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Microorganisms can remove metals from the surrounding environment with various mechanisms, either as metabolically mediated processes or as a passive adsorption of metals on the charged macromolecules of the cell envelope. Owing to the presence of a large number of negative charges on the external cell layers, exopolysaccharides (EPS)-producing cyanobacteria have been considered very promising as chelating agents for the removal of positively charged heavy metal ions from water solutions, and an increasing number of studies on their use in metal biosorption have been published in recent years. In this review, the attention was mainly focused on the studies aimed at defining the molecular mechanisms of the metal binding to the polysaccharidic exocellular layers. Moreover, the few attempts done in the use of EPS-producing cyanobacteria for metal biosorption at pilot scale and with real wastewaters are here reviewed, discussing the main positive issues and the drawbacks so far emerging from these experiments.

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.

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Aims:  The aim of this study was to assess the selective removal of Cu(II), Cr(III) and Ni(II) by strains of exopolysaccharide (EPS)‐producing cyanobacteria, and to investigate the interaction of sorption in solutions with multiple‐metals. Methods and Results:  Nine EPS‐producing cyanobacteria were tested for their ability to remove Cr, Cu and Ni in both single‐ and multiple‐metal solutions. In the single‐metal solutions, some of the strains showed very high values of metal uptake, however, only two of them showed the capability to selectively remove one or two of the metals present in the multiple‐metal solutions. In multi‐metal systems, the binding process was either noninteractive, synergistic or competitive between metal ions for different strains of cyanobacteria. Conclusions:  Cyanothece 16Som 2 showed significantly greater sorptive capacity for Cu (1·5–20×) and Cr (2–50×) than all other strains tested. The Nostoc PCC 7936 strain showed high specific and almost exclusive selectivity towards Cu, which suggests its use aimed at recovering this metal from multiple‐metal solutions. Significance and Impact of the Study:  To find out microbial sorbents with good metal selectivity may be very useful for building up processes aimed to recover valuable metals from industrial wastewaters.

The supportive and negative evidence for the stress gradient hypothesis (SGH) led to an ongoing debate among ecologists and called for new empirical and theoretical work. In this study, we took various biological soil crust (BSCs) samples along a spatial gradient with four environmental stress levels to examine the fitness of SGH in microbial interactions and evaluate its influence on biodiversity-function relationships in BSCs. A new assessment method of species interactions within hard-cultured invisible soil community was employed, directly based on denaturing gradient gel electrophoresis fingerprint images. The results showed that biotic interactions in soil phototroph community dramatically shifted from facilitation to dominant competition with the improvement of microhabitats. It offered new evidence, which presented a different perspective on the hypothesis that the relative importance of facilitation and competition varies inversely along the gradient of abiotic stress. The path analysis indicated that influence of biotic interactions (r=0.19, p< 0.05) on ecosystem functions is lower than other community properties (r=0.62, p<0.001), including soil moisture, crust coverage, and biodiversity. Furthermore, the correlation between species interactions and community properties was non-significant with low negative influence (r=−0.27, p> 0.05). We demonstrate that the inversion of biotic interaction as a response to the gradient of abiotic stresses existed not only in the visible plant community but also in the soil microbial community.

Intensive livestock farming cannot be uncoupled from the massive production of manure, requiring adequate management to avoid environmental damage. The high carbon, nitrogen and phosphorus content of pig manure enables targeted resource recovery. Here, fifteen integrated scenarios for recovery of water, nutrients and energy are compared in terms of technical feasibility and economic viability. The recovery of refined nutrients with a higher market value and quality, i.e., (NH4)2SO4 for N and struvite for P, coincided with higher net costs, compared to basic composting. The inclusion of anaerobic digestion promoted nutrient recovery efficiency, and enabled energy recovery through electricity production. Co-digestion of the manure with carbon-rich waste streams increased electricity production, but did not result in lower process costs. Overall, key drivers for the selection of the optimal manure treatment scenario will include the market demand for more refined (vs. separated or concentrated) products, and the need for renewable electricity production.

In this study, the chemical composition and the macromolecular features of the extracellular polysaccharidic (EPS) matrix of induced biological soil crusts (IBSCs) of different age, collected in the hyper-arid plateau of Hobq desert, Inner Mongolia, China, were investigated. No statistically significant correlation between the amount of extracellular carbohydrates (i.e., monosaccharides, oligosaccharides, and polysaccharides) and the age of IBSCs was found. On the other hand, the relative abundance of uronic acid in the EPSs increased with the maturation of the crusts. In the EPSs of the investigated samples, glucose, mannose, galactose, and uronic acids were the sugars showing the widest variations in their relative abundance, explaining much of the variance of the data. Results also showed higher relative contents of EPSs with high MW in the oldest IBSCs. It is possible to conclude that the characteristics of the EPS of the matrix of the investigated IBSCs cannot only be put in relation with the age of the crusts and the activity of phototrophic microorganisms, but most properly, it has to be taken into account the biotic interactions ongoing between EPS producers and consumers.