Federico Rossi

Role of Cyanobacterial Exopolysaccharides in Phototrophic Biofilms and in Complex Microbial Mats

Exopolysaccharides (EPSs) are an important class of biopolymers with great ecological importance. In natural environments, they are a common feature of microbial biofilms, where they play key protective and structural roles. As the primary colonizers of constrained environments, such as desert soils and lithic and exposed substrates, cyanobacteria are the first contributors to the synthesis of the EPSs constituting the extracellular polymeric matrix that favors the formation of microbial associations with varying levels of complexity called biofilms. Cyanobacterial colonization represents the first step for the formation of biofilms with different levels of complexity. In all of the possible systems in which cyanobacteria are involved, the synthesis of EPSs contributes a structurally-stable and hydrated microenvironment, as well as chemical/physical protection against biotic and abiotic stress factors. Notwithstanding the important roles of cyanobacterial EPSs, many aspects related to their roles and the relative elicited biotic and abiotic factors have still to be clarified. The aim of this survey is to outline the state-of-the-art of the importance of the cyanobacterial EPS excretion, both for the producing cells and for the microbial associations in which cyanobacteria are a key component.

Characteristics and role of the exocellular polysaccharides produced by five cyanobacteria isolated from phototrophic biofilms growing on stone monuments.

Three coccoid and two filamentous cyanobacterial strains were isolated from phototrophic biofilms exposed to intense solar radiation on lithic surfaces of the Parasurameswar Temple and Khandagiri caves, located in Orissa State, India. Based on to their morphological features, the three coccoid strains were assigned to the genera Gloeocapsosis and Gloeocapsa, while the two filamentous strains were assigned to the genera Leptolyngbya and Plectonema. Eleven to 12 neutral and acidic sugars were detected in the slime secreted by the five strains. The secretions showed a high affinity for bivalent metal cations, suggesting their ability to actively contribute to weakening the mineral substrata. The secretion of protective pigments in the polysaccharide layers, namely mycosporine amino acid-like substances (MAAs) and scytonemins, under exposure to UV radiation showed how the acclimation response contributes to the persistence of cyanobacteria on exposed lithoid surfaces in tropical areas.

Production and characterization of extracellular carbohydrate polymer from Cyanothece sp. CCY 0110

Cyanobacterial extracellular polymeric substances (EPS) are heteropolysaccharides that possess characteristics suitable for industrial applications, notably a high number of different monomers, strong anionic nature and high hydrophobicity. However, systematic studies that unveil the conditions influencing EPS synthesis and/or its characteristics are mandatory. In this work, Cyanothece sp. CCY 0110 was used as model organism. Our results revealed that this strain is among the most efficient EPS producers, and that the amount of RPS (released polysaccharides) is mainly related to the number of cells, rather than to the amount produced by each cell. Light was the key parameter, with high light intensity enhancing significantly RPS production (reaching 1.8 g L(-1)), especially in the presence of combined nitrogen. The data showed that RPS are composed by nine different monosaccharides (including two uronic acids), the presence of sulfate groups and peptides, and that the polymer is remarkably thermostable and amorphous in nature.

Use of cyanobacterial polysaccharides to promote shrub performances in desert soils: a potential approach for the restoration of desertified areas

The importance of cyanobacterial polysaccharides of biological soil crusts in sand surface stabilization and soil nutrient retention has been long acknowledged. However, the role of cyanobacterial polysaccharides as a source of nutrition to vascular plants in crusted areas is ignored. In this study, the chemical composition of the polysaccharide synthesized by Phormidium tenue and the effects of its presence on seed germination and seedling metabolism of the shrub Caragana korshinskii were investigated. The crude polysaccharide synthesized by P. tenue was composed of 15xa0% protein and 58xa0% carbohydrate and showed the presence of 12 different types of monosaccharides. The addition of the polysaccharide significantly (Pu2009<u20090.05) increased seed germination and metabolic activity of the seedling of the shrub C. korshinskii. The optimal concentration for vigor index, root length, root vigor, and total N and P contents was 10xa0mg/L polysaccharide; for the germination rate, nitrate reductase activity, carbohydrate content, chlorophyll, and Mg2+ content, the optimal was 60xa0mg/L polysaccharide, while for K+ and Ca2+ contents, photosynthetic efficiency and superoxide dismutase activity was 120xa0mg/L. The presence of the polysaccharide increased seed germination rate, ion uptake, and photosynthetic activity by affecting the electron transport chain and decreased oxidative damage by eliminating reactive oxygen species in C. korshinskii, thus promoting shrub performance in crusted desert areas.

