Formulation of stable Bacillus subtilis AH18 against temperature fluctuation with highly heat-resistant endospores and micropore inorganic carriers

Development of a heat-stable and orally delivered recombinant M2e-expressing B. subtilis spore-based influenza vaccine

Highly conserved ectodomain of influenza virus M2 protein (M2e) is an important target for the development of universal influenza vaccines. Today, the use of chemical or genetic fusion constructs have been undertaken to overcome the low immunogenicity of M2e in vaccine formulation. However, current M2e vaccines are neither orally delivered nor heat-stable. In this study, we evaluated the immune efficacy of an orally delivered recombinant M2e vaccine containing 3 molcules of M2e consensus sequence of influenza A viruses, termed RSM2e3. To accomplish this, CotB, a spore coat of Bacillus subtilis (B. subtilis), was used as a fusion partner, and heat-stable nonpathogenic B. subtilis spores were used as the carrier. Our results showed that CotB-M2e3 fusion had no effect on spore structure or function in the resultant recombinant RSM2e3 strain and that heterologous influenza virus M2e protein was successfully displayed on the surface of the recombinant RSM2e3 spore. Importantly, recombinant RSM2e3 spores elicited strong and long-term M2e-specific systemic and mucosal immune responses, completely protecting immunized mice from lethal challenge of A/PR/8/34(H1N1) influenza virus. Taken together, our study forms a solid basis for the development of a novel orally delivered and heat-stable influenza vaccine based on B. subtilis spore surface display.

Cyclic Lipopeptide Biosynthetic Genes and Products, and Inhibitory Activity of Plant-Associated Bacillus against Phytopathogenic Bacteria

The antibacterial activity against bacterial plant pathogens and its relationships with the presence of the cyclic lipopeptide (cLP) biosynthetic genes ituC (iturin), bmyB (bacillomycin), fenD (fengycin) and srfAA (surfactin), and their corresponding antimicrobial peptide products have been studied in a collection of 64 strains of Bacillus spp. isolated from plant environments. The most frequent antimicrobial peptide (AMP) genes were bmyB, srfAA and fenD (34-50% of isolates). Most isolates (98.4%) produced surfactin isoforms, 90.6% iturins and 79.7% fengycins. The antibacterial activity was very frequent and generally intense among the collection of strains because 75% of the isolates were active against at least 6 of the 8 bacterial plant pathogens tested. Hierarchical and correspondence analysis confirmed the presence of two clearly differentiated groups. One group consisted of Bacillus strains that showed a strong antibacterial activity, presented several cLPs genes and produced several isoforms of cLPs simultaneously, mainly composed of B. subtilis and B. amyloliquefaciens, although the last one was exclusive to this group. Another group was characterized by strains with very low or none antibacterial activity, that showed one or none of the cLP genes and produced a few or none of the corresponding cLPs, and was the most heterogenous group including B. subtilis, B. licheniformis, B. megaterium, B. pumilus, B. cereus and B. thuringiensis, although the last two were exclusive to this group. This work demonstrated that the antagonistic capacity of plant-associated Bacillus against plant pathogenic bacteria is related to the presence of cLP genes and to the production of the corresponding cLPs, and it is mainly associated to the species B. subtilis and B. amyloliquefaciens. Our findings would help to increase the yield and efficiency of screening methods to obtain candidate strains to biocontrol agents with a mechanism of action relaying on the production of antimicrobial cLPs.

Formulation development of the biocontrol agent Bacillus subtilis strain CPA-8 by spray-drying

AIMS

To prepare commercially acceptable formulations of Bacillus subtilis CPA-8 by spray-drying with long storage life and retained efficacy to control peach and nectarine brown rot caused by Monilinia spp.

METHODS AND RESULTS

CPA-8 24-h- and 72-h-old cultures were spray dried using 10% skimmed milk, 10% skimmed milk plus 10% MgSO(4) , 10% MgSO(4) and 20% MgSO(4) as carriers/protectants. All carriers/protectants gave good percentages of powder recovery (28-38%) and moisture content (7-13%). CPA-8 survival varied considerably among spray-dried 24-h- and 72-h-old cultures. Seventy-two hours culture spray dried formulations showed the highest survival (28-32%) with final concentration products of 1·6-3·3 × 10(9) CFU g(-1) , while viability of 24-h-old formulations was lower than 1%. Spray-dried 72-h-old formulations were selected to subsequent evaluation. Rehydration of cells with water provided a good recovery of CPA-8 dried cells, similar to other complex rehydration media tested. Spray-dried formulations stored at 4 ± 1 and 20 ± 1°C showed good shelf life during 6 months, and viability was maintained or slightly decreased by 0·2-0·3-log. CPA-8 formulations after 4- and 6 months storage were effective in controlling brown rot caused by Monilinia spp. on nectarines and peaches resulting in a 90-100% reduction in disease incidence.

CONCLUSIONS

Stable and effective formulations of biocontrol agent B. subtilis CPA-8 could be obtained by spray-drying.

SIGNIFICANCE AND IMPACT OF THE STUDY

New shelf-stable and effective formulations of a biocontrol agent have been obtained by spray-drying to control brown rot on peach.