SFTSV nucleoprotein mediates DNA sensor cGAS degradation to suppress cGAS-dependent antiviral responses.

Cyclic GMP-AMP synthase (cGAS) is an important DNA pattern recognition receptor that senses double-stranded DNA derived from invading pathogens or self DNA in cytoplasm, leading to an antiviral interferon response. A tick-borne Bunyavirus, severe fever with thrombocytopenia syndrome virus (SFTSV), is an RNA virus that causes a severe emerging viral hemorrhagic fever in Asia with a high case fatality rate of up to 30%. However, it is unclear whether cGAS interacts with SFTSV infection. In this study, we found that SFTSV infection upregulated cGAS RNA transcription and protein expression, indicating that cGAS is an important innate immune response against SFTSV infection. The mechanism of cGAS recognizing SFTSV is by cGAS interacting with misplaced mitochondrial DNA in the cytoplasm. Depletion of mitochondrial DNA significantly inhibited cGAS activation under SFTSV infection. Strikingly, we found that SFTSV nucleoprotein (N) induced cGAS degradation in a dose-dependent manner. Mechanically, N interacted with the 161-382 domain of cGAS and linked the cGAS to LC3. The cGAS-N-LC3 trimer was targeted to N-induced autophagy, and the cGAS was degraded in autolysosome. Taken together, our study discovered a novel antagonistic mechanism of RNA viruses, SFTSV is able to suppress the cGAS-dependent antiviral innate immune responses through N-hijacking cGAS into N-induced autophagy. Our results indicated that SFTSV N is an important virulence factor of SFTSV in mediating host antiviral immune responses. IMPORTANCE: Severe fever with thrombocytopenia syndrome virus (SFTSV) is a tick-borne RNA virus that is widespread in East and Southeast Asian countries with a high fatality rate of up to 30%. Up to now, many cytoplasmic pattern recognition receptors, such as RIG-I, MDA5, and SAFA, have been reported to recognize SFTSV genomic RNA and trigger interferon-dependent antiviral responses. However, current knowledge is not clear whether SFTSV can be recognized by DNA sensor cyclic GMP-AMP synthase (cGAS). Our study demonstrated that cGAS could recognize SFTSV infection via ectopic mitochondrial DNA, and the activated cGAS-stimulator of interferon genes signaling pathway could significantly inhibit SFTSV replication. Importantly, we further uncovered a novel mechanism of SFTSV to inhibit innate immune responses by the degradation of cGAS. cGAS was degraded in N-induced autophagy. Collectively, this study illustrated a novel virulence factor of SFTSV to suppress innate immune responses through autophagy-dependent cGAS degradation.

Bunyavirus SFTSV NSs utilizes autophagy to escape the antiviral innate immune response.

Severe fever with thrombocytopenia syndrome virus (SFTSV) nonstructural protein (NSs) is an important viral virulence factor that sequesters multiple antiviral proteins into inclusion bodies to escape the antiviral innate immune response. However, the mechanism of the NSs restricting host innate immunity remains largely elusive. Here, we found that the NSs induced complete macroautophagy/autophagy by interacting with the CCD domain of BECN1, thereby promoting the formation of a BECN1-dependent autophagy initiation complex. Importantly, our data showed that the NSs sequestered antiviral proteins such as TBK1 into autophagic vesicles, and therefore promoted the degradation of TBK1 and other antiviral proteins. In addition, the 8A mutant of NSs reduced the induction of BECN1-dependent autophagy flux and degradation of antiviral immune proteins. In conclusion, our results indicated that SFTSV NSs sequesters antiviral proteins into autophagic vesicles for degradation and to escape antiviral immune responses.

Reactivation of Epstein-Barr virus in SFTSV infected patients.

