Abstract
The survival of Listeria (L.) monocytogenes in foods and food production environments (FPE) is dependent on several genes that increase tolerance to stressors; this includes competing with intrinsic bacteria. We aimed to uncover genes that are differentially expressed (DE) in L. monocytogenes sequence type (ST) 121 strain 6179 when co-cultured with cheese rind bacteria. L. monocytogenes was cultivated in broth or on plates with either a Psychrobacter or Brevibacterium isolate from cheese rinds. RNA was extracted from co-cultures in broth after two or 12 hours and from plates after 24 and 72 hours. Broth co-cultivations with Brevibacterium or Psychrobacter yielded up to 392 and 601 DE genes, while plate co-cultivations significantly affected the expression of up to 190 and 485 L. monocytogenes genes, respectively. Notably, the transcription of virulence genes encoding the Listeria adhesion protein and Listeriolysin O were induced during plate and broth co-cultivations. The expression of several systems under the control of the global stress gene regulator, σB, increased during co-cultivation. A cobalamin-dependent gene cluster, responsible for the catabolism of ethanolamine and 1,2-propanediol, was upregulated in both broth and plate co-cultures conditions. Finally, a small non-coding (nc)RNA, Rli47, was induced after 72 hours of co-cultivation on plates and accounted for 50-90% of the total reads mapped to L. monocytogenes. A recent study has shown that Rli47 may contribute to L. monocytogenes stress survival by slowing growth during stress conditions through the suppression of branch-chained amino acid biosynthesis. We hypothesize that Rli47 may have an impactful role in the response of L. monocytogenes to co-cultivation by regulating a complex network of metabolic and virulence mechanisms.
Highlights
L. monocytogenes is the causative agent of the highly fatal foodborne illness listeriosis
The genera Brevibacterium and Psychrobacter are found on cheese rinds and as part of the endogenous environmental taxa of cheese production facilities; they may interact with L. monocytogenes ST121 strains in such systems [25,26,27,28,29] and were selected for this study
RNA integrity numbers (RIN) of extracted RNA ranged from 8.4–10, indicating that the extracted RNA was of high quality
Summary
L. monocytogenes is the causative agent of the highly fatal foodborne illness listeriosis. Despite the importance of inter-species competition [14], research analyzing L. monocytogenes gene expression in co-culture with other bacteria is limited and varies in depth and methods [15,16,17,18,19] Some of these studies have examined the gene expression of L. monocytogenes during co-cultivation with other bacteria using quantitative reverse transcriptase PCR and microarrays [15,16,17]. Neither of these methods are capable of detecting novel ncRNAs. Recently, ncRNA-dependent regulation of virulence and stress tolerance responses of L. monocytogenes has emerged as an important topic of investigation [20, 21]. We sought to elucidate the differential gene expression patterns of L. monocytogenes strain 6179 during co-cultivation with common food bacteria through transcriptome sequencing
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