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The worldwide increase in human population raises a big threat to the food security of each people as the land for agriculture is limited and even getting reduced with time. Therefore, it is essential that agricultural productivity should be enhanced significantly within the next few decades to meet the large demand of food by emerging population. Not to mention, too much dependence on chemical fertilizers for more crop productions inevitably damages both environmental ecology and human health with great severity. Exploitation of microbes as biofertilizers is considered to some extent an alternative to chemical fertilizers in agricultural sector due to their extensive potentiality in enhancing crop production and food safety. It has been observed that some microorganisms including plant growth promoting bacteria, fungi, Cyanobacteria , etc. have showed biofertilizer-like activities in the agricultural sector. Extensive works on biofertilizers have revealed their capability of providing required nutrients to the crop in sufficient amounts that resulted in the enhancement of crop yield. The present review elucidates various mechanisms that have been exerted by biofertilizers in order to promote plant growth and also provides protection against different plant pathogens. The aim of this review is to discuss the important roles and applications of biofertilizers in different sectors including agriculture, bioremediation, and ecology.

Current soil management strategies are mainly dependent on inorganic chemical-based fertilizers, which caused a serious threat to human health and environment. The exploitation of beneficial microbes as a biofertilizer has become paramount importance in agriculture sector for their potential role in food safety and sustainable crop production. The eco-friendly approaches inspire a wide range of application of plant growth promoting rhizobacteria (PGPRs), endo- and ectomycorrhizal fungi, cyanobacteria and many other useful microscopic organisms led to improved nutrient uptake, plant growth and plant tolerance to abiotic and biotic stress. The present review highlighted biofertilizers mediated crops functional traits such as plant growth and productivity, nutrient profile, plant defense and protection with special emphasis to its function to trigger various growth- and defense-related genes in signaling network of cellular pathways to cause cellular response and thereby crop improvement. The knowledge gained from the literature appraised herein will help us to understand the physiological bases of biofertlizers towards sustainable agriculture in reducing problems associated with the use of chemicals fertilizers.

Although inorganic fertilizers are known to raise environmental and health problems, the current agricultural practices are heavily dependent on the application of synthetic fertilizers and pesticides. In this study, we examined the effect of Chlorella vulgaris strain on germination of tomato and cucumber seeds. Seeds were germinated in culture medium containing algal strain and grown for 3, 6, 9 and 12 days to study its effect on growth parameters. As results, C. vulgaris suspension increased the seed growth compared to those of the control (sterilized culture medium) of seed germination. The best treatments were 0.17 and 0.25 g/L of algal suspension for the root and shoot lengths of tomato and cucumber seeds, respectively.

With the impending increase of the world population by 2050, more activities have been directed toward the improvement of crop yield and a safe environment. The need for chemical-free agricultural practices is becoming eminent due to the effects of these chemicals on the environment and human health. Actinomycetes constitute a significant percentage of the soil microbial community. The Streptomyces genus, which is the most abundant and arguably the most important actinomycetes, is a good source of bioactive compounds, antibiotics, and extracellular enzymes. These genera have shown over time great potential in improving the future of agriculture. This review highlights and buttresses the agricultural importance of Streptomyces through its biocontrol and plant growth-promoting activities. These activities are highlighted and discussed in this review. Some biocontrol products from this genus are already being marketed while work is still ongoing on this productive genus. Compared to more focus on its biocontrol ability, less work has been done on it as a biofertilizer until recently. This genus is as efficient as a biofertilizer as it is as a biocontrol.

Growing food crops in gold mine tailings is limited by low nitrogen and mercury contamination. Little is known about the responses of water spinach (Ipomoea aquatica L.) to nitrogen-fixing bacteria biofertilizer. This study aimed to analyze changes in growth media properties, growth, biomass of water spinach, and mercury in both tailings-based growth media and intact plants following the application of the nitrogen-fixing Azotobacter. A liquid inoculum of Azotobacter was analyzed before the experiment. A greenhouse experiment was arranged in a randomized block design to evaluate three inoculant concentrations. Acidity and electrical conductivity of the inoculant were 7.95 and 1.74 mS/cm, respectively, while the Azotobacter count was 9.18 on a log scale. Introducing 5% and 10% inoculants increased microbial counts, total nitrogen, and acidity of the growth media, as well as shoot growth and biomass, but did not affect root length. Azotobacter did not affect mercury levels in the soil but increased mercury accumulation in intact plants. Mercury levels in soil and plants remained higher than the maximum threshold value. While soil pH and nitrogen levels showed a positive correlation with plant growth, mercury concentration in the soil exhibited a significant negative correlation. Because of high mercury accumulation, the water spinach was not safe for cultivation.

The idea of eliminating the use of fertilizers which are sometimes environmentally unsafe is slowly becoming a reality because of the emergence of microorganisms that can serve the same purpose or even do better. Depletion of soil nutrients through leaching into the waterways and causing contamination are some of the negative effects of these chemical fertilizers that prompted the need for suitable alternatives. This brings us to the idea of using microbes that can be developed for use as biological fertilizers (biofertilizers). They are environmentally friendly as they are natural living organisms. They increase crop yield and production and, in addition, in developing countries, they are less expensive compared to chemical fertilizers. These biofertilizers are typically called plant growth-promoting bacteria (PGPB). In addition to PGPB, some fungi have also been demonstrated to promote plant growth. Apart from improving crop yields, some biofertilizers also control various plant pathogens. The objective of worldwide sustainable agriculture is much more likely to be achieved through the widespread use of biofertilizers rather than chemically synthesized fertilizers. However, to realize this objective it is essential that the many mechanisms employed by PGPB first be thoroughly understood thereby allowing workers to fully harness the potentials of these microbes. The present state of our knowledge regarding the fundamental mechanisms employed by PGPB is discussed herein.