Background: Severe fever with thrombocytopenia syndrome (SFTS) is an emerging hemorrhagic fever caused by a tick-borne bunyavirus SFTSV with case fatality up to 30%. The reactivation of Epstein-Barr virus (EBV) has been proven to occur in individuals with various immune suppression conditions. Methods: Here, we diagnosed 22 SFTSV infected patients with PCR in a hospital in Shandong Province, China in 2020. To understand the consequences of SFTSV infection leading to EBV reactivation, we examined EBV reactivation in SFTSV-infected patients with PCR and RT-PCR. Results: We found that EBV was reactivated in 18.2% (4/22) of SFTS patients, suggesting that EBV reactivation is common in SFTS patients. Compared with SFTS patients without EBV reactivation, SFTS patients with EBV-reactivation had a significantly lower median level of serum albumin (32.45 g/L vs. 26.95 g/L, p = 0.03) and a significantly higher median number of urine red blood cells (0 cells/µL vs. 9 cells/µL, p = 0.04). Conclusion: SFTS infection can reactivate EBV in patients, which may make the clinical condition of patients worsen.

Pathogenic Rickettsia, Anaplasma, and Ehrlichia in Rhipicephalus microplus ticks collected from cattle and laboratory hatched tick larvae.

BACKGROUND: The order Rickettsiales contains a group of vector-borne gram-negative obligate intracellular bacteria, which often cause human emerging infectious diseases and economic losses for dairy and meat industries. The purpose of this study is to investigate the distribution of the pathogens including Rickettsia spp., Anaplasma spp., and Ehrlichia spp. in the order Rickettsiales in ticks from Yueyang, a prefecture-level city of Hunan Province in Sothern China, and assess the potentiality of transovarial transmission of these rickettsial organisms. METHODS: Ticks were collected from cattle in a farm in Yueyang City and the tick DNA was used as template to amplify the htrA, rrs, gltA, ompA and ompB genes of Rickettsia as well as rrs and groEL genes of Anaplasma and Ehrlichia. RESULTS: All ticks (465) collected were the cattle tick, Rhipicephalus microplus. PCR showed the minimum infection rate (MIR) was 1.5% (7/465) for Candidatus Rickettsia xinyangensis, 1.9% (9/465) for C. Anaplasma boleense, 1.3% (6/465) for Anaplasma platys, 0.6% (3/465) for A. marginale, and 1.17% (2/465) for each of A. bovis, Ehrlichia minasensis, and a non-classified Ehrlichia sp. A human pathogen, C. Rickettsia xinyangensis and A. platys were detected in 100% (3/3) and 33.3% (2/6) laboratory-hatched larval pools from infected females respectively. CONCLUSION: Our study revealed a diversity of pathogenic rickettsial species in R. microplus ticks from Hunan Province suggesting a threat to people and animals in China. This study also provided the first molecular evidence for the potential transovarial transmission of C. Rickettsia xinyangensis and A. platys in R. microplus, indicating that R. microplus may act as the host of these two pathogens.

High prevalence and genetic diversity of hemoplasmas in bats and bat ectoparasites from China.

Hemoplasmas can cause severe hemolytic anemia in humans. To explore the genetic diversity and the potential transmission routes of hemoplasmas among bat population, bats and bat-ectoparasites including bat-flies, bat-mites, and bat-ticks were collected in Eastern and Central China from 2015 to 2021, and tested with PCR for hemoplasmas 16S rRNA gene. Based on 16S rRNA PCR, 18.0% (103/572) adult bats were positive for hemoplasmas, but none of 11 fetuses from hemoplasmas-positive pregnant bats was positive for hemoplasmas. These results indicated that adult bats had a high prevalence of hemoplasma, but vertical transmission of hemoplasmas did not occurr in the bats. Based on the 16S rRNA gene PCR, the minimum infection rate of bat-ectoparasite for hemoplasmas was 4.0% (27/676), suggesting that bat-ectoparasite also had a high prevalence for hemoplasmas. Phylogenetic analysis revealed that bat hemoplasmas from this study clustered into 4 genotypes (I-IV). Genotype I clustered together with hemoplasmas identified in bats from America. Genotype II shared high similarity with a human-pathogenic hemoplasma Candidatus Mycoplasma haemohominis. Genotype III and IV were unique, representing 2 new hemoplasma genotypes. Only genotype I was identified in both bats and all bat-ectoparasites including bat-flies, bat-mites, and bat-ticks. In conclusion, bats and bat-ectoparasites from China harbored abundant genetically diverse hemoplasmas including potential human-pathogenic hemoplasmas, indicating bats and bat-ectoparasites may play important roles in the maintenance and transmission of hemoplasmas in the natural foci.

