Extracellular electron transfer in microorganisms has been applied for bioelectrochemical synthesis utilizing microbes to catalyze anodic and/or cathodic biochemical reactions. Anodic reactions (electron transfer from microbe to anode) are used for current production and cathodic reactions (electron transfer from cathode to microbe) have recently been applied for current consumption for valuable biochemical production. The extensively studied exoelectrogenic bacteria Shewanella and Geobacter showed that both directions for electron transfer would be possible. It was proposed that gram-positive bacteria, in the absence of cytochrome C, would accept electrons using a cascade of membrane-bound complexes such as membrane-bound Fe-S proteins, oxidoreductase, and periplasmic enzymes. Modification of the cathode with the addition of positive charged species such as chitosan or with an increase of the interfacial area using a porous three-dimensional scaffold electrode led to increased current consumption. The extracellular electron transfer from the cathode to the microbe could catalyze various bioelectrochemical reductions. Electrofermentation used electrons from the cathode as reducing power to produce more reduced compounds such as alcohols than acids, shifting the metabolic pathway. Electrofuel could be generated through artificial photosynthesis using electrical energy instead of solar energy in the process of carbon fixation.

A strictly anaerobic, Gram-stain-positive, non-spore-forming, rod-shaped bacterial strain, designated BS-1^T, was isolated from an anaerobic digestion reactor during a study of bacteria utilizing galactitol as the carbon source. Its cells were 0.3–0.5 μm × 2–4 μm, and they grew at 35–45 °C and at pH 6.0–8.0. Strain BS-1^Tproduced H₂, CO₂, ethanol, acetic acid, butyric acid and caproic acid as metabolic end products of anaerobic fermentation. Phylogenetic analysis, based on the 16S rRNA gene sequence, showed that strain BS-1^Trepresented a novel bacterial genus within the familyRuminococcaceae,ClostridiumCluster IV. The type strains that were most closely related to strain BS-1^TwereClostridium sporosphaeroidesKCTC 5598^T(94.5 %),Clostridium leptumKCTC 5155^T(94.3 %),Ruminococcus bromiiATCC 27255^T(92.1 %) andEthanoligenens harbinenseYUAN-3^T(91.9 %). Strain BS-1^Thad 17.6 % and 20.9 % DNA–DNA relatedness values withC. sporosphaeroidesDSM 1294^TandC. leptumDSM 753^T, respectively. The major components of the cellular fatty acids were C_16 : 0dimethyl aldehyde (DMA) (22.1 %), C_16 : 0aldehyde (14.1 %) and summed feature 11 (iso-C_17 : 03-OH and/or C_18 : 2DMA; 10.0 %). The genomic DNA G+C content was 50.0 mol%. Phenotypic and phylogenetic characteristics allowed strain BS-1^Tto be clearly distinguished from other taxa of the genusClostridiumCluster IV. On the basis of these data, the isolate is considered to represent a novel genus and novel species withinClostridiumCluster IV, for which the nameCaproiciproducens galactitolivoransgen. nov., sp. nov. is proposed. The type species is BS-1^T( = JCM 30532^Tand KCCM 43048^T).

In this paper, the different applications of butyric acid and its current and future production status are highlighted, with a particular emphasis on the biofuels industry. As such, this paper discusses different issues regarding butyric acid fermentations and provides suggestions for future improvements and their approaches.