Changes in the properties of Bacillus thuringiensis after prolonged culture in a rich medium

Abstract

Aim: To investigate the effect of repeated culture in a rich medium on certain genetic, metabolic, pathogenic and structural characteristics of fresh isolates of Bacillus thuringiensis. Methods and Results: Four strains of B. thuringiensis, which had been isolated in vegetative form from leaf surfaces, were grown for 500 generations in batch culture in a rich medium. One of the strains, S4g, differed from the parent in the following respects: greater cell width; changed plasmid profile; complete loss of ability to produce δ‐endotoxins; loss of ability to produce β‐exotoxin and disruption of vip3 gene; radically different fatty acid composition; and altered metabolic activity. Two of the other evolved strains (S1g and S6g) showed differences in fatty acid profiles compared with the parents. Genetic finger‐printing showed that there were also mutations in the cry genes of two of the evolved strains (S1g and S2g). The δ‐endotoxins of strain S6g were significantly less toxic to the larvae of Pieris brassica compared with those of the parent and it also differed in the plasmid content. Conclusion: Radical and unpredictable changes can occur in fresh isolates of B. thuringiensis when subjected to growth in the laboratory. Significance and Impact of the Study: This is the first analysis of a Gram positive and biotechnologically significant bacterium after repeated laboratory culture. It is of great relevance to the biotechnological exploitation of B. thuringiensis that prolonged growth of environmental isolates on laboratory culture media can have profound effects on their structure, genome and virulence determinants.

Experimental evolution with a multicellular host causes diversification within and between microbial parasite populations-Differences in emerging phenotypes of two different parasite strains

“…We rather hypothesize that generating single clones by repeated culture in a rich medium (see Materials and Method section) might have led to changes in the pathogenic characteristics of Bt, as described by Bizzarri et al. (). Pathogenicity in Bt is mainly caused by cry toxins.…”

“…Considering these results and our experimental design, we assume that the transmission mode was not the reason for the extreme loss of virulence in our experiment. We rather hypothesize that generating single clones by repeated culture in a rich medium (see Materials and Method section) might have led to changes in the pathogenic characteristics of Bt, as described by Bizzarri et al (2008). Pathogenicity in Bt is mainly caused by cry toxins.…”

Development of a bacterial challenge test for gnotobiotic sea bass (Dicentrarchus labrax) larvae

“…This result was rather unexpected as most L. anguillarum strains (18 out of 21) isolated from diseased sea bass were serovar O1 (Larsen et al ., 1994). However, change in characteristics, including the loss or upregulation of virulence during prolonged culture, has been reported for several bacteria (Chosa et al ., 1989; De Windt et al ., 2006; Bizzarri et al ., 2008). The strain used in this study has been isolated more than 10 years ago.…”

Diversity ofBacillus cereusgroup strains is reflected in their broad range of pathogenicity and diverse ecological lifestyles

“…However, DNA–DNA hybridization was observed between strains of the different groups just below the threshold of 70%, which indicates that they are different species (Nakamura & Jackson, ; Guinebretiere et al ., ). To further complicate this matter, the most discriminatory characteristics of the different species are often plasmid‐encoded toxins (Rasko et al ., , b), which can be lost naturally in the environment (te Giffel et al ., ) or in the laboratory (Bizzarri et al ., ) and which have a high potential for horizontal transfer (Van der Auwera et al ., ; Yuan et al ., ; Modrie et al ., ). Finally, the taxonomical discussion has been influenced by the practical usefulness of discriminating between strains based on phenotypical similarly such as specific pathogenicity ( B. anthracis and B. thuringiensis ), psychrotolerance ( B. weihenstephanensis ) and colony morphology ( B. mycoides and B. pseudomycoide s) rather than on genetical relatedness (Guinebretiere et al ., ).…”