Micrococcus antarcticus

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Micrococcus antarcticus
Systematics
Department : Actinobacteria
Order : Actinomycetales
Subordination : Micrococcineae
Family : Micrococcaceae
Genre : Micrococcus
Type : Micrococcus antarcticus
Scientific name
Micrococcus antarcticus
Liu et al. 2000

Micrococcus antarcticus is a gram-positive bacterium that wasdiscovered in Antarctica in2000. It is a psychrophilic organism that can multiply at low temperatures. It grows aerobically , so only when oxygen is available. Its adaptation to the cold is the subject of research, for example which fatty acids are present in the lipids of the cell membrane .

features

Appearance

The cells of Micrococcus antarcticus are round, they are cocci . In light microscopic image is diplococci and inter alia also be Micrococcus luteus typical nibbles recognize. A single cell is about 0.5-0.8 µm in diameter  . In the Gram stain, M. antarcticus behaves gram-positive, i.e. it is stained blue by the dyes used. This is caused by a thick layer of murein in the cell wall . It has no flagella for active movement and cannot form persistent forms such as endospores . The cells grow into yellow colonies on solid culture media . These look slimy, but have a clear limit.

Growth and metabolism

Micrococcus antarcticus is strictly aerobic , it needs oxygen to grow. It behaves positively in the catalase and oxidase test . The optimal temperatures for cultivation are in the range of 15 to 17 ° C, growth also takes place at 0 ° C, it belongs to the psychrophilic ("cold-loving") organisms. There is no increase above 25 ° C. M. antarcticus can be cultivated well on a nutrient medium that contains peptone , yeast extract and glucose . The optimal pH value for growth is the neutral value pH 7.0.

As is common with Micrococcus species, the metabolism of M. antarcticus can be characterized as aerobic : It gains its energy through breathing and uses oxygen as an oxidizing agent . Furthermore, its metabolism can be characterized as chemoorganotrophic and heterotrophic , it is dependent on organic compounds as an energy source and also for the structure of the cells' own substances. As a substrate it can be used in this way, for. B. metabolize carbohydrates , these include fructose , fucose , rhamnose and turanose . No acid is formed, as would be typical for fermentation . He can also use some sugar alcohols , for example glycerine (glycerol), mannitol , xylitol and arabitol (this is derived from the sugar arabinose ). Other organic compounds that he can use as a source of carbon are gluconic acid , L - lactic acid , L - and D - malic acid , succinic acid and various amino acids .

Other biochemical features, such as the existing enzymes, can be used in a "colorful row" to identify M. antarcticus . In addition to the catalase and oxidase tests, which are positive for all Micrococcus species, the following characteristics can be used to distinguish them from the other species: M. antarcticus is able to break down starch through hydrolysis . The Voges-Proskauer reaction and the indole test are positive for him, as is the nitrate reduction . It does not have the enzyme urease to break down urea , nor does it have the enzyme arginine dihydrolase (ADH).

Similar to M. luteus , the bacterium is very sensitive to lysozyme , an antibacterial enzyme. Furthermore, it is inhibited in growth by several antibiotics . These include active ingredients from the group of penicillins ( benzylpenicillin , methicillin ), tetracyclines , macrolides ( erythromycin ), aminoglycosides ( streptomycin , neomycin ), gyrase inhibitors ( novobiocin ), polymyxins and chloramphenicol .

Chemotaxonomic Features

The Gram-positive bacteria are assigned to the two departments Firmicutes and Actinobacteria , while the former are characterized by a low GC content (the proportion of the nucleobases guanine and cytosine ) in the bacterial DNA , while this is high for the Actinobacteria. Micrococcus antarcticus belongs to this phylum and has a GC content of 66.4 mol percent. This is slightly less than that of the related species M. luteus (about 73 mol percent) and M. lylae (about 69 mol percent). The genome has not yet been fully sequenced (as of 2014) . However, the nucleotides of the 16S rRNA, a typical representative of ribosomal RNA for prokaryotes , were determined for phylogenetic studies .

The cell wall of M. antarcticus consists of the peptidoglycan typical of gram-positive bacteria . In the peptides it contains , L - lysine is the diagnostically important amino acid. The polysaccharide part contains mannosamine as an amino sugar . The branched fatty acids typical of Micrococcus species as a component of the lipids of the cell membrane can also be found in M. antarcticus : above all, anteiso -C 15: 0 ( anteiso- pentadecanoic acid) and iso -C 15: 0 ( iso- pentadecanoic acid) are acceptable 50% or 20% included. In addition to being branched in the carbon chain by a methyl group (-CH 3 ), these fatty acids also have the special feature that they belong to the odd-numbered fatty acids with a total of 15 carbon atoms . The main menaquinones are of the MK-8 and MK-8 (H 2 ) types .

