- Volume 164, Issue 11, 2018

Global Salmonella infection, especially in developing countries, is a health and economic burden. The use of antibiotic drugs in treating the infection is proving less effective due to the alarming rise of antibiotic-resistant strains of Salmonella, the effects of antibiotics on normal gut microflora and antibiotic-associated diarrhoea, all of which bring a growing need for alternative treatments, including the use of probiotic micro-organisms. However, there are issues with probiotics, including their potential to be opportunistic pathogens and antibiotic-resistant carriers, and their antibiotic susceptibility if used as complementary therapy. Clinical trials, animal trials and in vitro investigations into the prophylactic and therapeutic efficacies of probiotics have demonstrated antagonistic properties against Salmonella and other enteropathogenic bacteria. Nonetheless, there is a need for further studies into the potential mechanisms, efficacy and mode of delivery of yeast probiotics in Salmonella infections. This review discusses Salmonella infections and treatment using antibiotics and probiotics.

Wolbachia is the most widespread genus of endosymbiotic bacteria in the animal world, infecting a diverse range of arthropods and nematodes. A broad spectrum of associations from parasitism to mutualism occur, with a tendency to drive reproductive manipulation or influence host fecundity to spread infection through host populations. These varied effects of Wolbachia are exploited for public health benefits. Notably, the protection of insect hosts from viruses is being tested as a potential control strategy for human arboviruses, and the mutualistic relationship with filarial nematodes makes Wolbachia a target for antibiotic therapy of human and veterinary nematode diseases.

Under aerobic conditions, Crabtree-negative yeasts grow but do not ferment, and under anaerobic conditions, they ferment but do not grow. It is therefore believed that fermentation by these yeasts is sensitive to small variations of the operating parameters, e.g. dilution rate , mass transfer coefficient and oxygen solubility . However, this parametric sensitivity has never been quantified. Here, we present a method to quantify the parametric sensitivity of ethanol production in the Crabtree-negative yeast Scheffersomycesstipitis. The method is based on our experimental observation that S. stipitis cultures follow the principles of growth on mixtures of complementary substrates. Specifically, if a chemostat operating at fixed , and is fed with progressively increasing glucose feed concentrations , the culture passes through three regimes. (1) At low , the culture is carbon-limited and no ethanol is produced. (2) At high , the culture is oxygen-limited and ethanol is produced, but unused glucose is lost with the effluent. (3) At intermediate , both glucose and oxygen are limiting, and ethanol is produced without loss of glucose. Ethanol must therefore be produced in this dual-limited regime. The dual-limited regime can be predicted by simple unstructured models. It is characterized by the relation , where and denote the g of glucose consumed per g of oxygen during carbon- and oxygen-limited growth. Hence, the parametric sensitivity of fermentation by Crabtree-negative yeasts can be improved by targeting the yields and .

While the cell wall strictly controls cell size and morphology in bacteria, spheroplasts lack cell walls and can become enlarged in growth medium under optimal conditions. Optimal conditions depend on the bacterial species. We frequently observed extreme enlargement of spheroplasts of the radiation-resistant bacterium Deinococcus grandis in Difco Marine Broth 2216, but not in TGY broth (a commonly used growth medium for Deinococcus). Thorough investigation of media components showed that the presence of Mg2+ or Ca2+ promoted extreme spheroplast enlargement, synthesizing the outer membrane. Our findings strongly suggest that Mg2+ or Ca2+ enlarges spheroplasts, which could change the lipid composition of the spheroplast membrane.

Bacteria of the genus Mycoplasma have recently attracted considerable interest as model organisms in synthetic and systems biology. In particular, Mycoplasma pneumoniae is one of the most intensively studied organisms in the field of systems biology. However, the genetic manipulation of these bacteria is often difficult due to the lack of efficient genetic systems and some intrinsic peculiarities such as an aberrant genetic code. One major disadvantage in working with M. pneumoniae is the lack of replicating plasmids that can be used for the complementation of mutants and the expression of proteins. In this study, we have analysed the genomic region around the gene encoding the replication initiation protein, DnaA, and detected putative binding sites for DnaA (DnaA boxes) that are, however, less conserved than in other bacteria. The construction of several plasmids encompassing this region allowed the selection of plasmid pGP2756 that is stably inherited and that can be used for genetic experiments, as shown by the complementation assays with the glpQ gene encoding the glycerophosphoryl diester phosphodiesterase. Plasmid-borne complementation of the glpQ mutant restored the formation of hydrogen peroxide when bacteria were cultivated in the presence of glycerol phosphocholine. Interestingly, the replicating plasmid can also be used in the close relative, Mycoplasma genitalium but not in more distantly related members of the genus Mycoplasma. Thus, plasmid pGP2756 is a valuable tool for the genetic analysis of M. pneumoniae and M. genitalium.

