Chemotaxis in the archaebacterium Methanococcus voltae

Taxis in archaea

Microorganisms can move towards favorable growth conditions as a response to environmental stimuli. This process requires a motility structure and a system to direct the movement. For swimming motility, archaea employ a rotating filament, the archaellum. This archaea-specific structure is functionally equivalent, but structurally different, from the bacterial flagellum. To control the directionality of movement, some archaea make use of the chemotaxis system, which is used for the same purpose by bacteria. Over the past decades, chemotaxis has been studied in detail in several model bacteria. In contrast, archaeal chemotaxis is much less explored and largely restricted to analyses in halophilic archaea. In this review, we summarize the available information on archaeal taxis. We conclude that archaeal chemotaxis proteins function similarly as their bacterial counterparts. However, because the motility structures are fundamentally different, an archaea-specific docking mechanism is required, for which initial experimental data have only recently been obtained.

Taxis toward hydrogen gas by Methanococcus maripaludis

Knowledge of taxis (directed swimming) in the Archaea is currently expanding through identification of novel receptors, effectors, and proteins involved in signal transduction to the flagellar motor. Although the ability for biological cells to sense and swim toward hydrogen gas has been hypothesized for many years, this capacity has yet to be observed and demonstrated. Here we show that the average swimming velocity increases in the direction of a source of hydrogen gas for the methanogen, Methanococcus maripaludis using a capillary assay with anoxic gas-phase control and time-lapse microscopy. The results indicate that a methanogen couples motility to hydrogen concentration sensing and is the first direct observation of hydrogenotaxis in any domain of life. Hydrogenotaxis represents a strategy that would impart a competitive advantage to motile microorganisms that compete for hydrogen gas and would impact the C, S and N cycles.

Isolation and characterization of a copper-resistant methanogen from a copper-mining soil sample

A copper-resistant methanogen for which the CuSO4 MICs were approximately 2- to 36-fold higher than those for other methanogens tested was isolated from a copper-mining area in the upper peninsula of Michigan. The rod-shaped methanogen used H2-CO2 or formate, but not acetate or methanol, as a growth substrate. Standing incubation with H2-CO2 medium resulted in a mat-like surface growth, dependent on the presence of hydrogen. The presence of 1 mM cupric salt resulted in longer filamentous and intertwined cells. Antigenic fingerprinting, 16S rRNA gene analysis, morphology, and substrate use suggest that the new isolate is a novel strain of Methanobacterium bryantii that is able to use formate.