Bacterial lessons on organelle division

Mitochondria and chloroplasts arose from bacterial endosymbionts about a billion years ago. This ancestry is now showing us how these organelles divide in modem cells.

Diverse eukaryotes have retained mitochondrial homologues of the bacterial division protein FtsZ

Mitochondrial fission requires the division of both the inner and outer mitochondrial membranes. Dynamin-related proteins operate in division of the outer membrane of probably all mitochondria, and also that of chloroplasts – organelles that have a bacterial origin like mitochondria. How the inner mitochondrial membrane divides is less well established. Homologues of the major bacterial division protein, FtsZ, are known to reside inside mitochondria of the chromophyte alga Mallomonas, a red alga, and the slime mould Dictyostelium discoideum, where these proteins are likely to act in division of the organelle. Mitochondrial FtsZ is, however, absent from the genomes of higher eukaryotes (animals, fungi, and plants), even though FtsZs are known to be essential for the division of probably all chloroplasts. To begin to understand why higher eukaryotes have lost mitochondrial FtsZ, we have sampled various diverse protists to determine which groups have retained the gene. Database searches and degenerate PCR uncovered genes for likely mitochondrial FtsZs from the glaucocystophyte Cyanophora paradoxa, the oomycete Phytophthora infestans, two haptophyte algae, and two diatoms – one being Thalassiosira pseudonana, the draft genome of which is now available. From Thalassiosira we also identified two chloroplast FtsZs, one of which appears to be undergoing a C-terminal shortening that may be common to many organellar FtsZs. Our data indicate that many protists still employ the FtsZ-based ancestral mitochondrial division mechanism, and that mitochondrial FtsZ has been lost numerous times in the evolution of eukaryotes.

Trapping of a spiral-like intermediate of the bacterial cytokinetic protein FtsZ

The earliest stage in bacterial cell division is the formation of a ring, composed of the tubulin-like protein FtsZ, at the division site. Tight spatial and temporal regulation of Z-ring formation is required to ensure that division occurs precisely at midcell between two replicated chromosomes. However, the mechanism of Z-ring formation and its regulation in vivo remain unresolved. Here we identify the defect of an interesting temperature-sensitive ftsZ mutant (ts1) of Bacillus subtilis. At the nonpermissive temperature, the mutant protein, FtsZ(Ts1), assembles into spiral-like structures between chromosomes. When shifted back down to the permissive temperature, functional Z rings form and division resumes. Our observations support a model in which Z-ring formation at the division site arises from reorganization of a long cytoskeletal spiral form of FtsZ and suggest that the FtsZ(Ts1) protein is captured as a shorter spiral-forming intermediate that is unable to complete this reorganization step. The ts1 mutant is likely to be very valuable in revealing how FtsZ assembles into a ring and how this occurs precisely at the division site.

Changes in bacterial concentration in the liver correlate with that in the hepaticojejunostomy after bile duct reconstruction: implication in the pathogenesis of postoperative cholangitis

Postoperative cholangitis is a frequent and unpredictable complication of unknown etiology following bile duct reconstruction (BDR), particularly for biliary atresia. This study was undertaken to correlate the growth of bacteria in the hepaticojejunostomy with that in the liver after BDR. Quantitative bacterial culture was done on the specimens taken from the liver and from the hepaticojejunostomy at 1 week (group 1, n = 7), 1 month (group 2, n = 7), and 2 months (group 3, n = 7) following BDR with Roux-en-Y hepaticojejunostomy in piglets after 2 weeks of common bile duct ligation. The histological examination of the liver and the hepaticojejunostomy, as well as serial monitoring of hemogram and liver function tests, were performed to correlate the findings with the bacterial concentration of the liver and the hepaticojejunostomy following BDR. The bacterial concentration of the hepaticojejunostomy, expressed as log10 colony-forming units per gram (log10 CFU/g) of the hepaticojejunostomy, showed a progressive decrease from 8.38 ± 1.36 in group 1, 7.07 ± 2.54 in group 2, to 3.56 ± 1.31 in group 3 (p = 0.001). The log10 CFU/g of the liver also showed a progressive decrease from 5.02 ± 1.59 in group 1, 3.16 ± 1.56 in group 2, to 2.19 ± 1.09 in group 3 (p = 0.006). There was a significant positive correlation of the log10 CFU/g of the liver (n = 21) with that of the hepaticojejunostomy (n = 21) following BDR (r = 0.600, p = 0.004). Most of the infectious pathogens isolated from the liver were also isolated from the hepaticojejunostomy. The changes in hemoglobin, bilirubin, albumin, and ammonia significantly correlated with the changes of the bacterial concentration of the liver. The results of the study suggests that hepatic bacterial proliferation after BDR is significantly affected by microbial overgrowth in the bilioenteric anastomosis and is associated with deteriorated liver function and hemogram.

