Microbial metabolism of transparent exopolymer particles during the summer months along a eutrophic estuary system

This study explores the role of transparent exopolymer particles (TEP) as an additional carbon source for heterotrophic microbial activity in the eutrophic Qishon estuary. From the coastal station and upstream the estuary; TEP concentrations, β-glucosidase activity, bacterial production and abundance have gradually increased. TEP were often found as bio-aggregates, scaffolding algae, detritus matter and bacteria that likely formed hotspots for enhance microbial activity. To further demonstrate the link between TEP and heterotrophic bacterial activity, confined incubations with ambient and polysaccharide-enriched estuary water were carried out. Following polysaccharide addition, elevated (~50%) β-glucosidase activity rates were observed, leading to TEP hydrolysis. This newly formed bioavailable carbon resulted in significantly higher growth rates, with up to a 5-fold increase in heterotrophic bacterial biomass, comprising mostly high nucleic acid content bacteria. Taking together the findings from this research, we conclude that even in highly eutrophic environments heterotrophic bacteria may still be carbon limited. Further, TEP as a polysaccharide matrix can act as a metabolic surrogate, adding fresh bioavailable carbon through tight associations with bacteria in eutrophic ecosystems such as the Qishon estuary

Disciplines and the Categorization of Scientific Truth: The Case of Social Sciences in the Hebrew Wikipedia

For the general audience, Wikipedia is considered the source of “truth,” especially for scientific knowledge. While studies of Wikipedia usually focus on the accuracy of the knowledge within it, few studies have explored its hierarchy and categorization. This study aims to describe how scientific information is organized into disciplines in Wikipedia. I take as a case study the Hebrew Wikipedia and examine the representation and interrelations of five social sciences: sociology, anthropology, economics, political science, and psychology. I gather data from Wikipedia entries categorized under each of these disciplines and create a network that contains categories and subcategories derived from these entries. Using network analysis techniques, I estimate the strength of the relations between the disciplines. Results indicated that while sociology, anthropology, and political science are strongly linked to each other, psychology and economics are relatively isolated. As there is a hierarchical difference between these disciplines, the result is a hierarchical value of the scientific knowledge presented in these Wikipedia entries. An interesting case is the distance between economics and sociology, since under the subcategory “Inequality,” the entries are uniquely categorized under sociology or economics but rarely under both categories. I claim this is an example of a fractal walking the distinction between the two disciplines

Balancing photosynthetic electron flow is critical for cyanobacterial acclimation to nitrogen limitation

AbstractNitrogen limitation forces photosynthetic organisms to reallocate available nitrogen to essential functions. At the same time, it increases the probability of photo-damage by limiting the rate of energy-demanding metabolic processes, downstream of the photosynthetic apparatus. Non-diazotrophic cyanobacteria cope with this situation by decreasing the size of their phycobilisome antenna and by modifying their photosynthetic apparatus. These changes can serve two purposes: to provide extra amino-acids and to decrease excitation pressure. We examined the effects of nitrogen limitation on the form and function of the photosynthetic apparatus. Our aim was to study which of the two demands serve as the driving force for the remodeling of the photosynthetic apparatus, under different growth conditions. We found that a drastic reduction in light intensity allowed cells to maintain a more functional photosynthetic apparatus: the phycobilisome antenna was bigger, the activity of both photosystems was higher and the levels of photosystem (PS) proteins were higher. Pre-acclimating cells to Mn limitation, under which the activity of both PSI and PSII is diminished, results in a very similar response. The rate of PSII photoinhibition, in nitrogen limited cells, was found to be directly related to the activity of the photosynthetic apparatus. These data indicate that, under our experimental conditions, photo-damage avoidance was the more prominent determinant during the acclimation process. The combinations of limiting factors tested here is by no means artificial. Similar scenarios can take place under environmental conditions and should be taken into account when estimating nutrient limitations in nature

Derivation of species-specific hybridization-like knowledge out of cross-species hybridization results

BACKGROUND: One of the approaches for conducting genomics research in organisms without extant microarray platforms is to profile their expression patterns by using Cross-Species Hybridization (CSH). Several different studies using spotted microarray and CSH produced contradicting conclusions in the ability of CSH to reflect biological processes described by species-specific hybridization (SSH). RESULTS: We used a tomato-spotted cDNA microarray to examine the ability of CSH to reflect SSH data. Potato RNA was hybridized to spotted cDNA tomato and potato microarrays to generate CSH and SSH data, respectively. Difficulties arose in obtaining transcriptomic data from CSH that reflected those obtained from SSH. Nevertheless, once the data was filtered for those corresponding to matching probe sets, by restricting proper cutoffs of probe homology, the CSH transcriptome data showed improved reflection of those of the SSH. CONCLUSIONS: This study evaluated the relative performance of CSH compared to SSH, and proposes methods to ensure that CSH closely reflects the biological process analyzed by SSH