Waddlia chondrophila

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Scientific Classification

Domain: Bacteria
Phylum: Chlamydiae
Class: Chlamydiae
Order: Chlamydiales
Family: Waddliacea
Genus: Waddlia
Species: W. chondrophila

Introduction

Waddlia chondrophila (WSU 86-1044T) was initially discovered and isolated from the tissues of a first-trimester aborted bovine foetus at the Washington Animal Disease Diagnostic Laboratory.[1] W. chondrophila is a gram-negative, coccoid bacteria with 0.2 – 0.5 um in diameter.[1][2] It is characterized as an obligate intracellular organism, meaning it replicates within cytoplasmic vacuoles and exhibit structural characteristics. The organisms can be found in two forms: a reticulated form within a cytoplasmic vacuole and a dense infective form released from the cells.[3] Up till now, the species includes on the type strain, WSU 86-1044T (=ATCC VR 1470T).[4][5] The full length 16S rRNA gene sequence is 15% different from that of Chlamydiaceae species[4] and 12.8% different from Parachlamydia acanthamoebae[5]; thus, it’s in a separate family of the Chlamydiales.[6] The natural hosts and reservoir of this organism is in amoebae[7] so infections of human by W. chondrophila might have been an opportunistic accident. Despite the lack of knowledge regarding how the bacterial infection spreads, W. chondrophila has been recently associated with adverse pregnancy outcomes both in humans and animals.[8][9] In addition to linkage to miscarriage, the bacteria are shown to also cause respiratory tract infections.[7]

Genome

The bacterium possesses a 2’116’312 bp chromosome with a G+C content of 43.8% and a 15’593 bp of low-copy number circular plasmid with a G+C content of 37.6%.[10] Within the chromosome, 4.9% of W. chondrophila chromosome consist of a large number of repetitive sequences (>200 bp), which is significantly higher proportion than other sequenced Chlamydiales. The comparison between W. chondrophila chromosome and plasmid indicates that the plasmid is present in about 11 copies per cell, encoding 22 proteins with no homology to other chlamydial plasmid proteins. Numerous small regions (16-24 bp) were identified to have identical sequence in both the chromosome and the plasmid.[10]

Previous study identified 1934 protein coding genes in the organism’s genome as well as two sets of rRNAs and 37 tRNA genes, which represent 92% of the whole genome. Of all the conserved hypothetical, 156 proteins are most similar to hypothetical proteins from the Parachlamydiaceae family while the remainder show best BLAST hits against Eukaryotes, Archaea, Chlamydiaceae and various other bacterial phyla. The core genome of the organism, which includes components for DNA replication, transcription and RNA translation, shares great similarity to the core set of Chlamydiales genes. Despite having genes for nucleotide parasitism, the bacteria possess all enzymes to convert L-glutamine and all pyrimidine derivatives necessary of replication and transcription. Instead of having a complete purine biosynthesis pathway like in other members of the Chlamydiales order, an active purine conversion was identified in W. chondrophila.[10]

Growth and cytoskeletal embedding of W. chondrophila in HeLa cells

The ability of W. chondrophila to grow in mammalian cells has been established after experimental growth on HeLa cells (human cell lines) as well as various other human cells lines.[11] Colony growth was visible after 12 hours and progressed more rapidly at later stages. The observed bacteria growth exhibited cytosolic holes that increased in size over about 1 to 4 hours before gaining access to inclusions and being filled up by the bacteria. The cell structures appeared membranous and empty early inclusions.

Previous studies showed that the chlamydial cell wall differs from the majority of extracellular Gram-negative bacteria as it has a highly disulphide-linked proteinaceous layer in the infectious elementary body (infectious particle) (EB). Upon entering the cell, the EB releases itself from the organism by reducing the disulphide-linked proteins so that the bacteria swell in size. This process is tightly regulated by the conserved periplasmic chlamydial redox enzymes.[10]

The cytoskeletal components such as microtubules and actin were arranged around the W. chondrophila inclusion using confocal 3D construction. 11 The cytosolic membranous structures coated on the top of the cell grown on a solid support. The W. chondrophila inclusions is not as tightly embedded in cytoskeletal elements, which explains its irregular shape.[10]

Bacterial metabolism and energy production

In contrast to other members of the Chlamydiales order, W. chondrophila exhibits a degree of host independence with its ability to produce energy through oxidative phosphorylation.[10] To produce ATP energy, the bacteria use reduced cofactors from the complete TCA cycle and glycolysis along the electron transport chain. W. chondrophila contains both a F0F1 and V1V0 ATpase, the latter is conserved in the Chlamydiaceae, which enhances its energy production capacity and improves its adaptability in nutrient-poor environment. Furthermore, the organism contains the enzymatic components of the glyoxylate bypass, which enables the utilization of fatty acids or acetate in the form of acetyl-CoA as a carbon source.[10]

In addition to some differences in the ATP production pathway between W. chondrophila and other members in the Chlamydiales order, lipid metabolism in this organism exhibits features with the presence of additional enzymes for glycerophospholipid, glycerolipid and sphingolipid metabolism. More specifically, W. chondrophila contains a complete operon encoding the mevalonate pathway in the biosynthesis of isoprenoids.[10]

Mechanism of parasitism in human macrophages

Since the bacteria was first isolated in 1990, little is known about the pathogenesis of W. chondrophila until researchers investigated the mechanism of which the intracellular bacterium survives and proliferates within human host cells.[12] W. chondrophila enters and multiplies rapidly within human macrophages, including lysis of infected cells.[13] Macrophages are components of the innate immune response that efficiently invade and destroy bacteria. By infiltrating and resisting the anti-microbial functions of macrophages, this organism successfully breaks down the immune system in the host cells.[12] In particular, W. chondrophila immediately colocalize with mitochondria and endoplasmic reticulum (ER) resident proteins to begin bacterial replication. As the bacteria succeed in associating with the host’s mitochondria and the ER, W. chondrophila survives within human macrophages by evading the endocytic pathway. The intracellular trafficking of W. chondrophila in human macrophages represents a novel route that differs from the ones used by other members in Chlamydiales.[12]