Suppression by abscisic acid of lignin production and monolignol pathway gene expression in interactions of Arabidopsis with oomycete and bacterial pathogens

The phytohormone, abscisic acid (ABA) has been shown to influence the outcome of the interactions between various hosts with biotrophic and hemibiotrophic pathogens. Susceptibility to avirulent isolates can be induced in plants by addition of low physiological concentrations of ABA. In contrast, addition of ABA biosynthesis inhibitors induced resistance following challenge of plants by virulent isolates. ABA deficient mutants of Arabidopsis, such as aba1-1, were resistant to virulent isolates of Peronospora parasitica. In interactions of Arabidopsis with avirulent isolates of Pseudomonas syringae pv. tomato, susceptibility was induced following addition of ABA or imposition of drought stress. These results indicate a pivotal, albiet undefined, role for ABA in determining either susceptibility or resistance to pathogen attack. We have found that the production of the cell wall strengthening compound, lignin, is increased during resistant interactions of aba1-1 but suppressed in ABA-induced susceptible interactions. Using RT-PCR and microarray analysis we have found down-regulation by ABA of key genes of the phenylpropanoid pathway especially of those genes involved directly in lignin biosynthesis. ABA also down-regulates a number of genes in other functional classes including those involved in defence and cell signalling.

Water quality, bacterial flora and production in shrimp farms in Sri Lanka

This study investigated the possibilities of improvement in the brackish water shrimp culture industry in Sri Lanka. Feeding rates could be further reduced without negative effect on shrimp growth while improving effluent water quality. Improvements of feed quality and pond management practices were also suggested.

Conservation genetics of the New Holland mouse Pseudomys novaehollandiae, Waterhouse, 1843 (Rodentia: Muridae) : an analysis of mitochondrial DNA control region variation

An investigation of the genetic diversity of New Holland mouse populations using DNA. Ten distinct restriction enzyme fragment patterns or haplotypes were detected. From the fragment patterns, estimates of genetic divergence between the haplotypes revealed a degree of genetic structuring within New Holland mouse with four population assemblages apparent.

Molecular genetics and comparative genomics reveal RNAi is not functional in malaria parasites

Techniques for targeted genetic disruption in Plasmodium, the causative agent of malaria, are currently intractable for those genes that are essential for blood stage development. The ability to use RNA interference (RNAi) to silence gene expression
would provide a powerful means to gain valuable insight into the pathogenic blood stages but its functionality in Plasmodium remains controversial. Here we have used various RNA-based gene silencing approaches to test the utility of RNAi in malaria
parasites and have undertaken an extensive comparative genomics search using profile hidden Markov models to clarify whether RNAi machinery
exists in malaria. These investigative approaches revealed that Plasmodium lacks the enzymology required for RNAi-based ablation of gene expression
and indeed no experimental evidence for RNAi was observed. In its absence, the most likely explanations for previously reported RNAi-mediated knockdown are either the general toxicity of introduced RNA (with global down-regulation of gene expression) or a specific antisense effect mechanistically distinct from RNAi, which will need systematic
analysis if it is to be of use as a molecular genetic tool for malaria parasites.

