Effects of LPS from Rhodobacter sphaeroides, a Purple Non-Sulfur Bacterium (PNSB), on the Gene Expression of Rice Root.

The effects of lipopolysaccharide (LPS) from Rhodobacter sphaeroides, a purple non-sulfur bacterium (PNSB), on the gene expression of the root of rice (Oryza sativa) were investigated by next generation sequencing (NGS) RNA-seq analysis. The rice seeds were germinated on agar plates containing 10 pg/mL of LPS from Rhodobacter sphaeroides NBRC 12203 (type culture). Three days after germination, RNA samples were extracted from the roots and analyzed by RNA-seq. The effects of dead (killed) PNSB cells of R. sphaeroides NBRC 12203T at the concentration of 101 cfu/mL (ca. 50 pg cell dry weight/mL) were also examined. Clean reads of NGS were mapped to rice genome (number of transcript ID: 44785), and differentially expressed genes were analyzed by DEGs. As a result of DEG analysis, 300 and 128 genes, and 86 and 8 genes were significantly up- and down-regulated by LPS and dead cells of PNSB, respectively. The plot of logFC (fold change) values of the up-regulated genes of LPS and PNSB dead cells showed a significant positive relationship (r2 = 0.6333, p < 0.0001), indicating that most of the effects of dead cell were attributed to those of LPS. Many genes related to tolerance against biotic (fungal and bacterial pathogens) and abiotic (cold, drought, and high salinity) stresses were up-regulated, and the most strikingly up-regulated genes were those involved in the jasmonate signaling pathway, and the genes of chalcone synthase isozymes, indicating that PNSB induced defense response against biotic and abiotic stresses via the jasmonate signaling pathway, despite the non-pathogenicity of PNSB.

Recent progress in the use of purple non-sulfur bacteria as probiotics in aquaculture.

The use of probiotics in aquaculture is widely recognized as an ecological and cost-effective approach to raising healthy, pathogen-tolerant aquatic animals, including fish and shrimp. In particular for shrimp, probiotics are viewed as a promising countermeasure to the recent severe damage to the shrimp industry by bacterial and viral pathogens. Purple non-sulfur bacteria (PNSB) are Gram-negative, non-pathogenic bacteria with wide application potential in agriculture, wastewater treatment, and bioenergy/biomaterials production. In aquaculture, lactic bacteria and Bacillus are the major probiotic bacteria used, but PNSB, like Rhodopseudomonas and Rhodobacter, are also used. In this review, we summarize the previous work on the use of PNSB in aquaculture, overview the previous studies on the stimulation of innate immunity of shrimp by various probiotic microorganisms, and also share our results in the probiotic performance of Rhodovulum sulfidophilum KKMI01, a marine PNSB, which showed a superior effect in promotion of growth and stimulation of immunity in shrimp at a quite low concentration of 1 × 103 cfu (colony forming unit)/ml in rearing water.

Effects of Seed Bio-Priming by Purple Non-Sulfur Bacteria (PNSB) on the Root Development of Rice.

The effects of seed bio-priming (seed soaking) with purple non-sulfur bacteria (PNSB) on the grain productivity and root development of rice were examined by a field study and laboratory experiments, respectively. Two PNSB strains, Rhodopseudomonas sp. Tsuru2 and Rhodobacter sp. Tsuru3, isolated from the paddy field of the study site were used for seed bio-priming. For seed bio-priming in the field study, the rice seeds were soaked for 1 day in water containing a 1 × 105 colony forming unit (cfu)/mL of PNSB cells, and the rice grain productivities at the harvest time were 420, 462 and 504 kg/are for the control, strain Tsuru2-primed, and strain Tsuru3-primed seeds, respectively. The effects of seed priming on the root development were examined with cell pot cultivation experiments for 2 weeks. The total root length, root surface area, number of tips and forks were evaluated with WinRhizo, an image analysis system, and strains Tsuru2- and Tsuru3-primed seeds showed better root development than the control seeds. The effects of seed priming with the dead (killed) PNSB cells were also examined, and the seed priming with the dead cells was also effective, indicating that the effects were attributed to some cellular components. We expected the lipopolysaccharide (LPS) of PNSB as the effective component of PNSB and found that seed priming with LPS of Rhodobacter sphaeroides NBRC 12203 (type culture) at the concentrations of 5 ng/mL and 50 ng/mL enhanced the root development.

Probiotic Effects of a Marine Purple Non-Sulfur Bacterium, Rhodovulum sulfidophilum KKMI01, on Kuruma Shrimp (Marsupenaeus japonicus).

Purple non-sulfur bacteria (PNSB) are used as probiotics in shrimp aquaculture; however, no studies have examined the probiotic effects of PNSB in shrimp at the gene expression level. In this study, we examined the effects of a marine PNSB, Rhodovulum sulfidophilum KKMI01, on the gene expression of kuruma shrimp (Marsupenaeus japonicus). Short-term (3 days) effects of R. sulfidophilum KKMI01 on the gene expression in shrimp were examined using small-scale laboratory aquaria experiments, while long-term (145 days) effects of R. sulfidophilum KKMI01 on the growth performance and gene expression were examined using 200-ton outdoor aquaria experiments. Gene expression levels were examined using qRT-PCR. Results of the short-term experiments showed the upregulation of several molting-related genes, including cuticle proteins, calcification proteins, and cuticle pigment protein, suggesting that PNSB stimulated the growth of shrimp. The upregulation of several immune genes, such as prophenoloxidase, antimicrobial peptides, and superoxide dismutase, was also observed. In the 145-day outdoor experiments, the average body weight at harvest time, survival rate, and feed conversion ratio were significantly improved in PNSB-treated shrimp, and upregulation of molting and immune-related genes were also observed. When PNSB cells were added to the rearing water, the effective dosage of PNSB was as low as 103 cfu/mL, which was more than a million times dilution of the original PNSB culture (2-3 × 109 cfu/mL), indicating that R. sulfidophilum KKMI01 provides a feasible and cost-effective application as a probiotic candidate in shrimp aquaculture.

Isolation of purple nonsulfur bacteria from the digestive tract of ayu (Plecoglossus altivelis).

Purple nonsulfur bacteria (PNSB) reportedly have probiotic effects in fish, but whether they are indigenous in the digestive tract of fish is a question that requires answering. We attempted to isolate PNSB from the digestive tract of ayu (Plecoglossus altivelis) from the Kuma River (Kumamoto, Japan) and successfully isolated 12 PNSB strains. All the isolated PNSB belonged to the genus Rhodopseudomonas. Five Rhodopseudomonas strains were also isolated from the soil samples collected along the Kuma River. The phylogenetic tree based on the partial sequence of pufLM gene indicated that the PNSB from ayu and soil were similar. The effects of NaCl concentration in growth medium on growth were also compared between the PNSB from ayu and soil. The PNSB from ayu showed a better growth performance at a higher NaCl concentration, suggesting that the intestinal tract of ayu, a euryhaline fish, might provide suitable environment for halophilic microorganisms.