Nitrogen Fixing Azotobacter Species as Potential Soil Biological Enhancers for Crop Nutrition and Yield Stability

Abstract

Biological nitrogen fixation (BNF) refers to a microbial mediated process based upon an enzymatic “Nitrogenase” conversion of atmospheric nitrogen (N2) into ammonium readily absorbable by roots. N2-fixing microorganisms collectively termed as “diazotrophs” are able to fix biologically N2 in association with plant roots. Specifically, the symbiotic rhizobacteria induce structural and physiological modifications of bacterial cells and plant roots into specialized structures called nodules. Other N2-fixing bacteria are free-living fixers that are highly diverse and globally widespread in cropland. They represent key natural source of nitrogen (N) in natural and agricultural ecosystems lacking symbiotic N fixation (SNF). In this review, the importance of Azotobacter species was highlighted as both important free-living N2-fixing bacteria and potential bacterial biofertilizer with proven efficacy for plant nutrition and biological soil fertility. In addition, we described Azotobacter beneficial plant promoting traits (e.g., nutrient use efficiency, protection against phytopathogens, phytohormone biosynthesis, etc.). We shed light also on the agronomic features of Azotobacter that are likely an effective component of integrated plant nutrition strategy, which contributes positively to sustainable agricultural production. We pointed out Azotobacter based-biofertilizers, which possess unique characteristics such as cyst formation conferring resistance to environmental stresses. Such beneficial traits can be explored profoundly for the utmost aim to research and develop specific formulations based on inoculant Azotobacter cysts. Furthermore, Azotobacter species still need to be wisely exploited in order to address specific agricultural challenges (e.g., nutrient deficiencies, biotic and abiotic constraints) taking into consideration several variables including their biological functions, synergies and multi-trophic interactions, and biogeography and abundance distribution.

Toxic Effects of Thallium on Biological Indicators of Haplic Chernozem Health: A Case Study

“…When the soil was contaminated with Tl, the nitrogen balance in the soil did not change, and therefore, Azotobacter spp. abundance in the soil depended little on the concentration and duration of Tl exposure [50]. For radish germination, recovery was noted with an increase in exposure to 90 days.…”

Rhamnolipid Enhances the Nitrogen Fixation Activity of Azotobacter chroococcum by Influencing Lysine Succinylation

“…Azotobacter species were model organisms to study nitrogenase and the mechanisms of nitrogen fixation (Baars et al, 2016;Danyal et al, 2016;Rebelein et al, 2018). Meanwhile, Azotobacter species is important as free-living, nitrogen-fixing bacteria and potential bacterial biofertilizer (Sumbul et al, 2020;Aasfar et al, 2021). In addition, A. chroococcum has other characteristics, such as phosphorus hydrolysis, synthetic indoles, and alginate (Romero-Perdomo et al, 2017;Gawin et al, 2020).…”

The Participation of Microbiota in the Transformation of Nitrogen Compounds in the Soil—A Review

“…Numbers in the soil of Arthrobacter provide 5-25 kg N•ha −1 per year of this element, as well as cyanobacteria [27][28][29]. Clostridium bind 0.1-0.5 kg N•ha −1 per year [20].…”