Preservation of Rhizobium viability and symbiotic infectivity by suspension in water

Abstract

Three Rhizobiumjaponicum strains and two slow-growing cowpea-type Rhizobium strains were found to remain viable and able to rapidly nodulate their respective hosts after being stored in purified water at ambient temperatures for periods of 1 year and longer. Three fast-growing Rhizobium species did not remain viable under the same water storage conditions. After dilution of slow-growing Rhizobium strains with water to 103 to 105 cells ml-', the bacteria multiplied until the viable cell count reached levels of between 106 and 107 cells ml-1. The viable cell count subsequently remained fairly constant. When the rhizobia were diluted to 107 cells ml-1, they did not multiply, but full viability was maintained. If the rhizobia were washed and suspended at 109 cells ml-', viability slowly declined to 107 cells ml-' during 9 months of storage. Scanning electron microscopy showed that no major morphological changes took place during storage. Preservation of slow-growing rhizobia in water suspensions could provide a simple and inexpensive alternative to current methods for the preservation of rhizobia for legume inoculation.

Survival and infectivity of a Rhizobium meliloti strain maintained in water and buffer suspensions

“…Rhizobium meliloti B323 remained viable in phosphate buffer suspensions for 10 months, but failed to maintain viability in deionized water suspensions where viable cell count decreased. This behaviour was different from that reported by Crist et al (1984) for five strains of slow growing rhizobia, where they found that the micro-organisms remained viable after storage for more than 1 year. Presence of Ca2+, Mg2+ and Fe3+ ions, as was previously described by Postgate & Hunter (1962), enhanced cell viability higher at pH 5.5 than at pH 6.5.…”

“…Previous papers showed that bacteria suspended in water achieved and maintained a maximum viable concentration of 106-107 cells/ ml (Wakimoto er al. 1982;Crist et al 1984). When the initial concentration was higher the viability dropped, and when it was lower the viability increased in order to reach 106-107 cells/ml.…”

Slow-growing and oligotrophic soil bacteria phylogenetically close to Bradyrhizobium japonicum

“…The close phylogenetic relationship among B. japonicum, A. oligotrophica, B. denitri¢cans and the 11 G14127 54 80 53 37 51 120 60 92 100 61 99 46 20 G14130 30 30 44 31 41 46 49 30 32 100 35 38 9 Bradyrhizobium japonicum USDA110 26 26 37 36 33 38 35 36 34 40 35 100 2 Agromonas oligotrophica S58 16 11 14 16 14 20 16 16 16 20 18 19 100 DNB bacteria in the BANA domain was also supported by common features such as oligotrophy and slow growth rates. Crist et al [28] demonstrated that B. japonicum cells remained viable in puri¢ed water for 1 year or longer, and Ozawa and Doi [29] reported that the competitive nodulation ability of B. japonicum was increased by oligotrophic growth in puri¢ed water. Blastobacter spp.…”

Evidence supporting a non‐phloem source of water for export of solutes in the xylem of soybean root nodules

“…Soybean seeds {Glycine max (L.) Merr. cv Beeson 80] were planted in autoclaved silica sand and inoculated on the planting date with Bradyrhizobium japonicum USDA110; a water culture (Crist et al 1984) was used as inoculant. Plants were irrigated two or three times daily with a nutrient solution lacking combined nitrogen (Streeter 1974).…”