Promoter Boundaries for the luxCDABE and betIBA-proXWV Operons in Vibrio harveyi Defined by the Method Rapid Arbitrary PCR Insertion Libraries (RAIL)

Mobile-CRISPRi as a powerful tool for modulating Vibrio gene expression

CRISPRi (Clustered Regularly Interspaced Palindromic Repeats interference) is a gene knockdown method that uses a deactivated Cas9 protein (dCas9) that binds a specific gene target locus dictated by an encoded guide RNA (sgRNA) to block transcription. Mobile-CRISPRi is a suite of modular vectors that enable CRISPRi knockdowns in diverse bacteria by integrating IPTG-inducible dcas9 and sgRNA genes into the genome using Tn7 transposition. Here, we show that the Mobile-CRISPRi system functions robustly and specifically in multiple Vibrio species: Vibrio cholerae, Vibrio fischeri, Vibrio vulnificus, Vibrio parahaemolyticus, and Vibrio campbellii. We demonstrate efficacy by targeting both essential and non-essential genes that function to produce defined, measurable phenotypes: bioluminescence, quorum sensing, cell division, and growth arrest. We anticipate that Mobile-CRISPRi will be used in Vibrio species to systematically probe gene function and essentiality in various behaviors and native environments.IMPORTANCEThe genetic manipulation of bacterial genomes is an invaluable tool in experimental microbiology. The development of CRISPRi (Clustered Regularly Interspaced Palindromic Repeats interference) tools has revolutionized genetics in many organisms, including bacteria. Here, we optimized the use of Mobile-CRISPRi in five Vibrio species, each of which has significant impacts on marine environments and organisms that include squid, shrimp, shellfish, finfish, corals, and multiple of which pose direct threats to human health. The Mobile-CRISPRi technology is easily adaptable, moveable from strain to strain, and enables researchers to selectively turn off gene expression. Our experiments demonstrate Mobile-CRISPRi is effective and robust at repressing gene expression of both essential and non-essential genes in Vibrio species.

Mobile-CRISPRi as a powerful tool for modulating Vibrio gene expression

CRISPRi (Clustered Regularly Interspaced Palindromic Repeats interference) is a gene knockdown method that uses a deactivated Cas9 protein (dCas9) that binds a specific gene target locus dictated by an encoded guide RNA (sgRNA) to block transcription. Mobile-CRISPRi is a suite of modular vectors that enable CRISPRi knockdowns in diverse bacteria by integrating IPTG-inducible dcas9 and sgRNA genes into the genome using Tn 7 transposition. Here, we show that the Mobile-CRISPRi system functions robustly and specifically in multiple Vibrio species: Vibrio cholerae, Vibrio fischeri, Vibrio vulnificus, Vibrio parahaemolyticus , and Vibrio campbellii . We demonstrate efficacy by targeting both essential and non-essential genes that function to produce defined, measurable phenotypes: bioluminescence, quorum sensing, cell division, and growth arrest. We anticipate that Mobile-CRISPRi will be used in Vibrio species to systematically probe gene function and essentiality in various behaviors and native environments.

Engineering of the hypoxia-induced Pichia stipitis ADH2 promoter to construct a promoter library for Pichia pastoris

Hypoxia-inducible promoters of a wide range of activities are desirable for fine-tuning gene expression in response to oxygen limitation, especially for the Crabtree negative yeast Pichia pastoris (Komagataella phaffii) with a high oxygen consumption rate in large-scale fermentations. Here we constructed a hypoxia-inducible promoter library for P. pastoris through error-prone PCR of Pichia stipitis ADH2 promoter (PsADH2). The library of 30 selected promoters showing 0.4- to 5.5-fold of the PsADH2 activity was obtained through high-throughput screening in microplates using the reporter yeast-enhanced green fluorescent protein. Two strong promoters, AM23 and AM30, were further characterized in shake flask cultures at high and low dissolved oxygen levels. They responded more sensitively to the low dissolved oxygen level, achieving a 4.6-, 7.9-fold and 3.6-, 7.7-fold higher fluorescence intensity and transcript level, respectively, than the wild-type PsADH2. Their hypoxia-inducible properties were confirmed with two additional reporters: β-galactosidase and Vitreoscilla hemoglobin, to demonstrate the broad applicability of the promoter library. During the typical fermentation process in shake flasks, the promoter AM30 showed strong expression with cell growth and decreased oxygen levels, without any additional chemical inducers or operations. Since the potent industrial host P. pastoris is recognized as an easy to scale-up system, it is reasonable to expect that the obtained hypoxia-inducible promoter library may have great potential to enable convenient regulation of gene expression under industrial fermentations which are usually run under oxygen limitation due to high cell density cultivations.

