Environmental stresses inhibit splicing in the aquatic fungus Blastocladiella emersonii

Background  

Exposure of cells to environmental stress conditions can lead to the interruption of several intracellular processes, in particular those performed by macromolecular complexes such as the spliceosome.     

DNA rearrangements and phenotypic switching in prokaryotes

Microorganisms have numerous strategies for coping with environmental changes. In many systems, a single cell has the capacity to generate a seemingly infinite array of phenotypic variants in just a few generations of growth. The resulting heterogeneous population is well equipped for sudden environmental change; even if only a few cells in the population possess a phenotype needed for survival, these cells have the capacity to regenerate a similarly diverse population. Phenotypic switching in these systems usually results from high-frequency DNA rearrangements which are the subject of this review.     

Isolation of a second cryptic plasmid from Mycoplasma mycoides subsp. mycoides

Plasmids have rarely been detected in organisms constituting the genus Mycoplasma. Recently, the isolation of a cryptic plasmid from Mycoplasma mycoides subsp. mycoides has been described, and we report here the isolation of a second cryptic plasmid from this species. Restriction map and Southern blot analyses show that the second plasmid is distinct from the previously described plasmid, although a limited region of homology was detected. The availability of mycoplasmal cryptic plasmids may lead to the development of cloning vectors that replicate in these organisms.     

Gene transfer in Mycoplasma arthritidis: transformation, conjugal transfer of Tn916, and evidence for a restriction system recognizing AGCT.

Mycoplasma arthritidis is a rat pathogen causing a severe polyarthritis. The study of its pathogenic mechanisms has been hampered by the lack of genetic systems for use with M. arthritidis. Described here are procedures for genetic transformation of M. arthritidis and conjugal transfer of Tn916 from an enterococcal donor to M. arthritidis. The location of Tn916 insertion sites in the mycoplasmal chromosome was random, suggesting that Tn916 may be useful as an insertional mutagen in this organism. Additionally, a restriction and modification system was identified which presented a strong barrier to gene transfer. For transformation, the restriction system was circumvented by using DNA that was modified in vitro with the appropriate site-specific methylase (AluI).     

A chicken repetitive DNA sequence that is highly sensitive to single-strand specific endonucleases

A DNA sequence consisting of the 5-mer AGAGG repeated tandemly 32 times has been detected in a chicken genomic clone and found to be present in about 2000 copies per chicken genome. This sequence was highly susceptible to single-strand specific endonucleases isolated from Aspergillus oryzae (S1) and mung bean, but cleavage by a single-strand specific endonuclease isolated from Neurospora crassa occurred only at a pH below 5.5. Endonucleolytic cutting of the AGAGG sequence by the single-strand specific enzymes required a supercoiled substrate and was independent of ionic strength.     

Variations in the surface proteins and restriction enzyme systems of Mycoplasma pulmonis in the respiratory tract of infected rats

Restriction and modification (R-M) systems are generally thought to protect bacteria from invasion by foreign DNA. This paper proposes the existence of an alternative role for the phase-variable R-M systems encoded by the hsd loci of Mycoplasma pulmonis. Populations of M. pulmonis cells that arose during growth in different environments were compared with respect to R-M activity and surface antigen production. When M. pulmonis strain X1048 was propagated in laboratory culture medium, > 95% of colony-forming units (cfu) lacked R-M activity and produced the variable surface protein VsaA. Mycoplasmas isolated from the nose of experimentally infected rats also lacked R-M activity and produced VsaA. In contrast, the cell population of mycoplasmas isolated from the lower respiratory tract of the infected rats was more complex. The most dramatic results were obtained for mycoplasmas isolated from the trachea. At 14 days postinfection, 38% of mycoplasma isolates produced a Vsa protein other than VsaA, and 34% of isolates had active restriction systems. These data suggest that differences in selection pressures in animal tissues affect the surface proteins and the R-M activity of the mycoplasmal cell population. We propose that variations in the production of R-M activity and cell surface proteins are important for the survival of the mycoplasma within the host.     

Transposon mutagenesis of Mycoplasma gallisepticum by conjugation with enterococcus faecalis and determination of insertion site by direct genomic sequencing

Few genetic systems for studying mycoplasmas exist, but transposon Tn916 has been shown to transpose into the genomes of some species and can be used as an insertional mutagen. In the current study, the ability of Enterococcus faecalis to serve as a donor for the conjugative transfer of transposon Tn916 into the genome of the avian pathogen Mycoplasma gallisepticum strain PG31 was examined. Transconjugants were obtained at a frequency of > or =6 x 10(-8) per recipient CFU. To determine the transposon insertion site, an oligonucleotide primer corresponding to the 3' end of Tn916 was designed for the purpose of directly sequencing genomic DNA without PCR amplification. Using the direct sequencing approach, Tn916 was shown to insert into any of numerous sites in the M. gallisepticum genome. This is the first report of conjugal transposition of Tn916 into the M. gallisepticum genome. The ability to determine transposon insertion sites in mycoplasmas by genomic sequencing has not been previously described and allows rapid sequence analysis of transposon-generated mutants.     

Assessment of post extraction complications in Indians

Extraction is one of the commonest procedures in dentistry. Therefore, it is of interest to evaluate the post extraction complications in patients undergoing extractions of permanent teeth. A total of 70 adult patients who had undergone dental extractions and presented with post -operative complications were included in the study and evaluated. Data collected was statistically analyzed using SPSS software and results obtained. Most of the patients with post extraction complications were in the age group of 31-40 years (21.6%), followed by 21-30 (20.2%) and 61-70 years (20.2%). Dry socket (39.19%) was the common post extraction complication in our study especially in the age group of 31-40 years. There was a statistically significant association between age of the patients and the post extraction complications (p<0.001). In our study, post extraction complications were commonly observed in age group of 31-40 years with a predilection for males. Dry socket was the most common post extraction complication. Age of the patient has a significant effect on post extraction complications. However, gender, smoking habits and systemic diseases have no influence on post extraction complications.