Amino acid and synthetic molybdate (MoO4-2) chelates and their bioavailability to azotobacter bacteria at different temperatures

Abstract

The efficiency of biological nitrogen fixation by Azotobacter bacteria depends on the bioavailability of molybdenum, which is a key microelement of nitrogenase, and varies under conditions of temperature stress in regions with a temperate climate. The study aimed to compare the effectiveness of different chelated forms of molybdenum in supporting the growth, metabolic activity, and nitrogen-fixing ability of Azotobacter chroococcum bacteria under temperature stress conditions. The study was conducted in vitro on Ashby medium. Five sources of molybdenum were evaluated: unchelated sodium molybdate, amino acid chelates and synthetic chelates. Bioavailability was assessed by growth intensity, nitrogen accumulation in biomass, nitrogenase activity and total protein content. The results showed that amino acid chelates, especially histidine molybdate, provided the highest bioavailability of molybdenum. At optimal temperature, this option showed a 30.7% increase in bacterial growth intensity, a 37.1% increase in nitrogen accumulation, and a 40.2% increase in nitrogenase activity compared to the non-chelated form. Under conditions of temperature stress (18°C), the advantage of amino acid chelates was even more pronounced: the decrease in nitrogen fixation efficiency was only 40.0% for histidine molybdate versus 48.4% for non-chelated molybdate. The study established that amino acid chelates not only improve molybdenum transport into cells but also contribute to the stabilisation of the nitrogenase complex and maintain the overall metabolic status of bacteria under unfavourable conditions. The findings confirmed that amino acid molybdate chelates are promising for use in biological products because they increase the bioavailability of molybdenum and the resistance of nitrogen fixation to temperature stress. The results of the study can be used to develop effective Azotobacter-based biological products for regions with a temperate climate, which will help reduce the use of mineral fertilisers.