Structural Model for Covalent Adhesion of the Streptococcus pyogenes Pilus through a Thioester Bond

The human pathogen Streptococcus pyogenes produces pili that are essential for adhesion to host surface receptors. Cpa, the adhesin at the pilus tip, was recently shown to have a thioester-containing domain. The thioester bond is believed to be important in adhesion, implying a mechanism of covalent attachment analogous to that used by human complement factors. Here, we have characterized a second active thioester-containing domain on Cpa, the N-terminal domain of Cpa (CpaN). Expression of CpaN in Escherichia coli gave covalently linked dimers. These were shown by x-ray crystallography and mass spectrometry to comprise two CpaN molecules cross-linked by the polyamine spermidine following reaction with the thioester bonds. This cross-linked CpaN dimer provides a model for the covalent attachment of Cpa to target receptors and thus the streptococcal pilus to host cells. Similar thioester domains were identified in cell wall proteins of other Gram-positive pathogens, suggesting that thioester domains are more widely used and provide a mechanism of adhesion by covalent bonding to target molecules on host cells that mimics that used by the human complement system to eliminate pathogens.     

Streptococcus pyogenes in human plasma: adaptive mechanisms analyzed by mass spectrometry-based proteomics

Streptococcus pyogenes is a major bacterial pathogen and a potent inducer of inflammation causing plasma leakage at the site of infection. A combination of label-free quantitative mass spectrometry-based proteomics strategies were used to measure how the intracellular proteome homeostasis of S. pyogenes is influenced by the presence of human plasma, identifying and quantifying 842 proteins. In plasma the bacterium modifies its production of 213 proteins, and the most pronounced change was the complete down-regulation of proteins required for fatty acid biosynthesis. Fatty acids are transported by albumin (HSA) in plasma. S. pyogenes expresses HSA-binding surface proteins, and HSA carrying fatty acids reduced the amount of fatty acid biosynthesis proteins to the same extent as plasma. The results clarify the function of HSA-binding proteins in S. pyogenes and underline the power of the quantitative mass spectrometry strategy used here to investigate bacterial adaptation to a given environment.     

Plasmid transfer in natural soil: a case by case study with nitrogen-fixing Enterobacter

Abstract In strains of nitrogen-fixing Enterobacter agglomerans , isolated from the rhizosphere of cereals, the nif genes are located on large plasmids. Plasmid pEA9 (200 kb) is self-transmissible between closely related strains. To collect data on possible uncontrolled gene spread, for planned releases of such bacteria, plasmid pEA9 was labelled with transposons (Tn 1725 and Tn 5 ) and used in mating experiments between homologous Enterobacter strains with soil as substrate. The soil was from a plot into which an actual release was being planned. In the majority of experiments it was not sterilized.
Survival and plasmid transfer is described, as are variations in temperature, time, moisture, pH and soil packing. Further experiments were with or without added energy sources, and with or without plant roots. Under standard conditions (22°C, pH 5.2, 15.5% moisture, loose soil, 2 × 10⁷ inoculated donor and recipient cells each per g soil, 3 days incubation) sterilized soil gave low rates of plasmid transfer (10⁻⁶ per donor) but non-sterilized soil gave none. Adding Luria broth or sucrose to non-sterilized soil elicited strong cell propagation, together with plasmid transfer (optimum after incubation for 1 day: 10⁻⁴ exconjugants per donor). No transfer could be registered in the presence of wheat seedling roots for periods up to 5 weeks.     

Viable bacterial aerosol particle size distributions in the midsummer atmosphere at an isolated location in the high desert chaparral

The viable bacterial particle size distribution in the atmosphere at the Hanford Nuclear Reservation, Richland, WA during two, 1-week periods in June 1992, was observed at three intervals during the day (morning, midday and evening) and at three heights (2, 4, and 8 m) above ground level. The distributions were significantly different (P=0.01) between the two, 1-week sampling periods and between morning, midday, and evening observations, but not between the three heights. Approximately 30 to 50% fell into the largest particle size category; 7.0µm aerodynamic diameter. All particle size categories were at their minimum bacterial concentration at around noon, with the lowest concentrations in the smaller size categories (<2.1µm aerodynamic diameter). This suggests, that at this high desert location, solar radiation (SR) damage to airborne bacteria is particle size discriminatory. There is a relatively greater effect on the smaller size categories at midday and a relatively lesser effect in the morning and evening.     

Excitation delocalization in the bacteriochlorophyll c antenna of the green bacterium Chloroflexus aurantiacus as revealed by ultrafast pump-probe spectroscopy

Room temperature absorption difference spectra were measured on the femtosecond through picosecond time scales for chlorosomes isolated from the green bacterium Chloroflexus aurantiacus. Anomalously high values of photoinduced absorption changes were revealed in the BChl c Q_y transition band. Photoinduced absorption changes at the bleaching peak in the BChl c band were found to be 7–8 times greater than those at the bleaching peak in the BChl a band of the chlorosome. This appears to be the first direct experimental proof of excitation delocalization over many BChl c antenna molecules in the chlorosome.     