Pathogenicity

Micrococcus antarcticus is not pathogenic, it is assigned to risk group 1 by the Biological Agents Ordinance in conjunction with the TRBA ( Technical Rules for Biological Agents) 466 .

Occurrence and meaning

The Great Wall Station , where Micrococcus antarcticus was found

The bacterial strain T2 T was 2,000 at the Chinese Great Wall Station ( Great Wall station ) isolated. This is the People's Republic of China's first research station in the Antarctic . Closer investigations led to the result that the strain represents a newly discovered species - Micrococcus antarcticus . The first description was made by the Chinese scientist Hongcan Liu u. a. World icon

It has been known since 1887 that very cold locations are also colonized by bacteria, whereby the representatives found since then belong to very different departments . It is characterized by the fact that they can grow at temperatures around 0 ° C. It is assumed that microorganisms that were located in completely different habitats have adapted to the cold conditions in the course of evolution ; they are referred to as cold-adapted. Adaptation to the cold has an impact on the enzymes present in these organisms, and also on the components from which the cells are built so that metabolism and cell division can still take place at temperatures around the freezing point of water .

In M. antarcticus , for example, this concerns the fatty acids in the membrane lipids . As has already been established with other psychrophilic or psychrotolerant bacteria, these contain unsaturated and / or predominantly branched-chain fatty acids. In a Pseudomonas species that was found in the Antarctic soil, the content of anteiso -C 15: 0 ( anteiso- pentadecanoic acid) is more than 90%. This fatty acid is also predominant in M. antarcticus , along with iso- pentadecanoic acid. In order for the cell membrane to fulfill its functions, its fluidity is important. Whether a biomembrane is still fluid at a certain temperature depends essentially on the fatty acids contained in the lipids. Put simply, fatty acids with a lower melting point are advantageous because they are still liquid at low temperatures, while fatty acids with a higher melting point are already solid. If the melting points of the branched pentadecanoic acids are compared with that of the straight-chain pentadecanoic acid , this effect is of particular importance in the case of the anteiso - isomer . The consideration of the lipids present in the membrane is more precise; B. to phosphatidylcholine (diacylphosphatidylcholine). The temperature of the phase transition is significantly lower for the phosphatidylcholines with branched fatty acids (see table), the cell membrane is therefore still fluid even at 0 ° C.

Temperatures of the phase transition of the diacylphosphatidylcholines and melting points of the fatty acids
Fatty acid abbreviations Melting point of
the fatty acid in ° C		 Temperature of the phase transition of
the diacylphosphatidylcholine in ° C		 Structural formula
C 15: 0 52.5 34.2
Pentadecanoic acid. Svg
iso -C 15: 0 51.7 6.5
13-methyltetradecanoic acid. Svg
anteiso -C 15: 0 23.0 -16.7
12-methyltetradecanoic acid, svg

An enzyme from M. antarcticus is also being investigated under the aspect of cold adaptation. This is β-glucosidase (beta-glucosidase, EC  3.2.1.21 ), a cellulase that is involved in the breakdown of cellulose . The purpose of the study is to understand why this enzyme still shows substrate degradation activity at low temperatures . Such enzymes are of interest for biotechnology because they can be used to carry out reactions at low temperatures. First, the gene encoding this protein was sequenced in the genome of M. antarcticus . The bglU gene contains an open reading frame (orf) with a size of 1419 base pairs (bp) and was amplified by cloning . The associated recombinant protein BglU - the cold-adapted β-glucosidase - consists of 472 amino acids with a molecular mass of 48 kDa . In comparison to the “ mesophilic ” (active in the medium temperature range) GH1 β-glucosidase, a lower arginine content is characteristic here. The ratio of arginine to the sum of arginine and lysine is also smaller. BglU shows maximum activity at 25 ° C, but is thermally labile . Even at 30 ° C, half of the protein molecules are no longer active after 30 minutes.

Systematics

→ See also: Taxonomy of the Micrococcaceae family

Micrococcus antarcticus is one of nine species (as of 2014) of the genus Micrococcus , whose systematics is based on the research results of Stackebrandt et al. from 1995 has changed a lot. When assigning a newly discovered bacterial strain to a taxon , in addition to the chemotaxonomic characteristics, the biochemical or metabolic-physiological properties of the organism are examined and compared with known organisms. Since the end of the 20th century, molecular biological methods have increasingly been used to elucidate the tribal history - and the relationships between the organisms . For example, DNA sequences are compared using DNA-DNA hybridization and the 16S rRNA is also examined in prokaryotes.

