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 Marko 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 machine surfaces 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 of 347,854 bp and 124,421 bp lengths, respectively. Of the 3,720 genes predicted, 3,505 were protein-coding genes and 55 were structural-RNAs [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, 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).

Its common red-orange appearance stems from the production of carotenoids via the metabolism of tepernoids and polyketides [7]. 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. 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].

Ecology and Pathogenesis

Genetic evidence of these microorganisms have been found throughout the world. The geothermal areas in which Meiothermus species have been found include: Rockville, Maryland of the United States; Brawnschweig, Germany [1], Island of S. Miguel, Zores [9], Glysir area of Iceland [10], Tengchang hot spring in Yunnan, China [11]; Chandes-Aigues area in Auvergne region of France [12]; and hot spring at Sao Pedro de Sul, Central Portugal [13]. Optimum growth temperature varies from species to species with an average range of 50 to 65°C and an optimum pH of 8.0. None of the species grows at 70°C [1].