Beneficial effects of retroreflective materials in urban canyons: results from seasonal monitoring campaign

Urban Heat Island (UHI) is a phenomenon that happens in urban areas consisting in higher temperatures than those in the surrounding rural areas. Cool materials and urban forestry have been identified as the mean countermeasures to this phenomenon. The specific research target was to investigate the benefit that can be obtained by the application of new retro-reflective (RR) cool materials on building envelopes in urban canyons. An ideal RR is a high reflective material that reflect incident radiation backward to the same direction of incidence. The test facility is made of two twin arrays resembling urban canyons with different aspect ratios. On the East array a cool, white, diffusive material is applied. On the West array a cool, white Retro-Reflective (RR) material is applied. The result of a seasonal (summer) monitoring campaign is discussed, with a particular focus on the temperature trends inside canyons with the same geometry but different envelope materials. While temperatures measured by the vertical sensors reveal a higher surface temperature of the RR, air temperatures and pavements superficial temperatures are lower when RR are applied. These results suggest that RR materials have a cooling potential as coatings in urban canyons, and can thus improve urban climate conditions during summer.

Exocellular Polysaccharides in Microalgae and Cyanobacteria: Chemical Features, Role and Enzymes and Genes Involved in Their Biosynthesis

Extracellular polysaccharides (EPSs) produced by microalgae and cyanobacteria are molecules with a great ecological significance for the producing organisms, serving in a wide array of biological processes and increasing the organism tolerance to environmental stresses. In addition, due to their distinctive chemical, rheological properties and the biological activity of some of them, these macromolecules could find application in industrial, pharmaceutical and medical fields. In this chapter, the current knowledge regarding the structure and composition of EPSs, the factors eliciting their synthesis, and the related codifying genes involved is reviewed. It is also underlined and discussed how, notwithstanding the huge number of studies available, different aspects still need to be clarified. For example, there are limited informations concerning EPS synthetic pathways, and how these processes are influenced by environmental factors. Expand the knowledge on these aspects could help elaborating biotechnological strategies to increase the yields and direct the synthesis to polymers with desired characteristics.

Characterization of exopolysaccharides produced by seven biofilm-forming cyanobacterial strains for biotechnological applications

The molecular identification of seven biofilm-forming cyanobacteria and the characterization of their exopolysaccharides were made and considered in terms of potential biotechnological applications. The studied strains were isolated from phototrophic biofilms taken from various Italian sites including a wastewater treatment plant, an eroded soil, and a brackish lagoon. The polysaccharides were characterized by use of ion exchange chromatography, circular dichroism, and cytochemical stains. All strains produced exopolysaccharides with differing ratios of hydrophobic and hydrophilic moieties depending on the species, the polysaccharide fraction (i.e., whether capsular or released), and the ambient conditions. It was shown that the anionic nature of the exopolysaccharides was due to the presence of carboxylic and sulfated groups and is likely the main characteristic with industrial applicability. Potential biotechnological applications are discussed.

