Meiothermus

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Figure 1. Meiothermus silvanus. Image from Mark Kolari at the University of Helsinki [1]

Classification

Domain: Bacteria, Phylum: Deinococcus-Thermus, Class: Deinococci, Order: Thermales, Family: Thermaceae

Species

NCBI: Taxonomy

Meiothermus chiliarophilus

Meiothermus cerbereus

Meiothermus granaticius

Meiothermus rosaceus

Meiothermus ruber

Meiothermus rufus

Meiothermus silvanus

Meiothermus taiwanensis

Meiothermus timidus

Description and Significance

Figure 2. Microbial "slime" found in paper machines. Image from Mark Kolari at the University of Helsinki [2]

Before the recognition of the genus Meiothermus, the species under the genus Thermus were designated as either high or low-temperature species. The proposal of a new genus Meiothermus in 1996 was made to designate the phylogenetic, phenotypic, and chemotaxonomic distinctiveness of the species that have low optimum growth temperatures. Meiothermus indicates an organism living in a "less-hot" place [1]. The cells are 0.5 to 0.8 μm in diameter and cell length is variable - often forming short filaments. The colonies that form vary from red to yellow pigment and are often found in hydrothermal vents.

Meiothermus spp. have the ability to form biofilms and stick to any surface by using specific adhesion organelles [2]. Specifically, M. silvanus and M. ruber have been found to form colored biofilms on machine surfaces and spots in produced paper and board [3] - left unchecked, these biofoulers pose an economic threat to the paper industry [4]. Several techniques have been proposed to minimize biofilm growth on stainless steel and other materials used in the paper industry. One such technique used is the coating of stainless steel with diamond-like carbon or certain fluoropolymers to prevent adhesion and biofilm growth of Meiothermus spp. [2]. Another technique used is the inactivation of microbes by electrochemical oxidation to prevent biofilm formation - this technique inactivates microbes by electrochemically generating chlorine/hypochlorite [5].

Genome Structure

The entire genome of Meiothermus silvanus DSM 9946 has been sequenced and consist of a 3,249,394 bp long circular chromosome and two plasmids, pMESIL01 and pMESIL02, of 347,854 bp and 124,421 bp lengths, respectively. It's 16S rRNA is located on the chromosome at base pairs 7197 to 8677 on the negative strand and is 1481 bp long. Of the 3,720 genes predicted, 3,505 were protein-coding genes and 55 were structural-RNAs. Using the Conserved Domain Database, it was found that conserved domains were present in 2,782 of the 3,505 protein-coding gene sequences. The GC content for its chromosome, pMESIL01 and PMESIL02, are: 62%, 64%, and 66%, respectively. M. silvanus DSM 9946 was sequenced at the US Department of Energy Joint Genome Institute on June 4, 2010. [6]

Cell Structure, Metabolism and Life Cycle

Figure 3. "A: Electron micrograph of Meiothermus ruber forming a short filaments, B: Electron micrograph Meiothermus silvanus forming as individual cells". Image from Dr. Manfred Rohde of the Helmholz for Infection Research, Braunschweig [3]

Meiothermus spp., is a Gram-negative, aerobic microorganism that is variable in length and often forms short filaments. It is primarily an oxygenic chemoorganoheterotroph, but some species grow with nitrate as the terminal electron acceptor. As such, it utilizes such organic substrates such as starch, hexoses, pentoses, disaccharides, amino acids, and organic acids as both a carbon and energy source. The optimum growth conditions varies in a moderate temperature range (50-65°C) and alkaline environments (pH ~8.0).

The ability of thermophilic bacteria much like those from the genus Meiothermus to withstand high temperatures are thought to stem from the possession of special mechanisms for membrane stabilization. Meiothermus spp. most often have a red-orange appearance that stems from the production of carotenoids via the metabolism of tepernoids and polyketides [7]. Carotenoid production may be one of the mechanisms that these bacteria possess, based on the length of carotenoid molecules and its analogue to the fatty acids of the lipid bilayer [8]. In addition, the presence of polar lipids may play a role in this membrane stabilization; these polar lipids are not found in any other known group of bacteria except those of the genera Thermus, Meiothermus, and Deinococcus [9].

Ecology and Pathogenesis

Figure 4. "A and B: Electron micrograph of the crosswise pattern of a biofilm found in a bioreactor tank". Image from Dr. Bengt R. Johansson from the University of Göteborg, Sweden [4]

Genetic evidence of these microorganisms have been found throughout the world. The geothermal areas in which Meiothermus spp. have been found include: Rockville, Maryland of the United States; Brawnschweig, Germany [1], Island of S. Miguel, Zores [10], Glysir area of Iceland [10], Yunnan, China [12]; Chandes-Aigues area in Auvergne region of France [13]; and Sao Pedro de Sul, Central Portugal [14]. Microorganisms of the Meiothermus genus often are a dominant component of biofilm matrices in these dynamic environments. Figure 4 illustrates the filamentous crosswise pattern made by Meiothermus that is the dominant genus in biofilm composition [15]. The optimum growth conditions varies slightly from habitat to habitat with moderate temperatures (ranging from 50 to 65°C) and an alkaline environment (pH ~8.0) - no species grows beyond 70°C [1].