Capsular polysaccharides secreted by building façade colonisers: characterisation and adsorption to surfaces

Exopolysaccharides from Microalgae and Cyanobacteria: Diversity of Strains, Production Strategies, and Applications

Microalgae and cyanobacteria are photosynthetic organisms that can produce/accumulate biomolecules with industrial interest. Among these molecules, EPSs are macromolecular polysaccharidic compounds that present biological activities and physico-chemical properties, allowing to consider their valorization in diverse commercial markets, such as cosmetic, therapeutic, nutraceutic, or hydrocolloids areas. The number of microalgae and cyanobacteria strains described to produce such EPSs has increased in recent years as, among the 256 producing strains gathered in this review, 86 were published in the last 10 years (~33%). Moreover, with the rise of research on microalgae EPSs, a variety of monosaccharides compositions have been discovered, highlighting the versatility of these organisms. If some production strategies can be applied to increase EPS production yields, it appears that case by case studies are needed to promote EPS synthesis by a strain, as many responses exist. This paper proposes an up-to-date state of the art of the diversity of microalgae and cyanobacteria EPS-producing strains, associated to the variability of compositions. The strategies for the production and extraction of the polymers are also discussed. Finally, an overview of the biological activities and physico-chemical properties allow one to consider their use on several commercial markets.

Static Magnetic Fields Effects on Polysaccharides Production by Different Microalgae Strains

Microalgae are able to produce many valuable biomolecules, such as polysaccharides, that presents a large diversity of biochemical structures and functions as antioxidant, antifungal, anticancer, among others. Static magnetic fields (SMF) influence the metabolism of microorganisms and has been shown as an alternative to increase microalgae biomass, yield and compounds production. Especially, some studies have highlighted that SMF application could enhance carbohydrate content. This study aimed to evaluate different conditions of SMF on Spirulina and Chlorella in indoor and outdoor conditions, in order to confirm the influence of SMF on polysaccharides production, evaluating which polysaccharidic fraction could be enhanced by SMF and highlighting a possible modification in EPS composition. Starch from Chlorella and exopolysaccharides (EPS) from Spirulina were quantified and characterized. SMF increased the starch content in Chorella fusca biomass. EPS productions from A. platensis and Spirulina sp. were not significantly increased, and global composition appeared similar to the controls (constituted basically of 80–86% neutral sugars and 13–19% uronic acids). However, the monosaccharide composition analysis revealed a significant modification of composition, i.e., the amount of fucose, arabinose, rhamnose, galactose and glucuronic acid was increased, while the glucose content was decreased. SMF application led to significant modification of polysaccharides production and this study demonstrate that combining the outdoor conditions with SMF, the starch content and EPS composition was positively affected.

Cold Acclimation Improves the Desiccation Stress Resilience of Polar Strains of Klebsormidium (Streptophyta)

Biological soil crusts (BSCs) are complex communities of autotrophic, heterotrophic, and saprotrophic (micro)organisms. In the polar regions, these biocrust communities have essential ecological functions such as primary production, nitrogen fixation, and ecosystem engineering while coping with extreme environmental conditions (temperature, desiccation, and irradiation). The microalga Klebsormidium is commonly found in BSCs all across the globe. The ecophysiological resilience of various Klebsormidium species to desiccation and other stresses has been studied intensively. Here we present the results of transcriptomic analyses of two different Klebsormidium species, K. dissectum and K. flaccidum, isolated from Antarctic and Arctic BSCs. We performed desiccation stress experiments at two different temperatures mimicking fluctuations associated with global change. Cultures grown on agar plates were desiccated on membrane filters at 10% relative air humidity until the photosynthetic activity as reflected in the effective quantum yield of photosystem II [Y(II)] ceased. For both species, the response to dehydration was much faster at the higher temperature. At the transcriptome level both species responded more strongly to the desiccation stress at the higher temperature suggesting that adaptation to cold conditions enhanced the resilience of both algae to desiccation stress. Interestingly, the two different species responded differently to the applied desiccation stress with respect to the number as well as function of genes showing differential gene expression. The portion of differentially expressed genes shared between both taxa was surprisingly low indicating that both Klebsormidium species adapted independently to the harsh conditions of Antarctica and the Arctic, respectively. Overall, our results indicate that environmental acclimation has a great impact on gene expression and the response to desiccation stress in Klebsormidium.

