Question

Brucellosis, caused by gram-negative Brucella species, is a zoonotic disease with serious impact on the livestock industry. In animals, brucellosis can lead to abortions in females and sterility in males. In humans, brucellosis is rarely fatal, but it does cause systemic febrile (fever-causing) disease that can be debilitating. Brucella bacteria enter macrophages but are able to evade phagolysosomal fusion and so are able to survive intracellularly. Brucella, unlike other gramnegative bacteria, such as E. coli, has an unusual LPS that does not activate the innate immune responses. Comparison of the sequenced genomes of several strains that are nonpathogenic to humans (B. neotomae and B. ovis) to those that are pathogenic to humans (B. melitensis, B. abortus, and B. suis) has revealed that Brucella species are highly conserved overall (90% of the genes share 98 to 100% sequence identity at the nucleotide level, with a GC% of 57.3), except for certain distinct regions, called genomic islands (GIs). A group of researchers hypothesized that host specicity and virulence differences must stem from the limited genome diversity found in ve of these regions that are present in all pathogenic strains: GI-1 (8.1 kb; 9 open reading frames [ORFs]; GC% 53.2), GI-2 (15.1 kb; 20 ORFs; GC% 51.3), GI-3 (21 kb; 30 ORFs; GC% 52.3), GI-5 (44.1 kb; 42 ORFs; GC% 57.2), and GI-6 (7.5 kb; 10 ORFs; GC% 54.2). Comparing these GIs among the species to that of the human pathogen B. melitensis, the researchers found that GI-6 is absent in B. neotomae and GI-1, GI-2, and GI-5 are absent in B. ovis. Below is a schematic diagram of the genetic organization of the ORFs within GI-2. Based on sequence homology to other genes in the DNA database, the researchers were able to annotate some of the ORFs present. The arrows indicate the direction of transcription. OMP, outer membrane protein; Tnpase, transposase.

41-bp direct repeat 41-bp direct repeat EXTES Secretion protein Glycosyl transferase Tnpase Outer membrane protein tRNA ribosyl transferase Integrase tRNA Mannosyl transferase Tnpase

Considering all of the above information, name at least 5 features of GI-2 that led the researchers to propose that GI-2 might be a PAI. What is the most likely mode of HGT for GI-2 if it is a PAI? Be sure to provide your rationale.

Answer 1

5 features of GI- 2 are.

Due to lps alteration acriflaavin agglutination occurs,

Two ORFs BME 10998 and 10997 encode sugar transferases

and contribute to lps alteration

Rough lps resulting from GI2 deletion may affect pathogen associated molecular proteins and recognition by toll like receptors.

Pathogenicity islands PAI is virulence in development of disease.like hemolysin production, fimbria production.

Most likely mode of HGT horizontal gene transfer is transduction , becuase bacteriophage remnants have been found in PAI.