Introducing capnophilic lactic fermentation in a combined dark-photo fermentation process: a route to unparalleled H2 yields

Two-stage process based on photofermentation of dark fermentation effluents is widely recognized as the most effective method for biological production of hydrogen from organic substrates. Recently, it was described an alternative mechanism, named capnophilic lactic fermentation, for sugar fermentation by the hyperthermophilic bacterium Thermotoga neapolitana in CO2-rich atmosphere. Here, we report the first application of this novel process to two-stage biological production of hydrogen. The microbial system based on T. neapolitana DSM 4359T and Rhodopseudomonas palustris 42OL gave 9.4xa0mol of hydrogen per mole of glucose consumed during the anaerobic process, which is the best production yield so far reported for conventional two-stage batch cultivations. The improvement of hydrogen yield correlates with the increase in lactic production during capnophilic lactic fermentation and takes also advantage of the introduction of original conditions for culturing both microorganisms in minimal media based on diluted sea water. The use of CO2 during the first step of the combined process establishes a novel strategy for biohydrogen technology. Moreover, this study opens the way to cost reduction and use of salt-rich waste as feedstock.

Antibiotic delivery by liposomes from prokaryotic microorganisms: Similia cum similis works better.

To date the effectiveness of antibiotics is undermined by microbial resistance, threatening public health worldwide. Enhancing the efficacy of the current antibiotic arsenal is an alternative strategy. The administration of antimicrobials encapsulated in nanocarriers, such as liposomes, is considered a viable option, though with some drawbacks related to limited affinity between conventional liposomes and bacterial membranes. Here we propose a novel top-down procedure to prepare unconventional liposomes from the membranes of prokaryotes (PD-liposomes). These vectors, being obtained from bacteria with limited growth requirements, also represent low-cost systems for scalable biotechnology production. In depth physico-chemical characterization, carried out with dynamic light scattering (DLS) and Small Angle X-ray Scattering (SAXS), indicated that PD-liposomes can be suitable for the employment as antibiotic vectors. Specifically, DLS showed that the mean diameter of loaded liposomes was ∼200-300nm, while SAXS showed that the structure was similar to conventional liposomes, thus allowing a direct comparison with more standard liposomal formulations. Compared to free penicillin G, PD-liposomes loaded with penicillin G showed minimal inhibitory concentrations against E. coli that were up to 16-times lower. Noteworthy, the extent of the bacterial growth inhibition was found to depend on the microorganisms from which liposomes were derived.

Microbial fixation of CO2 in water bodies and in drylands to combat climate change, soil loss and desertification

The growing concern for the increase of the global warming effects due to anthropogenic activities raises the challenge of finding novel technological approaches to stabilize CO2 emissions in the atmosphere and counteract impinging interconnected issues such as desertification and loss of biodiversity. Biological-CO2 mitigation, triggered through biological fixation, is considered a promising and eco-sustainable method, mostly owing to its downstream benefits that can be exploited. Microorganisms such as cyanobacteria, green algae and some autotrophic bacteria could potentially fix CO2 more efficiently than higher plants, due to their faster growth. Some examples of the potential of biological-CO2 mitigation are reported and discussed in this paper. In arid and semiarid environments, soil carbon sequestration (CO2 fixation) by cyanobacteria and biological soil crusts is considered an eco-friendly and natural process to increase soil C content and a viable pathway to soil restoration after one disturbance event. Another way for biological-CO2 mitigation intensively studied in the last few years is related to the possibility to perform carbon dioxide sequestration using microalgae, obtaining at the same time bioproducts of industrial interest. Another possibility under study is the exploitation of specific chemotrophic bacteria, such as Ralstonia eutropha (or picketii) and related organisms, for CO2 fixation coupled with the production chemicals such as polyhydroxyalkanoates (PHAs). In spite of the potential of these processes, multiple factors still have to be optimized for maximum rate of CO2 fixation by these microorganisms. The optimization of culture conditions, including the optimal concentration of CO2 in the provided gas, the use of metabolic engineering and of dual purpose systems for the treatment of wastewater and production of biofuels and high value products within a biorefinery concept, the design of photobioreactors in the case of phototrophs are some of the issues that, among others, have to be addressed and tested for cost-effective CO2 sequestration.