Analysis of antibacterial and cytotoxic potential of medicinal plants from Cholistan desert,Pakistan

This study aimed to investigate the antibacterial and cytotoxic activity of 03 medicinal plants, Calligonum polygonides, Farsetia hamiltonii, and Pulcaria crispa, from Cholistan desert, Pakistan. The active constituents of plants species were extracted in 05 different solvents and the extracts were tested against various bacterial strains and brine shrimps. Although all Calligonum polygonides’s extracts except chloroform were active against Staphylococcus aureus the most active was the acetone extract (21 ± 0.00 mm at 200 μg/disc) and activity was better than Caricef (p-value 0.03). While its water extract was more potent (18 ± 1.45 mm at 200 μg/disc) than Augmentin and Caricef (p-value < 0.005). The methanol extract’s activity (15 ± 0.39 mm in 200 μg/disc) was comparable to Fucidin against Proteus vulgaris (p-value > 0.99) and activity of diethyl ether extract against Escherichia coli (10 ± 1.16 mm in 200 μg/disc) was same as of Urixin (p-value 0.91). Farsetia hamiltonii’s acetone extract against Pseudomonas aeruginosa (10 ± 0.15 mm in 1 μg/disc) was more active than Augmentin Caricef and Cefotax (p-value < 0.02) and against Staphylococcus aureus (15 ± 1.15 mm in 200 μg/disc) activity was higher than Caricef (p-value 0.03). All Pulicaria crispa’s extracts except water extract were found active against Staphylococcus aureus. However, the diethyl ether extract was most effective (25 + 0.00 mm at 150 μg /disc) and activity was more than Augmentin, Oxy-tetracycline, Fucidin, Urixin, Ceftriaxone (p-value < 0.05). Although all extracts were exhibited cytotoxic activity, the Calligonum polygonides’s acetone extract (100%), Farsetia hamiltonii’s diethyl ether extract (90%) and Pulicaria crispa’s methanol extract (100%) were most active at 1000 μg/ml concentration. This study validated the medicinal significance of the studied plants and thus opens the way for their therapeutic applications.     

1H NMR studies of the mercuric ion binding protein MerP: Sequential assignment,secondary structure and global fold of oxidized MerP

Summary The oxidized form of the mercuric ion binding protein MerP has been studied by two-dimensional NMR. MerP, which is a periplasmic water-soluble protein with 72 amino acids, is involved in the detoxification of mercuric ions in bacteria with resistance against mercury. The mercuric ions in the periplasmic space are first scavenged by the MerP protein, then transported into the cytoplasm by the membrane-bound transport protein MerT, and finally reduced to elementary (nontoxic) mercury by the enzyme mercuric reductase. In this work, the ¹H NMR spectrum of oxidized MerP (closed disulfide bridge) has been assigned by using homonuclear 2D NMR techniques. The secondary structure and global fold have been inferred from the nuclear Overhauser effect (NOE) data. The secondary structure comprises four -strands and two -helices, in the order ₁₁₂₃₂₄. The protein folds into an antiparallel -sheet, ₂₃₁₄, with the two antiparallel helices on one side of the sheet. The folding topology is similar to that of acylphosphatase, the activation domain of porcine pancreatic procarboxypeptidase B, the DNA-binding domain of bovine papillomavirus-1 E2 and the RNA-binding domains of the U1 snRNP A and hnRNP C proteins. However, there is no structural similarity between MerP and other bacterial periplasmic binding proteins.     

Genetic diversity of non-pathogenic Clavibacter strains isolated from tomato seeds

Clavibacter michiganensis subsp. michiganensis (Cmm) is a seed-transmitted, quarantine pathogen which causes bacterial wilt and canker of tomato. Despite efforts to prevent seed contamination, new introductions are regularly detected, associated with new regions of tomato seed production. It seems as if the expanding diversity of Cmm also challenges the limited host range.     

血清降钙素原鉴别病毒性感染、一般性细菌感染和重症细菌性感染的临床应用价值

目的:研究血清中降钙素原在病毒性感染、一般性细菌感染和重症细菌性感染患者中的应用价值。方法:选择2014年6月~2016年12月在我院重症医学科进行诊治的感染患者60例,按照患者感染的严重程度分为病毒性感染患者(A组)15例,一般细菌感染组(B组)22例以及重症细菌性感染组(C组)23例。三组患者均采取纠正水电解质平衡、抗生素抗感染和营养支持等对症治疗,并在入院后第1、3、5、7 d检测患者的血清降钙素原水平,比较三组治疗前后血清降钙素原水平的差异,观察三组血清降钙素原≥0.5μg/L的例数。结果:B组血清降钙素原≥0.5μg/L的例数为20例,占90.91%,C组血清降钙素原≥0.5μg/L的例数为21例,占91.30%,B组和C组之间相比无明显差异(P0.05),但A组血清降钙素原≥0.5μg/L的例数为3例,占20.00%,明显低于B组和C组血清降钙素原≥0.5μg/L的例数,差异均具有统计学意义(P0.05);C组入院后第1、3、5、7 d的血清降钙素原水平均明显高于B组的血清降钙素原水平,差异均具有统计学意义(P0.05);重症细菌性感染患者中,血清降钙素原≥0.5μg/L的患者存活率明显低于血清降钙素原0.5μg/L的患者(P0.05)。结论:血清中降钙素原水平对于重症感染患者的临床诊断和治疗具有较好的应用价值,对于医生判断重症感染患者的预后情况具有很好的效果,值得临床广泛应用推广。