The hop-tolerance gene
horA frequently found in beer-spoilage lactic acid bacteria (LAB) was investigated for sequence variability. Although the
horA gene was found to have less sequence variability relative to the LAB hop-tolerance gene
horC, a sequence insertion in
horA in some isolates resulted in early truncation of HorA translation. This truncated HorA was found in LAB both capable and incapable of growth in beer. Protein modeling revealed that the truncated HorA may retain some capacity to bind and sequester hop iso-α-acids but lacks the transport function essential for moving hop compounds out of the cell. Sequence analysis of LAB plasmids that contain
horA revealed a high level of conservation in all of the genes comprising the
horA gene cassette. Assessing whether a LAB isolated in a brewery setting is capable of making a full-length protein with intact hop transport function or a truncated HorA requires redesign of commonly used
horA polymerase chain reaction primers to target detection of
horA both with and without the sequence insertion. Keywords: Gene variance, Hop-tolerance gene,
horA, Lactic acid bacteria,
Lactobacillus,
Pediococcus, Protein modeling
Supplementary Fig. 1 shows predicted three-dimensional full model of HorA monomer bound to ATP and a close view of bound ATP.
