Air exposure study
Intermittent Air Exposure on Four-Stage and One-Stage Anaerobic Semi- Continuous Mixed-Acid Fermentation Microbial Communities
The goals of this study were to 1) identify the organisms present in the reactor communities and 2) evaluate the effects of fermentation train configuration and air exposure on microbial community structure. Samples of reactor slurry were collected at the end of each fermentation run. Community DNA was extracted from the reactor slurry and submitted to the Research and Testing Laboratory (MBRI, Lubbock, TX) for 16S rRNA pyrotag sequencing. This data set contains partial 454 sequencing runs of 16S rRNA data for each of the time points listed above.
This study evaluated the effect of intermittent air exposure on fermentation performance in anaerobic countercurrent fermentations for the carboxylate platform of the MixAlco Process.  Anaerobic mixed-acid fermentation is the core step of the MixAlco process, which converts lignocellulose into chemicals and fuel. Fermentation performance was compared between the strict fermentation trains, which had minimal oxygen contact, and the relaxed fermentation trains, which were subjected to the maximum oxygen exposure of an industrial-scale fermentation. The filter solids and liquids of the relaxed fermentation trains were exposed to air for 90 min every 56 hr.  The total acid concentrations were not significantly different between the strict four-stage train (4S) and relaxed four-stage train (4R) (23.0, 22.1 g?LLiq-1) nor between the strict one-stage train (1S) and relaxed one-stage train (1R) (17.2, 18.4 g? LLiq-1).  However, the strict trains produced a significantly greater proportion of higher molecular weight acids than the relaxed trains.  Air exposure had no significant affect on the exit yield or the bacterial profiles of the strict and relaxed fermentations.  However, the total biomass conversion was significantly higher for the relaxed trains when compared to the strict trains. The selectivity was significantly higher for the 4S train than the 4R train, but not significantly different for the 1S train when compared to 1R. While the most abundant bacterial genus for all fermentations was Prevotella, a strict anaerobe, this study shows that the mixed-culture community is oxygen tolerant as it maintains fermentation performance during oxygen-induced stress from the environment.