Salinity fluctuation influencing biological adaptation: growth dynamics and Na+ /K+ -ATPase activity in a euryhaline bacterium

Metagenomics analysis reveals effects of salinity fluctuation on diversity and ecological functions of high and low nucleic acid content bacteria

Salinity is a critical environmental factor in marine ecosystems and has complex and wide-ranging biological effects. However, the effects of changing salinity on diversity and ecological functions of high nucleic acid (HNA) and low nucleic acid (LNA) bacteria are not well understood. In this study, we used 16S rRNA sequencing and metagenomic sequencing analysis to reveal the response of HNA and LNA bacterial communities and their ecological functions to salinity, which was decreased from 26 ‰ to 16 ‰. The results showed that salinity changes had significant effects on the community composition of HNA and LNA bacteria. Among LNA bacteria, 14 classes showed a significant correlation between relative abundance and salinity. Salinity changes can lead to the transfer of some bacteria from HNA bacteria to LNA bacteria. In the network topology relationship, the complexity of the network between HNA and LNA bacterial communities gradually decreased with decreased salinity. The abundance of some carbon and nitrogen cycling genes in HNA and LNA bacteria varied with salinity. Overall, this study demonstrates the effects of salinity on diversity and ecological functions and suggests the importance of salinity in regulating HNA and LNA bacterial communities and functions.

Potential Role of the Anammoxosome in the Adaptation of Anammox Bacteria to Salinity Stress

The underlying adaptative mechanisms of anammox bacteria to salt stress are still unclear. The potential role of the anammoxosome in modulating material and energy metabolism in response to salinity stress was investigated in this study. The results showed that anammox bacteria increased membrane fluidity and decreased mechanical properties by shortening the ladderane fatty acid chain length of anammoxosome in response to salinity shock, which led to the breakdown of the proton motive force driving ATP synthesis and retarded energy metabolism activity. Afterward, the fatty acid chain length and membrane properties were recovered to enhance the energy metabolic activity. The relative transmission electron microscopy (TEM) area proportion of anammoxosome decreased from 55.9 to 38.9% under salinity stress. The 3D imaging of the anammox bacteria based on Synchrotron soft X-ray tomography showed that the reduction in the relative volume proportion of the anammoxosome and the concave surfaces was induced by salinity stress, which led to the lower energy expenditure of the material transportation and provided more binding sites for enzymes. Therefore, anammox bacteria can modulate nitrogen and energy metabolism by changing the membrane properties and morphology of the anammoxosome in response to salinity stress. This study broadens the response mechanism of anammox bacteria to salinity stress.

Transcriptome Analysis of Ice Plant Growth-Promoting Endophytic Bacterium Halomonas sp. Strain MC1 to Identify the Genes Involved in Salt Tolerance

Salt stress is an important adverse condition encountered during plant and microbe growth in terrestrial soil ecosystems. Currently, how ice plant (Mesembryanthemum crystallinum) growth-promoting endophytic bacteria (EB) cope with salt stress and regulate growth and the genes responsible for salt tolerance remain unknown. We applied RNA-Seq technology to determine the growth mechanism of the EB Halomonas sp. MC1 strain and the genes involved in salt tolerance. A total of 893 genes were significantly regulated after salt treatment. These genes included 401 upregulated and 492 downregulated genes. Gene Ontology enrichment and Kyoto Encyclopedia of Genes and Genomes analysis revealed that the most enriched genes included those related to the outer membrane-bounded periplasmic space, ATPase activity, catabolic process, and proton transmembrane transport. The quantitative real-time polymerase chain reaction data were similar to those obtained from RNA-Seq. The MC1 strain maintained survival under salt stress by regulating cellular and metabolic processes and pyruvate metabolism pathways such as organic and carboxylic acid catabolic pathways. We highlighted the response mechanism of Halomonas sp. MC1 to fully understand the dynamics of complex salt-microbe interactions.

Combined effects of food resources and exposure to ammonium nitrogen on population growth performance in the bacterivorous ciliate Paramecium caudatum

Ciliated protozoa (ciliates) play vital roles in biological wastewater-treatment processes, however, combined effects of abiotic and biotic factors as well as the importance of species-specificity of bacterial food organisms on population growth dynamics remain poorly understood, which are hampering the management and optimization of biological wastewater treatment processes. This study investigated the effects of food resources and ammonium nitrogen (NH₄⁺) exposure, both independently and in combination, on the population growth of the bacterivorous ciliate Paramecium caudatum. Results showed that, when fed with two different bacterial food organisms, population growth performance of P. caudatum differed significantly and increased with the addition of protozoa pellet medium. When exposed to NH₄⁺ population growth declined and metabolic enzyme activities were altered. The negative effects of NH₄⁺ on population growth could be weakened by supplementing the food resource with protozoa pellet media. In brief, it was confirmed that the existence of interactive effect of food resources and ammonium nitrogen, as well as the importance of species-specificity of bacterial food organisms on the population growth performance of ciliates. These findings might lead to the development of a valuable strategy for improving the performance of biological wastewater-treatment processes.