Phycobilisome breakdown effector NblD is required to maintain the cellular amino acid composition during nitrogen starvation

Nitrogen starvation induces a coordinated nitrogen-saving program in cyanobacteria. NblD is the 66-amino-acid effector of nitrogen-limitation-induced phycobilisome breakdown, which is believed to replenish the cellular amino acid pools. To address the physiological functions of NblD, the concentrations of amino acids, intermediates of the ornithine-ammonia cycle and several organic acids were measured during the response to nitrogen starvation in the cyanobacterium Synechocystis sp. PCC 6803 wild type and in an nblD-deletion strain. A characteristic signature of metabolite pool composition was identified, which shows that NblD-mediated phycobilisome degradation is required to maintain the cellular amino acid and organic acid pools during nitrogen starvation. Specific deviations from the wild type suggest wider-reaching effects that also affect such processes as redox homeostasis via glutathione and tetrapyrrole biosynthesis, both of which are linked to the strongly decreased glutamate pool, carbon fixation because the pool of 3-phosphoglyceric acid, the stable CO2 fixation product of RubisCO, was also decreased, and transcriptional reprogramming via an enhanced concentration of 2-oxoglutarate, the metabolite coregulator of the NtcA transcription factor. The essential role played by NblD in metabolic homeostasis is consistent with the widespread occurrence of NblD throughout the cyanobacterial radiation and the previously observed strong positive selection for the nblD gene under fluctuating nitrogen supply.

Properties of Aged Spores ofBacillus subtilis

ABSTRACTBacillusspores incubated on plates for 2 to 98 days at 37°C had identical Ca-dipicolinic acid contents, exhibited identical viability on rich- or poor-medium plates, germinated identically in liquid with all germinants tested, identically returned to vegetative growth in rich or minimal medium, and exhibited essentially identical resistance to dry heat and similar resistance to UV radiation. However, the oldest spores had a lower core water content and significantly higher wet heat and NaOCl resistance. In addition, 47- and 98-day spores had lost >98% of intact 16S and 23S rRNA and 97 to 99% of almost all mRNAs, although minimal amounts of mononucleotides were generated in 91 days. Levels of 3-phosphoglyceric acid (3PGA) also fell 30 to 60% in the oldest spores, but how the 3PGA was lost is not clear. These results indicate that (i) translation of dormant spore mRNA is not essential for completion of spore germination, nor is protein synthesis from any mRNA; (ii) in sporulation for up to 91 days at 37°C, the RNA broken down generates minimal levels of mononucleotides; and (iii) the lengths of time that spores are incubated in sporulation medium should be considered when determining conditions for spore inactivation by wet heat, in particular, in using spores to test for the efficacy of sterilization regimens.IMPORTANCEWe show that spores incubated at 37°C on sporulation plates for up to 98 days have lost almost all mRNAs and rRNAs, yet the aged spores germinated and outgrew as well as 2-day spores, and all these spores had identical viability. Thus, it is unlikely that spore mRNA, rRNA, or protein synthesis is important in spore germination. Spores incubated for 47 to 98 days also had much higher wet heat resistance than 2-day spores, suggesting that spore “age” should be considered in generating spores for tests of sterilization assurance. These data are the first to show complete survival of hydrated spores for ∼100 days, complementing published data showing dry-spore survival for years.

The E3 ligase VHL controls alveolar macrophage function via metabolic–epigenetic regulation

Metabolic pathways such as glycolysis or oxidative phosphorylation play a key role in regulating macrophage function during inflammation and tissue repair. However, how exactly the VHL–HIF–glycolysis axis is involved in the function of tissue-resident macrophages remains unclear. Here we demonstrate that loss of VHL in myeloid cells resulted in attenuated pulmonary type 2 and fibrotic responses, accompanied by reduced eosinophil infiltration, decreased IL-5 and IL-13 concentrations, and ameliorated fiber deposition upon challenge. VHL deficiency uplifted glycolytic metabolism, decreased respiratory capacity, and reduced osteopontin expression in alveolar macrophages, which impaired the function of type 2 innate lymphoid cells but was significantly reversed by HIF1α inhibition or ablation. The up-regulated glycolysis altered the epigenetic modification of osteopontin gene, with the metabolic intermediate 3-phosphoglyceric acid as a key checkpoint controller. Thus, our results indicate that VHL acts as a crucial regulatory factor in lung inflammation and fibrosis by regulating alveolar macrophages.