Natural Mediterranean Spotted Fever Foci, Qingdao, China.

We sequenced DNA from spleens of rodents captured in rural areas of Qingdao, East China, during 2013-2015. We found 1 Apodemus agrarius mouse infected with Rickettsia conorii, indicating a natural Mediterranean spotted fever foci exists in East China and that the range of R. conorii could be expanding.

Host specificity and genetic diversity of Bartonella in rodents and shrews from Eastern China.

Bartonella are vector-borne gram-negative facultative intracellular bacteria causing emerging infectious diseases worldwide, and two thirds of known Bartonella species are carried by rodents. We captured rodents, shrews and rodent ectoparasitic mites in rural areas of Qingdao City, Shandong Province, China from 2012 to 2021 and used the animal spleen tissues for the PCR amplification of Bartonella gltA and rpoB genes. PCR showed 9.4% (40/425) rodents, and 5.1% (12/235) shrews were positive for Bartonella. Seven Bartonella species including three novel species were identified in five rodent species and one shrew species, indicating the abundance and genetic diversity of Bartonella in rodents and shrews. The infection rate of each Bartonella species in the animal species was as below: novel Candidatus Bartonella crocidura in shrews Crocidura lasiura (5.1%, 12/235); novel Candidatus Bartonella cricetuli in hamsters Tscherskia triton (20%, 9/45); novel Candidatus Bartonella muris in striped field mice Apodemus agrarius (4.2%, 7/168) and house mice Mus musculus (1.5%, 2/135); Bartonella fuyuanensis in striped field mice (8.9%, 15/168) and house mice (0.7%, 1/135); Bartonella rattimassiliensis and Bartonella tribocorum in brown rats Rattus norvegicus (6.7%, 3/45 and 4.2%, 2/45, respectively); Bartonella queenslandensis in Chinese white-bellied rat Niviventer confucianus (12.5%, 1/8). These results suggest that Bartonella infected a variety of rodent and shrew species with high infection rate, but each Bartonella specie is restricted to infect only one or a few genetically closely related rodent species. In addition, Candidatus Bartonella cricetuli, Candidatus Bartonella muris and Bartonella coopersplainsensis were found in chigger Walchia micropelta (33.3%, 3/9), and B. fuyuanensis were found in chigger Leptotrombidium intermedium (4.1%, 1/24), indicating chiggers may be reservoirs of Bartonella. In conclusion, abundant genetic diversified Bartonella species are found to infect rodents, shrews and chiggers, but each Bartonella species has a strict rodent animal host specificity; and chigger mites may play a role in Bartonella transmission.

SFTSV infection in rodents and their ectoparasitic chiggers.

SFTSV, a tick-borne bunyavirus causing a severe hemorrhagic fever termed as severe fever with thrombocytopenia syndrome (SFTS). To evaluate the potential role of rodents and its ectoparasitic chiggers in the transmission of SFTSV, we collected wild rodents and chiggers on their bodies from a rural area in Qingdao City, Shandong Province, China in September 2020. PCR amplification of the M and L segments of SFTSV showed that 32.3% (10/31) of rodents and 0.2% (1/564) of chiggers (Leptotrombidium deliense) from the rodents were positive to SFTSV. Our results suggested that rodents and chiggers may play an important role in the transmission of SFTSV, although the efficiency of chiggers to transmit SFTSV needs to be further investigated experimentally.

