Transcriptional activity and role of plasmids of Lactobacillus brevis BSO 464 and Pediococcus claussenii ATCC BAA-344T during growth in the presence of hops

Whole-transcriptome analysis was performed on beer-spoilage organisms Lactobacillus brevis BSO 464 (Lb464) and Pediococcus claussenii ATCC BAA-344 (Pc344) when grown in growth-limiting concentrations of hop extract. This was done to delineate the hops-specific component of the total transcriptional response for these bacteria when growing in beer. The transcriptome of highly hop-tolerant isolate Lb464 had fewer genes with differential expression in response to a stronger challenge (i.e., higher bitterness units) of hop extract than did Pc344, highlighting the variable nature of hop-tolerance in beer-spoilage-related lactic acid bacteria. As Lb464 can grow in pressurized/gassed beer and Pc344 cannot, this indicates that the genetic and physiological response to hops alone does not dictate the overall beer-spoilage virulence of an isolate. The general response to hops in both isolates involves pathways of acid tolerance and intracellular pH homeostasis, with glutamate and citrate metabolism, and biogenic amine metabolism as additional major responses to the presence of hop extract by Lb464 and Pc344, respectively. A Pc344 chromosomal ABC transporter (PECL_1630) was more strongly expressed than the plasmid-located, hop-tolerance ABC transporter horA. PECL_1630 is suggested to be involved in import of ATP into the cell, potentially assisting the total bacterial community when facing hop stress. This transporter is found in other beer-related P. claussenii suggesting a putative species-specific beer-spoilage-related