Search

This paper concentrates on the location methods for strictly noncircular sources by widely separated arrays. The conventional two-step methods extract measurement parameters and then, estimate the positions from them. Compared with the conventional two-step methods, direct position determination (DPD) is a promising technique, which locates transmitters directly from original sensor outputs without estimating intermediate parameters in a single step, and thus, improves the location accuracy and avoids the data association problem. However, existing DPD methods mainly focus on complex circular sources without considering noncircular signals, which can be exploited to enhance the localization accuracy. This paper proposes a maximum likelihood (ML)-based DPD algorithm for strictly noncircular sources whose waveforms are unknown. By exploiting the noncircularity of sources, we establish an ML-based function in time domain under the constraint on the waveforms of signals. A decoupled iterative method is developed to solve the prescribed ML estimator with a moderate complexity. In addition, we derive the deterministic Cramer–Rao Bound (CRB) for strictly noncircular sources, and prove that this CRB is upper bounded by the associated CRB for circular signals. Simulation results demonstrate that the proposed algorithm has a fast convergence rate, and outperforms the other location methods in a wide range of scenarios.

Amphotericin B (AmB) is a polyene antibiotic produced by Streptomyces nodosus and has been used for >50 years in the treatment of acute systemic fungal infections. In the present study, we demonstrated that lysine, an essential amino acid, could enhance the effect of AmB against Candida albicans in vitro, although lysine itself did not exert a fungicidal effect. In addition, the combination of AmB with lysine could provide an enhanced action against Candida parapsilosis and Cryptococcus neoformans compared with AmB alone. Lysine could also enhance the antifungal effect of caspofungin or nystatin. An enhanced effect of the combination of lysine with AmB was observed for the prevention of biofilm and hypha formation. Furthermore, our results demonstrated that lysine-mediated oxidative damage, such as the generation of endogenous reactive oxygen species, may be the mechanism underlying the enhancing effect of lysine on AmB. Our results also showed that CaMCA1 gene plays an important role in increasing the sensitivity of C. albicans cells upon AmB treatment. Using AmB together with lysine may be a promising strategy for the therapy of disseminated candidiasis.

The prevalence of camera-equipped smartphones and optoelectronic displays opens up a novel framework for wireless communication-optical camera communication. With displays as transmitters and cameras as receivers, a reliable optical communication link is established. In practice, the frame synchronization between transmitters and receivers is an inevitable challenge confronted in this new communication mode, whereas few previous studies are involved in this issue. Thus, we dedicate to model the frame synchronization issue, discuss the phenomenon that the receiver might lose frames or capture mixed frames, and propose frame loss detecting algorithm based on statistic characteristics of difference frames, while maintaining perceptual transparency. Our preliminary experiments have confirmed the validity of the theoretical analysis and the proposed algorithms.

Amphotericin B (AmB) is a polyene antifungal drug widely used for systemic fungal infections. In this study, a metabonomic method using gas chromatography-mass spectrometry (GC/MS) was developed to characterize the metabolic profiles of Candida albicans cells exposed to AmB. Thirty-one differentially produced metabolites between AmB-treated and the control groups were identified, among which 10 metabolites were upregulated and 21 metabolites were downregulated. These differentially produced metabolites were mainly involved in polyamines synthesis, tricarboxylic acid (TCA) cycle, oxidative stress, glutathione metabolism, lipid synthesis and glycolysis. Further experiments showed that the polyamines including putrescine, spermidine, and spermine played an important role in the sensitivity of C. albicans cells upon AmB treatment, and combined use of AmB and inhibitors of polyamine biosynthesis pathway might be a potential antifungal strategy. This study provided a systemic view of the metabolic pattern in C. albicans upon exposure to AmB, which shed new light on the mechanisms of action of antifungal agents.

Amphotericin B (AmB) is a polyene antibiotic produced by Streptomyces nodosus and has been used for50 years in the treatment of acute systemic fungal infections. In the present study, we demonstrated that lysine, an essential amino acid, could enhance the effect of AmB against Candida albicans in vitro, although lysine itself did not exert a fungicidal effect. In addition, the combination of AmB with lysine could provide an enhanced action against Candida parapsilosis and Cryptococcus neoformans compared with AmB alone. Lysine could also enhance the antifungal effect of caspofungin or nystatin. An enhanced effect of the combination of lysine with AmB was observed for the prevention of biofilm and hypha formation. Furthermore, our results demonstrated that lysine-mediated oxidative damage, such as the generation of endogenous reactive oxygen species, may be the mechanism underlying the enhancing effect of lysine on AmB. Our results also showed that CaMCA1 gene plays an important role in increasing the sensitivity of C. albicans cells upon AmB treatment. Using AmB together with lysine may be a promising strategy for the therapy of disseminated candidiasis.

