Exometabolome characterization of high cell density culture perfusion and optimization of the cell specific perfusion rate

High cell density perfusion has the potential to generate intensified processes. A target for such perfusion process can be to maintain a steady state culture around 100 x 106 cells/mL. A challenge for the development of these processes is to minimize the medium consumption, to reduce the costs associated with this raw material and with the harvest processing. This is particularly true for processes at densities such as 100 x 106 cells/mL for which several reactor volumes per day are typically necessary. We have shown that cell specific perfusion rate (CSPR) is an approach, which has proven to enable densities of CHO cells above 200 x 106 cells/mL. To appreciate the impact of the cell density on the metabolic landscape in an antibody producing CHO cell perfusion culture using CSPR, multivariate data analysis of extracellular metabolomic data generated by high-resolution liquid chromatography–mass spectrometry (LC–MS) was carried on. We observed that the extracellular metabolic profile was by far more stable in perfusion mode than in fed-batch mode, despite a significantly larger range of cell densities in the former case. There was a strong correlation between the composition of the exometabolome and the viable cell density between 8 and 207 x 106 cells/mL. The cell specific glutamine consumption rate as well as, to some extent, the cell specific glucose consumption rate were only correlated with the composition of the exometabolome when the viable cell density was above 127 x 106 cells/mL. No correlations between the exometabolome and the cell specific productions of lactate, ammonia or antibody were observed. These results show that the metabolism of the cells was very stable at densities lower than 127 x 106 cells/mL. Above this density, the metabolic footprint analysis revealed variations of the cellular metabolism: in particular modifications associated with the glutathione metabolism were observed. We addressed the CSPR minimization by sequentially varying the cell density and/or the perfusion rate in a culture stabilized around 30 x 106 cells/mL by cell bleeds. In our system, we observed that the cell specific antibody production rate was independent of the CSPR below 52 pL/cell/day and positively correlated with this parameter above this value. Furthermore, the cell specific glucose consumption and lactate production rates increased with the CSPR. Interestingly, during the CSPR optimization, we showed that increasing the cell density was not systematically equivalent to reducing the perfusion rate despite the fact that the CSPR is equal to the ratio of the perfusion rate by the cell density. This was due to a substrate threshold determining the occurrence of different glucose consumption kinetics

Existing evidence related to soil retention of phosphorus from on-site wastewater treatment systems in boreal and temperate climate zones: a systematic map

BackgroundIn Sweden there are nearly one million soil-based on-site wastewater treatment systems (OWTSs). OWTSs may contribute to eutrophication of surface waters, due to the discharge of phosphorus (P). Hence, in certain cases, a high P removal rate (up to 90%) of OWTSs is required by Swedish authorities. Since these requirements may have costly consequences to property owners, it is debated whether they are too strict. In this debate, it is often claimed that the soil retention of P occurring in the natural environments may be underestimated by authorities. Soil retention is the inhibition of the transport of P through the ground, due to different chemical, physical and biological processes occurring there. These processes make the P transport slower, which may reduce the unwanted impact on receiving water bodies. However, the efficiency of soil retention of P remains unclear. The objective of this systematic map was to collect, code, organise and elucidate the relevant evidence related to the topic, to be able to guide stakeholders through the evidence base, and to support future research synthesising, commissioning, and funding. The systematic map was carried out in response to needs declared by the Swedish Agency for Marine and Water Management but the conclusions should be valid for a wider range of countries across boreo-temperate regions.MethodsSearches were made for peer-reviewed and grey literature using bibliographic databases, search engines, specialist websites, and stakeholder contacts. The references were screened for relevance according to a predefined set of eligibility criteria. A detailed database of the relevant studies was compiled. Data and metadata that enable evaluation and discussion of the character and quality of the evidence base were extracted and coded. Special focus was placed on assessing if existing evidence could contribute to policy and practice decision making. Descriptive information about the evidence base was presented in tables and figures. An interactive evidence atlas and a choropleth were created, displaying the locations of all studies.Review findings234 articles out of 10,797 screened records fulfilled the eligibility criteria. These articles contain 256 studies, performed in the field or in the laboratory. Six different study types were identified, based on where the measurements were conducted. Most studies, including laboratory studies, lack replicates. Most field studies are observational case studies.ConclusionsIt is not possible to derive valid generic measures of the efficiency of soil retention of P occurring in the natural soil environment from available research. Neither does the evidence base allow for answering the question of the magnitude of the potential impact of OWTSs on the P concentration in recipients on a general basis, or under what conditions OWTSs generally have such an impact. A compilation of groundwater studies may provide examples of how far the P may reach in x years, but the number of groundwater studies is insufficient to draw any general conclusions, given the complexity and variability of the systems. Future research should strive for replicated study designs, more elaborate reporting, and the establishment of a reporting standard

Absorption of light in InP nanowire arrays

An understanding of the absorption of light is essential for efficient photovoltaic and photodetection applications with III-V nanowire arrays. Here, we correlate experiments with modeling and verify experimentally the predicted absorption of light in InP nanowire arrays for varying nanowire diameter and length. We find that 2,000 nm long nanowires in a pitch of 400 nm can absorb 94% of the incident light with energy above the band gap and, as a consequence, light which in a simple ray-optics description would be travelling between the nanowires can be efficiently absorbed by the nanowires. Our measurements demonstrate that the absorption for long nanowires is limited by insertion reflection losses when light is coupled from the air top-region into the array. These reflection losses can be reduced by introducing a smaller diameter to the nanowire-part closest to the air top-region. For nanowire arrays with such a nanowire morphology modulation, we find that the absorptance increases monotonously with increasing diameter of the rest of the nanowire

UV exposure : A novel processing method to fabricate nanowire solar cells

We demonstrate a novel and rapid method for nanowire (NW) solar cell processing. NW arrays were embedded in photoresist. The strong absorption of light in the NWs leads to self-limited exposure of the resist, which enables selective removal of the exposed part of the resist, opening up for the tips of the NWs and further processing. The UV-exposure technology allows a fast and low-cost process compared to the conventional reactive ion etching method