Osmotic adjustment of marine protozoan thraustochytrids and demand for Na +

Thraustochytrids are lower fungi that grow in large amounts of Na +. Na + is involved in cell osmotic regulation and cell metabolism. Osmotic adjustment is accomplished by absorbing inorganic ions from the environment or changing the concentration of soluble substances in the cytoplasm. Osmotic adjustment through the plasma membrane is very important in the transport process. However, it is not clear how to regulate osmosis through the plasma membrane in marine protists.

Australian scientist Shabala et al. Used non-invasive micro-measurement techniques to reveal the ionic mechanism of osmotic regulation of marine protozoan thraustochytrids. It was found that hypotonicity caused significant outflow of Na +, Cl- and K + of Thraustochytrium, and osmotic adjustment was completed within 30 min of the initial stress. For this bacterium, Na + is the main contributor, and more than half of the osmotic adjustment, Cl- is the second contributor. The role of K + in osmotic adjustment is relatively small. The changes in Ca2 + and H + flow rates are mainly due to intracellular signal transduction. The ion flow data was sorted out through the growth experiment. Even when grown in an environment without Na +, as long as the proper osmotic potential is maintained, that is, when the osmotic potential adjusted by mannitol is the same as that of seawater, Thraustochytrium cells can grow normally. . This shows that Na + is not necessary for the growth of Thraustochytrids, because Na + is mainly involved in cell metabolism.

This work provided evidence for how bacteria regulated osmosis, and found that Thraustochytrid cells can grow normally in the absence of Na +, proving that the osmotic / swelling pressure of cells can also be regulated and regulated by other means.