For all living organisms, nitrogen is an essential element, while being the most limiting in ecosystems and for crop production. Despite the significant contribution of synthetic fertilizers, nitrogen requirements for food production increase from year to year, while the overuse of agrochemicals compromise soil health and agricultural sustainability. One alternative to overcome this problem is biological nitrogen fixation (BNF). Indeed, more than 60% of the fixed N on Earth results from BNF. Therefore, optimizing BNF in agriculture is more and more urgent to help meet the demand of the food production needs for the growing world population. This optimization will require a good knowledge of the diversity of nitrogen-fixing microorganisms, the mechanisms of fixation, and the selection and formulation of efficient N-fixing microorganisms as biofertilizers. Good understanding of BNF process may allow the transfer of this ability to other non-fixing microorganisms or to non-leguminous plants with high added value. This minireview covers a brief history on BNF, cycle and mechanisms of nitrogen fixation, biofertilizers market value, and use of biofertilizers in agriculture. The minireview focuses particularly on some of the most effective microbial products marketed to date, their efficiency, and success-limiting in agriculture. It also highlights opportunities and difficulties of transferring nitrogen fixation capacity in cereals.

Due to the constant growth of the human population and anthropological activity, it has become necessary to use sustainable and affordable technologies that satisfy the current and future demand for agricultural products. Since the nutrients available to plants in the soil are limited and the need to increase the yields of the crops is desirable, the use of chemical (inorganic or NPK) fertilizers has been widespread over the last decades, causing a nutrient shortage due to their misuse and exploitation, and because of the uncontrolled use of these products, there has been a latent environmental and health problem globally. For this reason, green biotechnology based on the use of microalgae biomass is proposed as a sustainable alternative for development and use as soil improvers for crop cultivation and phytoremediation. This review explores the long-term risks of using chemical fertilizers for both human health (cancer and hypoxia) and the environment (eutrophication and erosion), as well as the potential of microalgae biomass to substitute current fertilizer using different treatments on the biomass and their application methods for the implementation on the soil; additionally, the biomass can be a source of carbon mitigation and wastewater treatment in agro-industrial processes.

Phosphorus (P) is central to storing and exchange of energy and information in cells including those of microalgae. The overwhelming majority of microalgae are naturally acclimated to low-P environments; hence, they are capable of taking up and storing P in large amounts whenever it becomes available. The ability to take up more P than necessary for immediate growth is termed “luxury uptake.” Understanding this phenomenon constitutes a crucial insight into nutrient-driven processes in natural algal communities such as harmful algal blooms, as well as into the operation of algae-based technologies for sustainable usage of P such as recycling of the nutrient from wastewater to biofertilizers. The bulk of P acquired during luxury uptake is stored in the form of inorganic polyphosphate, the compound with nearly ubiquitous presence and multifaceted function in the cell. Although seminal works on luxury P uptake and polyphosphate metabolism were carried out fifty years ago, application of modern “omics” approaches and advanced imaging microscopy techniques enabled obtaining a deeper mechanistic insight into these processes. Nevertheless, our knowledge about luxury P uptake remains much more limited in comparison with that about P shortage and mechanism tolerance to this stress in microalgae. In this review the knowledge of luxury P uptake originating from classical phycological and biochemical methods is confronted with the recently obtained understanding of molecular mechanisms of P transport to the cell, polyphosphate biosynthesis, regulation, and genetic control of these processes. Biotechnological implications of the knowledge about luxury P uptake accumulated to date are discussed in the context of algae-based approaches to sustained usage of nutrients and industrial cultivation of microalgae.

Microalgae represent a potential sustainable alternative for the enhancement and protection of agricultural crops. Cellular extracts and dry biomass of the green alga Acutodesmus dimorphus were applied as a seed primer, foliar spray, and biofertilizer, to evaluate seed germination, plant growth, and fruit production in Roma tomato plants. A. dimorphus culture, culture growth medium, and different concentrations (0, 1, 5, 10, 25, 50, 75, and 100 %) of aqueous cell extracts in distilled water were used as seed primers to determine effects on germination. Seeds treated with A. dimorphus culture and with extract concentrations higher than 50 % (0.75 g mL⁻¹) triggered faster seed germination—2 days earlier than the control group. The aqueous extracts were also applied as foliar fertilizers at various concentrations (0, 10, 25, 50, 75, and 100 %) on tomato plants. Extract foliar application at 50 % (3.75 g mL⁻¹) concentration resulted in increased plant height and greater numbers of flowers and branches per plant. Two dry biomass treatments (50 and 100 g) were applied 22 days prior to seedling transplant and at the time of transplant to assess whether the timing of the biofertilizer application influenced the effectiveness of the biofertilizer. Biofertilizer treatments applied 22 days prior to seedling transplant enhanced plant growth, including greater numbers of branches and flowers, compared to the control group and the biofertilizer treatments applied at the time of transplant. The A. dimorphus culture, cellular extract, and dry biomass applied as a biostimulant, foliar spray, and biofertilizer, respectively, were able to trigger faster germination and enhance plant growth and floral production in Roma tomato plants.