Source of bacterial strains.

A key barrier to crop production is soil salinity, which is a serious and growing problem world-wide due to inadequate water drainage, saline ground water, or inadequate rainfall to wash away soil salts. There is substantial promise for plant-associated microbes isolated from halophytes (salt-tolerant plants) to enhance growth of salt-sensitive crop plants in salty soils. The objective of this study was to identify salt-tolerant bacteria from native halophytes and characterize their ability to stimulate the growth of alfalfa in salty soil conditions. Several halotolerant bacteria, including Kushneria, Halomonas, and Bacillus, were identified from the rhizosphere or roots of three halophyte species (Salicornia rubra, Sarcocornia utahensis, and Allenrolfea occidentalis) in a saline area south of Utah Lake, Utah, USA. Biochemical properties, including indole acetic acid production, biofilm formation, phosphate solubilization and siderophore production activities, which have been associated with plant growth promoting (PGP) activity, were characterized for several isolates. Selected strains were screened for the ability to stimulate growth of alfalfa in controlled laboratory experiments. Among these strains, two independent isolates of the genus Kushneria were found to have significant growth-promoting activity for inoculated alfalfa plants grown under saline conditions (0.205 M or 1.2% NaCl) that mimic common salinity levels of affected soils. Plants inoculated with a combination of two Kushneria strains that have salt-tolerant PGP (ST-PGP) properties exhibited a statistically significant increase in plant growth over uninoculated plants. A GFP marker confirmed presence of Kushneria in the roots of inoculated plants. Bacteria with ST-PGP activity will be a key resource to facilitate increased crop yield from land affected by salinity, and the data presented here for two Kushneria isolates are promising.

土壤盐渍化是作物生产的核心限制因素之一，因排水不足、地下盐水侵袭或降雨不足以淋洗土壤盐分，该问题在全球范围内日趋严峻。从盐生植物（halophytes）中分离得到的植物相关微生物，在盐碱土壤中促进盐敏感作物生长方面具有可观应用前景。本研究旨在从本土盐生植物中分离耐盐细菌，并解析其在盐碱土壤条件下促进苜蓿生长的能力。研究团队从美国犹他州犹他湖以南的盐碱区域内的三种盐生植物（Salicornia rubra、Sarcocornia utahensis及Allenrolfea occidentalis）的根际（rhizosphere）或根系中，分离得到了包括库齐涅氏菌属（Kushneria）、盐单胞菌属（Halomonas）和芽孢杆菌属（Bacillus）在内的多种耐盐细菌。研究对部分分离菌株的多项生化特性进行了表征，包括与植物促生（plant growth promoting, PGP）活性相关的吲哚乙酸（indole acetic acid）合成、生物膜（biofilm）形成、磷酸盐溶解（phosphate solubilization）及铁载体（siderophore）合成能力。研究人员通过可控室内实验，筛选出能够促进苜蓿生长的目标菌株。在这些菌株中，两株独立的库齐涅氏菌属（Kushneria）分离株，在模拟受盐碱影响土壤常见盐度的条件（0.205 M 或1.2% NaCl）下，对接种的苜蓿植株展现出显著的促生长活性。接种兼具耐盐植物促生（salt-tolerant PGP, ST-PGP）特性的两株库齐涅氏菌的组合菌株后，苜蓿植株的生长量较未接种对照组出现了具有统计学意义的显著提升。通过绿色荧光蛋白（Green Fluorescent Protein, GFP）标记，证实了接种植株根系内存在库齐涅氏菌。具备耐盐植物促生活性的细菌，将成为提升盐碱耕地作物产量的关键资源；本研究中获得的两株库齐涅氏菌分离株数据，也展现出良好的应用潜力。