Fuente: WIPO "tomato" The present invention relates to the field of protein nanofibrils originating from Bacillus sp. provided in a composition as additive to a biologically active substance, in particular to a microbial substance such as a pesticide or plant beneficial agent. More specifically, the present invention relates to a composition comprising an agriculturally bioactive substance and Alpha(helical) Endospore appendage (A-ENA) protein nanofibril materials, more precisely wherein said A-ENA protein nanofibrils are recombinantly produced and exogenously added to said bioactive substance of the composition, thereby functioning as coformulant or additive, and preferably increasing the biological activity of said substance. In particular, the composition of the invention comprises B. thuringiensis spores or cells and self-assembled (engineered or functionalized) A-ENA protein nanofibrils as coformulant, providing for an improved efficacy and/or application potential as pesticide or insecticide. The present invention further relates to a method for controlling plant growth and protection of plants or parts thereof from pest damage, in particular by applying said composition of the invention in an effective amount or formulation, wherein the presence of said A-ENA protein nanofibril coformulant or additive results in increased efficacy and/or virulence of the bioactive substance of said composition, in particular for bioactive substances comprising Bacillus sp. strains.