Vacuole inheritance regulates cell size and branching frequency of Candida albicans hyphae

Hyphal growth of Candida albicans is characterized by asymmetric cell divisions in which the subapical mother cell inherits most of the vacuolar space and becomes cell cycle arrested in G1, while the apical daughter cell acquires most of the cell cytoplasm and progresses through G1 into the next mitotic cell cycle. Consequently, branch formation in hyphal compartments is delayed until sufficient cytoplasm is synthesized to execute the G1 'START' function. To test the hypothesis that this mode of vacuole inheritance determines cell cycle progression and therefore the branching of hyphae, eight tetracycline-regulated conditional mutants were constructed that were affected at different stages of the vacuole inheritance pathway. Under repressing conditions, vac7 , vac8 and fab1 mutants generated mycelial compartments with more symmetrically distributed vacuoles and increased branching frequencies. Repression of VAC1 , VAM2 and VAM3 resulted in sparsely branched hyphae, with large vacuoles and enlarged hyphal compartments. Therefore, during hyphal growth of C. albicans the cell cycle, growth and branch formation can be uncoupled, resulting in the investment of cytoplasm to support hyphal extension at the expense of hyphal branching.     

Direct trade-off between cyanogenesis and resistance to a fungal pathogen in lima bean (Phaseolus lunatus L.)

1.  Plants are simultaneously attacked by multiple herbivores and pathogens. While some plant defences act synergistically, others trade-off against each other. Such trade-offs among resistances to herbivores and pathogens are usually explained by the costs of resistance, i.e. resource limitations compromising a plant's overall defence.
2.  Here, we demonstrate that trade-offs can also result from direct negative interactions among defensive traits. We studied cyanogenesis (release of HCN) of lima bean (Fabaceae: Phaseolus lunatus ) and effects of this efficient anti-herbivore defence on resistance to a fungal pathogen (Melanconiaceae: Colletotrichum gloeosporioides ).
3.  Leaf tissue destruction by fungal growth was significantly higher on high cyanogenic (HC) lima bean accessions than on low cyanogenic (LC) plants. The susceptibility of HC accessions to the fungal pathogen was strongly correlated to reduced activity of resistance-associated polyphenol oxidases (PPOs) in leaves of these plants. LC accessions, in contrast, showed high PPO activity, which was correlated with distinct resistance to C. gloeosporioides .
4.  Experimentally applied, gaseous HCN reduced PPO activity and significantly increased the size of lesions caused by C. gloeosporioides in LC leaves.
5.  Field observations of a wild lima bean population in Mexico revealed a higher infection rate of HC compared to LC plant individuals. The types of lesions observed on the different cyanogenic plants in nature were similar to those observed on HC and LC plants in the laboratory.
6.   Synthesis. We suggest that cyanogenesis of lima bean directly trades off with plant defence against fungal pathogens and that the causal mechanism is the inhibition of PPOs by HCN. Our findings provide a functional explanation for the observed phenomenon of the low resistance of HC lima beans in nature.     

Scavenging of superoxide and hydrogen peroxide in blue‐green algae (cyanobacteria)

Blue‐green algae (cyanobacteria) have evolved as the most primitive, oxygenic, plant‐type photosynthetic organisms. Within a single prokaryotic cell, they have uniquely accommodated both oxygenic photosynthesis and aerobic respiration, which are known to produce superoxide and hydrogen peroxide as inevitable byproducts. Two types of superoxide dismutase have been characterized in both N₂‐fixing and non‐N₂‐fixing cyanobacteria, namely cytosolic iron‐containing superoxide dismutase and thylakoid‐bound manganese‐containing superoxide dismutase. No qualitative differences between various cell types (vegetative cells, heterocysts) were found. In contrast to chloroplasts, most of the cyanobacterial species show catalatic activity. From two species the corresponding enzymes have been characterized as typical prokaryotic (bifunctional) catalase‐peroxidases with homologies to cytochrome c peroxidases and ascorbate peroxidases. In addition to catalatic activity, some strains exhibit ascorbate peroxidase activity, but to date there are no reports detailing purification and characterization.
Cyanobacteria were found to contain low intracellular ascorbate concentrations (30‐100 µ M ) and 2‐5 m M glutathione. Both monodehydroascorbate and glutathione reductase activities were detected in most species examined, whereas dehydroascorbate reductase activity was absent. The question as to whether a glutathione‐ascorbate cycle exists in cyanobacteria cannot be answered at present.     

Molecular characterization of Lactobacillus curvatus and Lact. sake isolated from sauerkraut and their application in sausage fermentations

Lactobacillus curvatus and Lact. sake are best adapted to meat fermentations and dominate the flora during the whole process. In fermenting sauerkraut, Leuconostoc mesenteroides subsp. mesenteroides is the major organism only during the early phase. In this environment Lact. curvatus and Lact. sake provide up to 50% of the microbial flora especially of the later phase, depending on the process conditions. Strains of Lact. curvatus and Lact. sake isolated from fermenting sauerkraut were identified by hybridization with species specific 23S rRNA-targeted oligonucleotide probes and further characterized. In 59 of 72 strains, plasmid DNA was detected. Small cryptic plasmids of 20 strains were found to be homologous with pLc2, a 2·6 kb plasmid from Lact. curvatus LTH683, which was originally isolated from meat. The ability to compete was investigated in fermenting sausages of two strains each of Lact. curvatus and Lact. sake isolated from sauerkraut. One strain each of Lact. curvatus and Lact sake was found to outnumber the meat-borne flora and govern the process.     

The N-terminus promotes oligomerization of the Escherichia coli initiator protein DnaA

Initiation of chromosome replication in Escherichia coli is governed by the interaction of the initiator protein DnaA with the replication origin oriC. Here we present evidence that homo-oligomerization of DnaA via its N-terminus (amino acid residues 1-86) is also essential for initiation. Results from solid-phase protein-binding assays indicate that residues 1-86 (or 1-77) of DnaA are necessary and sufficient for self interaction. Using a 'one-hybrid-system' we found that the DnaA N-terminus can functionally replace the dimerization domain of coliphage lambda cl repressor: a lambdacl-DnaA chimeric protein inhibits lambda plasmid replication as efficiently as lambdacI repressor. DnaA derivatives with deletions in the N-terminus are incapable of supporting chromosome replication from oriC, and, conversely, overexpression of the DnaA N-terminus inhibits initiation in vivo. Together, these results indicate that (i) oligomerization of DnaA N-termini is essential for protein function during initiation, and (ii) oligomerization does not require intramolecular cross-talk with the nucleotide-binding domain III or the DNA-binding domain IV. We propose that E. coli DnaA is composed of largely independent domains - or modules - each contributing a partial, though essential, function to the proper functioning of the 'holoprotein'.     

Screening of some Romanian plants for their activity against medically important insects

The effects of the action of extracts from 82 plant species included in 39 families of indigenous flora against the larvae and adults of house fly (Musca domestica), the mosquitoes (Aedes aegypti and Anopheles atroparvus) and the German cockroach (Blattella germanica) are presented. Some of the extracts were prepared from air-dried and ground plant material which was exhaustively extracted with successive solvents of different polarity: ethyl ether, ethyl alcohol and water. Other extracts were prepared either by distillation of the whole water extracts of 24 hours macerated plants or by water extraction from residues of plants remained after distillation. These plant extracts act as toxicants, growth and development and reproduction inhibitors and repellents. The differential responses induced by these plant extracts on assessed insects were influenced by several factors such as the plant species, the solvents used for extractions, the species and the stages of insect life and also the methods employed for evaluation. Some of the tested plants appear to have a great potential for providing safer insect control agents.