Multiple endogenous seed-born bacteria recovered rice growth disruption caused by Burkholderia glumae

Abstract

Burkholderia glumae is a causal agent of bacterial grain and seedling rot in rice, and is a threat to stable global food supply. The virulence of B. glumae was suppressed when it was inoculated on budding seed rather than on non-budding seed. To clarify the phenomena, pathogen titer inside the rice plant was measured by serial dilution plating of lysates from budding rice seedlings. Surprisingly, morphologically different types of colonies were observed on the plates. These ‘contaminated’ rice seed-born bacteria (RSB) were identified by sequencing 16S rRNA genes as three strains of Pseudomonas putida (RSB1, RSB10, RSB15) and Stenotrophomonas maltophilia (RSB2). All bacteria and B. glumae were simultaneously inoculated onto rice seeds, and all three P. putida RSBs suppressed the growth disruption caused by B. glumae, whereas RSB2 had no effect. Thus, the virulence was synergistically suppressed when co-treated with RSBs. The effect could be dependent on the high biofilm formation ability of RSB2. By comprehensive microbiota analysis, endogenous rice flora were changed by RSBs treatment. These results suggest the possibility of novel pathogen control through pre-treatment with endogenous beneficial microorganisms. The method would contribute substantially to the implementation of sustainable agriculture stated in Sustainable Development Goals of United Nations.

A Seed-Borne Bacterium of Rice, Pantoea dispersa BB1, Protects Rice from the Seedling Rot Caused by the Bacterial Pathogen Burkholderia glumae

“…To explore seed-borne bacteria that have biocontrol activity, we conducted a toxoflavin tolerance test. As toxoflavin is known to have antibacterial activity [ 10 ], the bacterial biocontrol agents against B. glumae may need to exhibit tolerance to this toxin. We examined the 10 IRBB1- and TN1-derived isolates of Pantoea and Paenibacillus and found that the latter were highly tolerant to toxoflavin ( Figure 3 A).…”

“…2, Sumitomo Chemical, Tokyo, Japan) and were grown in a growth chamber at 28 °C with 100% humidity under a 16 h:8 h photoperiod. Disease severity was evaluated by measuring the shoot length of the inoculated plants, as previously described [ 10 ].…”

“…To characterize the isolated bacteria, bacterial DNA was extracted using the DNeasy Blood &Tissue Kit (QIAGEN, Hilden, Germany), and PCR for the bacterial 16S rRNA gene was performed using universal primers. The PCR conditions were described previously [ 10 ], and the primer sequences are listed in Table S1 . The PCR fragments were sequenced using the BigDye Terminator v3.1 Cycle Sequencing Kit (Thermo Fisher Scientific, Waltham, MA, USA) and a SeqStudio Genetic Analyzer (Thermo Fisher Scientific), and they were annotated via the BLAST web service of the DNA Data Bank of Japan.…”

“…Toxoflavin is also known to exhibit antifungal and antibacterial activities. It inhibits the growth of multiple genera of bacteria, including the seed-borne bacteria of rice [ 10 ], and has shown antifungal activity against a broad range of fungi, indicating its potential as a new fungicide [ 11 ].…”

“…We previously demonstrated that four isolates of seed-borne bacteria of rice can improve rice seedling rot resistance. Seed treatment with three isolates of Pseudomonas putida (RSB1, 10, 15) suppresses rice growth disruption caused by B. glumae [ 10 ]. In contrast, Stenotrophomonas maltophilia RSB2 has no protective effect, but it can increase the protective effects of RSB1, 10, 15 by co-treatment, suggesting that rice seeds are promising sources of microbial biocontrol agents against seedling rot.…”