Immobilization of bacterial recombinant proteins

Recombinant α-L Rhamnosidase has several potential applications in citrus fruit juice processing industries. Immobilized recombinant α-L Rhamnosidase further provides an added advantage to this industrially important enzyme. Various techniques have been used to immobilize native rhamnosidase from fungal origin and applications were explored in great details by several workers. (Puri et al., 1996, 2000, 2001)

A recombinant rhamnosidase from a bacterial source was expressed in E.coli has been immobilized in calcium alginate beads (entrapment method). A batch bioreactor was created for the hydrolysis of naringin using immobilized recombinant α-L Rhamnosidase under shaking and stationary conditions and it was found to hydrolyze naringin effectively. The system was efficient to hydrolyze narigin under shaking conditions and was operationally stable up to 9 days. A high percent hydrolysis of naringin was achieved at pH 7.5 and 60˚C by immobilized rhamnosidase. Entrapped rhamnosidase was able to hydrolyze naringin content in kinnow juice repeatedly and this feature makes this technique economically suitable for debittering of fruit juices.

Insights into bacterial genome composition through variable target GC content profiling

This study presents a new computational method for guanine (G) and cytosine (C), or GC, content profiling based on the idea of multiple resolution sampling (MRS). The benefit of our new approach over existing techniques follows from its ability to locate significant regions without prior knowledge of the sequence, nor the features being sought. The use of MRS has provided novel insights into bacterial genome composition. Key findings include those that are related to the core composition of bacterial genomes, to the identification of large genomic islands (in Enterobacterial genomes), and to the identification of surface protein determinants in human pathogenic organisms (e.g., Staphylococcus genomes). We observed that bacterial surface binding proteins maintain abnormal GC content, potentially pointing to a viral origin. This study has demonstrated that GC content holds a high informational worth and hints at many underlying evolutionary processes. For online Supplementary Material, see www.liebertonline.com.

Bacterial genomic G + C composition-eliciting environmental adaptation

Bacterial genomes reflect their adaptation strategies through nucleotide usage trends found in their chromosome composition. Bacteria, unlike eukaryotes contain a wide range of genomic G + C. This wide variability may be viewed as a response to environmental adaptation. Two overarching trends are observed across bacterial genomes, the first, correlates genomic G + C to environmental niches and lifestyle, while the other utilizees intra-genomic G + C incongruence to delineate horizontally transferred material. In this review, we focus on the influence of several properties including biochemical, genetic flows, selection biases, and the biochemical-energetic properties shaping genome composition. Outcomes indicate a trend toward high G + C and larger genomes in free-living organisms, as a result of more complex and varied environments (higher chance for horizontal gene transfer). Conversely, nutrient limiting and nutrient poor environments dictate smaller genomes of low GC in attempts to conserve replication expense. Varied processes including translesion repair mechanisms, phage insertion and cytosine degradation has been shown to introduce higher AT in genomic sequences. We conclude the review with an analysis of current bioinformatics tools seeking to elicit compositional variances and highlight the practical implications when using such techniques.

DIOXOLANE NORBORNANE / NORBORNENE COMPOUNDS SUITABLE AS ANTIMICROBIAL AGENTS TO TREAT BACTERIAL INFECTIONS

The invention provides a compound including : A core having a first face and a second face; A binding portion attached to the first face of the core, wherein the binding portion is capable of binding to an anionic group present in a cell membrane of a microorganism; and A hydrophobic portion attached to the second face of the core, wherein the hydrophobic portion is capable of interacting with the cell membrane of the microorganism; and The core comprises a dioxolane norbornane / norbornene of formula (II): Or a salt or ion thereof, wherein R' is a moiety forming part of a hydrophobic portion; R2 is a first binding portion; and R3 is a seconding binding portion. The invention also provides compositions including at least one such compound. The invention also provides methods and uses for treatment or prophylaxis of infection of a mammal by a microorganism, and methods and uses for treating or preventing contamination of a substrate by a microorganism, using the compounds and compositions.