Benefits of Algal Extracts in Sustainable Agriculture. In: Hallmann A, Rampelotto PH, editors. Grand Challenges in Algae Biotechnology. Cham: Springer International Publishing; 2019. pp. 501-34. [DOI: 10.1007/978-3-030-25233-5_14]

Ubiquitin-like and ubiquitinylated proteins associated with the maternal cell walls of Scenedesmus obliquus 633 as identified by immunochemistry and LC-MS/MS proteomics

The cell walls of green algae Scenedesmus obliquus are complex, polymeric structures including an inner cellulose layer surrounded by an algaenan-containing trilaminar sheath. The process of autosporulation leads to the formation of sporangial (maternal) cell walls, which are released into the medium after sporangial autolysis. In this study, a fraction of maternal cell wall material (CWM) was isolated from the stationary phase cultures of Scenedesmus obliquus 633 and subjected to immunofluorescence microscopy using polyclonal anti-ubiquitin antibodies. The water-extracted polypeptide fraction from the maternal cell walls was then analyzed using immunoblotting and LC-MS/MS. An immunoanalysis showed the presence of several peptides reactive with polyclonal anti-ubiquitin serum, with apparent molecular masses of c. 12, 70, 120, 200, and > 250 kDa. Cell wall-associated peptides were identified on the basis of LC-MS/MS spectra across NCBI databases, including the Scenedesmaceae family (58 records), the Chlorophyceae class (37 records), and Chlamydomonas reinhardtii (18 records) corresponding to the signatures of 95 identified proteins. In particular, three signatures identified ubiquitin and ubiquitin-related proteins. In the maternal cell walls, immunoblotting analysis, immunofluorescence microscopy, and LC-MS/MS proteomics collectively demonstrated the presence of ubiquitin-like epitopes, ubiquitin-specific peptide signatures, and several putative ubiquitin conjugates of a higher molecular mass. These results support the presence of ubiquitin-like proteins in the extramembranous compartment of Scenedesmus obliquus 633 and suggest that protein ubiquitination plays a significant role in the formation and functional integrity of the maternal cell walls in green algae.

Isolation, Characterization, Moisturization and Anti-HepG2 Cell Activities of a Novel Polysaccharide from Cyanobacterium aponinum

Polysaccharides from cyanobacteria are extensively reported for their complex structures, good biocompatibility, and diverse bioactivities, but only a few cyanobacterial species have been exploited for the biotechnological production of polysaccharides. According to our previous study, the newly isolated marine cyanobacterium Cyanobacterium aponinum SCSIO-45682 was a good candidate for polysaccharide production. This work provided a systematic study of the extraction optimization, isolation, structural characterization, and bioactivity evaluation of polysaccharides from C. aponinum SCSIO-45682. Results showed that the crude polysaccharide yield of C. aponinum reached 17.02% by hot water extraction. The crude polysaccharides showed a porous and fibrous structure, as well as good moisture absorption and retention capacities comparable to that of sodium alginate. A homogeneous polysaccharide (Cyanobacterium aponinum polysaccharide, CAP) was obtained after cellulose DEAE-52 column and Sephadex G-100 column purification. CAP possessed a high molecular weight of 4596.64 kDa. It was mainly composed of fucose, galactose, and galacturonic acid, with a molar ratio of 15.27:11.39:8.64. The uronic acid content and sulfate content of CAP was 12.96% and 18.06%, respectively. Furthermore, CAP showed an in vitro growth inhibition effect on human hepatocellular carcinoma (HepG2) cells. The above results indicated the potential of polysaccharides from the marine cyanobacterium C. aponinum SCSIO-45682 as a moisturizer and anticancer addictive applied in cosmetical and pharmaceutical industries.

Prospects of phosphate solubilizing microorganisms in sustainable agriculture

Phosphorus (P), an essential macronutrient for various plant processes, is generally a limiting soil component for crop growth and yields. Organic and inorganic types of P are copious in soils, but their phyto-availability is limited as it is present largely in insoluble forms. Although phosphate fertilizers are applied in P-deficit soils, their undue use negatively impacts soil quality and the environment. Moreover, many P fertilizers are lost because of adsorption and fixation mechanisms, further reducing fertilizer efficiencies. The application of phosphate-solubilizing microorganisms (PSMs) is an environmentally friendly, low-budget, and biologically efficient method for sustainable agriculture without causing environmental hazards. These beneficial microorganisms are widely distributed in the rhizosphere and can hydrolyze inorganic and organic insoluble P substances to soluble P forms which are directly assimilated by plants. The present review summarizes and discusses our existing understanding related to various forms and sources of P in soils, the importance and P utilization by plants and microbes,, the diversification of PSMs along with mixed consortia of diverse PSMs including endophytic PSMs, the mechanism of P solubilization, and lastly constraints being faced in terms of production and adoption of PSMs on large scale have also been discussed.

Hydroponics with Microalgae and Cyanobacteria: Emerging Trends and Opportunities in Modern Agriculture

The global population is expected to reach 9.5 billion, which means that crop productivity needs to double to meet the growing population's food demand. Soil degradation and environmental factors, such as climate events, significantly threaten crop production and global food security. Furthermore, rapid urbanization has led to 55% of the world's population migrating to cities, and this proportion is expected to increase to 75% by 2050, which presents significant challenges in producing staple foods through conventional hinterland farming. Numerous studies have proposed various sustainable farming techniques to combat the shortage of farmable land and increase food security in urban areas. Soilless farming techniques such as hydroponics have gained worldwide popularity due to their resource efficiency and production of superior-quality fresh products. However, using chemical nutrients in a conventional hydroponic system can have significant environmental impacts, including eutrophication and resource depletion. Incorporating microalgae into hydroponic systems as biostimulants offers a sustainable and ecofriendly approach toward circular bioeconomy strategies. The present review summarizes the plant growth-promoting activity of microalgae as biostimulants and their mechanisms of action. We discuss their effects on plant growth parameters under different applications, emphasizing the significance of integrating microalgae into a closed-loop circular economy model to sustainably meet global food demands.

