Fine-structural alterations in Leishmania tropica within human macrophages exposed to antileishmanial drugs in vitro

The mechanism of action of antileishmanial compounds is poorly understood. Ultrastructural changes in Leishmania tropica within human macrophages exposed in vitro to Pentostam, pentamidine, amphotericin B, WR 6026, ketoconazole, and Formycin B were examined in these experiments. In Pentostam-treated cultures, some organisms exhibited diminished definition of mitochondrial and other membranes, while other organisms had completely disintegrated. Pentostam-exposed macrophages demonstrated loss of membrane definition in the absence of further alterations; it is therefore hypothesized that impaired macrophage membrane function may contribute towards the effect of this drug against macrophage-contained organisms. Leishmania parasites in pentamidine-treated cultures initially demonstrated swollen kinetoplasts and fragmentation of the kinetoplast DNA core. The initial observed effect of the other four drugs on the parasites was cytoplasmic condensation. These ultrastructural studies suggest that all five non-antimonial drugs may have different mechanisms of action than antimony (Pentostam) against Leishmania.     

Plasmodium falciparum: isolation and purification of spontaneously released merozoites by nylon membrane sieves

A new procedure for isolating spontaneously released merozoites from in vitro cultures of Plasmodium falciparum (FVO and FCB strains) is described. The mature forms of relatively synchronous cultures containing predominantly trophozoites and few schizonts were concentrated with Plasmagel and then incubated at 37 C, without adding fresh red blood cells, until trophozoites matured into schizonts. Merozoites which were subsequently released were harvested and freed from host red blood cell material by low-speed centrifugations and nylon membrane sieves (3- and 1.2-μm pore size). From a culture containing about 5.2 × 10⁹ mature-form parasites, a total of about 10.7 × 10⁹ merozoites were released during three consecutive harvests and about 69% of these merozoites were recovered after the isolation and purification procedures. As demonstrated by both light and electron microscopy, most merozoites were morphologically intact and the merozoite preparations were free of host cell constituents. SDS-acrylamide gel electrophoresis confirmed the absence of host cell material and also showed that merozoites had a complex protein pattern of apparent molecular weights between 225 and 15 kdaltons. Such purified merozoite preparations will be invaluable for malaria immunization studies, for identification of protective antigens of P. falciparum, and for other immunological and biochemical studies.     

Plasmodium falciparum: loss of knobs on the infected erythrocyte surface after long-term cultivation.

After long-term in vitro cultivation in human erythrocytes, variants of three strains of the malaria parasite Plasmodium falciparum no longer produce the “knob” alterations on the host erythrocyte surface. The time in continuous culture before knobs failed to appear ranged from 18 months for the Gambian strain FCR-4 to 33 months for the Vietnamese strain FCR-1. The loss of knobs is correlated with the inability to concentrate trophozoites, schizonts, and segmenters from these variant lines by the use of gelatin-containing media. This is the first report of a change in Plasmodium falciparum or its host cell as a consequence of long-term culture.     

Biodeterioration of Mayan buildings at uxmal and tulum,Mexico

Uxmal and Tulum are two important Mayan sites in the Yucatan peninsula. The buildings are mainly composed of limestone and grey/black discoloration is seen on exposed walls and copious greenish biofilms on inner walls. The principal microorganisms detected on interior walls at both Uxmal and Tulum were cyanobacteria; heterotrophic bacteria and filamentous fungi were also present. A dark‐pigmented mitosporic fungus and Bacillus cereus, both isolated from Uxmal, were shown to be acidogenic in laboratory cultures. Cyanobacteria belonging to rock‐degrading genera Synechocystis and Gloeocapsa were identified at both sites. Surface analysis previously showed that calcium ions were present in the biofilms on buildings at Uxmal and Tulum, suggesting the deposition of biosolubilized stone. Apart from their potential to degrade the substrate, the coccoid cyanobacteria supply organic nutrients for bacteria and fungi, which can produce organic acids, further increasing stone degradation.     

