Abstract
Many studies have shown that the space environment plays a pivotal role in changing the characteristics of conditional pathogens, especially their pathogenicity and virulence. However, Stenotrophomonas maltophilia, a type of conditional pathogen that has shown to a gradual increase in clinical morbidity in recent years, has rarely been reported for its impact in space. In this study, S. maltophilia was exposed to a simulated microgravity (SMG) environment in high-aspect ratio rotating-wall vessel bioreactors for 14days, while the control group was exposed to the same bioreactors in a normal gravity (NG) environment. Then, combined phenotypic, genomic, transcriptomic, and proteomic analyses were conducted to compare the influence of the SMG and NG on S. maltophilia. The results showed that S. maltophilia in simulated microgravity displayed an increased growth rate, enhanced biofilm formation ability, increased swimming motility, and metabolic alterations compared with those of S. maltophilia in normal gravity and the original strain of S. maltophilia. Clusters of Orthologous Groups (COG) annotation analysis indicated that the increased growth rate might be related to the upregulation of differentially expressed genes (DEGs) involved in energy metabolism and conversion, secondary metabolite biosynthesis, transport and catabolism, intracellular trafficking, secretion, and vesicular transport. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses showed that the increased motility might be associated the upregulation of differentially expressed proteins (DEPs) involved in locomotion, localization, biological adhesion, and binding, in accordance with the upregulated DEGs in cell motility according to COG classification, including pilP, pilM, flgE, flgG, and ronN. Additionally, the increased biofilm formation ability might be associated with the upregulation of DEPs involved in biofilm formation, the bacterial secretion system, biological adhesion, and cell adhesion, which were shown to be regulated by the differentially expressed genes (chpB, chpC, rpoN, pilA, pilG, pilH, and pilJ) through the integration of transcriptomic and proteomic analyses. These results suggested that simulated microgravity might increase the level of corresponding functional proteins by upregulating related genes to alter physiological characteristics and modulate growth rate, motility, biofilm formation, and metabolism. In conclusion, this study is the first general analysis of the phenotypic, genomic, transcriptomic, and proteomic changes in S. maltophilia under simulated microgravity and provides some suggestions for future studies of space microbiology.
Highlights
In recent decades, with the development of medicine and space technology, microbial space safety has become one of the hot spots in modern medical research
Under 20,000x scanning electron microscopy (SEM), it was found that S. maltophilia (SMO) was full and smooth, but there were unequal mucus-like substances in S. maltophilia in normal gravity (SMN) and Stenotrophomonas maltophilia in simulated microgravity (SMS), and SMS had more mucus-like substances than SMN (Figure 2)
Monitoring microorganisms in space stations plays an important role in monitoring the safety of spacecraft and the health of astronauts
Summary
With the development of medicine and space technology, microbial space safety has become one of the hot spots in modern medical research. The space environment involves microgravity, high pressure, low temperature, cosmic radiation, and malnourished environments (Horneck et al, 2010). Studies have showed that the space environment has some impacts on the immune system and motor system of humans, as well as on microorganisms in astronauts, such as growth rate, drug susceptibility, carbon source utilization and chemical sensitivity, biofilm formation ability, and motility (Taylor, 2015; Nadeau et al, 2016; Vaishampayan and Grohmann, 2019; Zhang et al, 2019). The impact of the space environment on microbes varies on different bacteria. The spaceship provides insulation from cosmic radiation and extreme temperature to some extent. Microgravity is a key influencing factor on astronauts and microbes
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