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Species
Arthrobacter Bacterium

Background Information
Arthrobacter bacterium are your typical soil bacteria that has been found to perform many important functions, such as reducing hexavalent chromium, which causes irritations to people and is known to degrade agricultural pesticides.

Morphology/Features
Arthrobacter is a sp. FB24 and has over 5,000,000 base pairs. Due to being recently discovered on Jun 6, 2005, there isn’t a lot published on it or known about it. They are coryneform bacteria, characterized by pleomorphism (the ability of some microorganisms to alter their morphology, reproductive, and even biological functions in response to their environments) and gram-positive phylum Actinobacteria. Due to having a complex life cycle that is marked by two distinct stages. While the cultures are relatively young, the cells have a slender rod-like structure that is stained by gram-negative testing. After about 30 hours the rod-shaped cells then become very short, a gram-positive rod and coccoid. They are also nonsporulating (organisms that haven’t been sporulated under the culture condition provided) and are members of actinomycetes. A lot of Arthrobacter have weak mobility as well. They have a very distinct method that they use for cell division known as “snapping division” also known as reversion, characterized by the outer cell wall rupturing at the joints. They have the ability to grow in mineral salts, pyridione broth, that have colonies of greenish metallic center. When looking at them under a microscope they have a rod-like structure that is visible when they are dividing and a cocci shape when they are in a stationary position.

Phylogeny/Genome Evolution
Arthrobacter is a member of the Micrococcaceae family, that belongs to the Actinobacteria phylum. They are often isolated from soils, where they present in biochemical cycles and decontamination. These bacteria are known for living in cold regions but their survival mechanisms of how they survive in these extreme cold environments like Antarctica are still not fully understood. By comparing their 16s genome, we can better understand their genomic features, which can ultimately help us better understand how they can survive these extreme environments in which they thrive. By using the 16s rRNA sequence, studies have found that a specific species of Arthrobacter was isolated from cryoconites. By comparing their 16s rRNA, it was determined that their genome consisting of PAMCS25564 was composed of circular chromosomes with a 4,170,970 bp with GC content of 66.74%. It’s believed to have 3,829 genes of which 3,613 of those are protein coding. They also have 147 pseudogenes, of which 15 are rRNA coding, and 51 are tRNA coding. Further testing, provided insight that suggested that the PAMCS556 had glycogen and trehalose metabolism pathways (degradation and biosynthesis) that were linked to carbohydrate-active enzymes. This genetic pattern study showed how CAZymes present in cold-adapted bacteria could adapt and survive in cold environments.

Metabolism
Arthrobacter are very nutritionally versatile, they are able to use a variety of substrates in their oxidative metabolism, which includes nicotine, nucleic acids, and many different herbicides and pesticides. Most Arthrobacter species use obligate aerobes, and most species of Arthrobacter use pure respiratory and never fermentative metabolism. However, some research has found that at least two species of Arthrobacter, A globiformis and A. nicotianae can use anaerobic metabolism. Arthrobacter found in upper layers of soil have been shown to frequently change the oxygen concentration of the soil, which has resulted in these Arthrobacter adapting to oxygen-independent growth to preserve themselves in times of oxygen limitations. These species have been shown to use nitrate as an electron acceptor at the end of their respiratory chain, resulting in the reduction of ammonia.

Relevance of Arthrobacter Bacterium
Arthrobacter along with other bacterial genera are used for industrial production of L-glutamate. With industrial applications, Arthrobacter is commonly grown with a low-cost sugar source, like cane or beet molasses, starch hydrolysates from corn or cassava tubers, and even tapioca. Arthrobacter has been found to play an important role in global biogeochemical cycles and decontamination of environments polluted. With their ability to respond to temperature, ionizing radiation, desiccation, oxygen radicals, and different ranges of chemicals have been able to describe their growth in a laboratory that is characterized by nutritional versatility that allows them to grow aerobically in a media using a wide range of carbon and nitrogen sources. There have been many Arthrobacter bacteria that have been isolated from a range of low-temperature environments, such as permafrost and glaciers. Due to the Earth having a large-scale cold biosphere and its importance to global biogeochemical cycles, and biotechnological potential of these psychrophiles and products has led to many studies about the significance of these psychrophiles. These studies aimed to discover the critical traits of psychrophiles isolated from lakes, glaciers, and wetlands of the Tibetan Plateau used more than 100 Arthrobacter genomes to study the traits and possibly explain why this genus of bacteria naturally accepts cold environments.

References and Citations
Arthrobacter. microbewiki. (n.d.). https://microbewiki.kenyon.edu/index.php/Arthrobacter#:~:text=Most%20species%20of%20Arthrobacter%20are%20obligate%20aerobes%2C%20but,A.%20globiformis%20and%20A.%20nicotianae%2C%20exhibit%20anaerobic%20metabolism. Han, S.-R., Kim, B., Jang, J. H., Park, H., & Oh, T.-J. (2021, June 2). Complete genome sequence of Arthrobacter sp.. PAMC25564 and its comparative genome analysis for elucidating the role of cazymes in cold adaptation. BMC genomics. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8171050/ Shen, L., Liu, Y., Allen, M. A., Xu, B., Wang, N., Williams, T. J., Wang, F., Zhou, Y., Liu, Q., & Cavicchioli, R. (2021, June 19). Linking genomic and physiological characteristics of psychrophilic Arthrobacter to metagenomic data to explain global environmental distribution - microbiome. BioMed Central. https://microbiomejournal.biomedcentral.com/articles/10.1186/s40168-021-01084-z#:~:text=Arthrobacter%20are%20reported%20to%20play%20important%20roles%20in,have%20been%20described%20%5B%2020%2C%2021%2C%2022%20%5D.