Isolation,culture condition optimization,and preliminary application of siderophore-producing strains

Abstract:

[Background] The key to promoting green agriculture is microbial fertilizer.Siderophore is a low molecular iron chelate produced by rhizosphere microorganisms,which can promote plant growth by chelating Fe³⁺.Therefore,it is of great significance to screen out the strains with high-yield siderophore.[Objective] In order to provide germplasm resources for the development of plant growth-promoting bacteria,we isolated high-yielding siderophore microorganisms from rhizosphere soil.[Methods] A fungal strain with high yield of siderophore was isolated and purified by chrome azurol sulfonate (CAS) overlay plate method.The strain was identified based on morphological observation and 18S rRNA gene analysis.The culture conditions for siderophore production were optimized by single factor experiment,and the growth-promoting effect of the strain was preliminarily investigated by hydroponic experiment of Chinese cabbage.[Results] Four strains of siderophore-producing fungi were isolated,one of which with strong siderophores-producing ability was numbered RL1 and preliminarily identified as Aspergillus niger.The optimal culture conditions for siderophore production of strain RL1 were as follows:initial pH 5.0,carbon source of glucose at 5 g/L,temperature at 20℃,culture time of 5 days,and rotational speed of 60 r/min.The fresh weight and photosynthetic pigment content of Chinese cabbage increased with the increase in the concentration of RL1 suspension.When the maximum concentration (3.2×10⁸ CFU/mL) of suspension was applied,the total fresh weight and the aboveground weight of Chinese cabbage increased by 75.0% and 74.4%,respectively,and the content of chlorophyll a,chlorophyll b,and carotenoid increased by 49.8%,70.9% and 26.7%,respectively.[Conclusion]In this study,a fungal strain RL1 with high-yield siderophore was isolated.High siderophore production of the strain was achieved at optimized culture conditions,and the strain could effectively promote the growth of Chinese cabbage seedlings.