Characterization of the Pyrroloquinoline Quinone Producing Rhodopseudomonas palustris as a Plant Growth-Promoting Bacterium under Photoautotrophic and Photoheterotrophic Culture Conditions

Rhodopseudomonas palustris is a purple non-sulfide bacterium (PNSB), and some strains have been proven to promote plant growth. However, the mechanism underlying the effect of these PNSBs remains limited. Based on genetic information, R. palustris possesses the ability to produce pyrroloquinoline quinone (PQQ). PQQ is known to play a crucial role in stimulating plant growth, facilitating phosphorous solubilization, and acting as a reactive oxygen species scavenger. However, it is still uncertain whether growth conditions influence R. palustris's production of PQQ and other characteristics. In the present study, it was found that R. palustris exhibited a higher expression of genes related to PQQ synthesis under autotrophic culture conditions as compared to acetate culture conditions. Moreover, similar patterns were observed for phosphorous solubilization and siderophore activity, both of which are recognized to contribute to plant-growth benefits. However, these PNSB culture conditions did not show differences in Arabidopsis growth experiments, indicating that there may be other factors influencing plant growth in addition to PQQ content. Furthermore, the endophytic bacterial strains isolated from Arabidopsis exhibited differences according to the PNSB culture conditions. These findings imply that, depending on the PNSB's growing conditions, it may interact with various soil bacteria and facilitate their infiltration into plants.

Amycolatopsis xuchangensis sp. nov. and Amycolatopsis jiguanensis sp. nov., isolated from soil

Two novel actinomycetes, designated strains CFH S0322^T and CFH S01580^T, were isolated from soil samples collected from Xuchang city and Ji Guan cave in Henan province, China, respectively. Their taxonomic positions were investigated by a polyphasic approach. The two isolates were Gram-reaction positive, non-motile, aerobic and catalase-positive actinomycetes. Phylogenetic analysis based on 16S rRNA gene sequence comparisons showed that the two isolates are closely related to the members of the genus Amycolatopsis, sharing high similarities with Amycolatopsis magusensis KCTC 29056^T (99.1 %, CFH S0322^T) and Amycolatopsis nigrescens DSM 44992^T (98.1 %, CFH S01580^T), respectively. The major whole cell sugars of strains CFH S0322^T and CFH S01580^T were arabinose and galactose and the predominant menaquinone was MK-9(H₄). The genomic DNA G+C contents of strains CFH S0322^T and CFH S01580^T were 70.6 and 68.6 mol%, respectively. Morphological, phylogenetic and chemotaxonomic results suggest that strains CFH S0322^T and CFH S01580^T are representatives of two new species, for which the names Amycolatopsis xuchangensis sp. nov. and Amycolatopsis jiguanensis sp. nov. are proposed. The type strains are CFH S0322^T (=NBRC 110769^T =KCTC 39516^T) and CFH S01580^T (=DSM 101526^T =CCTCC AA 2015032^T).

Classification of thermophilic actinobacteria isolated from arid desert soils, including the description of Amycolatopsis deserti sp. nov

The taxonomic position of 26 filamentous actinobacteria isolated from a hyper-arid Atacama Desert soil and 2 from an arid Australian composite soil was established using a polyphasic approach. All of the isolates gave the diagnostic amplification product using 16S rRNA oligonucleotide primers specific for the genus Amycolatopsis. Representative isolates had chemotaxonomic and morphological properties typical of members of the genus Amycolatopsis. 16S rRNA gene analyses showed that all of the isolates belong to the Amycolatopsis methanolica 16S rRNA gene clade. The Atacama Desert isolates were assigned to one or other of two recognised species, namely Amycolatopsis ruanii and Amycolatopsis thermalba, based on 16S rRNA gene sequence, DNA:DNA relatedness and phenotypic data; emended descriptions are given for these species. In contrast, the two strains from the arid Australian composite soil, isolates GY024(T) and GY142, formed a distinct branch at the periphery of the A. methanolica 16S rRNA phyletic line, a taxon that was supported by all of the tree-making algorithms and by a 100 % bootstrap value. These strains shared a high degree of DNA:DNA relatedness and have many phenotypic properties in common, some of which distinguished them from all of the constituent species classified in the A. methanolica 16S rRNA clade. Isolates GY024(T) and GY142 merit recognition as a new species within the A. methanolica group of thermophilic strains. The name proposed for the new species is Amycolatopsis deserti sp. nov.; the type strain is GY024(T) (=NCIMB 14972(T) = NRRL B-65266(T)).