Global trends in COVID-19.

The pandemic COVID-19 is certainly one of the most severe infectious diseases in human history. In the last 2 years, the COVID-19 pandemic has caused over 418.6 million confirmed cases and 5.8 million deaths worldwide. Young people make up the majority of all infected COVID-19 cases, but the mortality rate is relatively lower compared to older age groups. Currently, about 55.04% individuals have been fully vaccinated rapidly approaching to herd immunity globally. The challenge is that new SARS-CoV-2 variants with potential to evade immunity from natural infection or vaccine continue to emerge. Breakthrough infections have occurred in both SARS-CoV-2 naturally infected and vaccinated individuals, but breakthrough infections tended to exhibit mild or asymptomatic symptoms and lower mortality rates. Therefore, immunity from natural infection or vaccination can reduce SARS-CoV-2 pathogenicity, but neither can completely prevent SARS-CoV-2 infection/reinfection. Fortunately, the morbidity and mortality of COVID-19 continue to decline. The 7-day average cumulative case fatality of COVID-19 has decreased from 12.3% on the February 25, 2020, to 0.27% on January 09, 2022, which could be related to a decreased SARS-CoV-2 variant virulence, vaccine immunization, and/or better treatment of patients. In conclusion, elimination of SARS-CoV-2 in the world could be impossible or at least an arduous task with a long way to go. The best strategy to prevent COVID-19 pandemic is to expand inoculation rate of effective vaccines. As the population reaches herd immunity, the mortality rate of COVID-19 may continue to decrease, and COVID-19 could eventually become another common cold.

Oral and ocular transmission of severe fever with thrombocytopenia syndrome virus.

Background: Severe fever with thrombocytopenia syndrome virus (SFTSV) is a tick-borne bunyavirus that could cause a severe hemorrhagic fever termed SFTS with a high fatality rate of up to 30%. Importantly, SFTSV is frequently transmitted from person-to-person and patients' blood or excreta are considered as the risk factors for transmission of SFTSV. However, the mechanism of person-to-person transmission of SFTSV is still elusive. Methods: In this study, wild-type (WT) C57BL/6 J mice and a lethal SFTSV mouse model IFNAR-/- A129 mice were utilized to evaluate whether SFTSV could be transmitted via oral or ocular routes. C57BL/6 J mice were inoculated with cell-cultured SFTSV via oral and ocular inoculation. IFNAR-/- A129 mice were inoculated with cell-cultured SFTSV or SFTSV infected mouse acute sera via oral and ocular inoculation. Results: We found that SFTSV antibody positive rates in C57BL/6 J mice were 70% (7/10) and 30% (3/10) in the oral inoculation group and ocular inoculation group, respectively on day 21 post SFTSV inoculation. The mortality rates of IFNAR-/- mice with oral and ocular inoculation of cell-cultured SFTSV were 100% and 83.33% (5/6), respectively on day 6 post inoculation. The mortality rates of IFNAR-/- mice with oral and ocular inoculation of SFTSV infected mouse acute serum were 100% and 66.67% (4/6), respectively on day 9 post inoculation. Conclusions: Together, our results show that SFTSV can be transmitted effectively through oral and ocular membrane, suggesting exposure to SFTS positive excreta may be a high-risk factor of nosocomial transmission of SFTSV in hospitals and/or families. Family members and healthcare workers should be protected properly during taking care of SFTS patients to prevent SFTSV nosocomial infection.

Bats and their ectoparasites (Nycteribiidae and Spinturnicidae) carry diverse novel Bartonella genotypes, China.

