Control Of Filament Growth Research Articles

Conductive Filament Localization Within Crossbar Resistive Memories by Scanning Joule Expansion Microscopy

Control of filament growth within conductive bridge random access memories (CBRAM) is of crucial interest in order to ensure the reliability of such emerging devices. Here, we demonstrate that Scanning Joule Expansion Microscopy (SJEM) can be used to detect and precisely localize conductive filaments within operating crossbar CBRAM devices. Flexible memory devices based on Pd/Al2O3/Ag stacks are first elaborated at low temperature on polyimide substrate. These devices show set and reset operations at low voltage ( $4.3~\mu \text{m}$ is extracted at 50kHz and it is also demonstrated that the thermal expansion signal is proportional to the dissipated Joule power. We believe that the proposed procedure opens the way to reliability studies that can be applied to any family of memory device based on filamentary conduction.

Bulking control by low-dose ozonation of returned activated sludge in a full-scale wastewater treatment plant

Sludge bulking is still a problem in the operation of state-of-the-art wastewater treatment plants (WWTPs). The ozonation of returned activated sludge (RAS) is an innovative option as a non-specific measure for the control of filament growth. The applicability of sludge ozonation for bulking control of a large wastewater treatment plant was investigated. At a full-scale WWTP one lane was equipped with a sludge ozonation plant for RAS. The implemented sludge ozonation of RAS was tested against the two identical references lanes of the same WWTP. The positive effect on settleability could be clearly proven. Low-dose sludge ozonation could be a technical alternative in comparison with the established chemical measures for bulking control.

The Candida albicans Rgd1 is a RhoGAP protein involved in the control of filamentous growth

Rho proteins are essential regulators of polarized growth in eukaryotic cells. These proteins are down-regulated in vivo by specific Rho GTPase Activating Proteins (RhoGAP). We investigated the role of Rgd1 RhoGAP, encoded by the Candida albicans RGD1 gene. We demonstrated that CaCdc42, CaRho3 and CaRho4 proteins had an intrinsic GTPase activity and that CaRgd1 stimulates in vitro GTP hydrolysis of these GTPases. Deletion of RGD1 in C. albicans results in sensitivity to low pH as already described for rgd1Δ in Saccharomyces cerevisiae. The role of Rgd1 in survival at low pH is conserved in the two yeast species as the Ca RGD1 gene complements the Sc rgd1Δ sensitivity. By tagging the RhoGAP with GFP, we found that CaRgd1 is localized at the tip and cortex of growing cells and during cytokinesis at the septation sites in yeast and filamentous forms. We investigated the effect of CaRgd1 on the control of the polarized growth. Removing Ca RGD1 alleles increased filamentous growth and cells lacking CaRgd1 presented longer germ tubes. Conversely, RGD1 overexpression restricted hyphae growth. Our results demonstrate that Rgd1 is critical for filamentous formation in C. albicans especially for filamentous elongation.

Mss11p is a transcription factor regulating pseudohyphal differentiation, invasive growth and starch metabolism in Saccharomyces cerevisiae in response to nutrient availability

In Saccharomyces cerevisiae, the cell surface protein, Muc1p, was shown to be critical for invasive growth and pseudohyphal differentiation. The transcription of MUC1 and of the co-regulated STA2 glucoamylase gene is controlled by the interplay of a multitude of regulators, including Ste12p, Tec1p, Flo8p, Msn1p and Mss11p. Genetic analysis suggests that Mss11p plays an essential role in this regulatory process and that it functions at the convergence of at least two signalling cascades, the filamentous growth MAPK cascade and the cAMP-PKA pathway. Despite this central role in the control of filamentous growth and starch metabolism, the exact molecular function of Mss11p is unknown. We subjected Mss11p to a detailed molecular analysis and report here on its role in transcriptional regulation, as well as on the identification of specific domains required to confer transcriptional activation in response to nutritional signals. We show that Mss11p contains two independent transactivation domains, one of which is a highly conserved sequence that is found in several proteins with unidentified function in mammalian and invertebrate organisms. We also identify conserved amino acids that are required for the activation function.

