Toxin-Antitoxin Systems Alter Adaptation of Mycobacterium smegmatis to Environmental Stress.

Toxin-antitoxin (TA) systems are ubiquitous genetic elements in prokaryotes, but their biological importance is poorly understood. Mycobacterium smegmatis contains eight putative TA systems. Previously, seven TAs have been studied, with five of them being verified as functional. Here, we show that Ms0251-0252 is a novel TA system in that expression of the toxin Ms0251 leads to growth inhibition that can be rescued by the antitoxin Ms0252. To investigate the functional roles of TA systems in M. smegmatis, we deleted the eight putative TA loci and assayed the mutants for resistance to various stresses. Deletion of all eight TA loci resulted in decreased survival under starvation conditions and altered fitness when exposed to environmental stresses. Furthermore, we showed that deletion of the eight TA loci decreased resistance to phage infection in Sauton medium compared with the results using 7H10 medium, suggesting that TA systems might have different contributions depending on the nutrient environment. Furthermore, we found that MazEF specifically played a dominant role in resistance to phage infection. Finally, transcriptome analysis revealed that MazEF overexpression led to differential expression of multiple genes, including those related to iron acquisition. Altogether, we demonstrate that TA systems coordinately function to allow M. smegmatis to adapt to changing environmental conditions. IMPORTANCE Toxin-antitoxin (TA) systems are mechanisms for rapid adaptation of bacteria to environmental changes. Mycobacterium smegmatis, a model bacterium for studying Mycobacterium tuberculosis, encodes eight putative TA systems. Here, we constructed an M. smegmatis mutant with deletions of all eight TA-encoding genes and evaluated the resistance of these mutants to environmental stresses. Our results showed that different TA systems have overlapping and, in some cases, opposing functions in adaptation to various stresses. We suggest that complementary TA modules may function together to regulate the bacterial stress response, enabling adaptation to changing environments. Together, this study provides key insights into the roles of TA systems in resistance to various environmental stresses, drug tolerance, and defense against phage infection.

Occurrence, function and potential medicinal applications of the phytohormone abscisic acid in animals and humans.

Abscisic acid (ABA) is an important phytohormone that regulates plant growth, development, dormancy and stress responses. Recently, it was discovered that ABA is produced by a wide range of animals including sponges (Axinella polypoides), hydroids (Eudendrium racemosum), human parasites (Toxoplasma gondii), and by various mammalian tissues and cells (leukocytes, pancreatic cells, and mesenchymal stem cells). ABA is a universal signaling molecule that stimulates diverse functions in animals through a signaling pathway that is remarkably similar to that used by plants; this pathway involves the sequential binding of ABA to a membrane receptor and the activation of ADP-ribose cyclase, which results in the overproduction of the intracellular cyclic ADP-ribose and an increase in intracellular Ca²âº concentrations. ABA stimulates the stress response (heat and light) in animal cells, immune responses in leukocytes, insulin release from pancreatic ß cells, and the expansion of mesenchymal and colon stem cells. ABA also inhibits the growth and induces the differentiation of cancer cells. Unlike some drugs that act as cell killers, ABA, when functioning as a growth regulator, does not have significant toxic side effects on animal cells. Research indicated that ABA is an endogenous immune regulator in animals and has potential medicinal applications for several human diseases. This article summarizes recent advances involving the discovery, signaling pathways and functions of ABA in animals.

Cloning, microbial expression and structure-activity relationship of polyphenol oxidases from Camellia sinensis.

Polyphenol oxidase (PPO) can be used for organic synthesis and degradation of wastes and dyes in industries. Lack of enzyme sources is a major barrier for its application. A PPO gene, with a full length of 1.8kb without introns, was cloned by PCR from genomic DNA of five common cultivars of Camellia sinensis. They had a 98.2-99.9% degree of identity in nucleotides and 94.7-96.1% in amino acids and encoded a polypeptide of 599 amino acids with a signal peptide targeting the chloroplast and three Cu-binding domains. The mature PPO showed high expression and enzyme activity after refolding the inclusion bodies in Escherichia coli BL21 (DE3) using pET30c expression vector, but low expression in Pichia pastoris GS115 using both the secretory and non-secretory vectors pPICZalphaA and pPICZA. The expression of PPO mutants demonstrated that the signal sequences prevented recombinant gene expression in E. coli. PPO activity was not affected by the C-terminus and was slightly inhibited by the CuC domain. Other domains were important for its activity. A 3.1-fold increase in PPO activity over non-recombinant controls was obtained by expressing the PPO fragment without signal sequences and the CuC domain in E. coli BL21 (DE3) using the pET30c vector.

[Effect of Panax notoginseng saponins on human kidney fibroblast].

OBJECTIVE: To study the effect of Panax notoginseng saponins (PNS) on cell proliferation, type I collagen secretion and integrin beta 1 expression in human kidney fibroblast (KFB). METHODS: KFB were cultured and stimulated by PNS in vitro. The cell proliferation, type I collagen secretion and integrin beta 1 expression in KFB were measured by methyl thiazolyl tetrazolium (MTT), enzyme-linked immunoabsorbent assay (ELISA) and flowcytometry respectively. RESULTS: Within its optimal concentration range and effective time range, PNS could obviously inhibit the proliferation, type I collagen secretion and integrin beta 1 expression (all P < 0.05) in human KFB. CONCLUSION: PNS would possibly be an effective drug for renal interstitial fibrosis prevention and treatment.