Metabolic flux analysis and the NAD(P)H/NAD(P) + ratios in chemostat cultures of Azotobacter vinelandii

Azotobacter vinelandii is a bacterium that produces alginate and polyhydroxybutyrate (P3HB); however, the role of NAD(P)H/NAD(P) + ratios on the metabolic fluxes through biosynthesis pathways of these biopolymers remains unknown. The aim of this study was to evaluate the NAD(P)H/NAD(P) + ratios and the metabolic fluxes involved in alginate and P3HB biosynthesis, under oxygen-limiting and non-limiting oxygen conditions. The results reveal that changes in the oxygen availability have an important effect on the metabolic fluxes and intracellular NADPH/NADP + ratio, showing that at the lowest OTR (2.4 mmol L −1 h −1), the flux through the tricarboxylic acid (TCA) cycle decreased 27.6-fold, but the flux through the P3HB biosynthesis increased 6.6-fold in contrast to the cultures without oxygen limitation (OTR = 14.6 mmol L −1 h −1). This was consistent with the increase in the level of transcription of phbB and the P3HB biosynthesis. In addition, under conditions without oxygen limitation, there was an increase in the carbon uptake rate (twofold), as well as in the flux through the pentose phosphate (PP) pathway (4.8-fold), compared to the condition of 2.4 mmol L −1 h −1. At the highest OTR condition, a decrease in the NADPH/NADP + ratio of threefold was observed, probably as a response to the high respiration rate induced by the respiratory protection of the nitrogenase under diazotrophic conditions, correlating with a high expression of the uncoupled respiratory chain genes (ndhII and cydA) and induction of the expression of the genes encoding the nitrogenase complex (nifH). We have demonstrated that changes in oxygen availability affect the internal redox state of the cell and carbon metabolic fluxes. This also has a strong impact on the TCA cycle and PP pathway as well as on alginate and P3HB biosynthetic fluxes

Data from: Association between COL11A1 (rs1337185) and ADAMTS5 (rs162509) gene polymorphisms and lumbar spine pathologies in Chinese Han population: an observational study

Objectives: A previous study identified a significant association between several single nucleotide polymorphisms (SNPs) and lumbar disc degeneration (LDD) in Indians. To validate the association between these SNPs and specific lumbar spine pathologies, we performed a case-control study in Chinese Han population. Design: An observational study. Setting: University Hospital in Nanning, China. Participants: This study included 428 LDD patients and 400 normal controls. Outcome measures: LDD Patients were classified into 4 subgroups, including disc herniation only (Subgroup 1), discopathies or/and osteochondrosis associated with disc herniation (Subgroup 2), spinal stenosis or/and spondylolisthesis (Subgroup 3), and degenerative scoliosis (Subgroup 4). This study was conducted by examining 2 aspects: environmental factors and SNP genotyping. The environmental factors were evaluated with a questionnaire survey including questions about BMI, smoking habits, the physical demands of their job and exposure to vibrations. Rs1337185, rs5275, rs5277, rs7575934, rs3213718 and rs162509 were genotyped using a PCR-based Invader assay. Results: The physical workload was significantly higher in patients with lumbar spine pathologies than in the normal controls (P=0.035). The genotype and allele frequencies of rs1337185 and rs162509 were significantly different between the LDD patients and the normal controls. In rs1337185, a significant association was found between the C allele (risk allele) and the presence of disc herniation (OR=1.80; 95%CI= 1.21-2.68; P=0.003, adjusted P=0.012), and the presence of spinal stenosis and spondylolisthesis (OR=1.92; 95%CI=1.29-2.89; P= 0.001, adjusted P=0.004). In rs162509, the G allele represented 1.58-fold increased risk to suffer from disc herniation (OR=1.58; 95%CI=1.20-2.09; P=0.001, adjusted P=0.004). Conclusions: The SNPs rs1337185 in COL11A1 and rs162509 in ADAMTS5 are associated with susceptibility to LDD. The C allele of rs1337185 is risky for patients who are affected by lumbar pathologies such as disc herniation, stenosis and spondylolisthesis. The G allele of rs16250 represents a risk factor for the development of disc herniation

Unusual marine cyanobacteria/haptophyte symbiosis relies on N2 fixation even in N-rich environments

The microbial fixation of N2 is the largest source of biologically available nitrogen (N) to the oceans. However, it is the most energetically expensive N-acquisition process and is believed inhibited when less energetically expensive forms, like dissolved inorganic N (DIN), are available. Curiously, the cosmopolitan N2-fixing UCYN-A/haptophyte symbiosis grows in DIN-replete waters, but the sensitivity of their N2 fixation to DIN is unknown. We used stable isotope incubations, catalyzed reporter deposition fluorescence in-situ hybridization (CARD-FISH), and nanoscale secondary ion mass spectrometry (nanoSIMS), to investigate the N source used by the haptophyte host and sensitivity of UCYN-A N2 fixation in DIN-replete waters. We demonstrate that under our experimental conditions, the haptophyte hosts of two UCYN-A sublineages do not assimilate nitrate (NO3-) and meet little of their N demands via ammonium (NH4+) uptake. Instead the UCYN-A/haptophyte symbiosis relies on UCYN-A N2 fixation to supply large portions of the haptophyte's N requirements, even under DIN-replete conditions. Furthermore, UCYN-A N2 fixation rates, and haptophyte host carbon fixation rates, were at times stimulated by NO3- additions in N-limited waters suggesting a link between the activities of the bulk phytoplankton assemblage and the UCYN-A/haptophyte symbiosis. The results suggest N2 fixation may be an evolutionarily viable strategy for diazotroph-eukaryote symbioses, even in N-rich coastal or high latitude waters