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Your search keyword '"N. A. Held"' showing total 2 results
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2 results on '"N. A. Held"'

1. Co-occurrence of Fe and P stress in natural populations of the marine diazotroph Trichodesmium

Author

N. A. Held, E. A. Webb, M. M. McIlvin, D. A. Hutchins, N. R. Cohen, D. M. Moran, K. Kunde, M. C. Lohan, C. Mahaffey, E. M. S. Woodward, and M. A. Saito

Subjects
Ecology, QH540-549.5, Life, QH501-531, Geology, QE1-996.5
Abstract

Trichodesmium is a globally important marine microbe that provides fixed nitrogen (N) to otherwise N-limited ecosystems. In nature, nitrogen fixation is likely regulated by iron or phosphate availability, but the extent and interaction of these controls are unclear. From metaproteomics analyses using established protein biomarkers for nutrient stress, we found that iron–phosphate co-stress is the norm rather than the exception for Trichodesmium colonies in the North Atlantic Ocean. Counterintuitively, the nitrogenase enzyme was more abundant under co-stress as opposed to single nutrient stress. This is consistent with the idea that Trichodesmium has a specific physiological state during nutrient co-stress. Organic nitrogen uptake was observed and occurred simultaneously with nitrogen fixation. The quantification of the phosphate ABC transporter PstA combined with a cellular model of nutrient uptake suggested that Trichodesmium is generally confronted by the biophysical limits of membrane space and diffusion rates for iron and phosphate acquisition in the field. Colony formation may benefit nutrient acquisition from particulate and organic sources, alleviating these pressures. The results highlight that to predict the behavior of Trichodesmium, both Fe and P stress must be evaluated simultaneously.

Published
2020
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2. Identification and initial characterization of matrix metalloproteinases in the yellow fever mosquito, Aedes aegypti

Author

A M, Kantor, S, Dong, N L, Held, E, Ishimwe, A L, Passarelli, R J, Clem, and A W E, Franz

Subjects
Male, viruses, fungi, Genome, Insect, Molecular Sequence Data, Metamorphosis, Biological, virus diseases, Gene Expression, Matrix Metalloproteinases, Article, Gastrointestinal Tract, Aedes, Sequence Homology, Nucleic Acid, parasitic diseases, Animals, Humans, Female, Amino Acid Sequence, Chikungunya virus
Abstract

Aedes aegypti is a major vector for arboviruses such as dengue, chikungunya and Zika viruses. During acquisition of a viremic bloodmeal, an arbovirus infects mosquito midgut cells before disseminating to secondary tissues, including the salivary glands. Once virus is released into the salivary ducts it can be transmitted to another vertebrate host. The midgut is surrounded by a basal lamina (BL) in the extracellular matrix, consisting of a proteinaceous mesh composed of collagen IV and laminin. BL pore size exclusion limit prevents virions from passing through. Thus, the BL probably requires remodelling via enzymatic activity to enable efficient virus dissemination. Matrix metalloproteinases (MMPs) are extracellular endopeptidases that are involved in remodelling of the extracellular matrix. Here, we describe and characterize the nine Ae. aegypti encoded MMPs, AeMMPs 1-9, which share common features with other invertebrate and vertebrate MMPs. Expression profiling in Ae. aegypti revealed that Aemmp4 and Aemmp6 were upregulated during metamorphosis, whereas expression of Aemmp1 and Aemmp2 increased during bloodmeal digestion. Aemmp1 expression was also upregulated in the presence of a bloodmeal containing chikungunya virus. Using polyclonal antibodies, AeMMP1 and AeMMP2 were specifically detected in tissues associated with the mosquito midgut.

Published
2017

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