Surfactin secreted by Bacillus amyloliquefaciens Ba01 is required to combat Streptomyces scabies causing potato common scab

Bacillus velezensis Y6, a Potential and Efficient Biocontrol Agent in Control of Rice Sheath Blight Caused by Rhizoctonia solani

Rice sheath blight is a serious disease caused by Rhizoctonia solani that reduces rice yield. Currently, there is a lack of efficient and environmentally friendly control methods. In this study, we found that Bacillus velezensis (B. velezensis) Y6 could significantly inhibit the growth of mycelium in Rhizoctonia solani, and its control efficiency against rice sheath blight was 58.67% (p < 0.01) in a pot experiment. Lipopeptides play an important role in the control of rice sheath blight by B. velezensis Y6, among which iturin and fengycin are essential, and iturin W, a novel lipopeptide in B. velezensis, plays a major role in lipopeptide antagonism to Rhizoctonia solani. In the field, we also found that inoculation with B. velezensis Y6 can increase rice yield (dry weight) by 11.75%. Furthermore, the transcriptome profiling results of the rice roots revealed that there were a total of 1227 differential genes (DEGs) regulated when treated with Y6, of which 468 genes were up-regulated and 971 genes were down-regulated in rice roots compared with the control. Among them, the DEGs were mainly distributed in biological processes (BP) and were mainly enriched in response to stimulus (GO:0050896), response to stress (GO:0006950), and response to abiotic stimulus (GO:0009628). According to the KEGG pathway analysis, there were 338 DEGs classified into 87 KEGG functional pathway categories. Compared with the control, a large number of enriched genes were distributed in phenylpropanoid biosynthesis (map00940), glutathione metabolism (map00480), glycolysis/gluconeogenesis (map00010), and amino sugar and nucleotide sugar metabolism (map00520). In summary, this investigation provides a new perspective for studying the molecular mechanism of B. velezensis in controlling rice sheath blight.

Involvement of the Bacillus SecYEG Pathway in Biosurfactant Production and Biofilm Formation

With Bacillus species, about 30% of extracellular proteins are translocated through the cytoplasmic membrane, coordinated by the Sec translocase. This system mainly consists of the cytoplasmic ATPase SecA and the membrane-embedded SecYEG channel. The purpose of this work was to investigate the effects of the SecYEG export system on the production of industrial biomolecules, such as biosurfactants, proteases, amylases, and cellulases. Fifty-two isolates of Bacillus species were obtained from traditional fermented foods and then characterized using molecular microbiology methods. The isolates secreted exoenzymes that included cellulases, amylases, and proteases. We present evidence that a biosurfactant-like molecule requires the SecA ATPase and the SecYEG membrane channel for its secretion. In addition, we showed that biomolecules involved in biofilm formation required the SecYEG pathway. This work presents a novel seven-target fragment multiplex PCR assay capable of identification at the species level of Bacillus through a unique SecDF chromosomal gene. The bacterial membrane protein SecDF allowed the discrimination of Bacillus subtilis, B. licheniformis, B. amyloliquefaciens, and B. sonorensis. SecA was able to interact with AprE, AmyE, and TasA. The Rose Bengal inhibitor of SecA crucially affected the interaction of AprE, AmyE, TapA, and TasA with recombinant Gst-SecA. The Rose Bengal prevented Bacillus species from secreting and producing proteases, cellulases, amylases, and biosurfactant-like molecules. It also inhibited the formation of biofilm cell communities. The data support, for the first time, that the SecYEG translocon mediates the secretion of a biosurfactant-like molecule.

Biofilms formation in plant growth-promoting bacteria for alleviating agro-environmental stress

Biofilm formation represents a pivotal and adaptable trait among microorganisms within natural environments. This attribute plays a multifaceted role across diverse contexts, including environmental, aquatic, industrial, and medical systems. While previous research has primarily focused on the adverse impacts of biofilms, harnessing their potential effectively could confer substantial advantages to humanity. In the face of escalating environmental pressures (e.g., drought, salinity, extreme temperatures, and heavy metal pollution), which jeopardize global crop yields, enhancing crop stress tolerance becomes a paramount endeavor for restoring sufficient food production. Recently, biofilm-forming plant growth-promoting bacteria (PGPB) have emerged as promising candidates for agricultural application. These biofilms are evidence of microorganism colonization on plant roots. Their remarkable stress resilience empowers crops to thrive and yield even in harsh conditions. This is accomplished through increased root colonization, improved soil properties, and the synthesis of valuable secondary metabolites (e.g., ACC deaminase, acetin, 2,3-butanediol, proline, etc.). This article elucidates the mechanisms underpinning the role of biofilm-forming PGPB in bolstering plant growth amidst environmental challenges. Furthermore, it explores the tangible applications of these biofilms in agriculture and delves into strategies for manipulating biofilm formation to extract maximal benefits in practical crop production scenarios.

Biological control of potato common scab and growth promotion of potato by Bacillus velezensis Y6

Potato common scab, caused mainly by Streptomyces scabies, causes surface necrosis and reduces the economic value of potato tubers, but effective chemical control is still lacking. In this study, an attempt was made to control potato common scab by inoculating potatoes with Bacillus velezensis (B. velezensis) and to further investigate the mechanism of biological control. The results showed that B. velezensis Y6 could reduce the disease severity of potato common scab from 49.92 ± 25.74% [inoculated with Streptomyces scabies (S. scabies) only] to 5.56 ± 1.89% (inoculated with S. scabies and Y6 on the same day) and increase the potato yield by 37.32% compared with the control under pot experiment in this study. Moreover, in the field trial, it was found that Y6 could also significantly reduce disease severity from 13.20 ± 1.00% to 4.00 ± 0.70% and increase the potato yield from 2.07 ± 0.10 ton/mu to 2.87 ± 0.28 ton/mu (p < 0.01; Tukey's test). Furthermore, RNA-seq analysis indicated that 256 potato genes were upregulated and 183 potato genes were downregulated in response to B. velezensis Y6 inoculation. In addition, strain Y6 was found to induce the expression of plant growth-related genes in potato, including cell wall organization, biogenesis, brassinosteroid biosynthesis, and plant hormone transduction genes, by 1.01-4.29 times. As well as up-regulate hydroquinone metabolism-related genes and several transcription factors (bHLH, MYB, and NAC) by 1.13-4.21 times. In summary, our study will help to understand the molecular mechanism of biological control of potato common scab and improve potato yield.