Fucoidans, sulfated polysaccharides found in cell walls of brown algae, are considered as a promising antimicrobial component for various applications in medicine and the food industry. In this study, we compare the antibacterial properties of two fractions of fucoidan from the brown algae Fucus vesiculosus gathered in the littoral of the Barents Sea and sampled at different stages of purification. The crude fraction of fucoidan was isolated from algae by extraction with aqueous ethanol and sonication. The purified fraction was obtained by additional treatment of the crude fraction with a solution of calcium chloride. The structural features of both fractions were characterized in detail and their antibacterial effects against several Gram-positive and Gram-negative bacteria were compared by photometry, acridine orange staining assay, and atomic force microscopy. Fucoidan inhibited growth in all of the above microorganisms, showing a bacteriostatic effect with minimum inhibitory concentrations (MIC) in the range between 4 and 6 mg/mL, with E. coli being the most sensitive to both fractions. Changes in the chemical composition after treatment of the crude fraction with a solution of calcium chloride led to a decrease in the content of sulfates and uronic acids and diminished antibacterial activity.

Enzymes capable of modifying the sulfated polymeric molecule of fucoidan are mainly produced by different groups of marine organisms: invertebrates, bacteria, and also some fungi. We have discovered and identified a new strain of filamentous fungus Fusarium proliferatum LE1 (deposition number in Russian Collection of Agricultural Microorganisms is RCAM02409), which is a potential producer of fucoidan-degrading enzymes. The strain LE1 (RCAM02409) was identified on the basis of morphological characteristics and analysis of ITS sequences of ribosomal DNA. During submerged cultivation of F. proliferatum LE1 in the nutrient medium containing natural fucoidan sources (the mixture of brown algae Laminaria digitata and Fucus vesiculosus), enzymic activities of α-L-fucosidase and arylsulfatase were inducible. These enzymes hydrolyzed model substrates, para-nitrophenyl α-L-fucopyranoside and para-nitrophenyl sulfate, respectively. However, the α-L-fucosidase is appeared to be a secreted enzyme while the arylsulfatase was an intracellular one. No detectable fucoidanase activity was found during F. proliferatum LE1 growth in submerged culture or in a static one. Comparative screening for fucoidanase/arylsulfatase/α-L-fucosidase activities among several related Fusarium strains showed a uniqueness of F. proliferatum LE1 to produce arylsulfatase and α-L-fucosidase enzymes. Apart them, the strain was shown to produce other glycoside hydrolyses.

Microbially induced CaCO3 precipitation (MICP) is considered as an alternative green technology for cement self-healing and a basis for the development of new biomaterials. However, some issues about the role of bacteria in the induction of biogenic CaCO3 crystal nucleation, growth and aggregation are still debatable. Our aims were to screen for ureolytic calcifying microorganisms and analyze their MICP abilities during their growth in urea-supplemented and urea-deficient media. Nine candidates showed a high level of urease specific activity, and a sharp increase in the urea-containing medium pH resulted in efficient CaCO3 biomineralization. In the urea-deficient medium, all ureolytic bacteria also induced CaCO3 precipitation although at lower pH values. Five strains (B. licheniformis DSMZ 8782, B. cereus 4b, S. epidermidis 4a, M. luteus BS52, M. luteus 6) were found to completely repair micro-cracks in the cement samples. Detailed studies of the most promising strain B. licheniformis DSMZ 8782 revealed a slower rate of the polymorph transformation in the urea-deficient medium than in urea-containing one. We suppose that a ureolytic microorganism retains its ability to induce CaCO3 biomineralization regardless the origin of carbonate ions in a cell environment by switching between mechanisms of urea-degradation and metabolism of calcium organic salts.

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In the 1970s, the strain Geotrichum candidum Link 3C was isolated from rotting rope and since then has been extensively studied as a source of cellulose and xylan-degrading enzymes. The original identification of the strain was based only on morphological characters of the fungal mycelium in culture. Recent comparison of the internal transcribed spacer (ITS) fragments derived from the draft genome published in 2015 did not show its similarity to G. candidum species. Given the value of the strain 3C in lignocellulosic biomass degradation, we performed morphological and molecular studies to find the appropriate taxonomic placement for this fungal strain within the Ascomycota phylum. ITS, 18S rDNA, 28S rDNA sequences, and RPB2 encoding genes were used to construct phylogenetic trees with Maximum likelihood and Bayesian inference methods. Based on sequence comparison and multiple gene sequencing, we conclude that the fungal strain designated as Geotrichum candidum Link 3C should be placed into the genus Scytalidium (Pezizomycotina, Leotiomycetes) and is redescribed herein as Scytalidium candidum 3C comb. nov.

To date, the mechanisms of CaCO3 nucleus formation and crystal growth induced by bacterial cells still remain debatable. Here, an insight on the role of planktonic cells of Bacillus licheniformis DSMZ 8782 in the biomineralization is presented. We showed that during 14-days bacterial growth in a liquid urea/Ca2+-containing medium the transformation of CaCO3 polymorphs followed the classical pathway "ACC-vaterite-calcite/aragonite". By microscopic techniques, we detected the formation of extracellular matrix (ECM) around the cells at the stage of exponential growth and appearance of electron-dense inclusions at 24 h after the inoculation. The cells formed filaments and created a network, the nodes of which served as sites for further crystal growth. The ECM formation accompanied with the expression of proteins required for biofilm formation, the aldehyde/alcohol dehydrogenase, stress-associated Clp family proteins, and a porin family protein (ompA ortholog) associated with bacterial extracellular vesicles. We demonstrated that urea and CaCl2 acted as denaturing agents causing matrix formation in addition to their traditional role as a source of carbonate and Ca2+ ions. We showed that CaCO3 nucleation occured inside B. licheniformis cells and further crystal growth and polymorphic transformations took place in the extracellular matrix without attaching to the cell surface. The spatial arrangement of the cells was important for the active crystal growth and dependent on environmental factors. The extracellular matrix played a double role being formed as a stress response and providing a favorable microenvironment for biomineralization (a high concentration of ions necessary for CaCO3 crystal aggregation, fixation and stabilization).

Biomineralization is a universal process that has implications in a variety of areas, from civil engineering to medicine. While crystallization of amorphous CaCO3 formed in vitro is known to precede the vaterite-calcite/aragonite pathway, this process could be significantly altered when induced by bacteria, particularly within the extracellular matrix (ECM) of microbial cells. We used a combination of SEM, SANS, SAXS, FTIR and XRD methods to investigate the structure of CaCO3 formed during biomineralization induced by planktonic Bacillus cereus. Formation of precipitates in the presence of CaCl2 and urea was observed both during bacterial growth and in the medium devoid of bacteria and ECM (cell-free system). The pathway for polymorphic transformations of CaCO3 from the amorphous phase to vaterite and further to calcite was confirmed for the bacterium-induced mineralization and did not depend on the concentration of Ca2+ and urea. The structure of CaCO3 sediments differed when formed in cell-free and bacterial systems and varied depending on time and the medium composition. The rate of precipitation was accelerated in the presence of DNA, which had little effect on the solid phase structure in the cell-free system, while strongly affecting the structure and polymorphic composition of the precipitates in bacterial culture.