Oxidative phosphorylation system and cell culture media

Analysis of key genes for the survival of Pantoea agglomerans under nutritional stress

The absolute amount of nutrients on plant leaves is usually low, and the growth of epiphytic bacteria is typically limited by nutrient content. Thus, is of great significance to study the survival mechanism of epiphytes under nutritional stress for plant disease control. In this paper, Pantoea agglomerans CHTF15 isolated from walnut leaves was used to detect the key genes for the survival of the bacterium under simulated nutrient stress in artificial medium. Genome sequencing was combined with transposon insertion sequencing (Tn-seq) for the detection technique. A total of 105 essential genes were screened from the whole genome. The genes were mainly related to the nucleotide metabolism, protein metabolism, biological oxidation and the gene repair of bacteria analyzed by gene ontology (GO) enrichment analysis. Volcano map analysis demonstrated that the functions of the 15 genes with the most significant differences were generally related to the synthesis of amino acids or proteins, the nucleotide metabolism and homologous recombination and repair. Competitive index analysis revealed that the deletion of the genes dksA and epmA regulating protein synthesis, the gene ribB involved in the nucleotide metabolism and the gene xerD involved in recombination repair induced a significant reduction in the survival ability of the corresponding mutants in the 0.10 % YEP medium and the walnut leaf surface. The results act as a foundation for further in-depth research on the infection process and the mechanisms of pathogenic bacteria.

Two independent respiratory chains adapt OXPHOS performance to glycolytic switch

The structural and functional organization of the mitochondrial respiratory chain (MRC) remains intensely debated. Here, we show the co-existence of two separate MRC organizations in human cells and postmitotic tissues, C-MRC and S-MRC, defined by the preferential expression of three COX7A subunit isoforms, COX7A1/2 and SCAFI (COX7A2L). COX7A isoforms promote the functional reorganization of distinct co-existing MRC structures to prevent metabolic exhaustion and MRC deficiency. Notably, prevalence of each MRC organization is reversibly regulated by the activation state of the pyruvate dehydrogenase complex (PDC). Under oxidative conditions, the C-MRC is bioenergetically more efficient, whereas the S-MRC preferentially maintains oxidative phosphorylation (OXPHOS) upon metabolic rewiring toward glycolysis. We show a link between the metabolic signatures converging at the PDC and the structural and functional organization of the MRC, challenging the widespread notion of the MRC as a single functional unit and concluding that its structural heterogeneity warrants optimal adaptation to metabolic function.

Functional characterization of two variants of mitochondrial topoisomerase TOP1MT that impact regulation of the mitochondrial genome

TOP1MT encodes a mitochondrial topoisomerase that is important for mtDNA regulation and is involved in mitochondrial replication, transcription, and translation. Two variants predicted to affect TOP1MT function (V1 - R198C and V2 - V338L) were identified by exome sequencing of a newborn with hypertrophic cardiomyopathy. As no pathogenic TOP1MT variants had been confirmed previously, we characterized these variants for their ability to rescue several TOP1MT functions in KO cells. Consistent with these TOP1MT variants contributing to the patient phenotype, our comprehensive characterization suggests that both variants had impaired activity. Critically, we determined neither variant was able to restore steady state levels of mitochondrial-encoded proteins nor to rescue oxidative phosphorylation when re-expressed in TOP1MT KO cells. However, we found the two variants behaved differently in some respects; while the V1 variant was more efficient in restoring transcript levels, the V2 variant showed better rescue of mtDNA copy number and replication. These findings suggest that the different TOP1MT variants affect distinct TOP1MT functions. Altogether, these findings begin to provide insight into the many roles that TOP1MT plays in the maintenance and expression of the mitochondrial genome and how impairments in this important protein may lead to human pathology.

BrainPhys Neuronal Media Support Physiological Function of Mitochondria in Mouse Primary Neuronal Cultures

In vitro neuronal cultures are extensively used in the field of neurosciences as they represent an accessible experimental tool for neuronal genetic manipulation, time-lapse imaging, and drug screening. Optimizing the cultivation of rodent primary neuronal cultures led to the development of defined media that support the growth and maintenance of different neuronal types. Recently, a new neuronal medium, BrainPhys (BP), was formulated envisioning the mimicry of brain physiological conditions and suitability for cultured human iPSC-derived neurons and rat primary neurons. However, its advantages in mouse primary neuronal cultures and its effects in neuronal bioenergetics are yet to be demonstrated. In this study, we validated the beneficial use of BP in mouse primary neuronal cultures based on the observation that neuronal cultures in BP media showed enhanced ATP levels, which increased throughout neuronal maturation, a finding that correlates with higher mitochondrial activity and ATP production at later maturation stages, as well as an increased glycolysis response on mitochondrial inhibition and increased mitochondrial fuel flexibility. Taken together, our data demonstrate that BP medium promotes mitochondrial activity along with neuronal maturation of in vitro cultures.