Biology subjects

Slamti, L.

Publications and source records attributed to Slamti, L..

3 recordsLinked to original sources

bioRxiv2022

Quorum sensing peptidic inhibitor rescue host immune system eradication: a novel QS infectivity mechanism

Subverting the host immune system is a major task for any given pathogen to assure its survival and proliferation. For the opportunistic human pathogen Bacillus cereus (Bc), immune evasion enables the establishment of potent infections. In various species of the Bc group, the pleiotropic regulator PlcR and its cognate cell-cell signaling peptide PapR7 regulates virulence genes expression in response to fluctuations in population density, i.e., a quorum-sensing (QS) system. However, how QS exerts its effects during infections, and whether PlcR confers the immune evading ability remain unclear. Herein, we report how interception of the QS communication in Bc obliterates the ability to control the host immune system. Here we designed a peptide-based QS inhibitor that suppresses PlcR-dependent virulence factor expression and attenuates Bc infectivity in mouse models. We demonstrate that the QS peptidic inhibitor blocks host immune system-mediated eradication by reducing the expression of PlcR-regulated major toxins. Our findings provide the first evidence that Bc infectivity is regulated by QS circuit mediated destruction of the host immunity, thus reveal a new strategy to limit Bc virulence and enhance host defense. This peptidic quorum-quenching agent constitutes readily accessible chemical tool for studying how other pathogen QS systems modulate host immunity and forms a basis for development of anti-infective therapeutics.

microbiology↗

bioRxiv2022

A sporulation-independent way of life for Bacillus thuringiensis in the late stages of an infection

The formation of endospores has been considered as the unique mode of survival and transmission of sporulating Firmicutes due to the exceptional resistance and persistence of this bacterial form. However, the persistence of non-sporulated bacteria (Spo-) was reported during infection in Bacillus thuringiensis, an entomopathogenic sporulating Gram-positive bacterium. In this study, we investigated the behavior of a bacterial population in the late stages of an infection as well as the characteristics of the Spo- bacteria in the B. thuringiensis/Galleria mellonella infection model. Using fluorescent reporters coupled to flow cytometry as well as molecular markers, we demonstrated that the Spo- cells constitute about half of the population two weeks post-infection (pi) and that these bacteria present vitality signs. However, a protein synthesis and a growth recovery assay indicated that they are in a metabolically slowed-down state. Interestingly, they were extremely resistant to the cadaver environment which proved deadly for in vitro-grown vegetative cells and, strikingly, did not support spore germination. A transcriptomic analysis of this subpopulation at 7 days pi revealed a signature profile of this state. The expression analysis of individual genes at the cell level suggests that iron homeostasis is important at all stages of the infection, whereas the oxidative stress response seems of particular importance as the survival time increases. Altogether, these data show that non-sporulated bacteria are able to survive for a prolonged period of time and indicate that they engage in a profound adaptation process that leads to their persistence in the host cadaver.

microbiology↗

bioRxiv2022

Expression of the Bacillus thuringiensis vip3A insecticidal toxin gene is activated at the onset of stationary phase by VipR, an autoregulated transcription factor

The Vegetative insecticidal protein Vip3A is produced by some Bacillus thuringiensis strains from the mid-log growth phase to sporulation. Although Vip3A is important for the entomopathogenicity of B. thuringiensis, the vip3A gene regulation is unknown. In the B. thuringiensis kurstaki HD1 strain, vip3A is carried by the pBMB299 plasmid, which is absent in the closely related strain B. thuringiensis kurstaki HD73. Using a transcriptional fusion between the vip3A promoter and lacZ, we observed that the HD73 strain is unable to express vip3A. This result suggests that a specific regulator is required for vip3A expression. Assuming that the regulator gene is located on the same plasmid as vip3A, we transferred the pBMB299 from the HD1 strain to the HD73 strain. We found that Vip3A was produced in the HD73 strain containing pBMB299, suggesting that the regulator gene is located on this plasmid. Using this heterologous host and promoter-lacZ transcription fusions, we confirmed that VipR is essential to activate vip3A expression at the onset of stationary phase. We demonstrated that vipR transcription is positively autoregulated and the determination of the vipR and vip3A promoters pinpointed a putative VipR target upstream from the Sigma A-specific -10 region of these two promoters. Surprisingly, this conserved sequence was also found upstream of cry1I and cry2 genes. Finally, we showed that vip3A and vipR expression is drastically increased in a {Delta}spo0A mutant unable to initiate sporulation. In conclusion, we have characterized a novel regulator involved in the entomopathogenic potency of B. thuringiensis through a sporulation-independent pathway. ImportanceThe insecticidal properties of Bacillus thuringiensis are mainly due to Cry toxins which form a crystalline inclusion during sporulation. However, other proteins participate in the pathogenicity of the bacterium, notably the Vip3A toxins that are produced from vegetative growth to sporulation. The VipR regulator that activates vip3A gene expression at the onset of stationary phase is positively autoregulated and analysis of the promoter region of the vip3A and vipR genes reveals the presence of a highly conserved DNA sequence. This possible VipR target sequence is also found upstream of the cry2A and cry1I genes, suggesting that Cry toxins can be produced before the bacteria enter sporulation. Such a result could allow us to better understand the role of Cry and Vip3A toxins during the B. thuringiensis infectious cycle in insects, in addition to the primary role of the Cry toxins in the toxemia caused by ingestion of crystals.

microbiology↗