NaCl-sensitive mutant of Staphylococcus aureus has a Tn917-lacZ insertion in its ars operon

Genome Insights into the Novel Species Jejubacter calystegiae, a Plant Growth-Promoting Bacterium in Saline Conditions

Jejubacter calystegiae KSNA2T, a moderately halophilic, endophytic bacterium isolated from beach morning glory (Calystegia soldanella), was determined to be a novel species in a new genus in the family Enterobacteriaceae. To gain insights into the genetic basis of the salinity stress response of strain KSNA2T, we sequenced its genome using two complementary sequencing platforms (Illumina HiSeq and PacBio RSII). The genome contains a repertoire of metabolic pathways, such as those for nitrogen, phosphorus, and some amino acid metabolism pathways. Functional annotation of the KSNA2T genome revealed several genes involved in salt tolerance pathways, such as those encoding sodium transporters, potassium transporters, and osmoprotectant enzymes. Plant growth-promoting bacteria-based experiments indicated that strain KSNA2T promotes the germination of vegetable seeds in saline conditions. Overall, the genetic and biological analyses of strain KSNA2T provide valuable insights into bacteria-mediated salt tolerance in agriculture.

A genomic analysis of osmotolerance in Staphylococcus aureus

A key phenotypic characteristic of the Gram-positive bacterial pathogen, Staphylococcus aureus, is its ability to grow in low a_w environments. A homology transfer based approach, using the well characterised osmotic stress response systems of Bacillus subtilis and Escherichia coli, was used to identify putative osmotolerance loci in Staphylococcus aureus ST772-MRSA-V. A total of 17 distinct putative hyper and hypo-osmotic stress response systems, comprising 78 genes, were identified. The ST772-MRSA-V genome exhibits significant degeneracy in terms of the osmotic stress response; with three copies of opuD, two copies each of nhaK and mrp/mnh, and five copies of opp. Furthermore, regulation of osmotolerance in ST772-MRSA-V appears to be mediated at the transcriptional, translational, and post-translational levels.

Evolutionary Mechanisms of Long-Term Genome Diversification Associated With Niche Partitioning in Marine Picocyanobacteria

Marine picocyanobacteria of the genera Prochlorococcus and Synechococcus are the most abundant photosynthetic organisms on Earth, an ecological success thought to be linked to the differential partitioning of distinct ecotypes into specific ecological niches. However, the underlying processes that governed the diversification of these microorganisms and the appearance of niche-related phenotypic traits are just starting to be elucidated. Here, by comparing 81 genomes, including 34 new Synechococcus, we explored the evolutionary processes that shaped the genomic diversity of picocyanobacteria. Time-calibration of a core-protein tree showed that gene gain/loss occurred at an unexpectedly low rate between the different lineages, with for instance 5.6 genes gained per million years (My) for the major Synechococcus lineage (sub-cluster 5.1), among which only 0.71/My have been fixed in the long term. Gene content comparisons revealed a number of candidates involved in nutrient adaptation, a large proportion of which are located in genomic islands shared between either closely or more distantly related strains, as identified using an original network construction approach. Interestingly, strains representative of the different ecotypes co-occurring in phosphorus-depleted waters (Synechococcus clades III, WPC1, and sub-cluster 5.3) were shown to display different adaptation strategies to this limitation. In contrast, we found few genes potentially involved in adaptation to temperature when comparing cold and warm thermotypes. Indeed, comparison of core protein sequences highlighted variants specific to cold thermotypes, notably involved in carotenoid biosynthesis and the oxidative stress response, revealing that long-term adaptation to thermal niches relies on amino acid substitutions rather than on gene content variation. Altogether, this study not only deciphers the respective roles of gene gains/losses and sequence variation but also uncovers numerous gene candidates likely involved in niche partitioning of two key members of the marine phytoplankton.

