DNA SEQUENCE ANALYSIS OF OVERLAPPING CHROMOSOMAL DELETIONS IN TWO NINE MILE ISOLATES OF COXIELLA BURNETII

Abstract

Previous studies on the prototype Nine Mile strain of Coxiella bumetii has shown that two derivatives have overlapping deletions of chromosomal DNA. The Nine Mile phase I parent wild-type isolate is virulent, causing acute 0-fever. The two derivatives, Nine Mile II and RSA 514, have truncated lipopolysaccharide (LPS) structures which differ from the parent Nine Mile I complete smooth LPS. Nine Mile II is avirulent with a rough LPS. RSA 514 has a semi-rough LPS and infects immunocompetent hosts. RSA 514 is similar to Nine Mile II, and superior to 9 mile I, in its ability to gain entry into cells. However, RSA 514's semi-rough LPS only affords partial protection from the host's immune system. To gain information into the genetic basis for these LPS variations the DNA segment corresponding to the DNA deletion regions of Nine Mile ll and RSA 514 was sequenced. Sequence analysis showed the RSA 514 deletion to contain coding sequences for four rfb genes, which have been shown in enteric bacteria to encode for enzymes and/or regulatory functions required for the synthesis of the 0-antigen region of the LPS.