The Clues of the Discovery of New Pathogens Eventuated by the Horizontal Gene Transfer Among the Bacillus cereus Group Members

Genes, which constitute the biological basis of heredity, are DNA segments that give various structural and functional properties to the organism they are found in. Genes have become differentiated and highly conserved among microorganisms that have completed their evolutionary development and completely distanced from each other. However, horizontal gene transfers (HGT) can occur between microorganisms even though they have high structural similarities in the environment, especially in soil. An example, HGT can occur between the members of the Bacillus cereus group, and thus other species can develop into new life-threatening pathotypes by taking some virulence structures of the most pathogenic species-Bacillus anthracis. This study aimed to investigate some virulence genes (protective antigen-PA and capsule-cap) of B. anthracis in B. cereus group members isolated from soil, which is known as the reservoir of this group of bacteria and can easily trigger the genetic material exchange. The study material has consisted of 15 soil samples taken from 5 different locations in the Kars region (Turkey) contaminated with cattle carcasses that died with suspected anthrax. B. cereus group bacteria were obtained from the soil by in vitro cultural method, and the agent identification was performed by phenotypic and molecular methods (PCR). As a result, a total of 1350 Bacillus species was identified from the soil, including 123 B. anthracis, 303 B. mycoides, 348 B. thuringiensis and 576 B. cereus. DNAs obtained from all isolates other than B. anthracis were pooled at a final concentration of 4 ng/mL and as an average of 10 extracts and analyzed by PCR for the relevant virulence genes (PA and cap). While the PA gene was found in 6 (4.88%) of 123 DNA pools, the cap gene was not detected in any of the pooled DNA. All B. anthracis isolates were evaluated as fully virulent strains as they did not lose the PA and cap genes. The DNA pooling method has been an obstacle to the selection of gene positivity individually, however, it roughly offered some clues indicating the HGT. Thus, further studies with sampling and methodological diversities are needed that will enable the proof of HGT, which mediates the emergence of new pathotypes among the B. cereus group members.