PmrA/PmrB Two-Component System Regulation of lipA Expression in Pseudomonas aeruginosa PAO1

Evaluation of Edwardsiella piscicida basS and basR mutants as vaccine candidates in catfish against edwardsiellosis

Catfish farming is the largest aquaculture industry in the United States and an important economic driver in several southeastern states. Edwardsiella piscicida is a Gram-negative pathogen associated with significant losses in catfish aquaculture. Several Gram-negative bacteria use the BasS/BasR two-component system (TCS) to adapt to environmental changes and the host immune system. Currently, the role of BasS/BasR system in E. piscicida virulence has not been characterized. In the present study, two mutants were constructed by deleting the basS and basR genes in E. piscicida strain C07-087. Both mutant strains were characterized for virulence and immune protection in catfish hosts. The EpΔbasS and EpΔbasR mutants were more sensitive to acidic environments and produced significantly less biofilm than the wild-type. In vivo studies in channel catfish (Ictalurus punctatus) revealed that both EpΔbasS and EpΔbasR were significantly attenuated compared with the parental wild-type (3.57% and 4.17% vs. 49.16% mortalities). Moreover, there was significant protection, 95.2% and 92.3% relative percent survival (RPS), in channel catfish vaccinated with EpΔbasS and EpΔbasR against E. piscicida infection. Protection in channel catfish was associated with a significantly higher level of antibodies and upregulation of immune-related genes (IgM, IL-8 and CD8-α) in channel catfish vaccinated with EpΔbasS and EpΔbasR strains compared with non-vaccinated fish. Hybrid catfish (channel catfish ♀ × blue catfish ♂) challenges demonstrated long-term protection against subsequent challenges with E. piscicida and E. ictaluri. Our findings demonstrate BasS and BasR contribute to acid tolerance and biofilm formation, which may facilitate E. piscicida survival in harsh environments. Further, our results show that EpΔbasS and EpΔbasR mutants were safe and protective in channel catfish fingerlings, although their virulence and efficacy in hybrid catfish warrant further investigation. These data provide information regarding an important mechanism of E. piscicida virulence, and it suggests EpΔbasS and EpΔbasR strains have potential as vaccines against this emergent catfish pathogen.

Specific and Global RNA Regulators in Pseudomonas aeruginosa

Pseudomonas aeruginosa (Pae) is an opportunistic pathogen showing a high intrinsic resistance to a wide variety of antibiotics. It causes nosocomial infections that are particularly detrimental to immunocompromised individuals and to patients suffering from cystic fibrosis. We provide a snapshot on regulatory RNAs of Pae that impact on metabolism, pathogenicity and antibiotic susceptibility. Different experimental approaches such as in silico predictions, co-purification with the RNA chaperone Hfq as well as high-throughput RNA sequencing identified several hundreds of regulatory RNA candidates in Pae. Notwithstanding, using in vitro and in vivo assays, the function of only a few has been revealed. Here, we focus on well-characterized small base-pairing RNAs, regulating specific target genes as well as on larger protein-binding RNAs that sequester and thereby modulate the activity of translational repressors. As the latter impact large gene networks governing metabolism, acute or chronic infections, these protein-binding RNAs in conjunction with their cognate proteins are regarded as global post-transcriptional regulators.

Interplay between Regulatory RNAs and Signal Transduction Systems during Bacterial Infection

The ability of pathogenic bacteria to stably infect the host depends on their capacity to respond and adapt to the host environment and on the efficiency of their defensive mechanisms. Bacterial envelope provides a physical barrier protecting against environmental threats. It also constitutes an important sensory interface where numerous sensing systems are located. Signal transduction systems include Two-Component Systems (TCSs) and alternative sigma factors. These systems are able to sense and respond to the ever-changing environment inside the host, altering the bacterial transcriptome to mitigate the impact of the stress. The regulatory networks associated with signal transduction systems comprise small regulatory RNAs (sRNAs) that can be directly involved in the expression of virulence factors. The aim of this review is to describe the importance of TCS- and alternative sigma factor-associated sRNAs in human pathogens during infection. The currently available genome-wide approaches for studies of TCS-regulated sRNAs will be discussed. The differences in the signal transduction mediated by TCSs between bacteria and higher eukaryotes and the specificity of regulatory RNAs for their targets make them appealing targets for discovery of new strategies to fight against multi-resistant bacteria.

Influence of host genetics in shaping the rumen bacterial community in beef cattle

In light of recent host-microbial association studies, a consensus is evolving that species composition of the gastrointestinal microbiota is a polygenic trait governed by interactions between host genetic factors and the environment. Here, we investigated the effect of host genetic factors in shaping the bacterial species composition in the rumen by performing a genome-wide association study. Using a common set of 61,974 single-nucleotide polymorphisms found in cattle genomes (n = 586) and corresponding rumen bacterial community composition, we identified operational taxonomic units (OTUs), Families and Phyla with high heritability. The top associations (1-Mb windows) were located on 7 chromosomes. These regions were associated with the rumen microbiota in multiple ways; some (chromosome 19; position 3.0-4.0 Mb) are associated with closely related taxa (Prevotellaceae, Paraprevotellaceae, and RF16), some (chromosome 27; position 3.0-4.0 Mb) are associated with distantly related taxa (Prevotellaceae, Fibrobacteraceae, RF16, RFP12, S24-7, Lentisphaerae, and Tenericutes) and others (chromosome 23; position 0.0-1.0) associated with both related and unrelated taxa. The annotated genes associated with identified genomic regions suggest the associations observed are directed toward selective absorption of volatile fatty acids from the rumen to increase energy availability to the host. This study demonstrates that host genetics affects rumen bacterial community composition.