Haloarcula Marismortui
A Microbial Biorealm page on the genus Haloarcula Marismortui
Classification (1)
Higher order taxa
Cellular organisms; Archaea; Euryarchaeota; Halobacteria; Halobacteriales; Halobacteriaceae; Haloarcula
Species
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NCBI: Taxonomy |
Haloarcula marismortui
Description and significance
Haloarcula marismortui is a halophilic red Archaeon (from the Halobacteriaceae family) found in the Dead Sea, a high saline, low oxygen solubility, and high light intensity environment. Like other halophilic archaeal organisms, H. marismortui thrives in this extreme environment due to several adaptations in protein structure, metabolic strategies and physiologic responses. (2, 3)
It is important to have its genome sequenced because of its unique ability to survive in such an extreme environment. The three fold extremities listed above are not expected characteristics of an environment in which a particular organism is able to survive. Therefore, it is important to understand what physiologic responses are unique to the organism that allows it to thrive in such an extreme environment. This will allow researchers to understand the systems level mechanisms that underlie environmental response systems. Analyzing its genome also provides support for the previously proposed characteristics of halophilic archaea, like acidic proteome, as well as the evolution of their genome architecture. A better understanding of gene regulatory networks that influence protein-protein and protein-DNA interactions may also provide a framework for biotechnological applications in the future. See Application section below for a more detailed description. (2, 3)
It was isolated in the 1960s by Ginzburg et al. in the Dead Sea. It is very closely related to Haloarcula vallismortis, but differs in its cell morphology and ability to use different sugars and other compounds for function. (4)
Genome structure
H. marismortui has a genome that is 4275kb in size composed of nine replicons and 4242 protein coding genes. It is divided into high and low G+C content replicons. The large chromosome I is a 3132-kb replicon with a 62.36% G+C content. The other eight replicons are smaller, ranging from 33 to 410 kb with G+C contents ranging from 54.25% to 60.02%, averaging about 57%. This bipartite genome-content organization is generally found in all members of this group of organisms. The significance of this type of organization is unknown.
However, there are three small replicons in H. marismortui that encode functions that are essential for survival. Replicon pNG600 codes several genes that are found nowhere else in the genome of H. marismortuis: aconitase, a significant enzyme in the TCA cycle, a DNA polymerase B family protein, the large and small subunits of endonuclease VII, and two transcription factor B (TFB) orthologs. This replicon is also responsible for H. marismortuis’s ability to handle heavy metal stress. It encodes genes for about a dozen cation transport proteins that have various specificities, metal-ion dependent transcription regulators, and a mercuric reductase.
Replicon pNG700 codes for four essential enzymes used in folate metabolism: viz. methylenetetrahydrofolate dehydrogenase, 5, 10-methylentretrahydrofolate reductase, formyltetrahydrofolate synthetase and formimidoyltetrahydrofolate cyclodeaminase. It also codes for functions that act downstream to arginine breakdown.
Chromosome II is the third replicon that encodes essential functions. It encodes one of three rRNA operons, as well as carbamoyl phosphate synthase, succinate-semialdehyde dehydrogenase, pyruvate dehydrogenase, acetyl-CoA acetyltransferase, citrate lyase, and GMP synthase, which are all foundational in essential metabolic processes. (2)
Cell structure and metabolism
4.1 Unique Physiochemical properties
The proteome of H. marismortui is highly acidic in order to maintain the structure and function of proteins in a high saline cytoplasm. The acidic residues in these proteins are mostly present on the surface of the folded proteins, making its average isoelectric point a low 5.0. It is expected that having a less negative protein surface charge would cause them to be insoluble in such a high salinity environment. (3)
4.2 Metabolism
The major pathways for sugar breakdown in H. marismortui are glycolysis and the modified Entner-Doudoroff (ED) pathways. Energy and amino acid biosynthesis precursors are produced when the products of these pathways are acted upon by the TCA cycle enzymes. The H. marismortui genome sequence codes for enzymes that synthesize up to 16 amino acids. This is more than the standard eight amino acids that are typically coded for in other Halobacterium organisms. Energy and metabolic carbon and nitrogen are also produced via catabolism of amino acids. Inorganic carbons are fixed into sugars via the reductive carboxylate cycle, which uses phosphophenol pyruvate carboxylase and gluconeogensis enzymes. (3, 5)
4.3 Environmental Response System
Due to the high saline, low oxygen solubility, and high light intensity environment, H. marismortui has a complex photobiological response system that includes opsins, cryptochrome/photolyase, clock regulators and transducers. This characteristic is also found in Halobacterium sp. NRC-1. Opsin proteins take advantage of the high light intensity by using light energy to maintain physiological ion concentrations, facilitate phototaxis, and make energy via a proton gradient. There are six opsin genes in H. marismortui.
Transducers are important in communicating an environmental factor to the chemotaxis apparatus and metabolic pathways. That way, an organism is able to be sensitive to its environment and can change in response in order to better survive. H. marismortui encodes 21 proteins that are associated with transmembrane receptor proteins that act as transducers in the cell. (3)
Ecology
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Pathology
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Application to Biotechnology
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Current Research
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References
Edited by student of Rachel Larsen and Kit Pogliano