Terrigenous sediment-dominated reef platform infilling: an unexpected precursor to reef island formation and a test of the reef platform size–island age model in the Pacific

Low-lying coral reef islands are considered highly vulnerable to climate change, necessitating an improved understanding of when and why they form, and how the timing of formation varies within and among regions. Several testable models have been proposed that explain inter-regional variability as a function of sea-level history and, more recently, a reef platform size model has been proposed from the Maldives (central Indian Ocean) to explain intra-regional (intra-atoll) variability. Here we present chronostratigraphic data from Pipon Island, northern Great Barrier Reef (GBR), enabling us to test the applicability of existing regional island evolution models, and the platform size control hypothesis in a Pacific context. We show that reef platform infilling occurred rapidly (~4–5 mm yr⁻¹) under a “bucket-fill” type scenario. Unusually, this infilling was dominated by terrigenous sedimentation, with platform filling and subsequent reef flat formation complete by ~5000 calibrated years BP (cal BP). Reef flat exposure as sea levels slowly fell post highstand facilitated a shift towards intertidal and subaerial-dominated sedimentation. Our data suggest, however, a lag of ~1500 yr before island initiation (at ~3200 cal BP), i.e. later than that reported from smaller and more evolutionarily mature reef platforms in the region. Our data thus support: (1) the hypothesis that platform size acts to influence the timing of platform filling and subsequent island development at intra-regional scales; and (2) the hypothesis that the low wooded islands of the northern GBR conform to a model of island formation above an elevated reef flat under falling sea levels.

     

Genetic Admixture in the Culturally Unique Peranakan Chinese Population in Southeast Asia

The Peranakan Chinese are culturally unique descendants of immigrants from China who settled in the Malay Archipelago ∼300–500 years ago. Today, among large communities in Southeast Asia, the Peranakans have preserved Chinese traditions with strong influence from the local indigenous Malays. Yet, whether or to what extent genetic admixture co-occurred with the cultural mixture has been a topic of ongoing debate. We performed whole-genome sequencing (WGS) on 177 Singapore (SG) Peranakans and analyzed the data jointly with WGS data of Asian and European populations. We estimated that Peranakan Chinese inherited ∼5.62% (95% confidence interval [CI]: 4.76–6.49%) Malay ancestry, much higher than that in SG Chinese (1.08%, 0.65–1.51%), southern Chinese (0.86%, 0.50–1.23%), and northern Chinese (0.25%, 0.18–0.32%). A sex-biased admixture history, in which the Malay ancestry was contributed primarily by females, was supported by X chromosomal variants, and mitochondrial (MT) and Y haplogroups. Finally, we identified an ancient admixture event shared by Peranakan Chinese and SG Chinese ∼1,612 (95% CI: 1,345–1,923) years ago, coinciding with the settlement history of Han Chinese in southern China, apart from the recent admixture event with Malays unique to Peranakan Chinese ∼190 (159–213) years ago. These findings greatly advance our understanding of the dispersal history of Chinese and their interaction with indigenous populations in Southeast Asia.     

Methylated DNA/RNA in Body Fluids as Biomarkers for Lung Cancer

DNA/RNA methylation plays an important role in lung cancer initiation and progression. Liquid biopsy makes use of cells, nucleotides and proteins released from tumor cells into body fluids to help with cancer diagnosis and prognosis. Methylation of circulating tumor DNA (ctDNA) has gained increasing attention as biomarkers for lung cancer. Here we briefly introduce the biological basis and detection method of ctDNA methylation, and review various applications of methylated DNA in body fluids in lung cancer screening, diagnosis, prognosis, monitoring and treatment prediction. We also discuss the emerging role of RNA methylation as biomarkers for cancer.     

Plasmodium falciparum merozoites: isolation by density gradient centrifugation using Percoll and antigenic analysis

Merozoites of Plasmodium falciparum were isolated and immunocytochemically analyzed. Mature parasites from knobby (K+) and knobless (K-) strains were incubated for 4 to 5 hr in RPMI 1640 with 10% serum and 10% RBC extract. About 12 to 14% of the merozoites released were recovered by density gradient centrifugation using Percoll. From 1 to 3 X 10(9) merozoites were obtained per collection. The merozoite preparations were contaminated with 10% residual bodies, about 0.1% infected and uninfected erythrocytes, about 0.1% RBC-free trophozoites and schizonts, and numerous small (less than 0.5 microns) membrane vesicles. Merozoites from the K+ and K- strains were morphologically and, by an indirect, ferritin-labeled antibody assay using serum from immune Aotus, antigenically indistinguishable. Although the residual body coats reacted with the immune Aotus serum, the membrane vesicles, some of which were seen to be blebbing from merozoites, did not react with this serum or a serum against erythrocytes. This paper describes a procedure that can be used to obtain large numbers of merozoites with little contamination by host erythrocytes.