Mycoplasma hyopneumoniae is the causative agent of enzootic pneumonia in swine, an important disease worldwide. It has finite biosynthetic capabilities, including a deficit in de novo nucleotide synthesis. The source(s) for nucleotides in vivo are unknown, but mycoplasmas are known to carry membrane-bound nucleases thought to participate in the acquisition of nucleotides from host genomic DNA. Recent research has demonstrated that neutrophils can produce extracellular traps (NETs), chromatin NETs decorated with granular proteins to interact with and eliminate pathogens. We hypothesized that M. hyopneumoniae could utilize its membrane nuclease to obtain nucleotides from extracellular traps to construct its own DNA. Using the human monocytic cell line THP-1, we induced macrophage extracellular traps (METs), which are structurally similar to NETs. The thymidine analogue ethynyl deoxyuridine (EdU) was incorporated into THP-1 DNA and METs were induced. When incubated with M. hyopneumoniae, METs were degraded and the modified nucleotide label could be co-localized within M. hyopneumoniae DNA. When the nucleases were inhibited, MET degradation and nucleotide transfer were also inhibited. Controls confirmed that the EdU originated directly from the METs and not from free nucleotides arising from intracellular pools released during extrusion of the chromosomal DNA. M. hyopneumoniae incorporated labelled nucleotides more efficiently when ‘fed’ on METs than from free nucleotides in the medium, suggesting a tight linkage between nuclease degradation of DNA and nucleotide transport. These results strongly suggest that M. hyopneumoniae could degrade extracellular traps formed in vivo during infection and incorporate those host nucleotides into its own DNA.

The ubiquitous bacterial second messenger bis-(3′-5′)-cyclic dimeric GMP (c-di-GMP) is involved in the regulation of numerous processes including biofilm formation, motility, virulence, cell cycle and differentiation. In this study, we searched the genome of the ecologically important marine alphaproteobacterium Dinoroseobacter shibae DFL12T for genes encoding putative c-di-GMP-modulating enzymes. Overall, D. shibae was found to possess two diguanylate cyclases (Dshi_2814 and Dshi_2820) as well as two c-di-GMP-specific phosphodiesterases (Dhi_0329 and Dshi_3065). Recombinant expression and purification followed by enzymatic analysis revealed that all four proteins exhibit their proposed activity. Furthermore, adjacent to Dshi_2814 we identified a gene encoding a heme nitric oxide/oxygen binding (H-NOX) protein. These proteins are often found in association with c-di-GMP signal transduction pathways and modulate their function through binding of diatomic gases such as nitric oxide. Here, we demonstrate that H-NOX constitutes a functional unit together with the diguanylate cyclase Dshi_2814. NO-bound H-NOX strongly inhibits DGC activity. Based on these results, and with respect to previously published data including micro-array analysis, we propose an interlinkage of c-di-GMP signalling with cell–cell communication and differentiation in D. shibae.

The initial adaptive transcriptional response to nitrogen (N) starvation in Escherichia coli involves large-scale alterations to the transcriptome mediated by the transcriptional activator, NtrC. One of these NtrC-activated genes is yeaG, which encodes a conserved bacterial kinase. Although it is known that YeaG is required for optimal survival under sustained N starvation, the molecular basis by which YeaG benefits N starved E. coli remains elusive. By combining transcriptomics with targeted metabolomics analyses, we demonstrate that the methionine biosynthesis pathway becomes transcriptionally dysregulated in ΔyeaG bacteria experiencing sustained N starvation. It appears the ability of MetJ, the master transcriptional repressor of methionine biosynthesis genes, to effectively repress transcription of genes under its control is compromised in ΔyeaG bacteria under sustained N starvation, resulting in transcriptional derepression of MetJ-regulated genes. Although the aberrant biosynthesis does not appear to be a contributing factor for the compromised viability of ΔyeaG bacteria experiencing sustained N starvation, this study identifies YeaG as a novel regulatory factor in E. coli affecting the transcription of methionine biosynthesis genes under sustained N starvation.