Interaction of cytochrome c with the phosphorprotein phosvitin.

Candida krusei cytochrome c forms a molecular complex with phosphorprotein phosvitin in weakly alkaline solution of low ionic strength. At most, about 22 molecules of cytochrome c bind to a phosvitin molecule. The complex at the binding ratio below about 11 (half of the maximum ratio) as a much higher binding strength. Several lines of evidence indicate that the marked difference in the binding strength is due to the difference in negative charges on phosvitin molecule concerned in the binding of a cytochrome c molecule. The phosvitin-bound cytochrome c seems to have a preferred orientation with the front surface of the molecule containing the exposed heme edge in contact with the phosvitin molecule.     

Scale-up analysis of geometrically dissimilar single-use bioreactors

Cell culture scale-up is a challenging task due to the simultaneous change of multiple hydrodynamic process characteristics and their different dependencies on the bioreactor size as well as variation in the requirements of individual cell lines. Conventionally, the volumetric power input is the most common parameter to select the impeller speed for scale-up, however, it is well reported that this approach fails when there are huge differences in bioreactor scales. In this study, different scale-up criteria are evaluated. At first, different hydrodynamic characteristics are assessed using computational fluid dynamics data for four single-use bioreactors, the Mobius® CellReady 3 L, the Xcellerex™ XDR-10, the Xcellerex™ XDR-200, and the Xcellerex™ XDR-2000. On the basis of this numerical data, several potential scale-up criteria such as volumetric power input, impeller tip speed, mixing time, maximum hydrodynamic stress, and average strain rate in the impeller zone are evaluated. Out of all these criteria, the latter is found to be most appropriate, and the successful scale-up from 3 to 10 L bioreactor and to 200 L bioreactor is confirmed with cell culture experiments using Chinese Hamster Ovary cell cultivation.     

Modelling spatial patterns in host-associated microbial communities

Microbial communities exhibit spatial structure at different scales, due to constant interactions with their environment and dispersal limitation. While this spatial structure is often considered in studies focusing on free-living environmental communities, it has received less attention in the context of host-associated microbial communities or microbiota. The wider adoption of methods accounting for spatial variation in these communities will help to address open questions in basic microbial ecology as well as realize the full potential of microbiome-aided medicine. Here, we first overview known factors affecting the composition of microbiota across diverse host types and at different scales, with a focus on the human gut as one of the most actively studied microbiota. We outline a number of topical open questions in the field related to spatial variation and patterns. We then review the existing methodology for the spatial modelling of microbiota. We suggest that methodology from related fields, such as systems biology and macro-organismal ecology, could be adapted to obtain more accurate models of spatial structure. We further posit that methodological developments in the spatial modelling and analysis of microbiota could in turn broadly benefit theoretical and applied ecology and contribute to the development of novel industrial and clinical applications.     

The role of Rubisco and cell walls in the interspecific variation in photosynthetic capacity

Photosynthetic capacity is known to vary considerably among species. Its physiological cause and ecological significance have been one of the most fundamental questions in plant ecophysiology. We studied the contents of Rubisco (a key enzyme of photosynthesis) and cell walls in leaves of 26 species with a large variation in photosynthetic rates. We focused on photosynthetic nitrogen-use efficiency (PNUE, photosynthetic rate per nitrogen), which can be expressed as the product of Rubisco-use efficiency (RBUE, photosynthetic rate per Rubisco) and Rubisco nitrogen fraction (RNF, Rubisco nitrogen per total leaf nitrogen). RBUE accounted for 70% of the interspecific variation in PNUE. The variation in RBUE was ascribed partly to stomatal conductance, and other factors such as mesophyll conductance and Rubisco kinetics might also be involved. RNF was also significantly related to PNUE but the correlation was relatively weak. Cell wall nitrogen fraction (WNF, cell wall nitrogen per total leaf nitrogen) increased with increasing leaf mass per area, but there was no correlation between RNF and WNF. These results suggest that nitrogen allocation to cell walls does not explain the variation in PNUE. The difference in PNUE was not caused by a sole factor that was markedly different among species but by several factors each of which was slightly disadvantageous in low PNUE species. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.