Gravitaxis and graviperception in flagellates

Area of Science:

• Cell Biology
• Gravitational Biology
• Microbiology

Background:

• Gravitaxis, or orientation in response to gravity, is crucial for microorganisms.
• Previous theories suggested passive cell alignment, but active mechanisms are increasingly evident.

Purpose of the Study:

• To investigate the physiological mechanisms underlying gravitaxis in flagellates.
• To identify the specific cellular components involved in gravity perception.

Main Methods:

• Utilized slow-rotating centrifuges (0.12 x g) and parabolic rocket flights (TEXUS) during space missions (IML-2).
• Investigated the role of calcium ion channels using inhibitors like gadolinium and ionophore A23187.
• Employed PCR to identify mechanosensitive channel genes in Euglena.
• Visualized intracellular calcium changes using Calcium Crimson fluorophore and laser imaging.

Main Results:

• Gravitaxis threshold determined to be 0.12 x g.
• No adaptation to microgravity observed during spaceflight; gravitaxis lost in a long-term terrestrial system.
• Sedimenting statoliths ruled out; cytoplasmic pressure activating stretch-sensitive calcium channels identified as the mechanism.
• Gadolinium, A23187, and vanadate abolished gravitaxis, confirming calcium's role.
• Mechanosensitive channel gene identified in Euglena.
• Increased intracellular calcium observed during reorientation, confirmed in parabolic flights.

Conclusions:

• Gravitaxis in flagellates is an active physiological process mediated by mechanosensitive calcium channels.
• Cellular pressure on the membrane, leading to calcium influx, triggers reorientation.
• These findings have implications for understanding cellular responses to gravity and potential applications in life support systems.