Magnetic genes: Studying the genetics of biomineralization in magnetotactic bacteria.

Many species of bacteria can manufacture materials on a finer scale than those that are synthetically made. These products are often produced within intracellular compartments that bear many hallmarks of eukaryotic organelles. One unique and elegant group of organisms is at the forefront of studies into the mechanisms of organelle formation and biomineralization. Magnetotactic bacteria (MTB) produce organelles called magnetosomes that contain nanocrystals of magnetic material, and understanding the molecular mechanisms behind magnetosome formation and biomineralization is a rich area of study. In this Review, we focus on the genetics behind the formation of magnetosomes and biomineralization. We cover the history of genetic discoveries in MTB and key insights that have been found in recent years and provide a perspective on the future of genetic studies in MTB

The magnetosome model: insights into the mechanisms of bacterial biomineralization.

Though the most ready example of biomineralization is the calcium phosphate of vertebrate bones and teeth, many bacteria are capable of creating biominerals inside their cells. Because of the diversity of these organisms and the minerals they produce, their study may reveal aspects of the fundamental mechanisms of biomineralization in more complex organisms. The best-studied case of intracellular biomineralization in bacteria is the magnetosome, an organelle produced by a diverse group of aquatic bacteria that contains single-domain crystals of the iron oxide magnetite (Fe3O4) or the iron sulfide greigite (Fe3S4). Here, recent advances in our understanding of the mechanisms of bacterial magnetite biomineralization are discussed and used as a framework for understanding less-well studied examples, including the bacterial intracellular biomineralization of cadmium, selenium, silver, nickel, uranium, and calcium carbonate. Understanding the molecular mechanisms underlying the biological formation of these minerals will have important implications for technologies such as the fabrication of nanomaterials and the bioremediation of toxic compounds

Sentence repetition in Farsi-English bilingual children

The current study aimed to create an assessment that can be used in the future to measure the language abilities of Farsi-speaking children in a clinical setting. A Farsi sentence-repetition task was created that included structures organised into three levels of complexity from least to most complex. Twenty typically developing Farsi-English bilingual children between the ages of 6;3–11;6 were recruited from Farsi schools in Toronto, Canada. Signi cant di erences on the participants’ performance among the three levels were found with the lowest performance in the most complex sentences and the highest performance in the least complex ones. Speci c structures appeared to be more challenging than others within each level of complexity. The children’s decreasing performance with increasing complexity and the evidence that speci c structures are challenging within each level make the Farsi sentence repetition task a promising tool for assessing the language skills of Farsi-English speaking children

Genome Editing Method for the Anaerobic Magnetotactic Bacterium Desulfovibrio magneticus RS-1.

Magnetosomes are complex bacterial organelles that serve as model systems for studying bacterial cell biology, biomineralization, and global iron cycling. Magnetosome biogenesis is primarily studied in two closely related Alphaproteobacteria of the genus Magnetospirillum that form cubooctahedral-shaped magnetite crystals within a lipid membrane. However, chemically and structurally distinct magnetic particles have been found in physiologically and phylogenetically diverse bacteria. Due to a lack of molecular genetic tools, the mechanistic diversity of magnetosome formation remains poorly understood. Desulfovibrio magneticus RS-1 is an anaerobic sulfate-reducing deltaproteobacterium that forms bullet-shaped magnetite crystals. A recent forward genetic screen identified 10 genes in the conserved magnetosome gene island of D. magneticus that are essential for its magnetic phenotype. However, this screen likely missed mutants with defects in crystal size, shape, and arrangement. Reverse genetics to target the remaining putative magnetosome genes using standard genetic methods of suicide vector integration have not been feasible due to the low transconjugation efficiency. Here, we present a reverse genetic method for targeted mutagenesis in D. magneticus using a replicative plasmid. To test this method, we generated a mutant resistant to 5-fluorouracil by making a markerless deletion of the upp gene that encodes uracil phosphoribosyltransferase. We also used this method for targeted marker exchange mutagenesis by replacing kupM, a gene identified in our previous screen as a magnetosome formation factor, with a streptomycin resistance cassette. Overall, our results show that targeted mutagenesis using a replicative plasmid is effective in D. magneticus and may also be applied to other genetically recalcitrant bacteria.IMPORTANCE Magnetotactic bacteria (MTB) are a group of organisms that form intracellular nanometer-scale magnetic crystals though a complex process involving lipid and protein scaffolds. These magnetic crystals and their lipid membranes, termed magnetosomes, are model systems for studying bacterial cell biology and biomineralization and are potential platforms for biotechnological applications. Due to a lack of genetic tools and unculturable representatives, the mechanisms of magnetosome formation in phylogenetically deeply branching MTB remain unknown. These MTB contain elongated bullet-/tooth-shaped magnetite and greigite crystals that likely form in a manner distinct from that of the cubooctahedral-shaped magnetite crystals of the genetically tractable MTB within the Alphaproteobacteria Here, we present a method for genome editing in Desulfovibrio magneticus RS-1, a cultured representative of the deeply branching MTB of the class Deltaproteobacteria This marks a crucial step in developing D. magneticus as a model for studying diverse mechanisms of magnetic particle formation by MTB

Interpretable Few-shot Learning with Online Attribute Selection

Few-shot learning (FSL) is a challenging learning problem in which only a few samples are available for each class. Decision interpretation is more important in few-shot classification since there is a greater chance of error than in traditional classification. However, most of the previous FSL methods are black-box models. In this paper, we propose an inherently interpretable model for FSL based on human-friendly attributes. Moreover, we propose an online attribute selection mechanism that can effectively filter out irrelevant attributes in each episode. The attribute selection mechanism improves the accuracy and helps with interpretability by reducing the number of participated attributes in each episode. We propose a mechanism that automatically detects the episodes where the pool of human-friendly attributes are not adequate, and compensates by engaging learned unknown attributes. We demonstrate that the proposed method achieves results on par with black-box few-shot-learning models on four widely used datasets

A cognitive-oriented exploration of the development of translation competence: a case study of Iranian translation learners

This is a report on a qualitative research in relation to the development of translation competence (TC) in academia. The study aimed to map out the cognitive processes involved in problem-solving and provide a picture of the development of strategic TC and translation-notion in translation learners. A group of 20 Iranian students volunteered to take part in a think-aloud study. The participants were divided into four groups of G1 (pretranslational), G3 (early translational), G5 and G7 (translational), based on the number of semesters of language and translation training they had received. The ecological validity was established by availing the participants of any sources of documentation they preferred to use. The verbalisations of the participants were recorded and then transcribed into think-aloud protocols (TAPs). The analysis of TAPs revealed that students activated various configurations of decision-making processes and resourcing methods, and exhibit different conceptions of the notion-of-translation at different stages of TC development. The study also showed that the portrait of TC development featured strong reliance on automatised cognitive processes at pre-translational stage and increased evaluative processes, coupled with higher chances of success, at translational stage. The findings proved that the development of TC did not follow an incremental trajectory. They further indicated that the translation programmes as offered in universities tend to boost evaluative reflections on and conscious awareness of the translation process at the cost of decreasing the unconscious automatised processes. This suggests that from a process-oriented perspective, translation programmes do not seem to prepare the learners for translation-market requirements