Several Rhodopseudomonas palustris strains have been isolated from rice paddy fields in Taiwan by combining the Winogradsky column method and molecular marker detection. These isolates were initially screened by employing seed germination and seedling vigor assays to evaluate their potential as inoculants. To fulfill the demand in the present farming system for reducing the application of chemical fertilizers, we assessed the plant growth-promoting effects of the R. palustris YSC3, YSC4, and PS3 inoculants on Brassica rapa chinensis (Chinese cabbage) cultivated under a half quantity of fertilizer. The results obtained showed that supplementation with approximately 4.0×106 CFU g−1 soil of the PS3 inoculant at half the amount of fertilizer consistently produced the same plant growth potential as 100% fertility, and also increased the nitrogen use efficiency of the applied fertilizer nutrients. Furthermore, we noted that the plant growth-promotion rate elicited by PS3 was markedly higher with old seeds than with new seeds, suggesting it has the potential to boost the development of seedlings that were germinated from carry-over seeds of poor quality. These beneficial traits suggest that the PS3 isolate may serve as a potential PGPR inoculant for integrated nutrient management in agriculture.

A polyphasic approach was used to characterize a novel bacterium, designated strain TPP412T, isolated from a paddy soil in Taiwan. Strain TPP412T was Gram-stain-negative, facultatively anaerobic, rod-shaped, motile with a single polar flagellum and lacked bacteriochlorophyll. Growth was observed at 24-45 °C (optimal 25 °C), at pH 5.0-10.0 (optimal pH 7.0) and with 0-0.75 % (w/v) NaCl. Strain TPP412T showed highest 16S rRNA gene sequence similarity to members of the genera Rhodocyclus (94.1-94.5 %), Azospira (93.9-94.5 %) and Propionivibrio (93.4-94.4 %) and established a discrete taxonomic lineage in phylogenetic analysis. The major fatty acids found in strain TPP412T were C12 : 0, C12 : 0 3-OH, iso-C15 : 0 3-OH, C16 : 0, C16 : 1ω7c/C16 : 1ω6c and C18 : 1ω7c/C18 : 1ω6c. The major polar lipids consisted of phosphatidylmonomethylethanolamine, diphosphatidylglycerol, phosphatidylglycerol and an unidentified lipid. The polyamine pattern showed a predominance of putrescine and a minor amount of spermidine. The DNA G+C content was 58.4 mol% and the predominant quinone system was ubiquinone-8 (Q-8). The low 16S rRNA gene sequence similarity values (≤94.5%) and distinct phylogenetic clustering clearly distinguished strain TPP412T from other representatives of the family Rhodocyclaceae. Based on the discrete phylogenetic, phenotypic and chemotaxonomic traits together with results of comparative 16S rRNA gene sequence analysis, strain TPP412T is considered to represent a novel species of a new genus in the family Rhodocyclaceae, for which the name Oryzomicrobium terrae gen. nov., sp. nov. is proposed. The type strain of Oryzomicrobium terrae is TPP412T (=BCRC 80905T=JCM 30814T).