A cryptic Bacillus isolate exhibited narrow 16S rRNA gene sequence divergence with Bacillus thuringiensis and showed low maintenance requirements in hyper-osmotic complex substrate cultivations.

Abstract

A cryptic Bacillus (K90) isolate obtained from soil samples from the Kuwait desert exhibited lower maintenance requirements in complex substrate cultivations than Bacillus thuringiensis. A mathematical model was used to estimate apparent maintenance coefficients (m(c)) and these were found to be 0.336 and 0.041/h for B. thuringiensis and K90, respectively. The results also showed that the values of apparent maintenance coefficients were inversely related to the specific growth rates. Furthermore, 16S rRNA gene sequencing showed that K90 exhibited 99.81% sequence similarity to that of B. mojavensis and 92.9% with B. thuringiensis. It is evident from the dendrogram that the evolution of B. mojavensis (K90) (B. subtilis group), which may have originated after B. licheniformis could have been influenced by prolonged hyper-osmotic conditions, while B. thuringiensis that evolved before B. oleronius exhibited greater sensitivity as implied by the higher maintenance coefficient obtained for the hyper-osmotic cultures. As K90 exhibited low maintenance requirements in hyperosmotic cultures, close phylogenetic relationship with B. thuringiensis, along with the reported property of encapsulation of insecticidal crystal proteins (Cry) in Bacillus strains and endophytic nature of B. mojavensis, strongly suggest that K90 could be a promising surrogate host for the transgenic delivery of "Cry" proteins.