Dynamics of microbial contaminants is driven by selection during ethanol production

Abstract

Brazil is the second largest ethanol producer in the world and largest using sugarcane feedstock. Bacteria contamination is one of the most important issues faced by ethanol producers that seek to increase production efficiency. Each step of production is a selection event due to the environmental and biological changes that occur. Therefore, we evaluated the influence of the selection arising from the ethanol production process on diversity and composition of bacteria. Our objectives were to test two hypotheses, (1) that species richness will decrease during the production process and (2) that lactic acid bacteria will become dominant with the advance of ethanol production. Bacterial community assemblage was accessed using 16S rRNA gene sequencing from 19 sequential samples. Temperature is of great importance in shaping microbial communities. Species richness increased between the decanter and must steps of the process. Low Simpson index values were recorded at the fermentation step, indicating a high dominance of Lactobacillus. Interactions between Lactobacillus and yeast may be impairing the efficiency of industrial ethanol production.

Keywords: Distillery; Ethanolic fermentation; Microbial ecology; Selection; Sugarcane.

Fig. 1

Arrangement of the main ethanol production steps. Red dots show the steps sampled

Fig. 2

Observed richness in each step of ethanol production

Fig. 3

Relative abundance of the main genera found in each step of ethanol production

Fig. 4

Heatmap of the 20 most abundant OTUs found in each step of ethanol production

Fig. 5

Principal coordinates analysis (PCoA) using Bray-Curtis dissimilarity matrix for the samples of ethanol production process