Bartonella species are facultative intracellular bacteria and recognized worldwide as emerging zoonotic pathogens. Bartonella were isolated or identified by polymerase chain reaction (PCR) in bats and their ectoparasites worldwide, whereas the association between them was scarce, especially in Asia. In this study, a retrospective analysis with frozen samples was carried out to identify the genetic diversity of Bartonella in bats and their ectoparasites and to investigate the relationships of Bartonella carried by bats and their ectoparasites. Bats and their ectoparasites (bat flies and bat mites) were collected from caves in Hubei Province, Central China, from May 2018 to July 2020. Bartonella were screened by PCR amplification and sequencing of three genes (gltA, rpoB, and ftsZ). Bats, bat flies, and bat mites carried diverse novel Bartonella genotypes with a high prevalence. The sharing of some Bartonella genotypes between bats and bat flies or bat mites indicated a potential role of bat flies and bat mites as vectors of bartonellae, while the higher genetic diversity of Bartonella in bat flies than that in bats might be due to the vertical transmission of this bacterium in bat flies. Therefore, bat flies might also act as reservoirs of Bartonella. In addition, human-pathogenic B. mayotimonesis was identified in both bats and their ectoparasites, which expanded our knowledge on the geographic distribution of this bacterium and suggested a potential bat origin with bat flies and bat mites playing important roles in the maintenance and transmission of Bartonella.

Bunyavirus SFTSV exploits autophagic flux for viral assembly and egress.

Severe fever with thrombocytopenia syndrome virus (SFTSV) is an emerging negatively stranded enveloped RNA bunyavirus that causes SFTS with a high case fatality rate of up to 30%. Macroautophagy/autophagy is an evolutionarily conserved process involved in the maintenance of host homeostasis, which exhibits anti-viral or pro-viral responses in reaction to different viral challenges. However, the interaction between the bunyavirus SFTSV and the autophagic process is still largely unclear. By establishing various autophagy-deficient cell lines, we found that SFTSV triggered RB1CC1/FIP200-BECN1-ATG5-dependent classical autophagy flux. SFTSV nucleoprotein induced BECN1-dependent autophagy by disrupting the BECN1-BCL2 association. Importantly, SFTSV utilized autophagy for the viral life cycle, which not only assembled in autophagosomes derived from the ERGIC and Golgi complex, but also utilized autophagic vesicles for exocytosis. Taken together, our results suggest a novel virus-autophagy interaction model in which bunyavirus SFTSV induces classical autophagy flux for viral assembly and egress processes, suggesting that autophagy inhibition may be a novel therapy for treating or releasing SFTS.

SARS-CoV-2 ORF3a Induces Incomplete Autophagy via the Unfolded Protein Response.

In the past year and a half, SARS-CoV-2 has caused 240 million confirmed cases and 5 million deaths worldwide. Autophagy is a conserved process that either promotes or inhibits viral infections. Although coronaviruses are known to utilize the transport of autophagy-dependent vesicles for the viral life cycle, the underlying autophagy-inducing mechanisms remain largely unexplored. Using several autophagy-deficient cell lines and autophagy inhibitors, we demonstrated that SARS-CoV-2 ORF3a was able to induce incomplete autophagy in a FIP200/Beclin-1-dependent manner. Moreover, ORF3a was involved in the induction of the UPR (unfolded protein response), while the IRE1 and ATF6 pathways, but not the PERK pathway, were responsible for mediating the ORF3a-induced autophagy. These results identify the role of the UPR pathway in the ORF3a-induced classical autophagy process, which may provide us with a better understanding of SARS-CoV-2 and suggest new therapeutic modalities in the treatment of COVID-19.

SAFA initiates innate immunity against cytoplasmic RNA virus SFTSV infection.