Although ribosomal proteins (RPs) are components of the ribosome, and function centrally in protein synthesis, several lines of evidence suggest that S4 ribosomal proteins (Rps4ps) can function in other cellular roles. In Candida albicans, ribosomal protein S4 (Rps4p) is encoded by two distinct but highly similar genes, RPS41 (C2_10620W_A) and RPS42 (C1_01640W_A). Previous studies indicated that in Saccharomyces cerevisiae loss of one isoform generated distinct phenotypes. To probe this relationship in C. albicans, rps41Δ and rps42Δ homozygous null mutants were generated. The transcript levels of the RPS41 and RPS42 genes are asymmetric in C. albicans, RPS41 mRNA levels were similar in wild-type strains and rps42Δ null mutants, while RPS42 gene transcript levels were induced 20 fold relative to wild type in rps41Δ null mutants. We found that the rps41Δ homozygous null mutant showed a reduced growth rate, and had defects in filament formation in liquid media and on solid media, while these phenotypes were not observed in the rps42Δ mutant strain. Neither the rps41Δ nor rps42Δ mutant strains displayed differential sensitivity to azoles, although intriguingly ectopic expression of either RPS41 or RPS42 in a wild-type strain leads to decreased sensitivity to fluconazole (FLC). C. albicans cDNA microarray analysis experiments found that carbohydrate and nitrogen metabolic processes were repressed but transport-process-related genes were up-regulated in the rps41Δ mutant. Overall, our present study suggests that loss of the RPS41 gene but not its paralog the RPS42 gene can generate distinct phenotypes including effects on growth rate, morphological transitions, and susceptibility to osmotic stress due to the fact that mRNA levels of RPS41 is much higher than RPS42 in C. albicans.

The aim of this study was to investigate the effect of polyamine biosynthesis inhibitors on the activity of amphotericin B (AmB) against Candida albicans biofilms and to clarify the underlying mechanisms. The antibiofilm activity of AmB was significantly enhanced when used in combination with the polyamine biosynthesis inhibitors 1,4-diamino-2-butanone (DAB) and α-difluoromethylornithine (DFMO). Further study showed that DAB and DFMO also enhanced the antibiofilm activity of several other antifungal agents. Moreover, the combination of AmB and polyamine biosynthesis inhibitors resulted in an increase in intracellular levels of reactive oxygen species. In addition, caspase activity and transcription of the caspase-encoding gene CaMCA1 were greatly increased upon combined treatment with polyamine biosynthesis inhibitors and AmB. Consistently, the biofilm formed by a Δcamca1 mutant exhibited greater viability and lower caspase activity than that of the wild-type strain upon combined treatment. These data provide useful information for the development of new strategies to enhance the antibiofilm activities of antifungal agents.

Background: Candida albicans, the most common fungal pathogen related to colonization and biofilm formation on the surfaces of indwelling medical devices, shows high resistance to the most commonly used antifungal drugs. In this study, an ion-pairing chromatography-porous graphitic carbon column coupled with a time-of-flight mass spectrometry (IP-PGC-TOF/MS) system was developed for targeted and untargeted profiling of metabolites involved in biofilm and planktonic growth of C. albicans. Using untargeted profiling analysis, 16 differential metabolites were screened and identified as potential biomarkers, most of which were amino acids or related compounds. Based on untargeted profiling analysis, targeted quantitative analysis of 22 amino acids was established and carefully evaluated using stable isotope-labeled internal standards. Among them, 9 amino acids that were not screened by untargeted profiling were further characterized as new biomarkers. Finally, a total of 25 potential biomarkers were screened using the combined targeted and untargeted strategy, among which 16 were characterized for the first time. Our results confirmed that amino acid metabolism and polyamine metabolism were at a high level in biofilms, except for some new biomarkers including ornithine, arginine and proline that were directly related to ornithine. Further experiments were carried out on the ornithine decarboxylase-negative (spe1Δ) mutant, and the results showed that the consumption of ornithine for putrescine biosynthesis has a significant impact on biofilm formation and may prove to be a drug target for resolving drug resistance of C. albicans. This study provides a systematic view of changes in amino acid metabolism during C. albicans biofilm formation by a combination of targeted and untargeted profiling using an original IP-PGC-TOF/MS method. It is a feasible approach for characterizing subtle variations and screening novel biomarkers from the microbial metabolome.