Isolation and characterization of thermotolerant bacterium utilizing ammonium and nitrate ions under aerobic conditions

A thermotolerant bacterium, identified as Bacillus licheniformis, completely utilized 0.1% (w/v) NH₄NO₃ at 30 and 50°C under aerobic condition. The addition of 0.5 mM Fe²⁺ to the NH₄NO₃ medium markedly promoted the utilization of NH₄⁺ and NO₃⁻. At 50°C, of total nitrogen originally provided, 24% was taken up into the cells and 20% remained in the culture supernatant. Residual nitrogen (56%) was probably removed into the atmosphere. The cell extracts contained enzymes involved in denitrification. GC-MS demonstrated that NH₄ ¹⁵NO₃ had been converted to ¹⁵N₂O. These results indicate that the strain has denitrification ability under aerobic condition.     

Mitochondrial dysfunction in platelets and hippocampi of senescence-accelerated mice

Senescence-accelerated mice (SAM) strains are useful models to understand the mechanisms of age-dependent degeneration. In this study, measurements of the mitochondrial membrane potential (Δψ_m) of platelets and the Adenosine 5^′-triphosphate (ATP) content of hippocampi and platelets were made, and platelet mitochondria were observed in SAMP8 (faster aging mice) and SAMR1 (aging resistant control mice) at 2, 6 and 9 months of age. In addition, an Aβ-induced (Amyloid beta-protein) damage model of platelets was established. After the addition of Aβ, the Δψ_m of platelets of SAMP8 at 1and 6 months of age were measured. We found that platelet Δψ_m, and hippocampal and platelet ATP content of SAMP8 mice decreased at a relatively early age compared with SAMR1. The platelets of 6 month-old SAMP8 showed a tolerance to Aβ-induced damages. These results suggest that mitochondrial dysfunction might be one of the mechanisms leading to age-associated degeneration in SAMP mice at an early age and the platelets could serve as a biomarker for detection of mitochondrial function and age related disease.     

Photosynthesis of <Emphasis Type="Italic">Rehmannia glutinosa</Emphasis> subjected to drought stress is enhanced by choline chloride through alleviating lipid peroxidation and increasing proline accumulation

Rehmannia glutinosa seedlings were pretreated with choline chloride (CC) in concentrations of 0, 0.7, 2.1 and 3.5 mM, and then subjected to drought and rewatering treatment to study the effects of CC on the generation of reactive oxygen species (O₂⁻, H₂O₂), lipid peroxidation, proline accumulation, water status and photosynthesis. The results showed that pretreatment with CC alleviated the inhibition of SOD and APX activity caused by drought stress, and therefore, the rate of O₂⁻ production and H₂O₂ concentration were reduced and lipid peroxidation decreased in pretreated plants. CC pretreatment also accelerated accumulation of proline, maintained higher Ψw and RWC, deferred leaf water loss during drought stress and retarded the drop in proline concentration after rewatering. Consequently, drought-induced decreases in F_m/F₀, F_v/F_m, Φ_PS2, q_P, and A and increase in q_NP were inhibited and the recovery of photosynthesis after rewatering was quicker in pretreated plants. Although differences in F_v/F_m, Φ_PS2 and q_P between treatments were not significant, there was a general trend that the effects of CC increased with the rise of its concentrations. The data suggested that 2.1 mM of CC be suitable for alleviating lipid peroxidation, promoting proline accumulation, retarding leaf water loss and improving photosynthesis of R. glutinosa seedlings under drought stress.     

On Haldane's formulation of Luria and Delbrück's mutation model

Two formulations of Luria and Delbrück's mutation model have been in common use since the 1940s. While mathematicians focused their attention on the formulation of Lea and Coulson that assumes asynchronous cell growth, biologists found more appealing the formulation of Haldane that assumes synchronous cell growth. This article attempts to solve several outstanding issues for the latter formulation. First, it provides an exact, closed-form expression for the mutant distribution by correcting a minor error in the literature. Second, it presents a novel algorithm for computing the mutant distribution, which leads to novel methods for computing point and interval estimates of mutation rates based on the maximum likelihood principle. Third, it critically examines existing methods based on the mean number of mutants. Finally, it compares the two formulations to underline their strengths and shortcomings.     

Mutagenesis of a bacteriophage lytic enzyme PlyGBS significantly increases its antibacterial activity against group B streptococci

Group B streptococci (GBS) are the leading cause of neonatal meningitis and sepsis worldwide. Intrapartum antibiotic prophylaxis (IAP) is the current prevention strategy given to pregnant women with confirmed vaginal GBS colonization. Due to antibiotic resistance identified in GBS, we previously developed another strategy using a bacteriophage lytic enzyme, PlyGBS, to reduce vaginal GBS colonization. In this study, various DNA mutagenesis methods were explored to produce PlyGBS mutants with increased lytic activity against GBS. Several hyperactive mutants were identified that contain only the endopeptidase domain found in the N-terminal region of PlyGBS and represent only about one-third of the wild-type PlyGBS in length. Significantly, these mutants not only have 18–28-fold increases in specific activities compared to PlyGBS, but they also have a similar activity spectrum against several streptococcal species. One of the hyperactive mutants, PlyGBS90-1, reduced the GBS colonization from >5 logs of growth per mouse to <50 colony-forming units (cfu) 4 h post treatment (∼4-log reduction) using a single dose in a mouse vaginal model. A reduction in GBS colonization before delivery should significantly reduce neonatal GBS infection providing a safe alternative to IAP.     

C(i,j) matrix: a better numerical characterization for graphical representations of biological sequences

We find that the traditional numerical characterizations of biological sequences, such as E matrix, D/D matrix, L/L matrix and their "high order" matrices, have their limitations to characterize the biological sequences exactly, but they are widely used to analyze the biological sequences. Here, we propose a better numerical characterization for graphical representations of biological sequences, C(i,j) matrix. It is associated with the curvature of every point and has many advantages: (1) It can characterize the graphical representations for DNA sequences exactly, because it can overcome the limitation of the traditional matrices. (2) If we choose an appropriate fixed point, we can make the elements of the C(i,j) matrix less than or equal to 1.