Amino acid divergence in the ligand-binding pocket of Vibrio LuxR/HapR proteins determines the efficacy of thiophenesulfonamide inhibitors

The quorum-sensing signaling systems in Vibrio bacteria converge to control levels of the master transcription factors LuxR/HapR, a family of highly conserved proteins that regulate gene expression for bacterial behaviors. A compound library screen identified 2-thiophenesulfonamide compounds that specifically inhibit Vibrio campbellii LuxR but do not affect cell growth. We synthesized a panel of 50 thiophenesulfonamide compounds to examine the structure-activity relationship effects on Vibrio quorum sensing. The most potent molecule identified, PTSP (3-phenyl-1-(thiophen-2-ylsulfonyl)-1H-pyrazole), inhibits quorum sensing in multiple strains of V. vulnificus, V. parahaemolyticus, and V. campbellii at nanomolar concentrations. However, thiophenesulfonamide inhibition efficacy varies significantly among Vibrio species: PTSP is most inhibitory against V. vulnificus SmcR, but V. cholerae HapR is completely resistant to all thiophenesulfonamides tested. Reverse genetics experiments show that PTSP efficacy is dictated by amino acid sequence in the putative ligand-binding pocket: F75Y and C170F SmcR substitutions are each sufficient to eliminate PTSP inhibition. Further, in silico modeling distinguished the most potent thiophenesulfonamides from less-effective derivatives. Our results revealed the previously unknown differences in LuxR/HapR proteins that control quorum sensing in Vibrio species and underscore the potential for developing thiophenesulfonamides as specific quorum sensing-directed treatments for Vibrio infections.

The quorum-sensing systems of Vibrio campbellii DS40M4 and BB120 are genetically and functionally distinct

Vibrio campbellii BB120 (previously classified as Vibrio harveyi) is a fundamental model strain for studying quorum sensing in vibrios. A phylogenetic evaluation of sequenced Vibrio strains in Genbank revealed that BB120 is closely related to the environmental isolate V. campbellii DS40M4. We exploited DS40M4's competence for exogenous DNA uptake to rapidly generate greater than 30 isogenic strains with deletions of genes encoding BB120 quorum-sensing system homologues. Our results show that the quorum-sensing circuit of DS40M4 is distinct from BB120 in three ways: (i) DS40M4 does not produce an acyl homoserine lactone autoinducer but encodes an active orphan LuxN receptor, (ii) the quorum regulatory small RNAs (Qrrs) are not solely regulated by autoinducer signalling through the response regulator LuxO and (iii) the DS40M4 quorum-sensing regulon is much smaller than BB120 (~100 genes vs. ~400 genes, respectively). Using comparative genomics to expand our understanding of quorum-sensing circuit diversity, we observe that conservation of LuxM/LuxN proteins differs widely both between and within Vibrio species. These strains are also phenotypically distinct: DS40M4 exhibits stronger interbacterial cell killing, whereas BB120 forms more robust biofilms and is bioluminescent. These results underscore the need to examine wild isolates for a broader view of bacterial diversity in the marine ecosystem.

RAIL: A new tool for defining bacterial promoter regions

In this issue of the Journal of Bacteriology, Hustmyer and colleagues describe a new method for rapidly generating reporter libraries (Hustmyer citation). This RAIL technique (Rapid Arbitrary PCR Insertion Libraries) uses arbitrary PCR and isothermal DNA assembly to insert random fragments of promoter regions into reporter plasmids, resulting in libraries that can be screened to identify regions required for gene expression. This technique will likely be useful for a number of different genetic applications.

The 24th Annual Midwest Microbial Pathogenesis Meeting

The 24th Annual Midwest Microbial Pathogenesis Conference (MMPC) was held at the University of Notre Dame from August 25-27, 2017. The conference provided an opportunity for scientists from the Midwest to discuss new advances in microbial pathogenesis, including how pathogens promote disease, and how they interact with each other, the microbiome and the host. This commentary highlights the MMPC history, the topics presented at the conference and the reports in this issue.