Alternative low-cost process for large-scale production of Bacillus thuringiensis in a simple and novel culture system

Engineering the cell wall reactive groups of Plant Growth Promoting Rhizobacteria by culture strategy for heavy metal removal

This research delved into the effects of nutrient limitation on the level of sporulation and the cadmium adsorption capacity of the bacterium Bacillus sp. isolated from the rhizosphere of endemic soils in the Region of Valparaiso, Chile. The bacteria were subjected to nitrogen limitation in fed-batch mode and were compared to bacteria grown in batch culture without nutrient limitation. The cultures were carried out in a 3 L bioreactor with an external nitrogen supply of ammonium at a flow of 0.123 L h-1. The specific maximum growth rate was 0.42 h-1 in batch and 0.45 h-1 in the exponential phase of the fed-batch. The analysis of sporulation did not show any significant difference between the biomass coming from the fed-batch and batch cultures. It was found that maximum cadmium adsorption capacity varied with culture strategy. The dry biomass grown without nutrient limitation exhibited a maximum adsorption capacity for cadmium of 65.0 mgCd g-1biomass. Conversely, the limited biomass achieved a lower cadmium adsorption capacity of approximately 36.0 mgCd g-1biomass. FTIR analysis showed that nitrogen limitation induced changes in the composition of the outer cell wall, specifically an increase of deacetlylated polysaccharides, reducing the relative amount of secondary amines and proteins from the peptidoglycan matrix. Amino groups from acetylated polysaccharides and proteins have been associated elsewhere with greater cadmium affinity, which could explain the poor results obtained with the nitrogen-restricted biomass. This study shows that new physiological states displaying different adsorption capabilities were effectively obtained by engineering the cell coverage of the bacteria using varying culture strategies. The fed-batch culture proved to be a valuable tool for studying PGPR strains for biosorption and other applications. Exploring diverse nutrient limitations and other pollutants in this bacterium and other members of the PGPR family offer great opportunities to tailor biosorption strategies based on specific conditions, ultimately contributing to sustainable environmental solutions.

Endospore production of Bacillus spp. for industrial use

The increased occurrence of antibiotic resistance and the harmful use of pesticides are a major problem of modern times. A ban on the use of antibiotics as growth promoters in animal breeding has put a focus on the probiotics market. Probiotic food supplements are versatile and show promising results in animal and human nutrition. Chemical pesticides can be substituted by biopesticides, which are very effective against various pests in plants due to increased research. What these fields have in common is the use of spore-forming bacteria. The endospore-forming Bacillus spp. belonging to this group offer an effective solution to the aforementioned problems. Therefore, the biotechnological production of sufficient qualities of such endospores has become an innovative and financially viable field of research. In this review, the production of different Bacillus spp. endospores will be reviewed. For this purpose, the media compositions, cultivation conditions and bioprocess optimization methods of the last 20 years are presented and reflected.

Nutrient conditions determine the localization of Bacillus thuringiensis Vip3Aa protein in the mother cell compartment

Vip3Aa was first identified as a protein secreted during the vegetative growth phase of Bacillus thuringiensis (Bt) bacteria and which shows high insecticidal toxicity against lepidopteran insect pests (Estruch et al., 1996). Bt strains formulated as bio‐insecticides only had low amounts of Vip3Aa secreted to the medium. Here, we report that Vip3Aa proteins produced by three different Bt strains, including an industrial strain, were indeed not secreted to the culture solution when grown in sporulation medium, but were retained in the mother cell compartment. In order to further investigate the Vip3Aa secretion and location, we grew the strains in rich medium. We found that in rich medium, a fraction of Vip3Aa was secreted, suggesting that Vip3Aa secretion is nutrient‐dependent. Regardless of the growth conditions, we found that Vip3Aa retained in cell pellets exhibited high toxicity against Spodoptera frugiperda larvae. Hence, we speculate that the accumulation of Vip3Aa protein in the mother cell compartment under sporulation conditions could still be used as an efficient strategy for industrial production in commercial Bt strains.