In light of an increasing demand for energy and sustainable development, bioenergy production is a must. A carboxylate platform-based bioprocess now enables the conversion of organic waste into a valuable bioproduct via open culture fermentation due to a complex microbial activity. Caproic acid is one of the promising products that can be further processed into liquid biofuels. In this study we have shown stable, long-term production of n-caproate from acid whey by shaping the reactor microbiome in a UASB bioreactor. The reactor was operated at pH 5.5 with gradually decreasing hydraulic retention time. The results showed acceleration of n-caproate formation and the highest average n-caproate production rate that lasted for 37 days was 134.3 ± 30.9 mmolC L⁻¹ d⁻¹ (0.11 g L⁻¹ h⁻¹) (with a median of 146.1 mmolC L⁻¹ d⁻¹) and specificity between 58 and 83% (with a median of 79%). Microbiological studies showed the prevalence of fermentative microorganisms from the families Coriobacteriaceae, Ruminococcaceae and Prevotellaceae that are the likely agents for lactose and lactate to n-caproate conversion. A flow cytometry based evaluation of the reactor microbiome demonstrated the inherent heterogeneity of microbial subpopulations in terms of microbial activity at different points of fermentation.

Huntington's disease (HD) is a progressive autosomal dominant neurodegenerative disorder caused by the expansion of CAG repeats in the first exon of the huntingtin gene (HTT). The accumulation of polyglutamine-rich huntingtin proteins affects various cellular functions and causes selective degeneration of neurons in the striatum. Therapeutic strategies used to date to silence the expression of mutant HTT include antisense oligonucleotides, RNA interference-based approaches and, recently, genome editing with the CRISPR/Cas9 system. Here, we demonstrate that the CAG repeat tract can be precisely excised from the HTT gene with the use of the paired Cas9 nickase strategy. As a model, we used HD patient-derived fibroblasts with varied numbers of CAG repeats. The repeat excision inactivated the HTT gene and abrogated huntingtin synthesis in a CAG repeat length-independent manner. Because Cas9 nickases are known to be safe and specific, our approach provides an attractive treatment tool for HD that can be extended to other polyQ disorders.