Nuclear scaffold attachment factor A (SAFA) is a novel RNA sensor involved in sensing viral RNA in the nucleus and mediating antiviral immunity. Severe fever with thrombocytopenia syndrome virus (SFTSV) is a bunyavirus that causes SFTS with a high fatality rate of up to 30%. It remains elusive whether and how cytoplasmic SFTSV can be sensed by the RNA sensor SAFA. Here, we demonstrated that SAFA was able to detect SFTSV infection and mediate antiviral interferon and inflammatory responses. Transcription and expression levels of SAFA were strikingly upregulated under SFTSV infection. SAFA was retained in the cytoplasm by interaction with SFTSV nucleocapsid protein (NP). Importantly, SFTSV genomic RNA was recognized by cytoplasmic SAFA, which recruited and promoted activation of the STING-TBK1 signaling axis against SFTSV infection. Of note, the nuclear localization signal (NLS) domain of SAFA was important for interaction with SFTSV NP and recognition of SFTSV RNA in the cytoplasm. In conclusion, our study reveals a novel antiviral mechanism in which SAFA functions as a novel cytoplasmic RNA sensor that directly recognizes RNA virus SFTSV and mediates an antiviral response.

Integrated transcriptome profiling in THP-1 macrophages infected with bunyavirus SFTSV.

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a tick-borne bunyavirus that causes an emerging hemorrhagic fever termed SFTS with high mortality. However, knowledge of SFTSV-host interactions is largely limited. Here, we performed a global transcriptome analysis of mRNAs and lncRNAs in THP-1 macrophages infected with SFTSV for 24 and 48 h. A total of 2,334 differentially expressed mRNAs and 154 differentially expressed lncRNAs were identified with 577 mRNAs and 31 lncRNAs commonly changed at both time points. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that differentially expressed mRNAs were mainly associated with innate immune, cytokine signaling, systemic lupus erythematosus, and alcoholism. Differentially expressed lncRNAs were enriched in systemic lupus erythematosus, alcoholism, and ribosome. Bioinformatic analysis also revealed hub regulatory mRNAs including IL6, TNF, UBA52, SRC, IL10, CXCL10, and CDK1 and core regulatory lncRNAs including XLOC_083027 and XLOC_113317. Transcription factor analysis of the differentially expressed mRNAs revealed that IRF1, SPI1, SPIB, ELF5, and FEV were enriched during SFTSV infection. Taken together, our studies illustrate the complex interaction between THP-1 macrophages and SFTSV.

Unraveling the Underlying Interaction Mechanism Between Dabie bandavirus and Innate Immune Response.

The genus Bandavirus consists of seven tick-borne bunyaviruses, among which four are known to infect humans. Dabie bandavirus, severe fever with thrombocytopenia syndrome virus (SFTSV), poses serious threats to public health worldwide. SFTSV is a tick-borne virus mainly reported in China, South Korea, and Japan with a mortality rate of up to 30%. To date, most immunology-related studies focused on the antagonistic role of SFTSV non-structural protein (NSs) in sequestering RIG-I-like-receptors (RLRs)-mediated type I interferon (IFN) induction and type I IFN mediated signaling pathway. It is still elusive whether the interaction of SFTSV and other conserved innate immune responses exists. As of now, no specific vaccines or therapeutics are approved for SFTSV prevention or treatments respectively, in part due to a lack of comprehensive understanding of the molecular interactions occurring between SFTSV and hosts. Hence, it is necessary to fully understand the host-virus interactions including antiviral responses and viral evasion mechanisms. In this review, we highlight the recent progress in understanding the pathogenesis of SFTS and speculate underlying novel mechanisms in response to SFTSV infection.

Human-pathogenic relapsing fever Borrelia found in bats from Central China phylogenetically clustered together with relapsing fever borreliae reported in the New World.

Bats can harbor zoonotic pathogens causing emerging infectious diseases, but their status as hosts for bacteria is limited. We aimed to investigate the distribution, prevalence and genetic diversity of Borrelia in bats and bat ticks in Hubei Province, China, which will give us a better understanding of the risk of Borrelia infection posed by bats and their ticks. During 2018-2020, 403 bats were captured from caves in Hubei Province, China, 2 bats were PCR-positive for Borrelia. Sequence analysis of rrs, flaB and glpQ genes of positive samples showed 99.55%-100% similarity to Candidatus Borrelia fainii, a novel human-pathogenic relapsing fever Borrelia species recently reported in Zambia, Africa and Eastern China, which was clustered together with relapsing fever Borrelia species traditionally reported only in the New World. Multilocus sequence typing (MLST) and pairwise genetic distances further confirmed the Borrelia species in the bats from Central China as Candidatus Borrelia fainii. No Borrelia DNA was detected in ticks collected from bats. The detection of this human-pathogenic relapsing fever Borrelia in bats suggests a wide distribution of this novel relapsing fever Borrelia species in China, which may pose a threat to public health in China.

