Marine biology | EPFL Graph Search

Marine biology is the scientific study of the biology of marine life, organisms in the sea. Given that in biology many phyla, families and genera have some species that live in the sea and others that live on land, marine biology classifies species based on the environment rather than on taxonomy. A large proportion of all life on Earth lives in the ocean. The exact size of this large proportion is unknown, since many ocean species are still to be discovered. The ocean is a complex three-dimensional world covering approximately 71% of the Earth's surface. The habitats studied in marine biology include everything from the tiny layers of surface water in which organisms and abiotic items may be trapped in surface tension between the ocean and atmosphere, to the depths of the oceanic trenches, sometimes 10,000 meters or more beneath the surface of the ocean. Specific habitats include estuaries, coral reefs, kelp forests, seagrass meadows, the surrounds of seamounts and thermal vents, ti

Prediction and experimental evaluation of soil-water retention behavior of skeletal calcareous soils

Saeed Kouzegaran, Lyesse Laloui

Skeletal calcareous soils refer to soils consisting of skeletal remains of marine organisms. Although calcareous deposits are prevalent along coastal plains throughout the world, there is no study which investigates their behavior in unsaturated conditions. In these conditions, soil-water retention capacity is a fundamental parameter in relation to many geotechnical, environmental, and agricultural aspects. Water retention capacity of a soil is expected to be influenced by intra-particle pores unique to calcareous soils. Scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) used in the current study clearly revealed this special microstructural characteristic. To study water retention and hydraulic hysteresis behavior of skeletal calcareous soil (obtained from the Hormuz Island of Iran) compared with a reference silicate soil (obtained from the Netherlands), a series of tests were conducted using pressure plate and controlled-suction oedometer apparatuses. Test results showed that in similar grain-size distribution of these soils, water retention curves of calcareous and silica soils are almost the same in low suctions, but calcareous soil retains more water at higher suctions due to its intra-particle voids. In addition, owing to these microstructural pores, ratio of Sr reduction on wetting path of a hysteresis loop was found to be more for calcareous soil than for silicate soil. Besides, to find and/or modify a prediction method for water retention curve of calcareous soil with acceptable accuracy, several existing pedotransfer functions were evaluated. Results showed that models proposed by Zapata et al. (Geotech Spec Publ 99:84–124, 2000) and Saxton et al. (Soil Science Society of America Journal 50(4): 1031–1036, 1986) after some simple modifications provide accurate estimations for water retention curve of calcareous soils.

2020

Regulation of sedimentation rate shapes the evolution of multicellularity in a close unicellular relative of animals

Omaya Pierre Dudin

Significant increases in sedimentation rate accompany the evolution of multicellularity. These increases should lead to rapid changes in ecological distribution, thereby affecting the costs and benefits of multicellularity and its likelihood to evolve. However, how genetic and cellular traits control this process, their likelihood of emergence over evolutionary timescales, and the variation in these traits as multicellularity evolves are still poorly understood. Here, using isolates of the ichthyosporean genus Sphaeroforma-close unicellular relatives of animals with brief transient multicellular life stages-we demonstrate that sedimentation rate is a highly variable and evolvable trait affected by at least 2 distinct physical mechanisms. First, we find extensive (>300x) variation in sedimentation rates for different Sphaeroforma species, mainly driven by size and density during the unicellular-to-multicellular life cycle transition. Second, using experimental evolution with sedimentation rate as a focal trait, we readily obtained, for the first time, fast settling and multicellular Sphaeroforma arctica isolates. Quantitative microscopy showed that increased sedimentation rates most often arose by incomplete cellular separation after cell division, leading to clonal "clumping" multicellular variants with increased size and density. Strikingly, density increases also arose by an acceleration of the nuclear doubling time relative to cell size. Similar size- and density-affecting phenotypes were observed in 4 additional species from the Sphaeroforma genus, suggesting that variation in these traits might be widespread in the marine habitat. By resequencing evolved isolates to high genomic coverage, we identified mutations in regulators of cytokinesis, plasma membrane remodeling, and chromatin condensation that may contribute to both clump formation and the increase in the nuclear number-to-volume ratio. Taken together, this study illustrates how extensive cellular control of density and size drive sedimentation rate variation, likely shaping the onset and further evolution of multicellularity.

PUBLIC LIBRARY SCIENCE2022

Genetically Encoded Activators of Small Molecules for Imaging and Drug Delivery

Jade Noémie Nam Nguyen, Pablo Rivera Fuentes, Zacharias Thiel

Chemical biologists have developed many tools based on genetically encoded macromolecules and small, synthetic compounds. The two different approaches are extremely useful, but they have inherent limitations. In this Minireview, we highlight examples of strategies that combine both concepts to tackle challenging problems in chemical biology. We discuss applications in imaging, with a focus on super-resolved techniques, and in probe and drug delivery. We propose future directions in this field, hoping to inspire chemical biologists to develop new combinations of synthetic and genetically encoded probes.

WILEY-V C H VERLAG GMBH2020