Role of the Mitochondrial Genome During Early Development in Mice

The role of the mitochondrial genome in early development and differentiation was studied in mouse embryos cultured in vitro from the two to four cell stage to the blastocyst (about 100 cells). During this period the mitochondria undergo morphological differentiation: progressive enlargement followed by an increase in matrix density, in number of cristae, and in number of mitochondrial ribosomes. Mitochondrial ribosomal and transfer RNA synthesis occurs from the 8 to 16 cell stage on and contributes to the establishment of a mitochondrial protein-synthesizing system. Inhibition of mitochondrial RNA- and protein-synthesis by 0.1 µg/ml of ethidium bromide or 31.2 µg/ml of chloramphenicol permits essentially normal embryo development and cellular differentiation. Mitochondrial morphogenesis is also nearly normal except for the appearance of dilated and vesicular cristae in blastocyst mitochondria. Such blastocysts are capable of normal postimplantation development when transplanted into the uteri of foster mothers. Higher concentrations of these inhibitors have general toxic effects and arrest embryo development. It is concluded that mitochondrial differentiation in the early mouse embryo occurs through the progressive transformation of the preexisting mitochondria and is largely controlled by the nucleocytoplasmic system. Mitochondrial protein synthesis is required for the normal structural organization of the cristae in blastocyst mitochondria. Embryo development and cellular differentiation up to the blastocyst stage are not dependent on mitochondrial genetic activity

Characterization of shifts of koala (Phascolarctos cinereus) intestinal microbial communities associated with antibiotic treatment.

Koalas (Phascolarctos cinereus) are arboreal marsupials native to Australia that eat a specialized diet of almost exclusively eucalyptus leaves. Microbes in koala intestines are known to break down otherwise toxic compounds, such as tannins, in eucalyptus leaves. Infections by Chlamydia, obligate intracellular bacterial pathogens, are highly prevalent in koala populations. If animals with Chlamydia infections are received by wildlife hospitals, a range of antibiotics can be used to treat them. However, previous studies suggested that koalas can suffer adverse side effects during antibiotic treatment. This study aimed to use 16S rRNA gene sequences derived from koala feces to characterize the intestinal microbiome of koalas throughout antibiotic treatment and identify specific taxa associated with koala health after treatment. Although differences in the alpha diversity were observed in the intestinal flora between treated and untreated koalas and between koalas treated with different antibiotics, these differences were not statistically significant. The alpha diversity of microbial communities from koalas that lived through antibiotic treatment versus those who did not was significantly greater, however. Beta diversity analysis largely confirmed the latter observation, revealing that the overall communities were different between koalas on antibiotics that died versus those that survived or never received antibiotics. Using both machine learning and OTU (operational taxonomic unit) co-occurrence network analyses, we found that OTUs that are very closely related to Lonepinella koalarum, a known tannin degrader found by culture-based methods to be present in koala intestines, was correlated with a koala's health status. This is the first study to characterize the time course of effects of antibiotics on koala intestinal microbiomes. Our results suggest it may be useful to pursue alternative treatments for Chlamydia infections without the use of antibiotics or the development of Chlamydia-specific antimicrobial compounds that do not broadly affect microbial communities

Sodium Benzoate is Associated with Salmonella Typhi Resistant to Chloramphenicol

Background: There are many factors that govern growth and resistant of Salmonella typhi. A study had reported that the use of sodium benzoate caused antibiotic resistant. However, no study has directly evaluated the effect of sodium benzoate exposure on S. typhi sensitivity to chloramphenicol. The aim of this study was to evaluate the resistance or sensitivity of S. typhi to chloramphenicol after sodium benzoate exposure. Methods: The study was conducted in seven groups: three treatment groups (sodium benzoate insensitive S. typhi+8 µg/mL, 16 µg/mL, and 32 µg/mL of chloramphenicol), three positive control groups (sodium benzoate sensitive S. typhi+8 µg/mL, 16 µg/mL, and 32 µg/mL of chloramphenicol), and one negative control groups (sodium benzoate sensitive S. typhi+0 µg/mL of chloramphenicol). The effect of sodium benzoate exposure to S. typhi sensitivity to chloramphenicol was measured after 24 hours. Spearman test was used to analyzed this association. Results: In this study, we found that the average S. typhi growth in the treatment groups (A, B, C) was 445 CFU/mL, 385 CFU/mL, and 171 CFU/mL, respectively. While in the positive control group (D, E, F) was not obtained any S. typhi growth. Average S. typhi growth in the negative control group was 430 CFU/mL. Discussion: We found that sodium benzoate exposure inhibited S. typhi growth and affected S. typhi sensitivity to chloramphenicol (p<0.05). In addition, we found that 32 µg/mL chloramphenicol had the highest mean difference value, so this showed that the dose 32 µg/mL of chloramphenicol had the best effectiveness of various treatment groups (p<0.05). Conclusions: Sodium benzoate exposure can inhibit S. typhi growth and cause S. typhi resistant to chloramphenicol.&nbsp

