Isolation and identification of siderophores produced by cyanobacteria

Cyanobacterial blooms, iron, and environmental pollutants

Iron determines the abundance and diversity of life and controls primary production in numerous aqueous environments. Over the past decades, the availability of this metal in natural waters has decreased. Iron deficiency can apply a selective pressure on microbial aquatic communities. Each aquatic organism has their individual requirements for iron and pathways for metal acquisition, despite all having access to the common pool of iron. Cyanobacteria, a photosynthesizing bacterium that can accumulate and form so-called 'algal blooms', have evolved strategies to thrive in such iron-deficient aqueous environments where they can outcompete other organisms in iron acquisition in diverse microbial communities. Metabolic pathways for iron acquisition employed by cyanobacteria allow it to compete successfully for this essential nutrient. By competing more effectively for requisite iron, cyanobacteria can displace other species and grow to dominate the microbial population in a bloom. Aquatic resources are damaged by a diverse number of environmental pollutants that can further decrease metal availability and result in a functional deficiency of available iron. Pollutants can also increase iron demand. A pollutant-exposed microbe is compelled to acquire further metal critical to its survival. Even in pollutant-impacted waters, cyanobacteria enjoy a competitive advantage and cyanobacterial dominance can be the result. We propose that cyanobacteria have a distinct competitive advantage over many other aquatic microbes in polluted, iron-poor environments.

Microbial iron acquisition is influenced by spatial and temporal conditions in a glacial influenced river and estuary system

In Arctic regions, glaciers are major sources of iron to rivers and streams; however, estuaries are considered iron sinks due to the coagulation and flocculation processes that occur at higher salinities. It is unknown how iron dynamics in a glacial influenced river and estuary environment affect microbial mechanisms for iron acquisition. Microbial taxonomic and functional sequencing was performed on samples taken throughout the year from the Kenai River and the estuary, Alaska. Despite distinct iron, sodium, and other nutrient concentrations, the river and estuary did not have statistically different microbial communities nor was time of sampling significant. However, ferrous iron transport (Feo) system genes were more abundant in river environments, while siderophore genes were more abundant and diverse in estuary environments. Siderophore transport and iron storage genes were found in all samples, but gene abundance and distribution were potentially influenced by physical drivers such as discharge rates and nutrient distributions. Differences in iron metabolism between river and estuary ecosystems indicate environmental conditions drive microbial mechanisms to sequester iron. This could have implications for iron transport as the Arctic continues to warm.

Cyanobacteria Application Ameliorates Floral Traits and Outcrossing Rate in Diverse Rice Cytoplasmic Male Sterile Lines

In rice, cytoplasmic male sterility (CMS) represents an irreplaceable strategy for producing high-yielding hybrid rice based on the commercial exploitation of heterosis. Thereupon, enhancing floral traits and outcrossing rates in CMS lines increase hybrid seed production and ensure global food security. The exogenous application of cyanobacteria could enhance outcrossing rates in CMS lines and, accordingly, hybrid rice seed production. In the present study, we aimed at exploring the impact of cyanobacteria implementation such as Anabaena oryzae, Nostoc muscorum, and their mixture to promote the floral traits, outcrossing rates, and seed production in hybrid rice. The impact of cyanobacteria (Anabaena Oryza (T2), Nostoc muscorum (T3), and their combination (T4) versus the untreated control (T1) was investigated for two years on the growth, floral, and yield traits of five diverse CMS lines, namely IR69625A (L1), IR58025A (L2), IR70368A (L3), G46A (L4), and K17A(L5). The evaluated CMS lines exhibited significant differences in all measured floral traits (days to heading (DTH), total stigma length (TSL), stigma width (SW), duration of spikelet opening (DSO), spikelet opening angle (SOA)). Additionally, L4 displayed the uppermost total stigma length and stigma width, whereas L1 and L5 recorded the best duration of spikelet opening and spikelet opening angle. Notably, these mentioned CMS lines exhibited the highest plant growth and yield traits, particularly under T4 treatment. Strong positive relationships were distinguished between the duration of the spikelet opening, panicle exertion, panicle weight, seed set, grain yield, total stigma length, spikelet opening angle, stigma width, and number of fertile panicles per hill. Cyanobacteria is a potential promising tool to increase floral traits and seed production in hybrid rice.

