The Effects of Salts and Osmoprotectants on Enzyme Activities of Fructose-1,6-biphosphate Aldolases in a Halotolerant Cyanobacterium, Halothece sp. PCC 7418

Halotolerance, stress mechanisms, and circadian clock of salt-tolerant cyanobacteria

Cyanobacteria harbor a high level of physiological flexibility, which enables them to reside in virtually all available environmental niches, including extreme environments. In this review, we summarize the recent advancements in stress mechanisms of salt-tolerant (a.k.a. halotolerant) cyanobacteria. Omics approaches have been extensively employed in recent years to decipher mechanisms of halotolerance and to understand the relevance of halotolerance-associated gene regulatory networks. The vast knowledge from genome mining disclosed that halotolerant cyanobacteria possess extended gene families and/or clusters, encoding enzymes that synthesize unique osmoprotectants, including glycine betaine (GB), betaine derivatives, and mycosporine-like amino acids (MAAs). Comprehensive transcriptomic analyses were conducted using Halothece sp. PCC7418 (hereafter referred to as Halothece), a cyanobacterium that exhibits remarkable halotolerance. These studies revealed a specific transcriptional response when Halothece was subjected to salt stress, whereas salt and osmotic stresses were found to share a common transcriptomic response. Transcriptome and metabolite analyses of Halothece illustrated a complex dynamic relationship between the biosyntheses of osmoprotectants, as well as corresponding and ancillary pathways. Lastly, novel insights highlight the relationship between the molecular regulation of the circadian rhythm and salt stress tolerance. Since the circadian rhythm of gene expression was distorted under salt stress, halotolerant cyanobacteria may prioritize the adaptation to salt stress by attenuation of circadian rhythmicity. KEY POINTS: • Recent advancements in the understanding of stress mechanisms in halotolerant cyanobacteria are described based on omics analyses. • Transcriptome and metabolite analyses of Halothece illustrated a complex dynamic relationship between the biosyntheses of osmoprotectants, as well as corresponding and ancillary pathways. • Since salt stress affects the molecular regulation among clock-related proteins, salt stress may attenuate circadian rhythmicity.

Comparative transcriptome analysis of lethality in response to RNA interference of the oriental river prawn (Macrobrachium nipponense)

A previous study identified slow-tonic S2 tropomyosin and slow tropomyosin isoform as sex-related genes in Macrobrachium nipponense. Their functions were analyzed using RNA interference. However, more than half of the specimens died approximately 8-12 h after injection of the respective double-stranded RNAs (dsRNAs), and HE staining indicated that the heart and gills were the most likely tissues responsible for the resultant deaths. In the current study, we conducted a comparative transcriptomic study of the gills and hearts of M. nipponense to identify potential target genes associated with acute death after dsRNA injection. A total of 68,772 annotated unigenes were generated. In the heart, differentially expressed genes (DEGs) were mainly enriched in glycolysis/gluconeogenesis and oxidative phosphorylation, while the most relevant pathways in the gills were lysosome, phagosome, and peroxisome. Ten DEGs were screened out and analyzed under lethal hypoxic stress. Among these, fructose 1, 6-biphosphate-aldolase (FBA), glyceraldehyde 3-phosphate dehydrogenase (GDPDH), alcohol dehydrogenase class-3 (ADC3), ATP-synthase subunit 9 (ATPS9), and acid ceramidase-like (ACL) were all differentially expressed under hypoxic conditions. This study shed light on the lethal mechanism caused by interference with tropomyosin genes in M. nipponense, and identifies the related pathways and key genes that could help to improve stress resistance and tolerance in M. nipponense.

Engineering salt tolerance of photosynthetic cyanobacteria for seawater utilization

Photosynthetic cyanobacteria are capable of utilizing sunlight and CO₂ as sole energy and carbon sources, respectively. With genetically modified cyanobacteria being used as a promising chassis to produce various biofuels and chemicals in recent years, future large-scale cultivation of cyanobacteria would have to be performed in seawater, since freshwater supplies of the earth are very limiting. However, high concentration of salt is known to inhibit the growth of cyanobacteria. This review aims at comparing the mechanisms that different cyanobacteria respond to salt stress, and then summarizing various strategies of developing salt-tolerant cyanobacteria for seawater cultivation, including the utilization of halotolerant cyanobacteria and the engineering of salt-tolerant freshwater cyanobacteria. In addition, the challenges and potential strategies related to further improving salt tolerance in cyanobacteria are also discussed.