User:Biochem51/Treponema pallidum

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Lead

Treponema pallidum, formerly known as Spirochaeta pallida, is a Gram-negative microaerophilic spirochaete bacterium with various subspecies that cause the diseases syphilis, bejel (also known as endemic syphilis), and yaws. While it was previously believed to be transmitted only among humans, research has shown clear dissemination and pathogenesis in various mammals, including rabbits, mice, and monkeys. It is a helically coiled microorganism usually 6–15 μm long and 0.1–0.2 μm wide. T. pallidum's lack of either a tricarboxylic acid cycle or oxidative phosphorylation results in minimal metabolic activity. The treponemes have a cytoplasmic and an outer membrane. Using light microscopy, treponemes are visible only by using dark-field illumination. T. pallidum consists of three subspecies, T. p. pallidum, T. p. endemicum, and T. p. pertenue, each of which has a distinct associated disease.

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Outer membrane

The outer membrane (OM) of T. pallidum has several features that have made it historically difficult to research. These include details such as its low protein content, its fragility, and that it contains fewer sequences related to other gram negative outer membranes. Recent progress has been made utilizing genomic sequencing and advanced computational models. Treponemal outer membrane proteins are key factors for its pathogenesis, persistence, and immune evasion strategies. The relatively low protein content serves to prevent antigen recognition by the immune system and the proteins that do exist protrude out of the OM, enabling its interaction with the host. Treponema's reputation as a "stealth pathogen" is primarily due to this unique OM structure, which serves to evade immune detection .

TP0326

TP0326 is an ortholog of BamA. BamA apparatus will insert newly synthetized and exported outer membrane proteins into the outer membrane Outer membrane:

TP0965

TP0965 is a protein that is critical for membrane fusion in T. pallidum, and is located in the periplasm. TP0965 causes endothelial barrier dysfunction, a hallmark of late-stage pathogenesis of syphilis. It does this by reducing the expression of tight junction proteins, which in turn increases the expression of adhesion molecules and endothelial cell permeability, which eventually leads to disruption of the endothelial layer.

TP0453

TP0453 is a 287 amino acid protein associated with the inner membrane of the microbe's outer membrane. This protein lacks the extensive beta sheet structure that is characteristic of other membrane proteins, and does not traverse the outer membrane. TP0453's function has been hypothesized to be involved with control of nutrient uptake.

TP0624

Outer Membrane Protein A (OmpA) domain-containing proteins are necessary for maintaining structural integrity in Gram-negative bacteria. These domains contain peptidoglycan binding sites which creates a "structural bridge between the peptidoglycan layer and the outer memebrane." The protein TP0624 found in T. pallidum has been proposed to facilitate this structural link, as well as interactiosn between outer membrane proteins and corresponding domains on the thin peptidoglycan layer.

Culture

In the past century since its initial discovery, culturing the bacteria in vitro continuously has been the source of much debate and struggle for scientists. Without the ability to grow and maintain the bacteria in a laboratory setting, discoveries regarding its metabolism and antimicrobial sensitivity were greatly impaired. However, successful long-term cultivation of T. p. pallidum in vitro was reported in 2017. This was achieved using Sf1Ep epithelial cells from rabbits, which were a necessary condition for the continued multiplication and survival of the system. The medium TpCM-2 was used, an alteration of more simple media which previously only yielded a few weeks of culture growth. This success was the result of switching out minimal essential medium (MEM) with CMRL 1066, a complex tissue culture medium. With development, new discoveries about T. pallidum's requirements for growth and gene expression may occur and in turn, yield research beneficial for the treatment and prevention of syphilis, outside of a host. However, continuous efforts to grow T. pallidum in axenic culture have been unsuccessful, indicating that it does not satisfy Koch's postulates. The challenge likely stems from the organism's strong adaptation to residing in mammalian tissue, resulting in a reduced genome and significant impairments in metabolic and biosynthetic functions.

Electron micrograph image of T. pallidum, highlighted in gold

Genome

The chromosomes of the T. pallidum subspecies are small, about 1.14 Mbp. Their DNA sequences are more than 99.7% identical. T. p. pallidum was sequenced in 1998. This sequencing is significant due to T. pallidum not being capable of growing in a pure culture, meaning that this sequencing played an important role in understanding the microbes' functions. T. pallidum was found to rely on its host for many molecules provided by biosynthetic pathways, and it is missing genes responsible for encoding key enzymes in oxidative phosphorylation and the tricarboxylic acid cycle. The T. pallidum group and its reduced genome is likely the result of various adapations, such that it no longer contains the ability to synthesize fatty acids, nucleic acids, and amino acids, instead relying on its mammalian hosts for these materials. The recent sequencing of the genomes of several spirochetes permits a thorough analysis of the similarities and differences within this bacterial phylum and within the species. T. p. pallidum has one of the smallest bacterial genomes at 1.14 million base pairs, and has limited metabolic capabilities, reflecting its adaptation through genome reduction to the rich environment of mammalian tissue. The shape of T. pallidum is flat and wavy. To avoid antibodies attacking it, the cell has few proteins exposed on the outer membrane sheath. Its chromosome of about 1000 kilobase pairs is circular with a 52.8% G + C average. Sequencing has revealed a bundle of 12 proteins and some putative hemolysins are potential virulence factors of T. pallidum. About 92.9% of DNA was determined to be open reading frames, 55% of which had predicted biological functions.

Genome[edit]

The chromosomes of the T. pallidum species are small, about 1.14 Mbp. Their DNA sequences are more than 99.7% identical. About 92.9% of DNA was determined to be open reading frames, 55% of which had predicted biological functions. The genome ofT. pallidum was first sequenced in 1998. T. pallidum not capable of being in a pure culture, meaning that this sequencing played an important role in understanding the microbes' functions. T. pallidum was found to rely on its host for many molecules typically provided by biosynthetic pathways, and it is missing genes responsible for encoding key enzymes in oxidative phosphorylation and the tricarboxylic acid cycle. The recent sequencing of the genomes of several spirochetes permits a thorough analysis of the similarities and differences within this bacterial phylum and within the species. T. pallidum has one of the smallest bacterial genomes at 1.14 million base pairs, and has limited metabolic capabilities, reflecting its adaptation through genome reduction to the rich environment of mammalian tissue. T. pallidum is characterized by its helical, corkscrew-like shape. To avoid antibodies attacking it, the cell has few proteins exposed on the outer membrane sheath. Its chromosome is about 1000 kilobase pairs and is circular with a 52.8% G + C average. Sequencing has revealed a bundle of 12 proteins and some putative hemolysins are potential virulence factors of T. pallidum. These virulence factors are thought to contribute to the bacterium's ability to evade the immune system and cause disease.

Electron micrograph image of T. pallidum cultured on epithelial cells of cotton-tail rabbits.