agarases are spotlighted. From the literature reviewed after 2010, we have found that the recombinant β-agarases belonged to the families GH16, GH39, GH50, GH86, and GH118. Among that, GH39, GH50, and GH86 belonged to clan GH-A, while the GH16 family belonged to clan GH-B. It was observed that GH16 is the largest polyspecific glycoside hydrolase family with ample number of β-agarases and the families GH50 and GH118 were found to be monospecific with only β-agarase activity. And, out of 84 non-catalytic carbohydrate-binding modules (CBMs), only CBM6 and CBM13 were professed in β-agarases. We witnessed a larger heterogeneity in molecular, physiochemical, and catalytic characteristics of the recombinant β-agarases including molecular mass: 32-132 kDa, optimum pH: 4.5-9, optimum temperature 16-60 °C, K _M: 0.68-59.8 mg/ml, and V _max: 0.781-11,400 U/mg. Owing to this extensive range of heterogeneity, they have lion's share in the multibillion dollar enzyme market. This review provides a holistic insight to a few aspects of recombinant β-agarases which can be referred by the upcoming explorers to this area.

Metatranscriptomics and Amplicon Sequencing Reveal Mutualisms in Seagrass Microbiomes

Terrestrial plants benefit from many well-understood mutualistic relationships with root- and leaf-associated microbiomes, but relatively little is known about these relationships for seagrass and other aquatic plants. We used 16S rRNA gene amplicon sequencing and metatranscriptomics to assess potential mutualisms between microorganisms and the seagrasses Zostera marina and Zostera japonica collected from mixed beds in Netarts Bay, OR, United States. The phylogenetic composition of leaf-, root-, and water column-associated bacterial communities were strikingly different, but these communities were not significantly different between plant species. Many taxa present on leaves were related to organisms capable of consuming the common plant metabolic waste product methanol, and of producing agarases, which can limit the growth of epiphytic algae. Taxa present on roots were related to organisms capable of oxidizing toxic sulfur compounds and of fixing nitrogen. Metatranscriptomic sequencing identified expression of genes involved in all of these microbial metabolic processes at levels greater than typical water column bacterioplankton, and also identified expression of genes involved in denitrification and in bacterial synthesis of the plant growth hormone indole-3-acetate. These results provide the first evidence using metatranscriptomics that seagrass microbiomes carry out a broad range of functions that may benefit their hosts, and imply that microbe-plant mutualisms support the health and growth of aquatic plants.

Characterization and overexpression of a glycosyl hydrolase family 16 beta-agarase YM01-1 from marine bacterium Catenovulum agarivorans YM01T

Agar, usually extracted from seaweed, has a wide variety of industrial applications due to its gelling and stabilizing characteristics. Agarases are the enzymes which hydrolyze agar into agar oligosaccharides. The produced agar oligosaccharides have been widely used in cosmetic, food, and medical fields due to their biological functions. A beta-agarase gene, YM01-1, was cloned and expressed from a marine bacterium Catenovulum agarivorans YM01^T. The encoding agarase of YM01-1 consisted of 331 amino acids with an apparent molecular mass of 37.7 kDa and a 23-amino-acids signal peptide. YM01-1 belongs to glycoside hydrolase 16 (GH16) family based on the amino acid sequence homology. The optimum pH and temperature for its activity was 7.0 and 50 °C, respectively. YM01-1 was stable at a pH of pH 6.0-9.0 and temperatures below 45 °C. Thin layer chromatography (TLC) and ion trap mass spectrometer of the YM01-1 hydrolysis products displayed that YM01-1 was an endo-type β-agarase and degrades agarose, neoagarohexaose, neoagarotetraose into neoagarobiose. The K_m, V_max, K_cat and K_cat/K_m values of the YM01-1 for agarose were 8.69 mg/ml, 4.35 × 10³ U/mg, 2.4 × 10³ s^-1 and 2.7 × 10⁶ s^-1 M^-1, respectively. Hence, the enzyme with high agarolytic activity and single end product was different from other GH16 agarases, which has potential applications for the production of oligosaccharides with remarkable activities.