Role of Chlamydia-related bacteria in adverse pregnancy outcomes in human

Out of 15% of pregnancies ending in miscarriage, a cause is only identified in 50% of these cases. Several studies have implicated the role of W. chondrophila in human miscarriages.[8][9] In a study from 2004 – 2005 with 69 women with sporadic miscarriages (SM), 200 women with recurrent miscarriages (RM) and 169 control women with uneventful pregnancies, W. chondrophila was used as an antigen to induce IgG antibodies that can be observed under immunofluorescence.[9] Results from the study demonstrates a strong association between the presence of W. chondrophila-specific IgG antibodies and early fetal loss. Other conclusion drawn from this study involves connecting reactivation of a latent asymptomatic waddlial infection and/ or endometrial damage form a past infection to the mechanism of miscarriage due to W. chondrophila.[9]

References

  1. ↑ 1.0 1.1 Waddlia (2015), in Bergey’s Manual of Systematics of Archaea and Bacteria, pp 1–2. American Cancer Society.
  2. ↑ Rurangirwa, F. R., Dilbeck, P. M., Crawford, T. B., McGuire, T. C. & McElwain, T. F. (1999). Analysis of the 16S rRNA gene of micro-organism WSU 86-1044 from an aborted bovine foetus reveals that it is a member of the order Chlamydiales: proposal of Waddliaceae fam.nov., Waddlia chondrophila gen. nov., sp. nov. Int J Syst Bacteriol 49, 577–581.
  3. ↑ Rurangirwa, F. R., Dilbeck, P. M., Crawford, T. B., McGuire, T. C. & McElwain, T. F. (1999). Analysis of the 16S rRNA gene of micro-organism WSU 86-1044 from an aborted bovine foetus reveals that it is a member of the order Chlamydiales: proposal of Waddliaceae fam.nov., Waddlia chondrophila gen. nov., sp. nov. Int J Syst Bacteriol 49, 577–581.
  4. ↑ 4.0 4.1 Dilbeck, P. M., Evermann, 1. F., Crawford, T. B. & 7 other authors(1990). Isolation of previously undescribed rickettsia from an aborted bovine fetus. J Clin Microbiol28, 8 14-8 16.
  5. ↑ 5.0 5.1 Kocan, K. M., Crawford, T. B., Dilbeck, P. M., Evermann, 1. F. & McGuire, T. C. (1990). Development of rickettsia isolated from an aborted bovine fetus. J Bacterioll72, 5949-5955.
  6. ↑ Rurangirwa, F. R., Dilbeck, P. M., Crawford, T. B., McGuire, T. C. & McElwain, T. F. (1999). Analysis of the 16S rRNA gene of micro-organism WSU 86-1044 from an aborted bovine foetus reveals that it is a member of the order Chlamydiales: proposal of Waddliaceae fam.nov., Waddlia chondrophila gen. nov., sp. nov. Int J Syst Bacteriol 49, 577–581.
  7. ↑ 7.0 7.1 Collingro, A., Tischler, P., Weinmaier, T., Penz, T., Heinz, E., Brunham, R. C., Read, T. D., Bavoil, P. M., Sachse, K., Kahane, S., Friedman, M. G., Rattei, T., Myers, G. S. A., and Horn, M. (2011) Unity in Variety—The Pan-Genome of the Chlamydiae. Mol Biol Evol 28, 3253–3270.
  8. ↑ 8.0 8.1 Hornung, S., Thuong, B. C., Gyger, J., Kebbi-Beghdadi, C., Vasilevsky, S., Greub, G., and Baud, D. (2015) Role of Chlamydia trachomatis and emerging Chlamydia-related bacteria in ectopic pregnancy in Vietnam. Epidemiology & Infection 143, 2635–2638.
  9. ↑ 9.0 9.1 9.2 9.3 Baud, D., Thomas, V., Arafa, A., Regan, L., and Greub, G. (2007). Waddlia chondrophila, a potential agent of human fetal death. Emerg. Infect. Dis. 13, 1239–1243. doi: 10.3201/eid1308.070315.
  10. ↑ 10.0 10.1 10.2 10.3 10.4 10.5 10.6 10.7 Bertelli, C., Collyn, F., Croxatto, A., Rückert, C., Polkinghorne, A., Kebbi-Beghdadi, C., Goesmann, A., Vaughan, L., and Greub, G. (2010) The Waddlia Genome: A Window into Chlamydial Biology. PLOS ONE 5, e10890.
  11. ↑ Dille, S., Kleinschnitz, E.-M., Kontchou, C. W., Nölke, T., and Häcker, G. (2015) In Contrast to Chlamydia trachomatis, Waddlia chondrophila Grows in Human Cells without Inhibiting Apoptosis, Fragmenting the Golgi Apparatus, or Diverting Post-Golgi Sphingomyelin Transport. Infect. Immun. (Morrison, R. P., Ed.) 83, 3268–3280.
  12. ↑ 12.0 12.1 12.2 Croxatto, A., and Greub, G. (2010) Early intracellular trafficking of Waddlia chondrophila in human macrophages. Microbiology, 156, 340–355.
  13. ↑ Goy, G., Croxatto, A. & Greub, G. (2008). Waddlia chondrophila enters and multiplies within human macrophages. Microbes Infect 10, 556–562.
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