Bartonella henselae
A Microbial Biorealm page on the genus Bartonella henselae
Classification
Bartonella henselae was formerly known as Rochalimaea henselae. It was re-classified in 1993 (11).
Higher order taxa:
Domain: Bacteria, Phylum: Proteobacteria, Class: Alphaproteobacteria, Order: Rhizobiales, Family: Bartonellaceae (1)
Species:
Bartonella henselae
There are two serotypes of Bartonella henselae. Seroptype I is Houston-1 and Serotype 2 is Marseille. The classification is based on the differences in the 16S ribosomal DNA sequences (8).
Description and significance
Bartonella henselae is an aerobic, oxidase-negative, and slow growing Gram negative rod, slightly curved. It does not have flagella to facilitate its movement; however, there have been evidence of twitching motility. It requires very exact and fastidious conditions to grow in vitro. The temperature for optimal growth is 37 degrees Celsius and is highly dependent on the form and quantity of heme available. It is also very sensitive to changes in pH and has an explicit pH range of 6.8 to 7.2 (3). Under the microscope, the colonies are cauliflower-like (9).
Bartonella henselae was first discovered in a patient suffering from Cat Scratch Disease, though not identified, in the 1950s by Debre et al. The bacteria is found and can be isolated from erythrocytes of cats as well as lymph nodes of humans (6). It is important to use blood agar or chocolate agar plates and provide carbon dioxide. Colonies usually takes two to six weeks to form. The slow growth contributes to frequent misdiagnonsis. That is perhaps the reason why the bacterium was not identified until the 1990s with extensive work by Hensel, even though the first case of Cat Scratch Disease was described four decades prior (3). It is later discovered that this bacterium is associated with many other symptoms found in HIV-positive individuals.
Genome structure
Bartonella henselae has a circular genome. It uses mainly chromosomal genes for its virulence, according to research up to date (4). However, a potential plasmid has also been discovered, although, further research is needed to determine the full functionality. The genome was completely sequenced in 2004. It has a genome size of approximately 1.9 Mbp with an estimated coding fraction of 72.3%, slightly larger than that of Bartonella quintana with a genome size of 1.5 Mbp. The origin of replication is characterized by excess guanine and thymine nucleotides on the leading strand. There are 301 genes unique to Bartonella henselae. Approximately sixty-two percent of the genes on this bacterium are located on four sectors. They include a prophage region of 55 kb and three genomic islands of 72, 34, and 9 kb. On one side of the genomic islands are tRNAs and the other side, integrase genes. The 34 and 70 kb genomic islands have many copies of fhaC/hecB and fhaB. The fhaC/hecB gene makes a molecule that controls the transport of filamentous hemagglutinin, which is encoded by fhaB (18). The Bartonella henselae genome also has an unusually high number of repeated genes. Genomic islands are not present in Bartonella quintana, therefore, it does not make filamentous hemagglutinin. The two species are 98.7% identical in the 16S rRNA gene sequence. These two species derived some of their genes from Brucella melitensis (16).
The housekeeping genes of Bartonella henselae are 16S rDNA, eno, ftsZ, gltA, groEL, ribC, and rpoB. These genes function in the growth and metabolism of the bacterium. The ftsZ is homologous to that of Bartonella bacilliformis. It is located at the end of the operon consisting of genes ddlB, ftsQ, and ftsA, 5’-ddlB-ftsQ-ftsA-ftsZ-3’. ddlB facilitates cell wall biosynthesis by coding for homologues of D-alanine D-alanine ligase. FtsQ and FtsA are critical as well because they are involved in cell division. Promoters are also located in the ddlB, ftsQ, and ftsA open reading frames. These are essential to the bacterium because promoters help maintain high levels of FtsZ activity, very much like E. Coli to enhance the transcription of the ftsZ mRNA (16).
The plasmid consists of genes ribD, ribC, and ribE that encode for riboflavin deaminase (RibD) and subunits of riboflavin synthetase, RibC and RibE. Riboflavin is the precursor to important cofactors such as flavin mononucleotide and flavin adenine dinucleotide. These two cofactors are essential in electron transport and contribute to the basic energy metabolism of the cell (17).
Both serotypes of Bartonella henselae have virB4 genes that produce other virulent factors. It has 331 bp and further research of the virB operon indicates that the one in Bartonella henselae is homologous to the one in Agrobacterium tumefaciens, a bacterium known for its pathogenesis with the Type IV pili, however, their roles in virulence are still unknown (19). As mentioned earlier, there are different genotypes of Bartonella henselae. The lack of congruence between 16S rDNA shows that horizontal gene transfers occur between different B. henselae strains (8).
Cell structure and metabolism
The average size of the bacterium is 2 micrometers in length by 0.5 to 0.6 micrometers in width. There is no evidence of flagella and they are composed of octadecenoic and hexadecanoic fatty acids, similar to Bartonella quintana (9). The lipopolysaccharide from Bartonella henselae does not participate directly with pathogenicity, as most Gram negative bacteria secrete endotoxins through this structure (21).
Bartonella henselae has Type IV secretion systems (T4SSs) which are transporter complexes on membranes that help transport substrate molecules to target cells (14). The Type IV pili participate in the attachment to target cells. These pili undergo phase variation and may be the pathogenic determinant for Bartonella species. Different strains undergo different phase variations. Some are more pathogenic than others, such as Bartonella henselae strain 87-66 compared to ATCC 49793. Apparently, there is a positive correlation between the expression of pili and pathogenicity. Three important proteins released are BepD, BepE, BepF. BepD is phosphorylated after transmission into host cells. The effect of BepD is not clear as yet (14).
An unusual feature of Bartonella henselae is its inability to use glucose to derive energy, since glucose is abundant in mammalian hosts. This is due to the fact that it has an incomplete glycolysis pathway. Another closely related species Bartonella quintana uses a similar mechanism for metabolism as well. Both bacteria use amino acid catabolism to generate energy.This was confirmed with oxygen consumption and the production of carbon dioxide (3). It has been determined that Bartonella quintana metabolizes mainly succinate and glutamate. A few years later, it was determined that Bartonella henselae uses succinate and glutamate as well, along with histidine, asparigines, glycine, and serine from the growth medium.
Ecology
Describe any interactions with other organisms (included eukaryotes), contributions to the environment, effect on environment, etc.
Pathology
How does this organism cause disease? Human, animal, plant hosts? Virulence factors, as well as patient symptoms.
Application to Biotechnology
Does this organism produce any useful compounds or enzymes? What are they and how are they used?
Current Research
Enter summaries of the most recent research here--at least three required
References
1. Bartonella henselae NCBI classification reference: http://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?mode=Info&id=38323&lvl=3&lin=f&keep=1&srchmode=1&unlock
Edited by student of Rachel Larsen
