PGPR strain Paenibacillus polymyxa SQR-21 potentially benefits watermelon growth by re-shaping root protein expression.

Paenibacillus polymyxa (SQR-21) is not only a plant growth-promoting rhizobacteria, but also an effective biocontrol agent against Fusarium wilt disease of watermelon. For the better understanding and clarifying the potential mechanisms of SQR-21 to improve watermelon growth and disease resistance, a split-root methodology in hydroponic and LC-MS technology with the label free method was used to analyze the key root proteins involved in watermelon metabolism and disease resistance after the inoculation of SQR-21. Out of 623 identified proteins, 119 proteins were differentially expressed when treatment (SQR-21 inoculation) and control (no bacterial inoculation) were compared. Among those, 57 and 62 proteins were up-regulated and down-regulated, respectively. These differentially expressed proteins were identified to be involved in signal transduction (ADP-ribosylation factor, phospholipase D), transport (aspartate amino-transferase), carbohydratemetabolic (glucose-6-phosphate dehydrogenase, UDP-glucose pyrophosphorylase), defense and response to stress (glutathione S-transferase, Ubiquitin-activating enzyme E1), and oxidation-reduction process (thioredoxin peroxidase, ascorbate peroxidase). The results of this study indicated that SQR-21 inoculation on the watermelon roots benefits plant by inducing the expression of several proteins involved in growth, photosynthesis, and other metabolic and physiological activities.

Application of Bioorganic Fertilizer Significantly Increased Apple Yields and Shaped Bacterial Community Structure in Orchard Soil.

Application of bioorganic fertilizers has been reported to improve crop yields and change soil bacterial community structure; however, little work has been done in apple orchard soils where the biological properties of the soils are being degraded due to long-term application of chemical fertilizers. In this study, we used Illumina-based sequencing approach to characterize the bacterial community in the 0-60-cm soil profile under different fertilizer regimes in the Loess Plateau. The experiment includes three treatments: (1) control without fertilization (CK); (2) application of chemical fertilizer (CF); and (3) application of bioorganic fertilizer and organic-inorganic mixed fertilizer (BOF). The results showed that the treatment BOF increased the apple yields by 114 and 67 % compared to the CK and CF treatments, respectively. The treatment BOF also increased the soil organic matter (SOM) by 22 and 16 % compared to the CK and CF treatments, respectively. The Illumina-based sequencing showed that Acidobacteria and Proteobacteria were the predominant phyla and Alphaproteobacteria and Gammaproteobacteria were the most abundant classes in the soil profile. The bacterial richness for ACE was increased after the addition of BOF. Compared to CK and CF treatments, BOF-treated soil revealed higher abundance of Proteobacteria, Alphaproteobacteria and Gammaproteobacteria, Rhizobiales, and Xanthomonadales while Acidobacteria, Gp7, Gp17, and Sphaerobacter were found in lower abundance throughout the soil profile. Bacterial community structure varied with soil depth under different fertilizer treatments, e.g., the bacterial richness, diversity, and the relative abundance of Verruccomicrobia, Candidatus Brocadiales, and Skermanella were decreased with the soil depth in all three treatments. Permutational multivariate analysis showed that the fertilizer regime was the major factor than soil depth in the variations of the bacterial community composition. Two groups, Lysobacter and Rhodospirillaceae, were found to be the significantly increased by the BOF addition and the genus Lysobacter may identify members of this group effective in biological control-based plant disease management and the members of family Rhodospirillaceae had an important role in fixing molecular nitrogen. These results strengthen the understanding of responses to the BOF and possible interactions within bacterial communities in soil that can be associated with disease suppression and the accumulation of carbon and nitrogen. The increase of apple yields after the application of BOF might be attributed to the fact that the application of BOF increased SOM, and soil total nitrogen, and changed the bacterial community by enriching Rhodospirillaceae, Alphaprotreobateria, and Proteobacteria.

Long-Term Application of Bioorganic Fertilizers Improved Soil Biochemical Properties and Microbial Communities of an Apple Orchard Soil.

Soil biochemical properties and microbial communities are usually considered as important indicators of soil health because of their association with plant nutrition. In this study, we investigated the impact of long-term application of bioorganic fertilizer (BOF) on soil biochemical properties and microbial communities in the apple orchard soil of the Loess Plateau. The experiment included three treatments: (1) control without fertilization (CK); (2) chemical fertilizer application (CF); and (3) bioorganic fertilizer application (BOF). The high throughput sequencing was used to examine the bacterial and fungal communities in apple orchard soil. The results showed that the BOF treatment significantly increased the apple yield during the experimental time (2009-2015). The application of BOF significantly increased the activities of catalase and invertase compared to those in CK and CF treatments. The high throughput sequencing data showed that the application of BOF changed the microbial community composition of all soil depths considered (0-20 cm, 20-40 cm, and 40-60 cm), e.g., the relative abundance of bio-control bacteria (Xanthomonadales, Lysobacter, Pseudomonas, and Bacillus), Proteobacteria, Bacteroidetes, Ohtaekwangia, Ilyonectria, and Lecanicillium was increased while that of Acidobacteria, Chloroflexi, Gp4, Gp6 and Sphaerobacter was decreased. The increase in apple yield after the application of BOF might be due to increase in organic matter, total nitrogen and catalase and invertase activities of soil and change in the bacterial community composition by enriching Bacillus, Pseudomonas, Lysobacter, and Ohtaekwangia. These results further enhance the understanding on how BOFs alter soil microbial community composition to stimulate soil productivity.

Effects of volatile organic compounds from Streptomyces albulus NJZJSA2 on growth of two fungal pathogens.

A Streptomyces albulus strain NJZJSA2 was isolated from the forest soil sample of Tzu-chin Mountain (Nanjing China) and identified based on its morphological and physiological properties and 16S rDNA gene sequence analysis. The strain S. albulus NJZJSA2 was evaluated for the production of antifungal volatile organic compounds (VOCs) against two fungal pathogens. Results showed that the VOCs generated by S. albulus NJZJSA2 inhibited mycelial growth of Sclerotinia sclerotiorum (SS) and Fusarium oxysporum (FO) by 100 and 56.3%, respectively. The germination of SS sclerotia and FO conidia was completely inhibited in the presence of VOCs produced by S. albulus NJZJSA2 in vitro. In soil, the VOCs delayed the germination of SS sclerotia and inhibited the germination of FO conidia for 45 days. The strain S. albulus NJZJSA2 was able to produce 13 VOCs based on GC/MS analyses. Among those, six compounds were purchased and used for the antifungal activity assay. Three relatively abundant VOCs, 4-methoxystyrene, 2-pentylfuran, and anisole were proved to have antifungal activity. Microscopy analysis showed that the pathogen hyphae were shriveled and damaged after treatment with 4-methoxystyrene. These results suggest that the S. albulus strain NJZJSA2 produce VOCs that not only reduce the growth of SS and FO, but also significantly inhibit the SS sclerotia and FO conidia. The results are useful for the better understanding of biocontrol mechanisms by S. albulus strains and will help to improve the biological control efficiency of lethal plant diseases.