Microgravity and immune cells.

The microgravity environment experienced during spaceflight severely impaired immune system, making astronauts vulnerable to various diseases that seriously threaten the health of astronauts. Immune cells are exceptionally sensitive to changes in gravity and the microgravity environment can affect multiple aspects of immune cells through different mechanisms. Previous reports have mainly summarized the role of microgravity in the classification of innate and adaptive immune cells, lacking an overall grasp of the laws that microgravity effects on immune cells at different stages of their entire developmental process, such as differentiation, activation, metabolism, as well as function, which are discussed and concluded in this review. The possible molecular mechanisms are also analysed to provide a clear understanding of the specific role of microgravity in the whole development process of immune cells. Furthermore, the existing methods by which to reverse the damage of immune cells caused by microgravity, such as the use of polysaccharides, flavonoids, other natural immune cell activators etc. to target cell proliferation, apoptosis and impaired function are summarized. This review will provide not only new directions and ideas for the study of immune cell function in the microgravity environment, but also an important theoretical basis for the development of immunosuppression prevention and treatment drugs for spaceflight.

Impaired oxidative stress and sulfur assimilation contribute to acid tolerance of Corynebacterium glutamicum.

The industrial organism Corynebacterium glutamicum is often subjected to acid stress during large-scale fermentation for the production of bio-based chemicals. The capacity of the cells to thrive in acidic environments is a prerequisite for achieving high product yields. In this study, we obtained an acid-adapted strain using an adaptive laboratory evolution strategy. Physiological characterizations revealed that the adapted strain achieved improved cell viability after acid-stress challenge, with a higher cytoplasmic pHin level, a lower intracellular reactive oxygen species (ROS), and an enhanced morphological integrity of the cells, when compared to those of the original control strain. Transcriptome analysis indicated that several important cellular processes were altered in the adapted strain, including sulfur metabolism, iron transport, and central metabolic pathways. Further research displayed that KatA and Dps cooperatively mediated intracellular ROS scavenging, which was required for resistance to low-pH stress in C. glutamicum. Furthermore, the repression of sulfur assimilation by the McbR regulator also contributed to the improvement of acid-stress tolerance. Moreover, two copper chaperone genes cg1328 and cg3292 were found to be involved in promoting cell survival under acid-stress conditions. Finally, a new recombinant C. glutamicum strain with enhanced acid tolerance was generated by the combined overexpression of katA, dps, mcbR, and cg1328, showing 18.4 ± 2.5% higher biomass yields than the wild-type strain under acid-stress conditions. These findings will provide new insights into the understanding and genetic improvement of acid tolerance in C. glutamicum.