Free-living bacteria of the genus Azotobacter – significance, mechanisms of action and practical use in crop production and sustainable agriculture

Abstract

Crops grown today show high yield potential, and one of the conditions for realising this potential is to meet their increased nutrient requirements. Arable soils often lack adequate nitrogen, which results in reduced yields and reduced profitability of production. The low nitrogen content of the soil is usually supplemented by the application of mineral fertilisers, which can cause ammonia volatilisation and nitrate accumulation in the soil. Long-term and intensive use of nitrogen fertilisers also contributes to soil acidification, groundwater contamination and an imbalance in the biological ecosystem, for example by increasing the proportion of fungi in the soil microbial population. It is therefore crucial to develop integrated crop production strategies that sustainably increase crop productivity. No less important is the maintenance of soil quality and the reduction of soil degradation problems. Therefore, there is a growing interest in non-chemical methods of fertilisation and plant protection. Biologically active agents are being sought to protect plants and promote their growth. A number of biopreparations are available on the market that improve the humus-forming properties of soil, do not disturb the biological balance and increase plant yields. Their advantages include increasing the availability of elements needed by plants (nitrogen, phosphorus), as well as stimulating plant growth and development through the synthesis of phytohormones. The market for biopreparations is growing rapidly and forms the basis of plant protection in line with the European Green Deal and the ‚Field to Table’ strategy, which promote the reduction of use of synthetic mineral fertilisers and pesticides in favour of biological solutions. One of the preparations available on the market are vaccines containing free-living atmospheric nitrogen-fixing bacteria belonging to the genus Azotobacter.
This article highlights the importance of bacteria belonging to the genus Azotobacter as a potential ingredient in biopreparations to improve the growth, development and yield quality of many crops. Furthermore, the mechanisms used by Azotobacter spp. to promote plant growth (fixation of atmospheric nitrogen, solubilisation of phosphate, potassium and zinc, synthesis of phytohormones, vitamins, siderophores and protection against pathogens) are discussed. Attention has been drawn to the ability of bacteria of the genus Azotobacter to form cysts, which enables them to survive under adverse environmental conditions (high temperature, acidic pH, salinity). Current information on the importance and practical use of Azotobacter spp. in crop production and sustainable agriculture is also reviewed. The use of biopreparations based on Azotobacter spp. strains in agriculture allows for increased crop production and can contribute to meeting the food needs of the world’s ever-growing human population.