Environmental Chlamydiae - Assignment Example

Environmental Chlamydiae Appears Here] College Appears Here] The environment harbors various microorganisms which certainly have ecological importance. Some of these microorganisms however have a potential to become human pathogens. One of the microorganisms which show to have relevant medical importance is Chlamydiae which are one of the microorganisms which become successful in infecting humans (Horn et al., 2004). Lymphogranuloma venereum (LGV) and trachoma are two of the diseases caused by Chlamydia trachomatism (Arbique, 2008). It was first thought that Chlamydiae species infect only specific hosts but studies revealed that they found in fish, insects, turtles and amoeba. Ecological samplings also revealed that chlamydiae can be found in the environment including freshwater, soil, sewage and water conduit systems (Griffiths et al., 2005). The pathogenic chlamydiae are more confined on humans and other mammals whereas the environmental chlamydiae naturally occur within phylogenetically different host organisms (Department of Microbial Ecology, 2008). Characteristically, the chlamydiae species are obligate intracellular, coccoid bacteria. Its biphasic developmental cycle is considered to be the most distinguishing characteristic (Tortora et al., 2001). Their elementary body is the infective agent while the reticulate body is non-infectious (Collingro et al., 2005). Recently, another infective stage, the crescent body was described for the Parachlamydiaceae (Corsaro et al., 2006). Its developmental cycle involves important steps. First it facilitates the attachment of the elementary body to a receptor cell on the hosts cell surface. Then it enters the host cell through endocytosis. Inside the hosts cell, it reorganizes itself from the infective form to the replicative form which is the reticulate body. The reticulate bodies then undergo morphological changes to elementary bodies. These elementary bodies are released to infect other cells (Arbique, 2008). Unlike other microorganisms, Chlamydiae do not need insect vectors. They directly infect humans either by interpersonal contact or by airborne respiratory routes (Tortora at al., 2001). The untold diversity of chlamydiae was first revealed in 1990s when a chlamydia-like bacteria was recognized with free-living amoeba as endosymbiont. Since then, they have been considered as novel members of the order Chlamydiales. This discovery led to the reorganization of the chlamydial taxonomy as three new families were added (Collingro et al., 2005). Initially, the phylum Chlamydiae is composed of a single class which is Chlamydiae which is composed of the order Chlamydiales. With the addition of the three new families, this order is now composed of four families including the Chlamydiaceae, which contains all of the traditional chlamydiae species and the novel chlamydia species (Griffiths et al., 2005). These novel chlamydiae were proposed to be classified as Parachlamydiaceae, Simkaniaceae and Waddliaceae (Collingro et al., 2005). Since chlamydia-like species are found mostly in non-culturable sources, it is difficult to obtain information regarding it sequences. The only way to do so however, is through PCR amplification using primers based on 16S rRNA sequences and the clustering of any amplified sequence with the known chlamydiae species in the rRNA trees (Griffiths, 2005). To assign the symbionts to their evolutionary lineages, the application of the full cycle rRNA approach which included 16S rRNA sequencing and fluorescence in situ hybridization with 16S rRNA-targeted oligonucleotide probes was used (Horn et al., 2004). Fritsche et al. (2000) however used neighbor-joining, parsimony and distance matrix methods in analyzing the 16S rRNA gene sequences of acanthamoeba isolates with their aim to uncover the diversity of Chlamydiales. They further used fluorescently labeled oligonucleotide probes to target 16S rRNA to differentiate the two groups of intra-amoebal endosymbionts. Studies have shown that at some point in the evolutionary history, the Chlamydiales diverged which resulted to the present families. In spite of this divergence, all families under order Chlamydiales share common characteristics. The 16S rRNA of all families is about 80 to 90% related to each other. Except for endosymbionts of Parachlamydiaceae, all are obligate intracellular parasites. Only the elementary bodies of Parachlamydia acanthamoeba retain the Gram stain which may be explained by the thick cell envelopes. All the rest are Gram-negative. Pelomorphism is another distinct characteristic of their cells. Lastly, multiplication occurs inside membrane-bound cytoplasmic vacuoles (Moulder, 2008). Though environmental chlamydiae possess some striking difference compared to the pathogenic chlamydiae, it does show all the key features of the chlamydiae (Horn et al., 2004). This only means that they are the closest living relative of the pathogenic chlamydiae (Department of Microbial Ecology, 2008). Figure 1 shows that chlamydiae were a coherent group at one point but formed a deep branch in rRNA-based phylogenetic trees. Figure 1. Phylogeny of chlamydiae. Source: Horn et al., 2004: Science. Supposedly the family Chlamydiaceae refers to the pathogenic chlamydiae thus the term environmental chlamydiae was coined to designate the chlamydial species which does not fall to the group. Pathogenenicity however cannot solely differentiate the chlamydial species since environmental chlamydiae have been implicated as potential human pathogens (Corsaro, 2006). Seven hundred million years ago, the last common ancestor of pathogenic and symbiotic chlamydiae survived within eukaryotes and was used to intracellular survival (Horn et al., 2004). Parachlamydiaceae, Simkania negevensis, and Waddlia chondrophila have shown symbiotic relationship with amoeba (Corsaro, 2006). The history of symbiotic relationship between eukaryotes and chlamydiae contributes to its