Unusual features and molecular pathways of Staphylococcus aureus L-form bacteria

Staphylococcus aureus can be converted to cell wall-deficient L-form bacteria in specific environment which is associated with recurrent and persistent infections. The biophysical properties and molecular basis involved in S. aureus L-form formation are poorly understood. Here, S. aureus unstable L-form model was established not only in Newman strain, but also in ATCC 25923 and five different antibiotic-resistant clinical strains, and the morphology and mechanical properties of Newman strain L-forms were characterized by using atomic force microscopy. Meanwhile, zeta potential, growth and proliferation properties, and hemolysis of L-forms were determined. Gene expression changes involved in transition from S. aureus wild type into L-forms were identified. Our studies showed that L-form S. aureus presented pleomorphism, rough surface, and higher elasticity modulus. L-forms were characterized by less surface charge and had higher hemolysis than the walled form. The S. aureus L-form "fried egg" colony was derived from a single bacterium rather than from aggregation of different bacterial cells. Transcriptomics analysis revealed that several pathways involved in energy metabolism, stress response, protein synthesis, RNA metabolism, and virulence were involved in L-form formation in S. aureus. Our results shed new light on the biological properties and mechanisms underlying L-form formation in S. aureus. These findings will not only be useful for understanding the unique properties and mechanisms of L-form bacteria, but also provide therapeutic targets for developing more effective treatments for S. aureus L-forms.

High-throughput transposon sequencing highlights the cell wall as an important barrier for osmotic stress in methicillin resistant Staphylococcus aureus and underlines a tailored response to different osmotic stressors

Staphylococcus aureus is an opportunistic pathogen that can cause soft tissue infections but is also a frequent cause of foodborne illnesses. One contributing factor for this food association is its high salt tolerance allowing this organism to survive commonly used food preservation methods. How this resistance is mediated is poorly understood, particularly during long-term exposure. In this study, we used transposon sequencing (TN-seq) to understand how the responses to osmotic stressors differ. Our results revealed distinctly different long-term responses to NaCl, KCl and sucrose stresses. In addition, we identified the DUF2538 domain containing gene SAUSA300_0957 (gene 957) as essential under salt stress. Interestingly, a 957 mutant was less susceptible to oxacillin and showed increased peptidoglycan crosslinking. The salt sensitivity phenotype could be suppressed by amino acid substitutions in the transglycosylase domain of the penicillin-binding protein Pbp2, and these changes restored the peptidoglycan crosslinking to WT levels. These results indicate that increased crosslinking of the peptidoglycan polymer can be detrimental and highlight a critical role of the bacterial cell wall for osmotic stress resistance. This study will serve as a starting point for future research on osmotic stress response and help develop better strategies to tackle foodborne staphylococcal infections.

Staphylococcus aureus 2064 growth as affected by temperature and reduced water activity

Based on 247 growth data, the growth of S. aureus 2064 in dependence on temperatures (8-50°C) and a^w values (0.999-0.83) was described. Optimal values of a_wat all studied temperatures were determined by using Gibson model. Its compatibility was confirmed by several statistical indices, e.g. root mean square errors (RMSE 0.003-0.138), standard errors of prediction (%SEP 0.6-17.5). Cardinal values for S. aureus growth (T_min=7.7°C, T_opt=40.6°C, T_max=46.7°C, a_wmin=0.808, a_wopt=0.994, μ_opt=1.97 1/h) were determined by using CM model with indices RMSE=0.071, SEP=17.5%. Our findings can provide relevant growth information that can be used in S. aureus exposure assessment or in validation of other data regarding the growth of this opportunistic pathogen in foods.

