Influence of bacteria and salinity on diatom biogenic silica dissolution in estuarine systems

Dissolution of diatom biogenic silica (bSiO₂) in estuaries and its control by water salinity and bacteria were investigated using the river euryhaline species Cyclotella meneghiniana as a model. Laboratory-controlled bioassays conducted at different salinities with an estuarine bacteria inoculum showed a faster dissolution of diatom bSiO₂ at the lowest salinity where bacteria were the most abundant. However in another experiment, salinity increase clearly enhanced the dissolution of cleaned frustules (organic matter free). The presence of active bacteria might therefore predominate on the effect of salinity for freshly lysed diatoms whereas salinity might rather control dissolution of organic-matter-free frustule remains. Incubation of cultivated diatoms at different protease concentrations revealed that high proteolytic activities had little effect on bSiO₂ dissolution at a 1-month scale in spite of an efficient removal of organic matter from the frustules. Altogether it is hypothesized that bacterial colonization increases bSiO₂ dissolution by creating a microenvironment at the diatom surface with high ectoproteolytic activity but also via the release of metabolic byproducts since the presence of organic matter seems generally to facilitate diatom bSiO₂ dissolution.     

DNA methylation in different origin clonal offspring from a mature <Emphasis Type="Italic">Sequoiadendron giganteum</Emphasis> genotype

A meristem-issued rejuvenated line was obtained in 1986 from a 100-year-old Sequoiadendron giganteum tree and has been since then micropropagated in tissue culture conditions maintaining its juvenile-like characteristics. By contrast, grafts and rooted microcuttings from the same genotype planted in outdoor conditions for several years exhibited mature foliage traits and the grafts started to produce cones, which are obvious indicators of physiological aging. These three different clonal lines were compared with regard to global DNA methylation assessed by HPLC. The in vitro rejuvenated line showed a much higher level of DNA methylation (23% as average value) than the two other outdoor origins from the same clone which displayed similar degrees of global methylation (average values of 13.4% for the grafts and 13.8% for the cuttings). Overall these DNA global methylation values obtained for the first time in S. giganteum are consistent with the level of methylation reported for many plants using the same HPLC protocols. The fact that shoots exhibiting a juvenile-like leaf morphology can be characterized by higher DNA methylation than mature-like ones is discussed in relation to physiological aging, referring to other studies on the same topic.     

Phospho-ubiquitin-PARK2 complex as a marker for mitophagy defects

The E3 ubiquitin ligase PARK2 and the mitochondrial protein kinase PINK1 are required for the initiation of mitochondrial damage-induced mitophagy. Together, PARK2 and PINK1 generate a phospho-ubiquitin signal on outer mitochondrial membrane proteins that triggers recruitment of the autophagy machinery. This paper describes the detection of a defined 500-kDa phospho-ubiquitin-rich PARK2 complex that accumulates on mitochondria upon treatment with the membrane uncoupler CCCP. Formation of this complex is dependent on the presence of PINK1 and is absent in mutant forms of PARK2, whereby mitophagy is also arrested. These results signify a functional signaling complex that is essential for the progression of mitophagy. The visualization of the PARK2 signaling complex represents a novel marker for this critical step in mitophagy and can be used to monitor mitophagy progression in PARK2 mutants and to uncover additional upstream factors required for PARK2-mediated mitophagy signaling.     

Influence of long term treatment with 3-methylcholanthrene or carbaryl on mixed-function oxidase activity in 3T3 fibroblasts: Studies by microspectrofluorimetry on single cells

Using benzo(a)pyrene (BaP) as a probe for aryl hydrocarbon hydroxylase (AHH) activity, differences in mixed-function oxidase (MFO) activity were observed using microspectrofluorimetry in single living cells during long term treatment with 3-methylcholanthrene (3-MC) or carbaryl. Although these two compounds differ in chemical structure, similar effects were observed in 3T3 cell populations. The results suggest that the two compounds activate the same enzymatic system and that individual cells of a supposed homogeneous cell population are not equally sensitive to xenobiotics, i.e. subpopulations were observed which have differences in AHH activity.     