Process of infection with bacteriophage phi X 174 XXXVIII. Replication of phi chi 174 replicative form in vivo

The replication of bacteriophage phi X 174 replicative-form DNA has been studied by structural analysis of pulse-labeled replicative-intermediate molecules. Such intermediates were identified by pulse-labeling with [13H]thymidine and separated into four major fractions (A, B, C, and D) in a propidium diiodide-cesium chloride buoyand density gradient. Sedimentation analysis of each of these fractions suggests the following features of phi X replicative-form DNA replication in vivo. (i) At the end of one cycle of replication, one daughter replicative form (RFII) contains a nascent plus (+) strand of the unit viral length, and the other daughter RFII contains small fragments of nascent minus (-) strand. (ii) Asymmetry is also associated with production of the first supercoiled RFI after addition of pulse label in that only the minus strand becomes radioactive. (iii) A supercoiled DNA (RFI') seems to occur in vivo. This DNA is observed at a position of greater density in a propidium diiodide-cesium chloride buoyant density gradient than normal RFI. (iv) A novel DNA component is observed, at a density greater than RFI, which releases, in alkali, a plus strand longer (1.5 to 1.7 times) than the unit viral length. These results are discussed in terms of the possible sequence of events in phi X 174 replicative-form replication in vivo

Mitochondrial ribosome assembly in Neurospora. Structural analysis of mature and partially assembled ribosomal subunits by equilibrium centrifugation in CsCl gradients

In Neurospora, one protein associated with the mitochondrial small ribosomal subunit (S-5, Mr 52,000) is synthesized intramitochondrially and is assumed to be encoded by mtDNA. When mitochondrial protein synthesis is inhibited, either by chloramphenicol or by mutation, cells accumulate incomplete mitochondrial small subunits (CAP-30S and INC-30S particles) that are deficient in S-5 and several other proteins. To gain additional insight into the role of S-5 in mitochondrial ribosome assembly, the structures of Neurospora mitochondrial ribosomal subunits, CAP-30S particles, and INC-30S particles were analyzed by equilibrium centrifugation in CsCl gradients containing different concentrations of Mg+2. The results show (a) that S-5 is tightly associated with small ribosomal subunits, as judged by the fact that it is among the last proteins to be dissociated in CsCl gradients as the Mg+2 concentration is decreased, and (b) that CAP-30S and INC-30S particles, which are deficient in S-5, contain at most 12 proteins that are bound as tightly as in mature small subunits. The CAP-30S particles isolated from sucrose gradients contain a number of proteins that appear to be loosely bound, as judged by dissociation of these proteins in CsCl gradients under conditions in which they remain associated with mature small subunits. The results suggest that S-5 is required for the stable binding of a subset of small subunit ribosomal proteins

Site-specific incorporation of phosphotyrosine using an expanded genetic code.

Access to phosphoproteins with stoichiometric and site-specific phosphorylation status is key to understanding the role of protein phosphorylation. Here we report an efficient method to generate pure, active phosphotyrosine-containing proteins by genetically encoding a stable phosphotyrosine analog that is convertible to native phosphotyrosine. We demonstrate its general compatibility with proteins of various sizes, phosphotyrosine sites and functions, and reveal a possible role of tyrosine phosphorylation in negative regulation of ubiquitination

Genetic incorporation of D-Lysine into diketoreductase in Escherichia coli cells

D-Lysine has been genetically introduced into diketoreductase in E. coli cells by utilization of an orthogonal Ph tRNA /Lysyl-tRNA synthetase pair. This is the first report on the genetic incoporation of D-amino acids into proteins, which may be generally applicable to a wide variety of applications