Bidyut Ranjan Mohapatra

A Gram-stain-negative, non-motile and yellowish-orange colored bacterium, designated as Alg-005^T, was isolated from decomposing pelagic Sargassum biomass stranded off the coast of Barbados. The 16S rRNA gene analysis revealed that the strain Alg-005^T closely relates to Chryseobacterium daecheongense DSM 15,235^T (99.1%) and C. defluvii DSM 14,219^T (98.7%). Subsequently, genome-based analysis was performed to assess the evolutionary relatedness of strain Alg-005^T via determination of the overall genomic relatedness indices (OGRI) values, dDDH (digital DNA–DNA hybridization), ANI (average nucleotide identity), orthoANI (orthologous average nucleotide identity) and AAI (average amino acid identity). The dDDH, ANI, orthoANI and AAI values between the genome sequences of the strain Alg-005^T and its closest relative C. daecheongense DSM 15,235^T were recorded as 33.3%, 87.1%, 87.4% and 91.5%, respectively. These OGRI values were well below the recommended cut-off values (dDDH < 70%, ANI < 95–96%, orthoANI < 95–96% and AAI < 95%) for delineation of a novel bacterial species. The unique cellular fatty acids of the strain Alg-005^T compared to C. daecheongense DSM 15,235^T were identified as C14:0, iso-C14:0 3-OH, iso-C16:0, C16:1 ω7c/C16:1 ω6c, iso-C17:1 ω5c, iso-C17:1 ω7c, iso-C17:1 ω12c, C18:0 and C18:1 ω7c. The distinct phenotypic characteristics of the strain Alg-005^T compared to C. daecheongense DSM 15,235^T include, the utilization of D-galactose, L-histidine, α-ketoglutaric acid, L-maleic acid, D-maltose, propionic acid, quinic acid and D-salicin. Therefore, the strain Alg-005^T represents a novel species of genus Chryseobacterium, for which the name Chryseobacterium barbadense sp. nov. is proposed. The type strain is Alg-005^T (= DSM 117339^T = LMG 33495^T).

Alginate lyase has the potential for the ecofriendly depolymerization of alginate and generation of value-added products important in agriculture, bioenergy, food processing, medical diagnostic and pharmaceutical industries. Substantial research has focused on the cost-effective production of alginate lyase via screening of potent microbial isolates for use as biocatalysts and the optimization of fermentation media with low-cost feedstocks. This study evaluated the alginate lyase-producing efficacy of a novel Pseudomonas sp. LB56 (GenBank accession no. MT176182) isolated from Sargassum seaweed waste. The feedstock for solid-state fermentation (SSF) was decomposed Sargassum biomass amended with cow dung. The production of alginate lyase was maximal using 9.5 g Sargassum, 14 g cow dung and at pH 8 after optimization via a 2³–factorial central composite design. Comparative modelling and molecular docking studies were conducted to elucidate the 3D structure of the alginate lyase of this novel isolate, as well as to investigate its catalytic interactions with different polymeric sizes of alginate [polymannuronate (mannuronate disaccharide and mannuronate trisaccharide), polyguluronate (guluronate disaccharide and guluronate trisaccharide) and alginate]. The overall results suggest that biowaste (Sargassum seaweed amended with cow dung) can be used as a feedstock for economical production of alginate lyase. Additionally, the identified active site residues of alginate lyase, which were shared by different polymers of alginate, can be tailored via rational and/or combinatorial approaches for efficient biotransformation of alginate-enriched wastes into biologically active alginate oligomers and third generation biofuels.

