Ammonium excretion, auxin production and effects of maize inoculation with ethylenediamine-resistant mutants of Pseudomonas sp.

ABSTRACT Plant growth-promoting bacteria (PGPB) comprise part of plant microbiome of biotechnological interest due to their potential to decrease the use of agrochemicals in agriculture. Among the commonly found PGPB species, the Pseudomonas genus is known for high competitiveness and efficiency in expressing growth-promotion traits. To increase the contribution of diazotrophic Pseudomonas sp. to the plant nitrogen nutrition, the strain AZM-01 was chemically mutagenized with methyl methanesulfonate (MMS), following the selection for resistance to ethylenediamine (EDA). From the 13 EDA-resistant mutant strains selected, four showed increased the ammonium excretion, with the highest value reaching up to 284% increase as compared to the wild strain, and six strains were found to produce significantly more auxins than the wild strain. Two independent inoculation trials with the wild and EDA-resistant Pseudomonas were performed on maize, with the objective to study the influence of bacteria on seed germination and its potential to promote maize growth under N-limiting condition. In general, Pseudomonas inoculation modified the root architecture of germinating seeds, and increased biomass of maize plants grown under N-limiting conditions. Shoot dry weight of maize was increased by inoculation with several EDA-resistant mutants as compared to the strain AZM-01, with emphasis on the EDA-5 strain which supports biomass accumulation at equivalent amount of plants grown under full N supply. Significant correlations between in vitro and in vivo parameters were found although low coefficient values predominate. The strategy of random mutagenesis was found suitable to develop PGPB strains with higher potential to supply maize plants with nitrogen.

摘要 植物促生细菌（PGPB）是植物微生物组的组成部分，因其具备降低农业农用化学品使用量的潜力而受到生物技术领域的关注。在常见的PGPB物种中，假单胞菌属（Pseudomonas）以极强的竞争能力和高效表达促生性状的特性而闻名。为提升固氮假单胞菌属（Pseudomonas sp.）对植物氮营养的贡献，研究人员采用甲基磺酸甲酯（Methyl Methanesulfonate, MMS）对菌株AZM-01进行化学诱变，并通过乙二胺（Ethylenediamine, EDA）抗性筛选获得突变株。在筛选得到的13株EDA抗性突变株中，4株的铵盐分泌量显著提升，最高较野生菌株提升达284%；另有6株产生的生长素（Auxins）含量显著高于野生菌株。研究人员以野生型及EDA抗性假单胞菌为材料，对玉米开展了两组独立的接种试验，旨在探究这类细菌对种子萌发的影响，以及其在低氮条件下促进玉米生长的潜力。总体而言，假单胞菌接种可改变萌发种子的根系构型，并提升低氮培养条件下玉米植株的生物量。与原始菌株AZM-01相比，多株EDA抗性突变株的接种可提升玉米地上部干重，其中EDA-5菌株的效果尤为突出，其介导的生物量积累水平与全氮供应条件下生长的玉米相当。尽管多数相关系数较低，但体外与体内参数间仍存在显著相关性。本研究表明，随机诱变策略可用于开发具备更高玉米氮素供给潜力的PGPB菌株。