Like eukaryotes, bacteria express one or more serine/threonine kinases (STKs) that initiate diverse signaling networks. The STK from Streptococcus suis is encoded by a single-copy stk gene, which is crucial in stress response and virulence. To further understand the regulatory mechanism of STK in S. suis, a stk deletion strain (Δstk) and its complementary strain (CΔstk) were constructed to systematically decode STK characteristics by applying whole transcriptome RNA sequencing (RNA-Seq) and phosphoproteomic analysis. Numerous genes were differentially expressed in Δstk compared with the wild-type parental strain SC-19, including 320 up-regulated and 219 down-regulated genes. Particularly, 32 virulence-associated genes (VAGs) were significantly down-regulated in Δstk. Seven metabolic pathways relevant to bacterial central metabolism and translation are significantly repressed in Δstk. Phosphoproteomic analysis further identified 12 phosphoproteins that exhibit differential phosphorylation in Δstk. These proteins are associated with cell growth and division, glycolysis, and translation. Consistently, phenotypic assays confirmed that the Δstk strain displayed deficient growth and attenuated pathogenicity. Thus, STK is a central regulator that plays an important role in cell growth and division, as well as S. suis metabolism.

Acquisition and metabolism of carbohydrates are essential for host colonization and pathogenesis of bacterial pathogens. Different bacteria can uptake different lines of carbohydrates via ABC transporters, in which ATPase subunits energize the transport though ATP hydrolysis. Some ABC transporters possess their own ATPases, while some share a common ATPase. Here we identified MsmK, an ATPase from Streptococcus suis, an emerging zoonotic bacterium causing dead infections in pigs and humans. Genetic and biochemistry studies revealed that the MsmK was responsible for the utilization of raffinose, melibiose, maltotetraose, glycogen and maltotriose. In infected mice, the msmK-deletion mutant showed significant defects of survival and colonization when compared with its parental and complementary strains. Taken together, MsmK is an ATPase that contributes to multiple carbohydrates utilization and host colonization of S. suis. This study gives new insight into our understanding of the carbohydrates utilization and its relationship to the pathogenesis of this zoonotic pathogen.

To reduce the need for antibiotics in animal production, alternative approaches are needed to control infection. We hypothesized that overexpression of native defensin genes will provide food animals with enhanced resistance to bacterial infections. In this study, recombinant porcine beta-defensin 2 (PBD-2) was overexpressed in stably transfected PK-15 porcine kidney cells. PBD-2 antibacterial activities against Actinobacillus pleuropneumoniae, an important respiratory pathogen causing porcine contagious pleuropneumonia, were evaluated on agar plates. Transgenic pigs constitutively overexpressing PBD-2 were produced by a somatic cell cloning method, and their resistance to bacterial infection was evaluated by direct or cohabitation infection with A. pleuropneumoniae. Recombinant PBD-2 peptide that was overexpressed in the PK-15 cells showed antibacterial activity against A. pleuropneumoniae. PBD-2 was overexpressed in the heart, liver, spleen, lungs, kidneys, and jejunum of the transgenic pigs, which showed significantly lower bacterial loads in the lungs and reduced lung lesions after direct or cohabitation infection with A. pleuropneumoniae. The results demonstrate that transgenic overexpression of PBD-2 in pigs confers enhanced resistance against A. pleuropneumoniae infection.T he availability of antibiotics for treating bacterial infection has significantly improved the health of animals and humans. Administration of antibiotics at low doses to food animals has been practiced to promote better health and animal performance in many regions (1). To reduce the development of antimicrobial resistance, approaches to decrease antibiotic use in animal production are needed.Antimicrobial peptides (AMPs), a family of short cationic amphiphilic peptides with antimicrobial and immune modulation activities, exist in nearly every life form as natural anti-infective therapeutic agents (2). Some AMP genes have been used to generate transgenic (TG) mice to enhance resistance to bacterial infection. For example, expression of a synthetic cecropin-class lytic peptide in TG mice displayed enhanced resistance to Brucella abortus (3). Expression of an additional porcine cathelicidin peptide, PR-39, in mice showed increased resistance to group A Streptococcus infection (4). Furthermore, enhanced resistance to Actinobacillus suis infection was observed in proptegrin-1 TG mice (5). These studies demonstrate that AMPs potentially can lead to the development of infection-resistant animals, at least in TG mouse models. However, few reports are available on large food animals such as pigs.Defensins comprise a major family of AMPs, playing an important role in innate immunity. Porcine beta-defensin 2 (PBD-2) is thought to be an important AMP. PBD-2 provides a first line of defense against bacterial infection in pigs, because this AMP is highly expressed in epithelial cells (6, 7); moreover, PBD-2 demonstrates excellent antimicrobial activity with a broad spectrum but without hemolytic activity under physiological conditions (8).In the c...

Spermidine (Spd), spermine (Spm), and putrescine (Put), which are the most widely distributed cellular polyamines, are essential for normal growth and multiplication of both eukaryotic and prokaryotic cells. In this study, we identified the only putative polyamine transport system PotABCD in Streptococcus suis, a worldwide zoonotic Gram-positive pathogen causing lethal infections in humans and pigs. It was discovered that S. suis could uptake polyamines preferably Spd and Spm. By constructing a potA deleted mutant, we confirmed that PotABCD was responsible for polyamine uptake, and PotD bound to the protein of polyamines. The four PotABCD genes were co-transcribed with murB, a gene involved in peptidoglycan (PG) synthesis. Furthermore the roles of polyamine transport system in maintaining the PG structure were detected to understand the biological significance of this co-transcription. In contrast to the wild type, the mutant ΔpotA exhibited elongated chain length and abnormal cell division morphology. Phenotypic changes were attributed to be the up-regulation of genes involved in PG synthesis and hydrolysis in ΔpotA. Additionally, polyamines functioned not only as feedback regulators of PotA by inhibiting PotA activity but also as regulators on potABCD and genes involved in PG synthesis. This study reveals the functions of PotABCD in polyamine transport and the regulatory roles of polyamines in PG synthesis. Results provide new insights into the machineries contributing to normal growth and cell division of S. suis.