GSE109442
Membrane potential limits growth and substrate utilization in C. bescii, alleviation dramatically improves productivity
Caldicellulosiruptor bescii is an anaerobic hyper thermophile that can utilize a wide range of substrates. However, inhibitors released from biomass can result in unfavorable growth conditions and limit bioconversion to products. Medium as well as intracellular pH are conditions critical for growth and prone to change in effect of fermentation end or by products such as, CO2, organic acids etc. Growth pH for C. bescii as currently reported is a narrow range of 6.8-7.3. In this study, we examined the physiological and systems level responses of C. bescii to growth at acidic pH. Samples collected from bottles, controlled batch, fed-batch and chemostat systems were subjected to growth, product and integrated omics profiling.  It was discovered that in batch reactors, lowering pH from 7.2 to 6.0 at the mid-log phase, led to a significant increase in growth and product yields. Time course transcriptomics data collected from these batch reactors was analyzed to try and get a better understanding of the underlying mechanisms for improved growth. Overall design: Wild type strain DSM6725 was grown under batch fermentation conditions in two setups namely, control and treated fermenters in triplicates. In the control fermenter setup, cells were grown at pH 7.2 throughout the growth curve monitored whereas, in the treated fermenter setup, cells were grown at pH 7.2 until mid-log phase and pH was then lowered to 6.0 by acid addition. RNA-seq samples were collected at 5, 10, 30, 60 and 90 min time points post-acid addition from both control and treated fermenters.