A Glimpse at Siderophores Production by Anabaena flos-aquae UTEX 1444

In this study, a strain of Anabaena flos-aquae UTEX 1444 was cultivated in six different concentrations of iron (III). Cultures were extracted with organic solvents and analyzed using our dereplication strategy, based on the combined use of high-resolution tandem mass spectrometry and molecular networking. The analysis showed the presence of the siderophores’ family, named synechobactins, only in the zero iron (III) treatment culture. Seven unknown synechobactin variants were present in the extract, and their structures have been determined by a careful HRMS/MS analysis. This study unveils the capability of Anabaena flos-aquae UTEX 1444 to produce a large array of siderophores and may be a suitable model organism for a sustainable scale-up exploitation of such bioactive molecules, for the bioremediation of contaminated ecosystems, as well as in drug discovery.

Cyanobacteria: A Natural Source for Controlling Agricultural Plant Diseases Caused by Fungi and Oomycetes and Improving Plant Growth

Cyanobacteria, also called blue-green algae, are a group of prokaryotic microorganisms largely distributed in both terrestrial and aquatic environments. They produce a wide range of bioactive compounds that are mostly used in cosmetics, animal feed and human food, nutraceutical and pharmaceutical industries, and the production of biofuels. Nowadays, the research concerning the use of cyanobacteria in agriculture has pointed out their potential as biofertilizers and as a source of bioactive compounds, such as phycobiliproteins, for plant pathogen control and as inducers of plant systemic resistance. The use of alternative products in place of synthetic ones for plant disease control is also encouraged by European Directive 2009/128/EC. The present up-to-date review gives an overall view of the recent results on the use of cyanobacteria for both their bioprotective effect against fungal and oomycete phytopathogens and their plant biostimulant properties. We highlight the need for considering several factors for a proper and sustainable management of agricultural crops, ranging from the mechanisms by which cyanobacteria reduce plant diseases and modulate plant resistance to the enhancement of plant growth.

Plant-cyanobacteria interactions: Beneficial and harmful effects of cyanobacterial bioactive compounds on soil-plant systems and subsequent risk to animal and human health

Plant-cyanobacteria interactions occur in different ways and at many different levels, both beneficial and harmful. Plant-cyanobacteria interactions, as a beneficial symbiosis, have long been demonstrated in rice-growing areas (Poaceae) where the most efficient nitrogen-fixing cyanobacteria are present in paddies. Moreover, cyanobacteria may in turn produce and/or secrete numerous bioactive compounds that have plant growth-promoting abilities or that may make the plant more resistant to abiotic or biotic stress. In recent years, there has been a growing worldwide interest in the use of cyanobacterial biomass as biofertilizers to replace chemical fertilizers, in part to overcome increasing organic-farming demands. However, the potential presence of harmful cyanotoxins has delayed the use of such cyanobacterial biomass, which can be found in large quantities in freshwater ecosystems around the world. In this review, we describe the existing evidence for the positive benefit of plant-cyanobacteria interactions and discuss the use of cyanobacterial biomass as biofertilizers and its growing worldwide interest. Although mass cyanobacterial blooms and scums are a current and emerging threat to the degradation of ecosystems and to animal and human health, they may serve as a source of numerous bioactive compounds with multiple positive effects that could be of use as an alternative to chemical fertilizers in the context of sustainable development.

PGPR in Agriculture: A Sustainable Approach to Increasing Climate Change Resilience

