The novel cis-encoded antisense RNA AsrC positively regulates the expression of rpoE-rseABC operon and thus enhances the motility of Salmonella enterica serovar typhi

DegS protease regulates the motility, chemotaxis, and colonization of Vibrio cholerae

In bacteria, DegS protease functions as an activating factor of the σ^E envelope stress response system, which ultimately activates the transcription of stress response genes in the cytoplasm. On the basis of high-throughput RNA sequencing, we have previously found that degS knockout inhibits the expression of flagellum synthesis- and chemotaxis-related genes, thereby indicating that DegS may be involved in the regulation of V. cholerae motility. In this study, we examined the relationships between DegS and motility in V. cholerae. Swimming motility and chemotaxis assays revealed that degS or rpoE deletion promotes a substantial reduction in the motility and chemotaxis of V. cholerae, whereas these activities were restored in ΔdegS::degS and ΔdegSΔrseA strains, indicating that DegS is partially dependent on σ^E to positively regulate V. cholerae activity. Gene-act network analysis revealed that the cAMP-CRP-RpoS signaling pathway, which plays an important role in flagellar synthesis, is significantly inhibited in ΔdegS mutants, whereas in response to the overexpression of cyaA/crp and rpoS in the ΔdegS strain, the motility and chemotaxis of the ΔdegS + cyaA/crp and ΔdegS + rpoS strains were partially restored compared with the ΔdegS strain. We further demonstrated that transcription levels of the flagellar regulatory gene flhF are regulated by DegS via the cAMP-CRP-RpoS signaling pathway. Overexpression of the flhF gene in the ΔdegS strain partially restored motility and chemotaxis. In addition, suckling mouse intestinal colonization experiments indicated that the ΔdegS and ΔrpoE strains were characterized by the poor colonization of mouse intestines, whereas colonization efficacy was restored in the ΔdegSΔrseA, ΔdegS + cyaA/crp, ΔdegS + rpoS, and ΔdegS + flhF strains. Collectively, our findings indicate that DegS regulates the motility and chemotaxis of V. cholerae via the cAMP-CRP-RpoS-FlhF pathway, thereby influencing the colonization of suckling mouse intestines.

Small RNAs beyond Model Organisms: Have We Only Scratched the Surface?

Small RNAs (sRNAs) are essential regulators in the adaptation of bacteria to environmental changes and act by binding targeted mRNAs through base complementarity. Approximately 550 distinct families of sRNAs have been identified since their initial characterization in the 1980s, accelerated by the emergence of RNA-sequencing. Small RNAs are found in a wide range of bacterial phyla, but they are more prominent in highly researched model organisms compared to the rest of the sequenced bacteria. Indeed, Escherichia coli and Salmonella enterica contain the highest number of sRNAs, with 98 and 118, respectively, with Enterobacteriaceae encoding 145 distinct sRNAs, while other bacteria families have only seven sRNAs on average. Although the past years brought major advances in research on sRNAs, we have perhaps only scratched the surface, even more so considering RNA annotations trail behind gene annotations. A distinctive trend can be observed for genes, whereby their number increases with genome size, but this is not observable for RNAs, although they would be expected to follow the same trend. In this perspective, we aimed at establishing a more accurate representation of the occurrence of sRNAs in bacteria, emphasizing the potential for novel sRNA discoveries.

Mutual interplay between ArcA and σE orchestrates envelope stress response in Shewanella oneidensis

To survive and thrive in harsh and ever-changing environments, intricate mechanisms have evolved for bacterial cells to monitor perturbations impacting the integrity of their envelope and to mount an appropriate response to contain or repair the damage. In this study, we report in Shewanella oneidensis a previously undescribed mechanism for the envelope defect resulting from the loss of Arc, a two-component transcriptional regulatory system crucial for respiration. We uncovered σ^E , a master regulator establishing and maintaining the integrity of the cell envelope in γ-proteobacteria, as the determining factor for the cell envelope defect of the arcA mutant. When ArcA is depleted, σ^E activity is compromised by enhanced production of anti-σ^E protein RseA. Surprisingly, S. oneidensis σ^E is not essential for viability, but becomes so in the absence of ArcA. Furthermore, we demonstrated that there is an interplay between these two regulators as arcA expression is affected by availability of σ^E . Overall, our results underscore functional interplay of regulatory systems for envelope stress response: although each of the systems may respond to perturbation of particular components of the envelope, they are functionally intertwined, working together to form an interconnected safety net.

