No abstract

Branched C5 alcohols are promising biofuels with favorable combustion properties. A mevalonate (MVA)-based isoprenoid biosynthetic pathway for C5 alcohols was constructed in Escherichia coli using genes from several organisms, and the pathway was optimized to achieve over 50% theoretical yield. Although the MVA pathway is energetically less efficient than the native methylerythritol 4-phosphate (MEP) pathway, implementing the MVA pathway in bacterial hosts such as E. coli is advantageous due to its lack of endogenous regulation. The MVA and MEP pathways intersect at isopentenyl diphosphate (IPP), the direct precursor to isoprenoid-derived C5 alcohols and initial precursor to longer chain terpenes, which makes independent regulation of the pathways difficult. In pursuit of the complete "decoupling" of the MVA pathway from native cellular regulation, we designed novel IPP-bypass MVA pathways for C5 alcohol production by utilizing promiscuous activities of two enzymes, phosphomevalonate decarboxylase (PMD) and an E. coli-endogenous phosphatase (AphA). These bypass pathways have reduced energetic requirements, are further decoupled from intrinsic regulation, and are free from IPP-related toxicity. In addition to these benefits, we demonstrate that reduced aeration rate has less impact on the bypass pathway than the original MVA pathway. Finally, we showed that performance of the bypass pathway was primarily determined by the activity of PMD. We designed PMD mutants with improved activity and demonstrated titer increases in the mutant strains. These modified pathways would be a good platform for industrial production of isopentenol and related chemicals such as isoprene.

Branched five carbon (C5) alcohols are attractive targets for microbial production due to their desirable fuel properties and importance as platform chemicals. In this study, we engineered a heterologous isoprenoid pathway in E. coli for the high-yield production of 3-methyl-3-buten-1-ol, 3-methyl-2-buten-1-ol, and 3-methyl-1-butanol, three C5 alcohols that serve as potential biofuels. We first constructed a pathway for 3-methyl-3-buten-1-ol, where metabolite profiling identified NudB, a promiscuous phosphatase, as a likely pathway bottleneck. We achieved a 60% increase in the yield of 3-methyl-3-buten-1-ol by engineering the Shine-Dalgarno sequence of nudB, which increased protein levels by 9-fold and reduced isopentenyl diphosphate (IPP) accumulation by 4-fold. To further optimize the pathway, we adjusted mevalonate kinase (MK) expression and investigated MK enzymes from alternative microbes such as Methanosarcina mazei. Next, we expressed a fusion protein of IPP isomerase and the phosphatase (Idi1~NudB) along with a reductase (NemA) to diversify production to 3-methyl-2-buten-1-ol and 3-methyl-1-butanol. Finally, we used an oleyl alcohol overlay to improve alcohol recovery, achieving final titers of 2.23 g/L of 3-methyl-3-buten-1-ol (~70% of pathway-dependent theoretical yield), 150 mg/L of 3-methyl-2-buten-1-ol, and 300 mg/L of 3-methyl-1-butanol.

Our findings of mostly comparable patient and caregiver outcomes in assisted PD and self-care PD suggest that caregiver burden and QoL should not be a barrier to using assisted PD.

The IPP-bypass pathway was optimized to substantially improve isoprenol titer. 2. PMD mutant was introduced for MVAP conversion with high efficiency. 3. Isoprenol titer reached 3.7 g/L in batch cultures at 44% of the theoretical yield. 4. The highest isoprenol titer (10.8 g/L) was achieved in fed-batch fermentations. 5. Use of a solvent overlay improved titer by removing the toxic final product.

Peritoneal dialysis regimes offer flexibility and autonomy under the support of PD teams. Although outcomes for most QOL domains measured were equivalent, PD patients are more satisfied with care but are at risk for emotional distress and provide poor ratings of physical health. Further research is needed to explore the expansion of standards of care to address psychosocial needs in PD populations.

Sociocultural factors rather than comorbid burden may help identify patients at risk for depression. The high rates of anxiety and depression underlie the importance for monitoring and intervention in dialysis care.

Peritoneal dialysis (PD) is advocated as treatment of choice for most end-stage renal disease (ESRD) patients, including elderly and frail patients. It typically requires caregiver involvement to support care at home. The purpose of this study was to examine changes in burden and quality of life (QOL) in caregivers of prevalent PD patients over 12 months. Data were collected in 44 caregivers of PD patients (mean age 38.4 ± 6.3 years; 60% female) in Singapore at baseline and 12 months. Measures included demographics, the Lay Care-Giving for Adults Receiving Dialysis (LC-GAD), Zarit Burden Interview (ZBI), and the World Health Organization Quality of Life instrument (WHOQOL-BREF). Paired t-tests indicate a significant decrease in task-related aspects of caregiving ( p = 0.04), particularly in relation to personal hygiene ( p < 0.01), over time. Cognitive aspects of caregiving remained unchanged. Perceived burden, however, significantly increased ( p < 0.01), with significantly more caregivers reporting moderate to severe caregiver burden at follow-up (28%) relative to baseline (13%; p < 0.01). There was a significant reduction in psychological health (under WHOQOL) ( p = 0.01). Study findings indicate an increase in caregiver burden and a reduction in psychological health despite a reduction in task-related aspects of caregiving, supporting a further exploration of the “wear-and-tear” hypothesis among this population. Intervention strategies are needed.