Screening, evaluation, and selection of yeasts with high ammonia production ability under nitrogen free condition from the cherry tomato (Lycopersicon esculentum var. cerasiforme) rhizosphere as a potential bio-fertilizer

Abstract

Nitrogen (N) is an essential element for plant development and metabolism. It can be synthesized as nitrogenous substances that plants need, such as amino acids and nucleic acids. However, the N sources that plants can use directly are nitrate and ammonium, which either come from chemical fertilizers or are produced by microorganisms. However, too much chemical fertilizer causes nitrate accumulation in the soil of crops and leads to soil salinity. Applying bio-fertilizers to overcome land degradation caused by chemical fertilizers has been a public concern over the last few decades. Here, we collected the wild cherry tomato to isolate yeasts from its rhizosphere and evaluate their ability to promote plant growth. A total of 118 yeast strains were isolated from the rhizosphere and evaluated for their growth ability on nitrogen (N)-free media, ammonia production, and plant growth-promoting abilities. We reported that 66 yeasts showed growth ability on the N-free plate and all could produce ammonia (from 0.31 to 474.75 μg/mL) and indole-3-acetic acid (from 17.65 to 789.41 μM) with tryptophan as the precursor. Plant growth promotion was observed in Arabidopsis and baby pak choy plants following treatment with the yeast-producing N source as compared to control. We also found that only specific yeast strains could promote plant growth and development. It is suggested that plants may require suitable levels of yeast-producing ammonium. These results highlight the potential use of yeasts as bio-fertilizers under controlled and field conditions.