Growing environmental concerns are potentially narrowing global yield capacity of agricultural systems. Climate change is the most significant problem the world is currently facing. To meet global food demand, food production must be doubled by 2050; over exploitation of arable lands using unsustainable techniques might resolve food demand issues, but they have negative environmental effects. Current crop production systems are a major reason for changing global climate through diminishing biodiversity, physical and chemical soil degradation, and water pollution. The over application of fertilizers and pesticides contribute to climate change through greenhouse gas emissions (GHG) and toxic soil depositions. At this crucial time, there is a pressing need to transition to more sustainable crop production practices, ones that concentrate more on promoting sustainable mechanisms, which enable crops to grow well in resource limited and environmentally challenging environments, and also develop crops with greater resource use efficiency that have optimum sustainable yields across a wider array of environmental conditions. The phytomicrobiome is considered as one of the best strategies; a better alternative for sustainable agriculture, and a viable solution to meet the twin challenges of global food security and environmental stability. Use of the phytomicrobiome, due to its sustainable and environmentally friendly mechanisms of plant growth promotion, is becoming more widespread in the agricultural industry. Therefore, in this review, we emphasize the contribution of beneficial phytomicrobiome members, particularly plant growth promoting rhizobacteria (PGPR), as a strategy to sustainable improvement of plant growth and production in the face of climate change. Also, the roles of soil dwelling microbes in stress amelioration, nutrient supply (nitrogen fixation, phosphorus solubilization), and phytohormone production along with the factors that could potentially affect their efficiency have been discussed extensively. Lastly, limitations to expansion and use of biobased techniques, for instance, the perspective of crop producers, indigenous microbial competition and regulatory approval are discussed. This review largely focusses on the importance and need of sustainable and environmentally friendly approaches such as biobased/PGPR-based techniques in our agricultural systems, especially in the context of current climate change conditions, which are almost certain to worsen in near future.

Prospection of cyanobacteria producing bioactive substances and their application as potential phytostimulating agents

This work clarifies some of the substances involved with the biostimulant effect shown by 28 cyanobacteria isolated from different aquatic environments. The production of salicylic acid, cytokinins, siderophores and phosphate solubilization were analyzed in vitro, as well as the phytostimulant/phytotoxic effect on watercress seeds at two different extract concentrations (0.5 and 0.2 mg mL-1). The most prominent plant growth promoting cyanobacteria were verified in vivo at two different doses (0.5 and 0.1 mg mL-1). 21.4 % and 7.1 % of the tested strains produced siderophores or phosphate solubilization, respectively. The production of salicylic acid was stood out for the strains Calothrix SAB-B797, Nostoc SAB-B1300 and Nostoc SAB-M612, while Nostoc SAB-M251 and Trichormus SAB-M304 were noticeable regard to cytokinin production. The highest values of germination occurred when the extracts were applied in low dose (0.5 mg mL-1). Nostoc SAB-M612 provoked the stimulation of aerial and radicular growth in cucumber seedlings.

Antimicrobial activity and bioactive profiling of heterocytous cyanobacterial strains using MS/MS-based molecular networking

The rapid emergence of resistance in pathogenic bacteria together with a steep decline in economic incentives has rendered a new wave in the drug development by the pharmaceutical industry and researchers. Since cyanobacteria are recognized as wide producers of pharmaceutically important compounds, we investigated thirty-four cyanobacterial extracts prepared by solvents of different polarities for their antimicrobial potential. Almost all tested cyanobacterial strains exhibited some degree of antimicrobial bioactivity, with more general effect on fungal strains compared with bacteria. Surprisingly ~50% of cyanobacterial extracts exhibited specific activity against one or few bacterial indicator strains with Gram-positive bacteria being more affected. Extracts of two most promising strains were subjected to activity-guided fractionation and determination of the minimum inhibitory concentration (MIC) against selected bacterial and fungal isolates. Multiple fractions were responsible for their antimicrobial effect with MIC reaching low-micromolar concentrations and in some of them high level of specificity was recorded. Twenty-six bioactive fractions analyzed on LC-HRMS/MS and Global Natural Product Social Molecular Networking (GNPS) online workflow using dereplication resulted in identification of only forty-nine peptide spectrum matches (PSMs) with eleven unique metabolites spectrum matches (MSMs). Interestingly, only three fractions from Nostoc calcicola Lukešová 3/97 and four fractions from Desmonostoc sp. Cc2 showed the presence of unique MSMs suggesting the presence of unknown antimicrobial metabolites among majority of bioactive fractions from both the strains. Our results highlight potential for isolation and discovery of potential antimicrobial bioactive lead molecules from cyanobacterial extracts.