Studies on the extrachromosomal DNA of Bacillus thuringiensis var. thuringiensis

Abstract

An extracromosomal  DNA  was  isolated  from  B.  thuringiensis var thuringiensis and  characterized molecular  weight was  found  to  be  approx.  10  x 10^6.  The  covalently closed  nature  of  the  molecule was  confirmed  by  CsCl-ethdium  bromide  centrifugation,  agarose  gel  electlophoresis  and electron  microscopy.  The extrachromosomal DNA  wa  isolated  at  various  stages of growth, under different growth conditions  (with  varying  concentrations  of  cys).  Two  modes  of  existence  for the extrachromosomal  DNA  were  suggested:  (a)  an  autonomous  cyloplasmic  form  and  (b)  a  cryptic  form  in  which presumably was  integrued  into the  genomic  DNA.  It  is  suggested  that  some  og  the  crystal  protein  and  major  spore  coat  protein  could  have  been  coded  for  by  the extrarchromosomal DNA  B.  thuringiensis var thuringiensis  while it  is  in  an  extrachromosomal  state.  In  the  integrated  stale  the  extrachromosomal DNA  is  non-functional.