Effect of arsenic (III and V) on oxidative stress parameters in resistant and susceptible Staphylococcus aureus

The presented study deals with the observation of properties of methicillin-susceptible Staphylococcus aureus (MSSA) and methicillin-resistant S. aureus (MRSA) in the toxic arsenic environment and influence of arsenic on antioxidant capacity. Two forms of arsenic (As(III), As(V)) with different concentrations were used for induction of the oxidative stress in tested strains. Microbiological methods showed that the growth inhibition of MSSA was higher than that of MRSA in presence of both arsenic ions. As(III) showed 24% and 33% higher anti-microbial effects than As(V) against MSSA and MRSA respectively. A similar result was found also in the experiment of reduction of biofilm-formation. By using spectrophotometry, it was revealed that As(III) induced higher antioxidant production in both bacterial cultures. Methicillin-susceptible S. aureus produced an app. 50 mg equivalent of gallic acid (GAE/1 mg of protein) and MRSA produced an app. 15 mg of GAE/1 mg of protein. The productions of metallothionein in MSSA and MRSA were decreased up to 62.41% and 55.84% respectively in presence of As ions. Reduction of As(III) and As(V) concentrations leads to a decrease in antioxidant production and increased the formation of metallothionein. All of these changes in the results were found to be significant statistically. Taken together, these experiments proved that in comparison with MSSA, MRSA is less susceptible not only to the antimicrobial effects of antibiotics but also against effects caused by metalloids, as arsenic. Thus, it can be stated that MRSA abounds with complex defensive mechanisms, which may in the future constitute significant problem in the efficiency of antibiotics alternatives as metal ions or nanoparticles.

Adaptive Metabolism in Staphylococci: Survival and Persistence in Environmental and Clinical Settings

Staphylococci are highly successful at colonizing a variety of dynamic environments, both nonpathogenic and those of clinical importance, and comprise the list of pathogens of global public health significance. Their remarkable survival and persistence can be attributed to a host of strategies, one of which is metabolic versatility—their ability to rapidly alter their metabolism in the presence of transient or long-term bacteriostatic and bactericidal conditions and facilitate cellular homeostasis. These attributes contribute to their widespread dissemination and challenging eradication particularly from clinical settings. The study of microbial behaviour at the metabolite level provides insight into mechanisms of survival and persistence under defined environmental and clinical conditions. This paper reviews the range of metabolic modulations that facilitate staphylococcal acclimatization and persistence in varying terrestrial and host conditions, and their public health ramifications in these settings.

Genomic insights into the virulence and salt tolerance of Staphylococcus equorum

To shed light on the genetic background behind the virulence and salt tolerance of Staphylococcus equorum, we performed comparative genome analysis of six S. equorum strains. Data on four previously published genome sequences were obtained from the NCBI database, while those on strain KM1031 displaying resistance to multiple antibiotics and strain C2014 causing haemolysis were determined in this study. Examination of the pan-genome of five of the six S. equorum strains showed that the conserved core genome retained the genes for general physiological processes and survival of the species. In this comparative genomic analysis, the factors that distinguish the strains from each other, including acquired genomic factors in mobile elements, were identified. Additionally, the high salt tolerance of strains enabling growth at a NaCl concentration of 25% (w/v) was attributed to the genes encoding potassium voltage-gated channels. Among the six strains, KS1039 does not possess any of the functional virulence determinants expressed in the other strains.

Transcriptional profiling of Staphylococcus aureus during growth in 2 M NaCl leads to clarification of physiological roles for Kdp and Ktr K+ uptake systems

Staphylococcus aureus exhibits an unusually high level of osmotolerance and Na(+) tolerance, properties that support survival in various host niches and in preserved foods. The genetic basis of these traits is not well understood. We compared the transcriptional profiles of S. aureus grown in complex medium with and without 2 M NaCl. The stimulon for growth in high-osmolality media and Na(+) included genes involved in uptake of K(+), other compatible solutes, sialic acid, and sugars; capsule biosynthesis; and amino acid and central metabolism. Quantitative PCR analysis revealed that the loci responded differently from each other to high osmolality imposed by elevated NaCl versus sucrose. High-affinity K(+) uptake (kdp) genes and capsule biosynthesis (cap5) genes required the two-component system KdpDE for full induction by osmotic stress, with kdpA induced more by NaCl and cap5B induced more by sucrose. Focusing on K(+) importers, we identified three S. aureus genes belonging to the lower-affinity Trk/Ktr family that encode two membrane proteins (KtrB and KtrD) and one accessory protein (KtrC). In the absence of osmotic stress, the ktr gene transcripts were much more abundant than the kdpA transcript. Disruption of S. aureus kdpA caused a growth defect under low-K(+) conditions, disruption of ktrC resulted in a significant defect in 2 M NaCl, and a ΔktrC ΔkdpA double mutant exhibited both phenotypes. Protective effects of S. aureus Ktr transporters at elevated NaCl are consistent with previous indications that both Na(+) and osmolality challenges are mitigated by the maintenance of a high cytoplasmic K(+) concentration.