A novel cis antisense RNA AsfD promotes Salmonella enterica serovar Typhi motility and biofilm formation

Bacterial non-coding RNAs (ncRNAs) can participate in multiple biological processes, including motility, biofilm formation, and virulence. Using high-throughput sequencing and transcriptome analysis of Salmonella enterica serovar Typhi (S. Typhi), we identified a novel antisense RNA located at the opposite strand of the flhDC operon. In this study, a northern blot and qRT-PCR were used to confirm the expression of this newfound antisense RNA in S. Typhi. Moreover, 5' RACE and 3' RT-PCR were performed to reveal the molecular characteristics of the antisense RNA, which was 2079 nt - 2179 nt in length, covered the entire flhDC operon sequence, and termed AsfD. The level of AsfD expression was higher during the stationary phase of S. Typhi and activated by the regulators, OmpR and Fis. When AsfD was overexpressed, the level of flagellar gene flhDC transcription increased; moreover, the level of fliA and fljB expression, as well as the motility and biofilm formation of S. Typhi were also enhanced. The results of this study suggest that AsfD is likely to enhance the motility and biofilm formation of S. Typhi by up-regulating flhDC expression.

The world of asRNAs in Gram-negative and Gram-positive bacteria

Bacteria exhibit an amazing diversity of mechanisms controlling gene expression to both maintain essential functions and modulate accessory functions in response to environmental cues. Over the years, it has become clear that bacterial regulation of gene expression is still far from fully understood. This review focuses on antisense RNAs (asRNAs), a class of RNA regulators defined by their location in cis and their perfect complementarity with their targets, as opposed to small RNAs (sRNAs) which act in trans with only short regions of complementarity. For a long time, only few functional asRNAs in bacteria were known and were almost exclusively found on mobile genetic elements (MGEs), thus, their importance among the other regulators was underestimated. However, the extensive application of transcriptomic approaches has revealed the ubiquity of asRNAs in bacteria. This review aims to present the landscape of studied asRNAs in bacteria by comparing 67 characterized asRNAs from both Gram-positive and Gram-negative bacteria. First we describe the inherent ambiguity in the existence of asRNAs in bacteria, second, we highlight their diversity and their involvement in all aspects of bacterial life. Finally we compare their location and potential mode of action toward their target between Gram-negative and Gram-positive bacteria and present tendencies and exceptions that could lead to a better understanding of asRNA functions.

Phenotypic characterization, virulence, and immunogenicity of Pseudomonas plecoglossicida rpoE knock-down strain

Pseudomonas plecoglossicida, a temperature dependent bacterial pathogen in fish, expresses rpoE gene that is sensitive to temperature and probably critical for pathogen virulence and disease development. In this study, the rpoE silence strain rpoE-RNAi-1 was constructed by gene knock-down. The rpoE-RNAi-1 displayed significant changes in biofilm formation, swarming motility, adhesion and virulence. Meanwhile, vaccination of grouper with rpoE-RNAi-1 led to a relative percent survival (RPS) value of 85% after challenged with the wild-type P. plecoglossicida. qRT-PCR assays showed that vaccination with rpoE-RNAi-1 enhanced the expression of immune-related genes, including MHC-I, MHC-II, IgM, and IL-1β, indicating that it was able to induce humoral and cell-mediated immune response in grouper. These results validated the possibility of rpoE as a potential target for constructing P. plecoglossicida live attenuated vaccine.

Relation of the pdxB-usg-truA-dedA Operon and the truA Gene to the Intracellular Survival of Salmonella enterica Serovar Typhimurium

Salmonella is the genus of Gram-negative, facultative intracellular pathogens that have the ability to infect large numbers of animal or human hosts. The S. enterica usg gene is associated with intracellular survival based on ortholog screening and identification. In this study, the λ-Red recombination system was used to construct gene deletion strains and to investigate whether the identified operon was related to intracellular survival. The pdxB-usg-truA-dedA operon enhanced the intracellular survival of S. enterica by resisting the oxidative environment and the usg and truA gene expression was induced by H₂O₂. Moreover, the genes in this operon (except for dedA) contributed to virulence in mice. These findings indicate that the pdxB-usg-truA-dedA operon functions in resistance to oxidative environments during intracellular survival and is required for in vivo S. enterica virulence. This study provides insight toward a better understand of the characteristics of intracellular pathogens and explores the gene modules involved in their intracellular survival.