SFTSV Infection Induced Interleukin-1ß Secretion Through NLRP3 Inflammasome Activation.

Severe fever with thrombocytopenia syndrome virus (SFTSV) is an emerging tick-borne virus that causes hemorrhagic fever. Previous studies showed that SFTSV-infected patients exhibited elevated levels of pro-inflammatory cytokines like interleukin-1ß (IL-1ß), indicating that SFTSV infection may activate inflammasomes. However, the detailed mechanism remains poorly understood. Herein, we found that SFTSV could stimulate the IL-1ß secretion in the infected human peripheral blood mononuclear cells (PBMCs), human macrophages, and C57/BL6 mice. We demonstrate that the maturation and secretion of IL-1ß during SFTSV infection is mediated by the nucleotide and oligomerization domain, leucine-rich repeat-containing protein family, pyrin-containing domain 3 (NLRP3) inflammasome. This process is dependent on protease caspase-1, a component of the NLRP3 inflammasome complex. For the first time, our study discovered the role of NLRP3 in response to SFTSV infection. This finding may lead to the development of novel drugs to impede the pathogenesis of SFTSV infection.

Calcium-responsive kinase LadS modulates type I-F CRISPR-Cas adaptive immunity.

The CRISPR-Cas systems are recently discovered adaptive immune strategies in bacteria and archaea against foreign genetic elements. Although gene-editing enabled by CRISPR-Cas9 has shown great promise for clinical application, little is known about potential mechanisms of CRISPR-Cas systems for regulating their own gene expression and altering the virulence within bacteria. Here, Gram-negative bacterium Pseudomonas aeruginosa PA14 that contains a Type I-F CRISPR-Cas system was used to study the mechanism endogenous CRISPR-Cas of regulation mechanism. We delineated the role of calcium as a positive regulator of the transcription of cas/csy complex and CRISPR-Cas immunity through the two-component system (TCS) protein kinase LadS. Furthermore, we identified a LadS downstream post-transcriptional regulator, RsmA, which targeted translation region of cas mRNA via A(N)GGA motif. Importantly, calcium-mediated influencing of CRISPR-Cas system was dependent on LadS and RsmA. Altogether, our findings uncover the previously unrecognized role of LadS/RsmA in modulating Type I-F CRISPR-Cas system via sensing calcium.

Identification of cGAS as an innate immune sensor of extracellular bacterium Pseudomonas aeruginosa.

Cyclic GMP-AMP synthase (cGAS) is reported essential for detecting intracellular bacteria. However, it remains to be determined whether and how cGAS is involved in extracellular bacterial infection. Here, we report that cGAS is essential for mediating type I interferon (IFN) production in infection by multiple extracellular pathogens, including Pseudomonas aeruginosa, Klebsiella pneumoniae, and Staphylococcus aureus. In addition, the canonical cGAS-stimulator of interferon gene (STING)-IFN axis is required for protecting mice from P. aeruginosa-induced mouse acute pulmonary infection, confirmed in cGAS pathway-specific gene deficiency mouse models. cGAS -/- and STING -/- mice exhibited reduced type I IFNs production, excessive inflammatory response accompanied with decreased resistance to P. aeruginosa challenge. Unfolded protein response was also modulated by cGAS through IRF3 and type I IFNs under P. aeruginosa infection. Collectively, these findings uncover the importance of cGAS in initiating immune responses against extracellular bacterial infection.