The applications of β-mannanase for environmentally friendly manufacture of biofuels, biological detergents and health-promoting manno-oligosaccharides have garnered research interests for sustainable and cost-effective production of this industrially important enzyme by identifying potent microorganisms to be applied as the biocatalyst and by using cheap feedstocks in the fermentation medium. The current study has optimized the solid-state fermentation (SSF) conditions with cow dung as the economical feedstock for maximal production of β-mannanase by a novel Streptomyces sp. LB66 (GenBank accession no. MT228944) isolated from Sargassum seaweed waste. Furthermore, homology modelling and molecular docking approaches were applied to elucidate the 3D-structure and enzyme–substrate interactions of modelled β-mannanase. The optimization of SSF components via a 2³-factorial central composite design recorded the maximal β-mannanase production (36.8 ± 1.74 U/mg-protein) with 18 g cow dung, and at pH 7.5 and 30 °C incubation temperature. Molecular docking of modelled β-mannanase with mannobiose, mannotriose and mannotetraose as substrates displayed participations of six shared active site residues (Arg46, Ala54, Val56, Gln279, Leu281 and Gly282) for the binding. These identified active site residues can be targeted via directed evolution approaches in tailoring the enzymatic traits for overproduction of β-mannanase and in ecofriendly bioprocessing of diverse lignocellulosic and seaweed waste.

The potential applications of β-mannanase in bioenergy, biorefinery, detergent, fodder, food processing, oil and gas, pharmaceutical, pulp and paper and textile industries, and the high cost of commercially available enzyme have attracted considerable research efforts to identify potent microbial strains for cost-effective production of this enzyme. The advantage of microbial biocatalyst is that the crude enzyme can be used directly in bioprocessing instead of the purified enzyme. In this study, β-mannanase was extracted from a novel Streptomyces sp. Alg-S25 (GenBank accession no. MK494177) and immobilized onto chitosan nanoparticles using glutaraldehyde as a crosslinker. The covalent binding of β-mannanase onto chitosan nanoparticles was confirmed by Fourier-transform infrared spectroscopy. The functionalized chitosan nanoparticles retained 83.6% ± 3.46% of β-mannanase activity. Free and immobilized β-mannanase of this novel Streptomyces sp. Alg-S25 displayed maximal activities at pH 7.5 and at temperature 50 °C and 55 °C, respectively. Immobilized β-mannanase exhibited higher values of activation energy (47.4 kJ/mol), enthalpy (44.9 kJ/mol) and entropy (–73.5 J/mol/K) of catalysis compared to the free enzyme. The substrate-specific kinetic analysis suggested that the immobilized β-mannanase had a strong affinity toward locust bean galactomannan by showing a low K _m (4.94 mg/mL) and a high V _max (93.5 U/mg-protein) values. Furthermore, the immobilized β-mannanase was not affected by 2% NaCl and retained 81.2% of the maximal activity after 10 cycles of successive reuse. These results indicate the potential of chitosan nanoparticle-immobilized β-mannanase for sustainable and cost-effective bioprocessing of mannan-containing agricultural, forest, seaweed and industrial wastes.

The pathogenesis of mycoplasmas requires their attachment to the epithelial mucosa membrane of the host cells, followed by colonisation and necrotic destruction of the submucosal tissue. The extent of this pathogenesis depends on the ability of species of Mycoplasma to effectively attach and invade the host’s tissue. In this regard, the cytadherence tip organelle has evolved within the mycoplasmas to accomplish this feat. However, species of Mycoplasma that do not possess the specialized structure remain virulent with the use of surface-membrane lipoproteins. The lipoprotein ligands bind to sulfatides and sialoglycoconjugates on the host’s mucosa membranes. This host-mycoplasma interaction, though poorly studied, appears to have a wide underlying array of complex molecular mechanisms, which after activation trigger cytadherence, immunomodulation and virulence. Mycoplasmas with their highly redundant minimal genomes display dynamic genotypic and phenotypic plasticity; a trait that has allowed them to adapt, persist and survive successfully in adverse niches through circumvention and tempering of the host’s humoral immune response. Additionally, the linkages between the mycoplasmas persistence and chronic inflammatory diseases in humans necessitate examining the host-mycoplasma interaction at the proteogenomic level. This paper provides an overview on the molecular mechanisms involved in cytadherence, surface-membrane antigenic variation and survival strategies of human urogenital mycoplasmas.