Listeria monocytogenes Relies on the Heme-Regulated Transporter hrtAB to Resist Heme Toxicity and Uses Heme as a Signal to Induce Transcription of lmo1634, Encoding Listeria Adhesion Protein

Abstract

For pathogenic bacteria, host-derived heme represents an important metabolic cofactor and a source for iron. However, high levels of heme are toxic to bacteria. We have previously shown that excess heme has a growth-inhibitory effect on the Gram-positive foodborne pathogen Listeria monocytogenes, and we have learned that the LhrC1-5 family of small RNAs, together with the two-component system (TCS) LisRK, play a role in the adaptation of L. monocytogenes to heme stress conditions. However, a broader knowledge on how this pathogen responds to heme toxicity is still lacking. Here, we analyzed the global transcriptomic response of L. monocytogenes to heme stress. We found that the response of L. monocytogenes to excess heme is multifaceted, involving various strategies acting to minimize the toxic effects of heme. For example, heme exposure triggers the SOS response that deals with DNA damage. In parallel, L. monocytogenes shuts down the transcription of genes involved in heme/iron uptake and utilization. Furthermore, heme stress resulted in a massive increase in the transcription of a putative heme detoxification system, hrtAB, which is highly conserved in Gram-positive bacteria. As expected, we found that the TCS HssRS is required for heme-mediated induction of hrtAB and that a functional heme efflux system is essential for L. monocytogenes to resist heme toxicity. Curiously, the most highly up-regulated gene upon heme stress was lmo1634, encoding the Listeria adhesion protein, LAP, which acts to promote the translocation of L. monocytogenes across the intestinal barrier. Additionally, LAP is predicted to act as a bifunctional acetaldehyde-CoA/alcohol dehydrogenase. Surprisingly, a mutant lacking lmo1634 grows well under heme stress conditions, showing that LAP is not required for L. monocytogenes to resist heme toxicity. Likewise, a functional ResDE TCS, which contributes to heme-mediated expression of lmo1634, is not required for the adaptation of L. monocytogenes to heme stress conditions. Collectively, this study provides novel insights into the strategies employed by L. monocytogenes to resist heme toxicity. Our findings indicate that L. monocytogenes is using heme as a host-derived signaling molecule to control the expression of its virulence genes, as exemplified by lmo1634.

Transcriptome Sequencing of Listeria monocytogenes Reveals Major Gene Expression Changes in Response to Lactic Acid Stress Exposure but a Less Pronounced Response to Oxidative Stress

“…LAP is a bifunctional, highly conserved alcohol-acetaldehyde dehydrogenase which is essential in promoting the systemic spread of L. monocytogenes during infection (Pandiripally et al, 1999;Drolia et al, 2018). Previous research has demonstrated lap upregulation during nutrient starvation and low glucose (Jaradat and Bhunia, 2002), heme stress (Dos Santos et al, 2018), and oxygen limited environments (Burkholder et al, 2009). In our data, lap was significantly downregulated in both 6179 and R479a with log2fold changes of -5.10 and -2.99, respectively.…”

Heme-induced genes facilitate endosymbiont (Sodalis glossinidius) colonization of the tsetse fly (Glossina morsitans) midgut

“…A large percentage of these heme-induced genes mapped to orthologues in the ‘transcription’ COG category, suggesting complex transcriptional networks aid in adaptation to this environment by fine tuning gene expression including significant alteration of expression of transcriptional regulators in Sgm . Other bacterial transcriptomes show similar patterns of inducing transcription-related functions in response to blood or heme [15–17]. Importantly, we also observed that a selection of Sgm genes induced in response to high heme culture conditions were similarly induced in Sgm that resided within the gut of replete as opposed to starved tsetse flies.…”

Impact of bacterial microcompartment-dependent ethanolamine and propanediol metabolism on Listeria monocytogenes interactions with Caco-2 cells

“…However, both pdu induced and non-induced control cells contain internalin B, Q8Y7G3 encoded putative membrane bound zinc metalloprotease (Lmo1318) involved in release of Q8Y436 peptide pheromone encoding lipoprotein A, PplA (Lmo2637), that conceivably supports activation of PrfA [43, 44], and Listeria Adhesion Protein (LAP, lmo1634), involved in host cell invasion [45], with the latter protein significantly higher expressed in pdu non-induced cells.…”