sentences:  Unlike the latter, the genome of "R. prowazekii", however, contains a complete set of genes encoding for the tricarboxylic acid cycle and the respiratory chain complex.Still, the genomes of the "Rickettsia", as well as the mitochondria, are frequently said to be "small, highly derived products of several types of reductive evolution".The recent discovery of another parallel between "Rickettsia" and viruses may become a basis for fighting HIV infection.