Biological Soil Crusts of Arctic Svalbard-Water Availability as Potential Controlling Factor for Microalgal Biodiversity

In the present study the biodiversity of biological soil crusts (BSCs) formed by phototrophic organisms were investigated on Arctic Svalbard (Norway). These communities exert several important ecological functions and constitute a significant part of vegetation at high latitudes. Non-diatom eukaryotic microalgal species of BSCs from 20 sampling stations around Ny-Ålesund and Longyearbyen were identified by morphology using light microscopy, and the results revealed a high species richness with 102 species in total. 67 taxa belonged to Chlorophyta (31 Chlorophyceae and 36 Trebouxiophyceae), 13 species were Streptophyta (11 Klebsormidiophyceae and two Zygnematophyceae) and 22 species were Ochrophyta (two Eustigmatophyceae and 20 Xanthophyceae). Surprisingly, Klebsormidium strains belonging to clade G (Streptophyta), which were so far described from Southern Africa, could be determined at 5 sampling stations. Furthermore, comparative analyses of Arctic and Antarctic BSCs were undertaken to outline differences in species composition. In addition, a pedological analysis of BSC samples included C, N, S, TP (total phosphorus), and pH measurements to investigate the influence of soil properties on species composition. No significant correlation with these chemical soil parameters was confirmed but the results indicated that pH might affect the BSCs. In addition, a statistically significant influence of precipitation on species composition was determined. Consequently, water availability was identified as one key driver for BSC biodiversity in Arctic regions.

Primitive Extracellular Lipid Components on the Surface of the Charophytic Alga Klebsormidium flaccidum and Their Possible Biosynthetic Pathways as Deduced from the Genome Sequence

Klebsormidium flaccidum is a charophytic alga living in terrestrial and semiaquatic environments. K. flaccidum grows in various habitats, such as low-temperature areas and under desiccated conditions, because of its ability to tolerate harsh environments. Wax and cuticle polymers that contribute to the cuticle layer of plants are important for the survival of land plants, as they protect against those harsh environmental conditions and were probably critical for the transition from aquatic microorganism to land plants. Bryophytes, non-vascular land plants, have similar, but simpler, extracellular waxes and polyester backbones than those of vascular plants. The presence of waxes in terrestrial algae, especially in charophytes, which are the closest algae to land plants, could provide clues in elucidating the mechanism of land colonization by plants. Here, we compared genes involved in the lipid biosynthetic pathways of Arabidopsis thaliana to the K. flaccidum and the Chlamydomonas reinhardtii genomes, and identified wax-related genes in both algae. A simple and easy extraction method was developed for the recovery of the surface lipids from K. flaccidum and C. reinhardtii. Although these algae have wax components, their surface lipids were largely different from those of land plants. We also investigated aliphatic substances in the cell wall fraction of K. flaccidum and C. reinhardtii. Many of the fatty acids were determined to be lipophilic monomers in K. flaccidum, and a Fourier transform infrared spectroscopic analysis revealed that their possible binding mode was distinct from that of A. thaliana. Thus, we propose that K. flaccidum has a cuticle-like hydrophobic layer composed of lipids and glycoproteins, with a different composition from the cutin polymer typically found in land plant cuticles.

Resistance of cyanobacterial fouling on architectural paint films to cleaning by water jet

Mortar panels painted with three different white acrylic coatings were exposed to the environment in urban (São Paulo) and rural (Pirassununga) sites in Brazil for 7 years. After this time, all panels were almost equally discoloured, and paint detachment was observed to only a small degree. The biofilms were composed mainly of cyanobacteria and filamentous fungi, principal genera being Gloeocapsa and Chroococcidiopsis of the cyanobacteria, and Cladosporium and Alternaria of the fungi. Two of the three paints in Pirassununga became covered by a pink film that contained red-encapsulated Gloeocapsa and clay particles. The third, an 800% elastomeric matt formulation, became discoloured with a grey, only slightly pink, film, although the same cyanobacteria were present. The levels of paint detachments from all films in both locations were low, with rating range of 0-1 of a maximum 5 (100% detachment). After high-pressure water jetting, paint detachments increased at both locations, up to 2 in Pirassununga and 3 in São Paulo. Discoloration decreased; L*A*B* analysis of surface discoloration showed that ΔE (alteration in colour from the original paint film) changed from 28-39 before cleaning to 13-16 afterwards. The pink coloration was not entirely removed from Pirassununga samples, suggesting that cyanobacterial cells are difficult to detach, and microscopic analysis of the biofilms confirmed that Gloeocapsa was still present as the principal contaminant on all surfaces, with Chroococcidiopsis being present as the second most common. Almost no fungi were detected after water jet application.

Adhesion of façade coating colonisers, as mediated by physico-chemical properties

The adhesion of Klebsormidium flaccidum, Stichococcus bacillaris and Chlorella cf. mirabilis, three strains of green microalgae isolated from biofilms on façade coatings were investigated in a parallel plate flow chamber. The model surfaces tested were glass slides, and -CH(3) (mediated by octadecyltrichlorosilane [OTS] and hexamethyldisilazane [HMDZ] modification) and -NH(2) (aminopropyltriethoxysilane [APS] modification) terminated self-assembled monolayers. Algal physicochemical properties were evaluated by the microbial adhesion to solvents (MATS) assay and by contact angle measurements. The model surfaces were characterised by X-ray photoelectron spectroscopy analysis and by contact angle measurements. Predicted adhesion trends were then compared to in vitro measurements. The adhesion strength of the three algal strains followed the trend: APS > OTS > HMDZ > glass. The adhesion process thus seemed to be mediated by hydrophobic and electrostatic interactions, and was shown to be influenced by the algal culture age and the initial contact time.