Ultrastructure and cytochemistry of in vitro interactions of the antagonistic bacteria Bacillus cereus X16 and B. thuringiensis 55T with Fusarium roseum var. sambucinum [Solanum tuberosum L.]

• Published in: Journal of plant pathology 2002-07, Vol.84 (2), p.83-93
• Main Authors: Cherif, M, Sadfi, N, Boubaker, A. (Institut National Agronomique de Tunisie, Tunis. Lab. de Phytopathologie), Benhamou, N. (Universite Laval, Quebec (Canada)), Boudabbous, A. (Campus Universitarie, Tunis (Tunisie). Lab. de Microbiologie), Hajlaoui, M.R. (Institut National de la Recherche Agronomique (INRA) de Tunisie, Ariana. Lab. de Cryptogamie-Bacteriologie), Tirilly, Y. (Ecole Superieure de Microbiologie et Securite Alimentaire de Brest, Plouzane (France))
• Format: Article
• Language: English
• Subjects: ANTAGONISM; ANTAGONISME; ANTAGONISMO; Bacillus; BACILLUS CEREUS; BACILLUS THURINGIENSIS; BIOLOGICAL CONTROL; CELL WALLS; CONTROL BIOLOGICO; CONTROLLO BIOLOGICO; CULTURE MEDIA; Cytoplasm; ESPORAS; Fungi; FUSARIUM; Hyphae; Liquids; LUTTE BIOLOGIQUE; MEDIO DE CULTIVO; MICROSCOPIA; MICROSCOPIE; MICROSCOPY; MILIEU DE CULTURE; PARED CELULAR; PARETI CELLULARI; PAROI CELLULAIRE; Pathogens; Phytopathology; SOLANUM TUBEROSUM; SPORE; SPORES; SUBSTRATI DI COLTURA; TOSSICITA; TOXICIDAD; TOXICITE; TOXICITY; TUBERCULE; TUBERCULO; TUBERI; TUBERS; ULTRAESTRUCTURA; ULTRASTRUCTURE; ULTRASTRUTTURA
• ISSN: 1125-4653; 2239-7264

The present studies were undertaken to investigate the interaction of the bacterial antagonists Bacillus cereus X16 and B. thuringiensis 55T with Fusarium roseum var. sambucinum, the causal agent of potato dry rot. On wounded potato tubers, both bacilli effectively suppressed the development of Fusarium dry rot. Nevertheless, confrontation of the fungal pathogen with the antagonists on nutrient agar revealed that B. cereus X16 induced a strong visible inhibition zone, but B. thuringiensis 55T did not. Light microscopy of the interaction regions after confrontation with B. cereus X16 on nutrient agar generally showed apparently intact fungal cells with densely stained protoplasm, indicating that the inhibition was due to stasis rather than toxicity. By contrast, in presence of B. thuringiensis, Fusarium cells appeared markedly damaged, with partial to complete cell wall disintegration and disorganization and generally complete loss of protoplasm. These observations suggest that, contrary to our expectations, antibiotic and chitinolytic activities of B. thuringiensis 55T may be highly significant in the parasitism of the pathogen. Confrontation in liquid medium revealed that both bacteria completely inhibited the germination of Fusarium macroconidia and resulted in their destruction. This suggests that, to produce their fungitoxic and hydrolytic effects, the two bacteria should make intimate contact with Fusarium cells [Questi studi sono stati intrapresi per studiare l'interazione dell'antagonismo di Bacillus cereus X16 e Bacillus thuringiensis 55T con Fusarium roseum var. sambucinum, agente causale del marciume secco della patata. Su tuberi feriti di patata, entrambi i bacilli hanno contrastato efficacemente lo sviluppo del marciume secco da Fusarium. Pero' il confronto tra i due in un terreno di agar ha rivelato un maggiore effetto del Bacillus cereus. Al microscopio si e' visto che l'effetto di inibizione e' dovuto piu' all'arresto di sviluppo che alla tossicita'. Per contrasto, la presenza di B. thuringiensis danneggia fortemente le cellule di Fusarium, disintegrando la parete cellulare e il protoplasma. Queste osservazioni suggeriscono che, al contrario delle nostre aspettative, le attivita' antibiotiche e chitinolitiche di B. thuringiensis 55T possono essere altamente significative nel parassitismo dell'agente patogeno. Il confronto nel mezzo liquido ha rivelato che entrambi i batteri hanno inibito completamente la germinazione dei macroconidi di Fusar