Fungal and bacterial glycoconjugats interactions: specific mechanism between lectin producing fungi and bacillus biocontrol strains?

The mechanisms involved in the antagonistic action of biocontrol agents are intensively studied and several types were identified. A special attention was accorded to Bacillus strains that exhibit broad host spectrum against fungal pathogens. By studying in vitro interaction between some Bacillus biocontrol strains and some plant pathogenic fungal strains belonging to Botrytis cinerea, Penicillium sp. and Sclerotinia sclerotiorum species, a precipitation line was observed at the inhibition area level. This outcome was detected in co-cultivation of the biocontrol bacteria with the mentioned fungal species described as specific lectins producers, but not when strains of Alternaria, Fusarium or Pythium were used. The present study included in vitro co-cultivation of the biocontrol strains with B. cinerea on PDA medium supplemented with different carbon sources, sugars that are known to be interacting with different kind of carbohydrate-binding proteins. Significant differences in bacterial growth limitation were observed when the precipitation line was more evident and a reduced inhibition of the fungal growth was registered. Based on the fact that carbohydrate-binding proteins, also referred as lectin or agglutinins, have functions in defense responses to pathogen invaders, two hypotheses may be issued: there could be a chain reaction by which the biocontrol bacteria induces a defense mechanism in some fungi, and the lectin or lectin-like producing fungi reacts in self-defense and bind the nutrients so that the antagonistic bacteria are limited in growth and that certain substrates, enriched with particular carbohydrates, facilitate the activation of some defense mechanism in fungi against some antagonistic bacteria“, as a possible consequence of the low bacterial glycoproteins specificity for those carbohydrates, compared with the lectins or lectin-like compounds of some fungi that can precipitate the carbohydrate nutrients as defense mechanism against antagonistic bacteria, similar to the nutritional competition.