IMPORTANCE

There is general agreement that the osmotolerance and Na(+) tolerance of Staphylococcus aureus are unusually high for a nonhalophile and support its capacity for human colonization, pathogenesis, and growth in food. Nonetheless, the molecular basis for these properties is not well defined. The genome-wide response of S. aureus to a high concentration, 2 M, of NaCl revealed the upregulation of expected genes, such as those for transporters of compatible solutes that are widely implicated in supporting osmotolerance. A high-affinity potassium uptake system, KdpFABC, was upregulated, although it generally plays a physiological role under very low K(+) conditions. At higher K(+) concentrations, a lower-affinity and more highly expressed type of K(+) transporter system, Ktr transporters, was shown to play a significant role in high Na(+) tolerance. This study illustrates the importance of the K(+) status of the cell for tolerance of Na(+) by S. aureus and underscores the importance of monovalent cation cycles in this pathogen.

Staphylococcus aureus requires cardiolipin for survival under conditions of high salinity

Background

The ability of staphylococci to grow in a wide range of salt concentrations is well documented. In this study, we aimed to clarify the role of cardiolipin (CL) in the adaptation of Staphylococcus aureus to high salinity.

Results

Using an improved extraction method, the analysis of phospholipid composition suggested that CL levels increased slightly toward stationary phase, but that this was not induced by high salinity. Deletion of the two CL synthase genes, SA1155 (cls1) and SA1891 (cls2), abolished CL synthesis. The cls2 gene encoded the dominant CL synthase. In a cls2 deletion mutant, Cls1 functioned under stress conditions, including high salinity. Using these mutants, CL was shown to be unnecessary for growth in either basal or high-salt conditions, but it was critical for prolonged survival in high-salt conditions and for generation of the L-form.

Conclusions

CL is not essential for S. aureus growth under conditions of high salinity, but is necessary for survival under prolonged high-salt stress and for the generation of L-form variants.

Epicatechin gallate, a component of green tea, reduces halotolerance in Staphylococcus aureus

Staphylococcus aureus grows in the presence of high-salt concentrations. The green tea polyphenolic compound epicatechin gallate (ECg) extended the staphylococcal lag phase to values greater than 6 h in the presence of NaCl, KCl and LiCl; this effect was not observed with epicatechin. Osmoprotectants glycine betaine and l-proline were unable to relieve the effect of ECg on halotolerance. The capacity of ECg to suppress staphylococcal growth in the presence of salt suggests that this molecule could be used to aid the preservation of salt-containing foods.

Characterization of a multicopper oxidase gene from Staphylococcus aureus

A multicopper oxidase gene from Staphylococcus aureus was cloned and overexpressed. Purified recombinant multicopper oxidase oxidized the substrate 3,3'-dimethoxybenzidine in the presence of copper. Disruption of mco showed copper sensitivity and H(2)O(2) resistance, suggesting roles for mco in copper homeostasis and oxidative stress response. Northern blot analysis showed copper-induced mco transcription.

Factors characterizing Staphylococcus epidermidis invasiveness determined by comparative genomics

Virulence mechanisms of the leading nosocomial pathogen Staphylococcus epidermidis are poorly understood. We used microarray-based genome-wide comparison of clinical and commensal S. epidermidis strains to identify putative virulence determinants. Our study revealed high genetic variability of the S. epidermidis genome, new markers for invasiveness of S. epidermidis, and potential targets for drug development against S. epidermidis infections.