No abstract

Candida albicans forms unconstricted hyphae in serum-containing medium that are divided into discrete compartments. Time-lapse photomicroscopy, flow cytometry, and a novel three-dimensional imaging system were used to demonstrate that the kinetics and cell cycle events accompanying hyphal development were correlated with dynamic changes in vacuole morphology and the pattern of vacuole inheritance. Apical cells of hyphae underwent continuous extension before and after the first cytokinesis event. However, the resulting mother cell and sub-apical compartments did not immediately reenter the cell cycle and instead underwent cell cycle arrest before reentering the cycle. Vacuole was inherited asymmetrically at cytokinesis so that the distal, arrested compartments inherited most vacuole and the growing apical cell inherited most cytoplasm. Hydroxyurea release experiments demonstrated that the arrested, vacuolated hyphal compartments were in the G 1 phase of the cycle. The period of cell cycle arrest was decreased by the provision of assimilatable forms of nitrogen, suggesting that the hyphal cell cycle is regulated by nitrogen limitation that results in sup-apical cell cycle arrest. This pattern of growth is distinct from that of the synchronous, symmetrical development of pseudohyphae of C. albicans and other yeast species. These observations suggest that the cellular vacuole space correlates with alterations in the cell cycles of different cell types and that the total organelle space may influence size-regulated functions and hence the timing of the eukaryotic cell cycle.Candida albicans is the major fungal pathogen of humans (5, 47) and now represents the fourth most common agent of microbial lethal septicemia in immunocompromised patients, with a morbidity of around 50% (8). Virulence of C. albicans is related to a combination of phenotypic traits, including its ability to form filamentous forms of either pseudohyphae or true hyphae (20). Pseudohyphae are branching chains of elongated yeast cells and are common to many dimorphic yeast species, including Saccharomyces cerevisiae, while true hyphae are parallel sided, are not formed by S. cerevisiae, and are formed only by two Candida species, C. albicans and C. dubliniensis (10, 13, 14, 34). The formation of true unconstricted germ tubes in serum is used in the clinical diagnosis of C. albicans (18,24). Hyphal conversion has often been regarded as a virulence factor promoting tissue invasion (40,42,54,58), although the true status of this morphogenetic transition as a virulence factor has yet to be evaluated fully (20, 49). Here we describe how the cell cycle of C. albicans is modulated during true hyphal growth. These modulations are correlated with the asymmetric inheritance of vacuole at cytokinesis, which responds to the nutrient status of the growth medium and may influence cell size-regulated functions that control cell cycle progression.Vegetative growth of fungi occurs by the formation of either unicellular buds or branching pseudohyphae or hyphae, which ...

Biological air filters have been proposed as a cost-effective technology for reducing odor emissions from intensive swine production facilities. In this work we present results from the application of membrane inlet mass spectrometry (MIMS) for continuously monitoring the removal of odorous compounds in biological air filters. The sensitivity and selectivity were tested on synthetic samples of selected odorous compounds, and linearity and detection limits in the lower ppb range were demonstrated for all compounds tested (methanethiol, dimethyl sulfide, carboxylic acids, 4-methylphenol, aldehydes, indole, and skatole) except trimethylamine. The method was applied in situ at two full-scale filters installed at swine houses. The results have been compared with analyses by thermal desorption gas chromatography-mass spectrometry (TD-GC/MS), and odor was measured by olfactometry. By comparison with TD-GC/MS, observed MIMS signals were assigned to 4-methylphenol, 4-ethylphenol, indole, skatole, the sum of volatile reduced organic sulfur compounds (ROS), and three subgroups of carboxylic acids. The removal rates were observed to be related to air-water partitioning with removal efficiencies in the range of 0 to 50% for low-soluble organic sulfur compounds and high removal efficiencies (typically 80-100%) for more soluble phenols and carboxylic acids. Based on the results and published odor threshold values, it is estimated that the low removal efficiency of ROS is the main limitation for achieving a higher odor reduction.

No abstract

No abstract