Identification and Characterization of a Cis Antisense RNA of the rpoH Gene of Salmonella enterica Serovar Typhi

Antisense RNAs from complementary strands of protein coding genes regulate the expression of genes involved in many cellular processes. Using deep sequencing analysis of the Salmonella enterica serovar Typhi (S. Typhi) transcriptome, a novel antisense RNA encoded on the strand complementary to the rpoH gene was revealed. In this study, the molecular features of this antisense RNA were assessed using northern blotting and rapid amplification of cDNA ends. The 3,508 nt sequence of RNA was identified as the antisense RNA of the rpoH gene and was named ArpH. ArpH was found to attenuate the invasion of HeLa cells by S. Typhi by regulating the expression of SPI-1 genes. In an rpoH mutant strain, the invasive capacity of S. Typhi was increased, whereas overexpression of ArpH positively regulates rpoH mRNA levels. Results of this study suggest that the cis-encoded antisense RNA ArpH is likely to affect the invasive capacity of S. Typhi by regulating the expression of rpoH.

A 3' UTR-derived non-coding RNA RibS increases expression of cfa and promotes biofilm formation of Salmonella enterica serovar Typhi

Bacterial non-coding RNAs (ncRNAs) are widely studied and found to play important roles in regulating various cellular processes. Recently, many ncRNAs have been discovered to be transcribed or processed from 3' untranslated regions (3' UTRs). Here we reported a novel 3' UTR-derived ncRNA, RibS, which could influence biofilm formation of Salmonella enterica serovar Typhi (S. Typhi). RibS was confirmed to be a ∼700 nt processed product produced by RNase III-catalyzed cleavage from the 3' UTR of riboflavin synthase subunit alpha mRNA, RibE. Overexpression of RibS increased the expression of the cyclopropane fatty acid synthase gene, cfa, which was located at the antisense strand. Biofilm formation of S. Typhi was enhanced by overexpressing RibS both in the wild type strain and cfa deletion mutant. Deletion of cfa attenuated biofilm formation of S. Typhi, while complementation of cfa partly restored the phenotype. Moreover, overexpressing cfa enhanced the biofilm formation of S. Typhi. In summary, RibS has been identified as a novel ncRNA derived from the 3' UTR of RibE that promotes biofilm formation of S. Typhi, and it appears to do so, at least in part, by increasing the expression of cfa.

The malS-5′UTR regulates hisG, a key gene in the histidine biosynthetic pathway in Salmonella enterica serovar Typhi

Bacterial noncoding RNAs (ncRNA) regulate diverse cellular processes, including virulence and environmental fitness. The malS 5′ untranslated region (named malS-5′UTR) was identified as a regulatory ncRNA that increases the invasive capacity of Salmonella enterica serovar Typhi. An IntaRNA search suggested base pairing between malS-5′UTR and hisG mRNA, a key gene in the histidine biosynthetic pathway. Overexpression of malS-5′UTR markedly reduced bacterial growth in minimal medium without histidine. Overexpression of malS-5′UTR increased mRNA from his operon genes, independently of the bax gene, and decreased HisG protein in Salmonella Typhi. RNA structure analysis showed base pairing of the malS-5′UTR RNA with the hisG mRNA across the ribosome binding site. Thus, we propose that malS-5′UTR inhibited hisG translation, probably by base pairing to the Shine–Dalgarno sequence.

RpoE promotes invasion and intracellular survival by regulating SPI-1 and SPI-2 in Salmonella enterica serovar Typhi

AIM

To demonstrate the role of RpoE during the later stage of hyperosmotic stress in Salmonella.

MATERIALS & METHODS

Expressions of SPI-1 and SPI-2 under hyperosmotic stress for 120 min were investigated by a microarray, and the invasion and intracellular survival of wild-type and ΔrpoE strains were compared. The global differential expression of bacterial proteins between the wild-type and ΔrpoE strains was examined after 120 min of hyperosmotic stress.

RESULTS

SPI-1 and SPI-2 were repressed, and the invasion and intracellular survival were defected in the ΔrpoE strain. Thirteen bacterial-associated proteins and 11 secreted proteins differed significantly between the wild-type and ΔrpoE strains.

CONCLUSION

RpoE may promote invasion and intracellular survival by regulating the expression of SPI-1 and SPI-2.