virulence factors. Virulence phenotype was strongly inclined to the influence of the adaptation to new habitats compared to ancestry (Moulder, 2008). Comparative analysis of genome can be a very useful tool in identifying the molecular characteristics which are distinct to species of bacteria. Horn et al. (2004 conducted a genome analysis on the Acanthamoeba sp. endosymbiont UWE25, a Protochlamydia amoebophila and found that it was twice as large as any pathogenic chlamydia. Based on their observation, UWE25 is composed of few pseudogenes and gene remnants which mostly affect transposase genes. This only means that these chlamydiae have already stabilized. When its genes were compared with pathogenic chlamydiae using FastA reciprocal best matches, it revealed that there was only little conservation gene order between the species which is suggestive of a massive reorganization of gene order during the divergence of environmental chlamydiae and pathogenic chlamydiae. The genome size reduction of the pathogenic chlamydiae during evolution also contributed to the conservation of gene order between the species. These chlamydial species thrive in different niches thereby promoting to the differences in their genes. The pathogenic chlamydiae which thrive in a more homeostatic environment tend to loss more genes. The difference is further illustrated by the number of rRNA operons between these species, in which UWE25 displayed a higher number. Another significant difference between these chlamydial species is the presence of 1093 CDSs in UWE25 while it is absent in all other chlamydial genomes. It was also observed that there is high number of cyanobacterial and plant gene homologs in UWE25 compared to pathogenic chlamydiae, and that UWE25 shares the unique ribosomal superoperon structure with pathogenic chlamydiae, cyanobacteria, and chloroplasts which supports the ancient relationship between chlamydiae and cyanobacteria which is shown in figure 2. Figure 2. Shows the phylogenetic relationship of Chlamydiales to other Bacteria and to chloroplasts and mitochondria. Source www.chlamydiae.com. The first report about the clinical significance of environmental chlamydiae was based on the observation on the sera of 500 patients who acquired pneumonia of unknown cause. An indirect immunofluorescence assay with the elementary bodies of Halls coccus (an environmental Parachlamydia isolate having an almost identical 16S rRNA gene sequence to P. acanthamoebae) as the antigen. Since the result showed that about 1% of the tested sera showed increased antibody titer, it was concluded that the organism is a potential human pathogen. The clinical significance of the species Neochlamydia hartmannellae has not yet been established; though it was observed that it has a role in ocular infections. This is further supported by the recovery of UWC22 which is a Neochlamydia sp. strain from the contact lens of a patient with keratitis. The species Parachlamydiaceae might be involved in bronchities, atherosclerosis and urogenital infections since the 16S rRNA which is related to the species were amplified from the cells of the patients with bronchitis and arterial samples (Corsaro, 2006). Environmental chlamydiae although differentiated from the pathogenic chlamydiae show characteristics which makes it a close relative of the pathogenic chlamydiae. Aside from that, it also show pathogenecity which far exceeded its pathogenic counterparts since it has the ability to infect humans and animals. Based on the studies about environmental chlamydiae, there is evidence that its pathogenecity can be linked to its evolutionary history. The studies which dealt with its history really give enlightenment about the existence of environmental chlamydiae. References Arbique, Judy (2008). Chlamydiae Bacteria: Sexually Transmitted Infections (STI), Pneumonia and Zoonoses. Retrieved August 24, 2008, from http://microbiology.suite101.com/article.cfm/chlamydia_infection. Collingro, Astrid; Poppert, Sven; Heinz, Eva; Schmitz-Esser, Stephan; Essig, Andreas; Schweikert, Michael; Wagner, Michael and Horn, Matthias (2005). Recovery of an environmental chlamydia strain from activated sludge by co-cultivation with Acanthamoeba sp. Microbiology151, 301-309. Corsaro, Daniele and Greub, Gilbert (2006). Pathogenic Potential of Novel Chlamydiae and Diagnostic Approaches to Infections Due to These Obligate Intracellular Bacteria. Clinical Microbiology Review, vol. 19, no. 2, pp. 283-297. Fritsche, Thomas R.; Horn, Matthias; Wagner, Michael; Herwig, Russell P.; Schleifer, Karl-Heinz and Gautom, Romesh K. (2000). Phylogenetic Diversity among Geographically Dispersed Chlamydiales Endosymbionts Recovered from Clinical and Environmental Isolates of Acanthamoeba spp. Applied and Environmental Microbiology, vol. 66, no. 6, p. 2613-2619. Griffiths, Emma; Petrich, Astrid K. and Gupta, Radhey S. (2005). Conserved indels in essential proteins that are distinctive characteristics of Chlamydiales and provide novel means for their identification. Microbiology 151, 2647-2657. Horn, Matthias and Wagner, Michael (2004). Bacterial endosymbionts of free-living amoebae. Journal of Eukaryotic Microbiology, vol. 51, is. 5, pp. 509-514. Horn, Matthias; Collingro, Astrid; Schmitz-Esser, Stephan; Beier, Cora L.; Purkhold, Ulrike; Fartmann, Berthold; Brandt, Petra; Nyakatura, Gerald J.; Droege, Marcus; Frishman, Dmitrij; Rattei, Thomas; Mewes, Hans-Werner and Wagner, Michael (2004). Illuminating the Evolutionary History of Chlamydiae. Science, vol. 304, no. 5671, pp. 728-730. Moulder, J.W. (2008). Chlamydiales Evolution: Evolution Index. Retrieved August 24, 2008, from http://www.chlamydiae.com/Evolution_index.asp. Tortora, Gerald, J.; Funke, Berdell R. and Case, Christine L. (2001). Microbiology: An Introduction. Addison-Wesley Longman, Inc. (2008). Environmental Chlamydiae. Retrieved August 24, 2008, from Department of Microbial Ecology Website http://www.microbial-ecology.net/envchlamydia.asp Read More