The comparison of the nucleotide sequence of the 16S rRNA shows a great agreement with the Micrococcus species M. luteus and M. lylae known at the time of the investigation , with M. luteus being more closely related with an agreement of 94.4%. In comparison with M. luteus, the DNA-DNA hybridization shows an agreement of 34.4%, with M. lylae it is 28.8%. This is significantly less than 70.0%, which is considered a criterion for a new species. After the location in the Antarctic, the discoverers suggested the name Micrococcus antarcticus , which is recognized according to the rules for the systematics of bacteria . The name Micrococcus psychrophilum is also used. So far, five bacterial strains have been deposited in various collections of microorganisms .

Individual evidence

  1. ^ Hans G. Schlegel, Christiane Zaborosch: General microbiology . 7th edition. Thieme Verlag, Stuttgart / New York 1992, ISBN 3-13-444607-3 , p. 25.99 .
  2. ↑ a b c d e f g h i j H. Liu, Y. Xu, Y. Ma, P. Zhou: Characterization of Micrococcus antarcticus sp. nov., a psychrophilic bacterium from Antarctica. In: International journal of systematic and evolutionary microbiology. Volume 50, Number 2, March 2000, pp. 715-719, ISSN  1466-5026 . PMID 10758880 .
  3. ↑ a b Michael T. Madigan, John M. Martinko, Jack Parker: Brock Mikrobiologie. German translation edited by Werner Goebel, 1st edition. Spektrum Akademischer Verlag GmbH, Heidelberg / Berlin 2000, ISBN 978-3-8274-0566-1 , p. 558.
  4. ↑ a b c E. Stackebrandt, C. Koch, O. Gvozdiak, P. Schumann: Taxonomic dissection of the genus Micrococcus: Kocuria gen. Nov., Nesterenkonia gen. Nov., Kytococcus gen. Nov., Dermacoccus gen. Nov. , and Micrococcus Cohn 1872 gen. emend. In: International journal of systematic bacteriology. Volume 45, Number 4, October 1995, pp. 682-692, ISSN  0020-7713 . PMID 7547287 .
  5. ↑ Micrococcus luteus. In: National Center for Biotechnology Information (NCBI) Genome website . Retrieved January 5, 2014 .
  6. ↑ Micrococcus antarcticus strain T2 16S ribosomal RNA, partial sequence. In: Nucleotide website of Micrococcus antarcticus of the National Center for Biotechnology Information (NCBI) . Retrieved January 5, 2014 .
  7. ↑ a b c d Toshi Kaneda: Iso- and anteiso-fatty acids in bacteria: biosynthesis, function, and taxonomic significance. In: Microbiological reviews. Volume 55, Number 2, June 1991, pp. 288-302, ISSN  0146-0749 . PMID 1886522 . PMC 372815 (free full text). (Review).
  8. ↑ TRBA (Technical Rules for Biological Agents) 466: Classification of prokaryotes (Bacteria and Archaea) into risk groups. In: Website of the Federal Institute for Occupational Safety and Health (BAuA). April 25, 2012, p. 137 , accessed November 17, 2013 .
  9. ^ Chinese Antarctic Great Wall Station. In: Official website of the Chinese Arctic and Antarctic Administration . Retrieved January 5, 2014 .
  10. ↑ Anne-Monique Gounot: Bacterial life at low temperature: physiological aspects and biotechnological implications. In: The Journal of applied bacteriology. Volume 71, Number 5, November 1991, pp. 386-397, ISSN  0021-8847 . doi : 10.1111 / j.1365-2672.1991.tb03806.x . PMID 1761432 . (Review).
  11. ↑ HX Fan, LL Miao u. a .: Gene cloning and characterization of a cold-adapted β-glucosidase belonging to glycosyl hydrolase family 1 from a psychrotolerant bacterium Micrococcus antarcticus. In: Enzyme and microbial technology. Volume 49, Number 1, June 2011, pp. 94-99, ISSN  1879-0909 . doi : 10.1016 / j.enzmictec.2011.03.001 . PMID 22112277 .
  12. ↑ a b Jean Euzéby, Aidan C. Part: Genus Micrococcus. In: List of Prokaryotic names with Standing in Nomenclature ( LPSN ). Retrieved January 5, 2014 .
  13. ↑ Taxonomy Browser Micrococcus antarcticus. In: National Center for Biotechnology Information (NCBI) website . Retrieved January 6, 2014 .
  14. ↑ Strain Passport Micrococcus antarcticus. In: StrainInfo website (information collected about bacterial strains in over 60 biological resource centers (BRCs)). Retrieved January 6, 2014 .