University of California, Santa Cruz

About: University of California, Santa Cruz is a education organization based out in Santa Cruz, California, United States. It is known for research contribution in the topics: Galaxy & Population. The organization has 15541 authors who have published 44120 publications receiving 2759983 citations. The organization is also known as: UCSC & UC, Santa Cruz.

Primary production, sinking fluxes and the microbial food web

Abstract: The size distribution of pelagic producers and the size and trophic position of consumers determine the composition and magnitude of sinking fluxes from the surface communities in a simple model of oceanic food webs. Picoplankton, the dominant producers in the model, contribute little to the sinking material, due primarily to the large number of trophic steps between picoplankton and the consumers that produce the sinking particles. Net phytoplankton are important contributors to the sinking materials, despite accounting for a small fraction of the total primary production. These net phytoplankton, especially those capable of nitrogen fixation, also dominate the fraction of the new production that is exported on its first pass through the food chain. The sinking flux is strongly determined by the community structure of the consumers and varies by an order of magnitude for different food webs. The model indicates that generalist grazers, zooplankton that consume a broad size spectrum of prey (including pico-and nanoplankton), play a critical role in exporting particles. The role of generalists that occasionally form swarms, such as thaliaceans (salps and doliolids), can be particularly difficult to assess. Short-term studies probably miss the relatively infrequent population blooms of these grazers, events that could control the average, long-term exports from surface oceanic communities.

Bacterial Extracellular Polysaccharides in Biofilm Formation and Function.

Abstract: Microbes produce a biofilm matrix consisting of proteins, extracellular DNA, and polysaccharides that is integral in the formation of bacterial communities. Historical studies of polysaccharides revealed that their overproduction often alters the colony morphology and can be diagnostic in identifying certain species. The polysaccharide component of the matrix can provide many diverse benefits to the cells in the biofilm, including adhesion, protection, and structure. Aggregative polysaccharides act as molecular glue, allowing the bacterial cells to adhere to each other as well as surfaces. Adhesion facilitates the colonization of both biotic and abiotic surfaces by allowing the bacteria to resist physical stresses imposed by fluid movement that could separate the cells from a nutrient source. Polysaccharides can also provide protection from a wide range of stresses, such as desiccation, immune effectors, and predators such as phagocytic cells and amoebae. Finally, polysaccharides can provide structure to biofilms, allowing stratification of the bacterial community and establishing gradients of nutrients and waste products. This can be advantageous for the bacteria by establishing a heterogeneous population that is prepared to endure stresses created by the rapidly changing environments that many bacteria encounter. The diverse range of polysaccharide structures, properties, and roles highlight the importance of this matrix constituent to the successful adaptation of bacteria to nearly every niche. Here, we present an overview of the current knowledge regarding the diversity and benefits that polysaccharide production provides to bacterial communities within biofilms.

Radial Velocities for 889 Late-Type Stars*

Abstract: We report radial velocities for 844 FGKM-type main-sequence and subgiant stars and 45 K giants, most of which had either low-precision velocity measurements or none at all. These velocities differ from the stand- ard stars of Udry et al. by 0.035 km s � 1 (rms) for the 26 FGK standard stars in common. The zero point of our velocities differs from that of Udry et al.: hVPresentVUdry i¼þ 0:053 km s � 1 . Thus, these new velocities agree with the best known standard stars both in precision and zero point, to well within 0.1 km s � 1 . Nonetheless, both these velocities and the standards suffer from three sources of systematic error, namely, convective blueshift, gravitational redshift, and spectral type mismatch of the reference spectrum. These sys- tematic errors are here forced to be zero for G2 V stars by using the Sun as reference, with Vesta and day sky as proxies. But for spectral types departing from solar, the systematic errors reach 0.3 km s � 1 in the F and K stars and 0.4 km s � 1 in M dwarfs. Multiple spectra were obtained for all 889 stars during 4 years, and 782 of them exhibit velocity scatter less than 0.1 km s � 1 . These stars may serve as radial velocity standards if they remain constant in velocity. We found 11 new spectroscopic binaries and report orbital parameters for them. Subject headings: binaries: spectroscopic — catalogs — stars: fundamental parameters — stars: kinematics — stars: late-type — techniques: radial velocities — techniques: spectroscopic On-line material: machine-readable tables