A Docker Instead of a Dbl

Overexpression of Dock180 can stimulate nucleotide exchange on the guanosine triphosphatase (GTPase) Rac, promoting such cellular responses as membrane ruffling and phagocytosis, and this effect is enhanced if two other proteins are also expressed, ELMO1 and the adaptor CrkII. These data suggested that Dock180 is a guanine exchange factor (GEF) for Rac; however, Dock180 lacks the Dbl homology (DH) domain responsible for GEF activity in all other known GEFs. Brugnera et al. investigated in vitro and in transfected cells Dock180's GEF activity and identified a new domain, which they call Docker, that bound to Rac and promoted GTP loading. The docker domain is conserved in other members of the mammalian Dock180 family and in a protein encoded by a yeast gene implicated in the control of filamentous growth. These domains from Dock2 and the protein encoded in the yeast gene also interacted with Rac in vitro. Mutations in the Docker domain or the ELMO binding domain prevented the stimulation of membrane ruffles or particle engulfment in cells transfected with the mutated Dock180 and ELMO1. Coprecipitation of Dock180 and Rac in transfected cells was enhanced if ELMO was also transfected into the cells, suggesting that ELMO1 may promote the Dock180-Rac interaction. However, the mechanism by which these proteins work together to regulate Rac activity remains unknown. E. Brugnera, L. Haney, C. Grimsley, M. Lu, S. F. Walk, A.-C. Tosello-Trampont, I. G. Macara, H. Madhani, G. R. Fink, K. S. Ravichandran, Unconventional Rac-GEF activity is mediated through the Dock180-ELMO complex. Nat. Cell Biol. 4 , 574-582 (2002). [Online Journal]

Operation with biological nutrient removal with stable nitrification and control of filamentous growth

Bromma WWTP is the second largest wastewater treatment plant in Stockholm, Sweden. To meet new regulations regarding nitrogen removal the plant needs to be operated with nitrogen removal all year round. In previous years, severe bulking problems during the winter have made it impossible to maintain nitrification during colder temperatures. Microscopic examination of the activated sludge has increased the understanding of bulking. The bulking is mainly due to excessive growth of filamentous organisms, mainly Microthrix parvicella. By operating the plant with a high F/M ratio and decreasing the F/M ratio when filamentous growth occurs, excessive growth of these organisms can be avoided. The nitrification rate is optimized by adjusting the concentration of mixed liquid suspended solids in the tanks so that the nitrification is complete and by operating the tanks at a DO concentration of 4 mg/l. By this process strategy it is now possible to operate the plant with nitrification all year round.

Operation with biological nutrient removal with stable nitrification and control of filamentous growth

Bromma WWTP is the second largest wastewater treatment plant in Stockholm, Sweden. To meet new regulations regarding nitrogen removal the plant needs to be operated with nitrogen removal all year round. In previous years, severe bulking problems during the winter have made it impossible to maintain nitrification during colder temperatures. Microscopic examination of the activated sludge has increased the understanding of bulking. The bulking is mainly due to excessive growth of filamentous organisms, mainly Microthrix parvicella. By operating the plant with a high F/M ratio and decreasing the F/M ratio when flamentous growth occurs, excessive growth of these organisms can be avoided. The nitrification rate is optimized by adjusting the concentration of mixed liquid suspended solids in the tanks so that the nitrification is complete and by operating the tanks at a DO concentration of 4 mg/l. By this process strategy it is now possible to operate the plant with nitrification all year round.

Control of filamentous growth by mating and cyclic-AMP inUstilago

Mating between compatible haploid cells of the corn smut fungus, Ustilago maydis, results in a switch from budding to filamentous growth. We are analyzing the multiallelic b incompatibility locus that governs maintenance of the infectious, filamentous dikaryon. Specificity regions have been identified in the N-terminal portions of the bE and bW genes at the b locus. In addition, we have found that heterozygosity at the b locus attenuates fusion. This result suggests that b gene products may exert a negative influence on some processes, in addition to their generally recognized role in maintaining filamentous growth. The b genes have also been characterized in Ustilago hordei. This species has a bipolar mating system in which the b genes are linked to genes required for pheromone production and response to form one large mating-type region (MAT locus) with two allelic specificities. In a separate study, we have discovered that defects in adenylate cyclase result in constitutive filamentous growth and greatly reduce the virulence of U. maydis on corn seedlings. Mutations have been identified that suppress the adenylate cyclase defect and restore budding growth. Sequence analysis revealed that one of the suppressor mutations is in the gene encoding the regulatory subunit of cAMP-dependent protein kinase (PKA). Mutants altered in PKA activity have the interesting phenotype of multiple budding and frequent mislocalization of the bud site. Key words: smut, dimorphism, b locus, sex.