In vivo morphogenesis and growth characteristics of phages CM (Myoviridae) virulent forRhizobium meliloti

FourRhizobium meliloti bacteriophages belonging to theMyoviridae family of tailed phages were studied. Burst sizes (50–100 virulent particles per infected cell), adsorption rates (2.6–4.1×10^–9 ml/min), and latent periods (2–4 h) made this group heterogeneous. However, these characteristics indicate an important infection ability compared with other rhizobiophages. In vivo morphogenesis of phage CM1, studied by electron microscopy, seems to have steps similar to those of some other tailed phages such as coliphages.     

Phylogenetic diversification of immunoglobulin genes and the antibody repertoire

Immunoglobulins are encoded by a large multigene system that undergoes somatic rearrangement and additional genetic change during the development of immunoglobulin-producing cells. Inducible antibody and antibody-like responses are found in all vertebrates. However, immunoglobulin possessing disulfide-bonded heavy and light chains and domain-type organization has been described only in representatives of the jawed vertebrates. High degrees of nucleotide and predicted amino acid sequence identity are evident when the segmental elements that constitute the immunoglobulin gene loci in phylogenetically divergent vertebrates are compared. However, the organization of gene loci and the manner in which the independent elements recombine (and diversify) vary markedly among different taxa. One striking pattern of gene organization is the "cluster type" that appears to be restricted to the chondrichthyes (cartilaginous fishes) and limits segmental rearrangement to closely linked elements. This type of gene organization is associated with both heavy- and light-chain gene loci. In some cases, the clusters are "joined" or "partially joined" in the germ line, in effect predetermining or partially predetermining, respectively, the encoded specificities (the assumption being that these are expressed) of the individual loci. By relating the sequences of transcribed gene products to their respective germ-line genes, it is evident that, in some cases, joined-type genes are expressed. This raises a question about the existence and/or nature of allelic exclusion in these species. The extensive variation in gene organization found throughout the vertebrate species may relate directly to the role of intersegmental (V<==>D<==>J) distances in the commitment of the individual antibody-producing cell to a particular genetic specificity. Thus, the evolution of this locus, perhaps more so than that of others, may reflect the interrelationships between genetic organization and function.      

Influence of growth phases and desiccation on the degrees of unsaturation of fatty acids and the survival rates of rhizobia

The influence of growth phase on the evolution of cellular fatty acids (CFA) and survival of Sinorhizobium and Bradyrhizobium during desiccation and storage at different levels of relative humidity (R.H.) was studied. Lactobacillic, cis vaccenic and palmitic acids were the major fatty acids of S. meliloti RCR 2011, B. elkanii USDA 120 and B. japonicum 3.2, whatever the growth phase. An exchange of cis vaccenic with lactobacillic acid was observed during the course of growth. The degree of unsaturation (% unsaturated CFA/% saturated CFA = u/s ratio) was significantly higher during the mid logarithmic phase of growth. Survival rates immediately after desiccation were unaffected by the growth phase and the R.H. Furthermore, no correlation was found between survival rate and u/s ratio. During the course of desiccation, the u/s ratio of rhizobia decreased but the decrease was largely independent of the R.H. Optimum R.H. values for storage were in the range 22–67·8%, and S. meliloti was significantly more tolerant than the bradyrhizobia. Cells of rhizobia harvested in the lag phase of growth were more resistant to protracted storage than cells at other growth phases. Again, no correlation was found between u/s ratio and survival rates, despite the expected practical significance for screening for drought-tolerant micro-organisms.     

What can we learn from noncoding regions of similarity between genomes?

Background  

In addition to known protein-coding genes, large amounts of apparently non-coding sequence are conserved between the human and mouse genomes. It seems reasonable to assume that these conserved regions are more likely to contain functional elements than less-conserved portions of the genome.     

An interlaboratory comparison of physiological and genetic properties of four Saccharomyces cerevisiae strains

To select a Saccharomyces cerevisiae reference strain amenable to experimental techniques used in (molecular) genetic, physiological and biochemical engineering research, a variety of properties were studied in four diploid, prototrophic laboratory strains. The following parameters were investigated: 1) maximum specific growth rate in shake-flask cultures; 2) biomass yields on glucose during growth on defined media in batch cultures and steady-state chemostat cultures under controlled conditions with respect to pH and dissolved oxygen concentration; 3) the critical specific growth rate above which aerobic fermentation becomes apparent in glucose-limited accelerostat cultures; 4) sporulation and mating efficiency; and 5) transformation efficiency via the lithium-acetate, bicine, and electroporation methods. On the basis of physiological as well as genetic properties, strains from the CEN.PK family were selected as a platform for cell-factory research on the stoichiometry and kinetics of growth and product formation.     

Biological and physico-chemical assessment of hydroxyapatite (HA) with different porosity

HA with specific internal porosities was loaded with different antibiotics (ATBs) and then tested on its microbiological effectiveness. The HA purity was controlled with X-ray diffraction, IR and Raman spectrometry. Varying the sintering temperature and/or adding graphite and PMMA as porogenous agents lead to obtained micro- and meso-porosities. The biological tests concerned cell viability, proliferation and morphology (SEM), and the cytochemical staining of actin and vinculin. The micro- and meso-porous HA samples had an internal pore size of 1-10 microm and 10-50 microm, respectively. X-ray diffraction and FTIR confirmed the high purity of the HA. The cell viability tests with L132 cells confirmed the excellent cytocompatibility of HA, the graphite powder and the ATB vancomycine. Proliferation rate was assessed with MC3T3-E1 osteoblasts. All HA samples produced a higher proliferation than the controls; the micro-porous HA inducing the highest cell growth. The ATB impregnated HA also stimulated cell proliferation but in lower extend. Cytochemical staining of osteoblasts revealed a well-developed cytoskeleton with strong stress fibres. Labelling of the focal adhesion contacts with anti-vinculin showed a less developed adhesion process in the cells on the different HA substrates. It was possible to realize a highly pure hydroxyapatite with different but controlled porosities by varying the sintering temperature and/or addition of a porogenous agents. This purity and the micro-porosity stimulate significantly cell growth.     

Antibacterial activation of hydroxyapatite (HA) with controlled porosity by different antibiotics

In order to prevent the increasing frequency of per-operative infections, bioceramics can be loaded with anti-bacterial agents, which will release with respect to their chemical characteristics. A novel hydroxyapatite (HA) was elaborated with specific internal porosities for using as a bone-bioactive antibiotic (ATB) carrier material. UV spectrophotometry and bacteria inhibition tests were performed for testing the ATB adsorption and the microbiological effectiveness after loading with different antibiotics. The impregnation time, ATB impregnating concentration, impregnation condition and other factors, which might influence the ATB loading effect, were studied by exposure to different releasing solvents and different pathogenic bacteria: Staphylococcus aureus, Staphylococcus epidermidis and Escherichia coli. It clearly showed that the facility of ATB loading on this porous HA is even possible just under simple non-vacuum impregnation conditions in a not-so-long impregnating interval. The results also showed that, for all three types of ATB (vancomycin, ciprofloxacin and gentamicin), adsorbed amount on the micro-porous HA were hugely higher than that on dense HA. The micro-porosity of test HA had also significantly prolonged the release time of antibiotics even under mimic physiological conditions. Furthermore, it also has primarily proved by a pilot test that the antibacterial efficiency of crude micro-porous HA could be further significantly improved by other methods of functionalization such as cold plasma technique.