In Vitro Evaluation of Bacterial Bioagents and Fungicides Efficiency against Rhizoctonia solani Isolates the Causal agent of Black Scurf Disease of Potato

The efficacy of two isolates of bacterial bioagents and two fungicides via, Rhizoctonia solani isolates were evaluated in vitro. In the dual culture assays, significance inhibition ratio of R. solani hyphal growth was obtained in all treatments of Pesudomonas fluoresnces and Bacillis subtilis compared to control. Also, Bacillus subtilis exhibit the highest significant suppression for the mycelial growth of R. solani isolates more than Pseudemonas fluorescens, and the ratios of inhibition differed according to the bioagents and R. solani isolates similar to those results in antifungal activity technique. The volatile metabolite studies revealed that in the first period (three days) inhibition percentage significantly differed according to the tested isolates of R. solani and the applied bioagents, B. subtilis gave the highest inhibition (57.41%) in R. solani isolate 3. Similarly in P. fluoresnces treatments, the highest inhibition was (57.41%) was detected in isolate 3 of R. solani considering that the second tested time period (five day inoculation). B. subtilis showed highest inhibition value on isolate 1, on the other hand P. flouresnce showed high value of inhibition on isolate 2, whereas the lowest inhibition values were produced on isolate 1.Non volatile activity both bacterial bioagents isolates showed different values of inhibition on R. solani isolates. On the other hand Rezolex was most effective against R. solani at two concentrations (0.2 and 0.3), however Topsin-M showed fluctuate inhibition values at two concentration used (0.04% and 0.075%). Further incubation of plates showed suppressed the formation of sclerotia by all the antagonists tested. The results implied that the extent of inhibition by B. subtilis and P. fluoresnces rovides the use of excellent potential antagonists capable of controlling the R. solani in vitro.

Antibacterial Mechanisms of Orostachys Cartilaginous Cell Cultures: Effect on Cell Permeability and Respiratory Metabolism of Bacillis Subtilis

Orostachys cartilaginous of Crassulaceae family is a plant native to the Changbai Mountain area, China. Although O. cartilaginous has various medicinal values, its product development and production are restricted by the insufficient resource available. O. cartilaginous cell cultures possess an efficient antibacterial effect against Bacillis subtilis, but the underlying mechanism is not clear yet. Therefore, this study investigated the effects of extract from bioreactor cultured O. cartilaginous cells (OE) on B. subtilis cell permeability and respiratory metabolism to provide a reference for the further utilization of O. cartilaginous cell cultures. Results showed alkaline phosphatase activity, electrical conductivity, nucleic acid and protein contents in B. subtilis suspensions were significantly increased (p < 0.01) by OE treatment, indicating the occurrence of cell damage or increase in cell permeability. OE inhibited B. subtilis respiration, and the combination groups of OE+iodoacetic acid (IA) and OE+sodium phosphate (SP) showed low superposition rates (approximately 35%), revealing that OE likely affected IA- and SP-represented metabolic pathways. The activities of B. subtilis enzymes, specifically, hexokinase and pyruvate kinase in the Embden-Meyerhof (EMP) pathway and glucose-6-phosphate dehydrogenase in the pentose phosphate (HMP) pathway, decreased after OE treatment. This result proved that OE inhibited B. subtilis respiration by regulating the EMP and HMP pathways.

A Mutation in the Bacillus subtilis rsbU Gene That Limits RNA Synthesis during Sporulation