Diversity of Anopheles species and trophic behavior of putative malaria vectors in two malaria endemic areas of northwestern Thailand

We determined the species diversity, blood‐feeding behavior, and host preference of Anopheles mosquitoes in two malaria endemic areas of Tak (Mae Sot District) and Mae Hong Son (Sop Moei District) Provinces, located along the Thai border with Myanmar, during a consecutive two‐year period. Anopheline mosquitoes were collected using indoor and outdoor human‐landing captures and outdoor cow‐baited collections. Mosquitoes were initially identified using morphological characters, followed by the appropriate multiplex AS‐PCR assay for the identification of sibling species within Anopheles (Cellia) complexes and groups present. Real‐time PCR was performed for parasite‐specific detection in mosquitoes (Plasmodium spp. and Wuchereria bancrofti). A total of 7,129 Anopheles females were captured, 3,939 from Mae Sot and 3,190 from Sop Moei, with 58.6% and 37% of all anophelines identified as An. minimus, respectively. All three malaria vector complexes were detected in both areas. One species within the Minimus Complex (An. minimus) was present along with two related species in the Funestus Group, (An. aconitus, An. varuna), two species within the Dirus Complex (An. dirus, An. baimaii), and four species within the Maculatus Group (An. maculatus, An. sawadwongporni, An. pseudowillmori, and An. dravidicus). The trophic behavior of An. minimus, An. dirus, An. baimaii, An. maculatus, and An. sawadwongporni are described herein. The highest An. minimus densities were detected from February through April of both years. One specimen of An. minimus from Mae Sot was found positive for Plasmodium vivax.     

Mutations in mating-type genes greatly decrease repeat-induced point mutation process in the fungus Podospora anserina.

RIP (Repeat-Induced point Mutation) and PR (Premeiotic Recombination) are two developmentally regulated processes in filamentous ascomycetes. RIP detects and mutates duplicated DNA sequences, while PR results in deletion of the interstitial sequence between cis-duplicated DNA sequences. These two silencing processes take place between fertilization and premeiotic replication, a period during which the mating-type genes play an active role in several developmental processes. Previous studies have shown that mutations in the mating-type genes affect the development of the fruiting body. This study provides evidence that mutations in the mating-type genes reduce the frequency of RIP and PR. It establishes that alleles which have the more stringent effect on fruiting-body development, have also the strongest effect on RIP and PR frequencies. We propose two models for the relation between mating-type genes and RIP and PR, one based on the direct control of RIP and PR by mating-type regulatory proteins, the other based on an indirect effect through the control of a development step during which RIP and PR take place.     

Poly-l -lysine-gold complexes used at different pH are probes for differential detection of glycosaminoglycans and phosphoproteins in the predentine and dentine of rat incisor

Summary At neutral pH, poly-l-lysine-gold complexes labelled the predentine extensively, whereas in dentine the number of gold complexes was reduced by half. Hyaluronidase pretreatment of the section at pH 6.8, prior to labelling, suppressed most of the staining in predentine and did not affect dentine. In contrast, alkaline phosphatase pretreatment at pH 9 enhanced the gold complex labelling in predentine and removed most of the labelling in dentine. This proves that at pH 7.2, the polyanions which are stained include a heterogeneous population of glycosaminoglycans, located in predentine, and phosphoproteins, visualized in dentine. At acidic pH levels (2.9 and 1.1), the number of scored gold complexes decreased, but the ratio between predentine and dentine labelling remained constant. Hyaluronidase pretreatment removed or firmly reduced the gold complex labelling both in predentine and dentine, whereas alkaline phosphatase pretreatment of the sections at pH 9 prior to labelling did not induce any change. This argues in favour of an increased specificity of polylysine-gold complex staining for glycosaminoglycans, stained at low pH in both predentine and dentine. Differential staining of glycosaminoglycans and phosphoproteins according to the pH provides a useful tool for studying the role played respectively by the two matrix components in dentine mineralization.