The Utilization of Carbon Sources Mixture (Glucose, Glycerol and Formate) and Generation of Fermentation End-Products by $Escherichia$ $Coli$

Abstract

In this study anaerobic utilization of mixed carbon sources (glucose, glycerol, formate) and generation of fermentation end-products by Escherichia coli at slightly alkaline and slightly acidic pHs was investigated at the first time. It has been shown that E. coli is able to perform co-fermentation of glucose and glycerol in the presence of external formate. The latter was utilized by bacterial cells at first. Acetate is the permanent product (25–50 mM) during both glucose and glycerol utilization. It has been revealed that composition of fermentation end-products depends not only on external pH, but also on co-utilization of substrates.

The role of Escherichia coli FhlA transcriptional activator in generation of proton motive force and FOF1‐ATPase activity at pH 7.5

“…As glycerol fermentation extended reasonably later in wt, the quantitative and qualitative difference between end-products from glucose and glycerol at pH 7.5 reported being apparent. 4 High concentration ethanol (22-80 mM) was observed starting from 2 hr in fhlA mutant (2-240 hr) at pH 7.5 (see Figure 2b), which was directly related to the earlier fermentation of glycerol. 9 These amounts were mentioned in the wt later when the main utilization of glycerol was observed hr; see Figure 2a).…”

“…3.1 | Specific growth rate, substrates utilization, and fermentation end-products generation during fermentation of mixed carbon sources in wt and fhlA mutant strain E. coli bacteria utilize the mixture of different carbon sources in the absence of external electron acceptors, which was shown previously. 4,5,7,8,19 It is important to study the role of proton ATPase on cell specific growth rate (μ), as F O F 1 is one of the main Δp generators and all bacteria require Δp to grow and remain viable under replicating and non-replicating conditions. [34][35][36] To reveal the role of F O F 1 on μ DCCD was applied and it was shown that μ was impaired by DCCD 50% in wt at pH 7.5.…”

“…Carbon Conversion Efficiency (CCE) was determined by the following formula: CCE = C 2 *100%/C 1 , where C 1 is the concentration of carbons in the substrates (mM) during the given period, C 2 is the concentration of carbons in the fermentation end product (mM) during the same period of growth. 4,27 The substrate utilization rate was calculated as difference of decreasing concentration of substrate per hour, and end-product generation rate was determined as difference of increasing concentration of product per hour and expressed in mmol hr −1.4,27…”

“…Specific growth rate (μ) was determined by regular measurement of optical density (OD) until the stationary phase with doubling time as described before. 4,8,27 DCCD with 0.2 mM final concentration was used as indicated.…”

“…Escherichia coli is one of the most well studied microorganisms which can grow and utilize wide range of substrates such as glucose, glycerol both separate and in mixtures. [1][2][3][4] Nowadays, revealing and further application of metabolic processes, bioenergetic characteristics, and activity of key enzymes during fermentation of mixed carbon sources has been considered as one of the ways to prolong and optimize fermentation process. 5 Among fermentation end products different organic acids, bio-hydrogen (bio-H 2 ) and bioethanol are highly valuable and promising alternative fuels.…”