ABSTRACT Mutants of Bacillis subtilis that are temperature sensitive for RNA synthesis during sporulation were isolated after selection with a 32P suicide agent. Whole-genome sequencing revealed that two of the mutants carried an identical lesion in the rsbU gene, which encodes a phosphatase that indirectly activates SigB, the stress-responsive RNA polymerase sigma factor. The mutation appeared to cause RsbU to be hyperactive, because the mutants were more resistant than the parent strain to ethanol stress. In support of this hypothesis, pseudorevertants that regained wild-type levels of sporulation at high temperature had secondary mutations that prevented expression of the mutant rsbU gene. The properties of these RsbU mutants support the idea that activation of SigB diminishes the bacterium's ability to sporulate. IMPORTANCE Most bacterial species encode multiple RNA polymerase promoter recognition subunits (sigma factors). Each sigma factor directs RNA polymerase to different sets of genes; each gene set typically encodes proteins important for responses to specific environmental conditions, such as changes in temperature, salt concentration, and nutrient availability. A selection for mutants of Bacillus subtilis that are temperature sensitive for RNA synthesis during sporulation unexpectedly yielded strains with a point mutation in rsbU, a gene that encodes a protein that normally activates sigma factor B (SigB) under conditions of salt stress. The mutation appears to cause RsbU, and therefore SigB, to be active inappropriately, thereby inhibiting, directly or indirectly, the ability of the cells to transcribe sporulation genes.

Control of target spot of tomato with fungicides, systemic acquired resistance activators, and a biocontrol agent

Control of target spot of tomato, caused by the fungus Corynespora cassiicola (Berk. &amp; Curt.) Wei., was studied in three seasons in southern Florida, USA. The strobilurin fungicide azoxystrobin and a combination product of mancozeb and fumoxate provided excellent control of target spot. In these treatments, accumulated disease severity values were only 10&ndash;15% of those in the untreated control and marketable yields were doubled. Excellent disease control also was achieved with acibenzolar-S-methyl, a systemic acquired resistance activator (SAR). This compound reduced defoliation of tomato plants by 42% compared to the control. An experimental compound, BAS 510 02, provided good control of target spot, reducing defoliation by 40% and increasing marketable yields by 34%. Harpin protein and Bacillis subtilis strain QST 713 were not effective for control of target spot.

Production by Bacillis subtilis of brown sporulation-associated pigments

The mode of production of the brown pigments of Bacillus subtilis 168 L-4, pigments frequently used as phenotypic markers for sporulation in this organism, has been studied. A defined liquid medium which promoted maximal pigment formation was developed. Five brown components, which could be resolved by thin-layer chromatography, were produced in the culture broth. Removal of cells from the medium at the end of logarithmic growth did not alter the type or amount of the pigments formed, indicating that the cells excreted pigment precursors into the medium during growth. Pigment formation from the precursors was found to occur by an oxygen-requiring, base-dependent, Mn2+- requiring, nonenzymatic pathway. Pigment production was also stimulated by the presence of tyrosine and histidine in the medium. The increases in extracellular pH often associated with spore formation in B. subtilis might be the cause of the concomitant appearance of brown pigments.

Sporulation in Bacillis subtilis. Biochemical changes

1. During the course of growth and sporulation of Bacillus subtilis in chemically defined media, measurements were made of 16 different parameters, including the specific activities of nine intracellular enzymes. 2. Towards the end of exponential growth, proteolytic activity increased and reached a maximum soon after growth ceased. 3. In the presence of an excess of phosphate the specific activity of alkaline phosphatase increased fivefold at the end of exponential growth. 4. The specific activity of malate dehydrogenase remained at a high constant level throughout sporulation, but the specific activity of fumarase showed a two- to three-fold increase 5–9hr. after the end of exponential growth. 5. Aconitase activity was barely detectable during exponential growth in a glucose–glutamate medium, but increased rapidly when glutamate was replaced by citrate or when the glucose in the medium was exhausted. 6. The specific activity of alanine dehydrogenase increased threefold 1–5hr. after the end of exponential growth. 7. The specific activity of soluble NADH oxidase doubled 4–6hr. after the end of exponential growth. 8. Glucose dehydrogenase was undetectable until 4hr. after the end of exponential growth, but its specific activity increased 20-fold over the next 3–4hr. 9. The onset of refractility, the synthesis of 2,6-dipicolinic acid and the appearance of heat-resistance occurred in this order some 6–12hr. after the end of exponential growth. 10. The significance of these changes is discussed in relation to the morphological development of the spore.