Study of pesticidal activity of bioactive compounds of Neowestiellopsis persica strain A1387 in improving the antioxidative and antimicrobial activity of wheat to sunn pest

Cyanobacteria have been recognized for their advantageous impact on plant growth and development. The application of certain techniques has the potential to enhance various aspects of plant development, including growth, yield, proximate content (such as protein and carbohydrate levels), as well as the ability to withstand abiotic stresses such as herbicide exposure. The current investigation focused on examining the influence of bioactive compounds derived from the cyanobacterium Neowestiellopsis persica strain A1387 on enhancing the antioxidant and anyimicrobial activity of wheat plants in their defense against the plant pathogenic Sunn pest. The findings of the study indicate that the levels of H2O2 and GPx in wheat plants that were infected with aphids were significantly elevated compared to the treatments where aphids and cyanobacteria extract were present. The confirmation of these results was achieved through the utilization of confocal and fluorescent microscope tests, respectively. Furthermore, the findings indicated that the constituents of the cyanobacterial extract augmented the plant's capacity to withstand stress by enhancing its defense mechanisms. In a broader context, the utilization of cyanobacterial extract demonstrated the ability to regulate the generation and impact of oxygen (O2) and hydrogen peroxide (H2O2), while concurrently enhancing the functionality of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) enzymes within wheat plants. This facilitation enabled the plants to effectively manage oxidative stress. Moreover, the findings of the antibacterial activity assessment conducted on the extract derived from cyanobacteria demonstrated notable susceptibility. The bacteria that exhibited the highest sensitivity to the extract of cyanobacterium Neowestiellopsis persica strain A1387 were staphylococcus aureus and pseudomonas aeruginosa. Conversely, salmonella typhi demonstrated the greatest resistance to the aforementioned extract. The potential impact of cyanobacteria extract on the antioxidative response of wheat plants to sunn pest infestation represents a novel contribution to the existing body of knowledge on the interaction between wheat plants and aphids.

Cyanobacteria as a Valuable Natural Resource for Improved Agriculture, Environment, and Plant Protection

Taking into consideration, the challenges faced by the environment and agro-ecosystem make increased for suggestions more reliable methods to help increase food security and deal with difficult environmental problems. Environmental factors play a critical role in the growth, development, and productivity of crop plants. Unfavorable changes in these factors, such as abiotic stresses, can result in plant growth deficiencies, yield reductions, long-lasting damage, and even death of the plants. In reflection of this, cyanobacteria are now considered important microorganisms that can improve the fertility of soils and the productivity of crop plants due to their different features like photosynthesis, great biomass yield, ability to fix the atmospheric N2, capability to grow on non-arable lands, and varied water sources. Furthermore, numerous cyanobacteria consist of biologically active substances like pigments, amino acids, polysaccharides, phytohormones, and vitamins that support plant growth enhancement. Many studies have exposed the probable role of these compounds in the alleviation of abiotic stress in crop plants and have concluded with evidence of physiological, biochemical, and molecular mechanisms that confirm that cyanobacteria can decrease the stress and induce plant growth. This review discussed the promising effects of cyanobacteria and their possible mode of action to control the growth and development of crop plants as an effective method to overcome different stresses.

Graphical Abstract

Integrated microalgal biorefinery for the production and application of biostimulants in circular bioeconomy

Adverse detrimental impacts of environmental pollution over the health regimen of people has driven a shift in lifestyle towards cleaner and natural resources, especially in the aspects of food production and consumption. Microalgae are considered a rich source of high value metabolites to be utilized as plant growth biostimulants. These organisms however, are underrated compared to other microbial counterparts, due to inappropriate knowledge on the technical, enviro-economical constrains leading to low market credibility. Thus, to avert these issues, the present review comprehensively discusses the biostimulatory potential of microalgae interactively combined with circular bio-economy perspectives. The biochemical content and intracellular action mechanism of microalgal biostimulants were described. Furthermore, detailed country-wise market trends along with the description of the existing regulatory policies are included. Enviro-techno-economic challenges are discussed, and the consensus need for shift to biorefinery and circular bio-economy concept are emphasized to achieve sustainable impacts during the commercialization of microalgal biostimulants.

The Use of Microalgae and Cyanobacteria in the Improvement of Agricultural Practices: A Review on Their Biofertilising, Biostimulating and Biopesticide Roles

The increase in worldwide population observed in the last decades has contributed to an increased demand for food supplies, which can only be attained through an improvement in agricultural productivities. Moreover, agricultural practices should become more sustainable, as the use of chemically-based fertilisers, pesticides and growth stimulants can pose serious environmental problems and lead to the scarcity of finite resources, such as phosphorus and potassium, thus increasing the fertilisers’ costs. One possible alternative for the development of a more sustainable and highly effective agriculture is the use of biologically-based compounds with known activity in crops’ nutrition, protection and growth stimulation. Among these products, microalgal and cyanobacterial biomass (or their extracts) are gaining particular attention, due to their undeniable potential as a source of essential nutrients and metabolites with different bioactivities, which can significantly improve crops’ yields. This manuscript highlights the potential of microalgae and cyanobacteria in the improvement of agricultural practices, presenting: (i) how these photosynthetic microorganisms interact with higher plants; (ii) the main bioactive compounds that can be isolated from microalgae and cyanobacteria; and (iii) how microalgae and cyanobacteria can influence plants’ growth at different levels (nutrition, protection and growth stimulation).