Photosynthetic efficiency of Chlorella sorokiniana in a turbulently mixed short light‐path photobioreactor

To be able to study the effect of mixing as well as any other parameter on productivity of algal cultures, we designed a lab‐scale photobioreactor in which a short light path (SLP) of (12 mm) is combined with controlled mixing and aeration. Mixing is provided by rotating an inner tube in the cylindrical cultivation vessel creating Taylor vortex flow and as such mixing can be uncoupled from aeration. Gas exchange is monitored on‐line to gain insight in growth and productivity. The maximal productivity, hence photosynthetic efficiency, of Chlorella sorokiniana cultures at high light intensities (1,500 μmol m^?1 s^?1) was investigated in this Taylor vortex flow SLP photobioreactor. We performed duplicate batch experiments at three different mixing rates: 70, 110, and 140 rpm, all in the turbulent Taylor vortex flow regime. For the mixing rate of 140 rpm, we calculated a quantum requirement for oxygen evolution of 21.2 mol PAR photons per mol O₂ and a yield of biomass on light energy of 0.8 g biomass per mol PAR photons. The maximal photosynthetic efficiency was found at relatively low biomass densities (2.3 g L^?1) at which light was just attenuated before reaching the rear of the culture. When increasing the mixing rate twofold, we only found a small increase in productivity. On the basis of these results, we conclude that the maximal productivity and photosynthetic efficiency for C. sorokiniana can be found at that biomass concentration where no significant dark zone can develop and that the influence of mixing‐induced light/dark fluctuations is marginal. © 2010 American Institute of Chemical Engineers Biotechnol. Prog., 2010     

Power consumption and maximum energy dissipation in a milliliter‐scale bioreactor

Mean power consumption and maximum local energy dissipation were measured as function of operating conditions of a milliliter‐scale stirred tank bioreactor (V = 12 mL) with a gas‐inducing impeller. A standard laboratory‐scale stirred tank bioreactor (V = 1,200 mL) with Rushton turbines was used as reference. The measured power characteristics (Newton number as function of Reynolds number) were the same on both scales. The changeover between laminar and turbulent flow regime was observed at a Reynolds number of 3,000 with the gas‐inducing stirrer on a milliliter‐scale. The Newton number (power number) in the turbulent flow regime was 3.3 on a milliliter‐scale, which is close to values reported for six‐blade Rushton turbines of standard bioreactors. Maximum local energy dissipation (ε_max) was measured using a clay/polymer flocculation system. The maximum local energy dissipation in the milliliter‐scale stirred tank bioreactor was reduced compared with the laboratory‐scale stirred tank at the same mean power input per unit mass (ε_ø), yielding ε_max/ε_ø ≈ 10 compared with ε_max/ε_ø ≈ 16. Hence, the milliliter‐scale stirred tank reactor distributes power more uniformly in the reaction medium. These results are in good agreement with literature data, where a decreasing ε_max/ε_ø with increasing ratio of impeller diameter to reactor diameter is found (d/D = 0.7 compared with d/D = 0.4). Based on these data, impeller speeds can now be easily adjusted to achieve the same maximum local energy dissipation at different scales. This enables a more reliable and robust scale‐up of bioprocesses from milliliter‐scale to liter‐scale reactors. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2010     

Pathogen proteomes during infection: A basis for infection research and novel control strategies

Infectious diseases cause tremendous mortality and morbidity worldwide. Rising antimicrobial resistance and the lack of new drugs cause an increasingly alarming crisis in infectious disease control. New system-level approaches are likely to help understand complex host/pathogen interactions as a basis for rational development of novel antibiotics and vaccines. Proteome analysis of pathogens in infected tissues comprehensively reveals functionally relevant pathogen activities during infection. It also highlights potential targets for antimicrobial chemotherapy as well as promising antigens for vaccination. Integration of these data with complementary large-scale data helps to further prioritize candidates for in-depth experimental analysis. Here, I discuss some of these approaches with a special emphasis on the model pathogen Salmonella.     

Response of Pseudomonas putida KT2440 to phenol at the level of membrane proteome

This study led to the extension and refinement of our current model for the global response of Pseudomonas putida KT2440 to phenol by getting insights into the adaptive response mechanisms involving the membrane proteome. A two-dimensional gel electrophoresis based protocol was optimized to allow the quantitative comparison of membrane proteins, by combining inner and outer membrane fractionation with membrane protein solubilization using the detergent dodecylmaltoside. Following phenol exposure, a coordinate increased content of protein subunits of known or putative solvent efflux pump systems (e.g. TtgA, TtgC, Ttg2A, Ttg2C, and PP_1516-7) and a decreased content of porins OprB, OprF, OprG and OprQ was registered, consistent with an adaptive response to reduce phenol intracellular concentration. This adaptive response may in part be mediated by post-translational modifications, as suggested by the relative content of the multiple forms identified for a few porins and efflux pump subunits. Results also suggest the important role of protein chaperones, of cell envelope and cell surface and of a more active respiratory chain in the response to phenol. All these mechanistic insights may be extended to Pseudomonas adaptation to solvents, of possible impact in biodegradation, bioremediation and biocatalysis.     

Nighttime sap flow of Acacia mangium and its implications for nighttime transpiration and stem water storage

Aims Nighttime sap flow of trees may indicate transpiration and/or recharge of stem water storage at night. This paper deals with the water use of Acacia mangium at night in the hilly lands of subtropical South China. Our primary goal was to reveal and understand the nature of nighttime sap flow and its functional significance.Methods Granier's thermal dissipation method was used to determine the nighttime sap flux of A. mangium. Gas exchange system was used to estimate nighttime leaf transpiration and stomatal conductance of studied trees.Important findings Nighttime sap flow was substantial and showed seasonal variation similar to the patterns of daytime sap flow in A. mangium. Mean nighttime sap flow was higher in the less precipitation year of 2004 (1122.4 mm) than in the more precipitation year of 2005 (1342.5 mm) since more daytime transpiration and low soil water availability in the relatively dry 2004 can be the cause of more nighttime sap flow. Although vapor pressure deficit and air temperature were significantly correlated with nighttime sap flow, they could only explain a small fraction of the variance in nighttime sap flow. The total accumulated water loss (E L) by transpiration of canopy leaves was only ~2.6–8.5% of the total nighttime sap flow (E t) during the nights of July 17–18 and 18–19, 2006. Therefore, it is likely that the nighttime sap flow was mainly used for refilling water in the trunk. The stem diameter at breast height, basal area and sapwood area explained much more variance of nighttime water recharge than environmental factors and other tree form features, such as tree height, stem length below the branch, and canopy size. The contribution of nighttime water recharge to the total transpiration ranged from 14.7 to 30.3% depending on different DBH class and was considerably higher in the dry season compared to the wet season.     

Landscape genetics indicate recently increased habitat fragmentation in African forest‐associated chafers

Today, indigenous forests cover less than 0.6% of South Africa's land surface and are highly fragmented. Most forest relicts are very small and typically occur in fire‐protected gorges along the eastern Great Escarpment. Yet, they hold a unique and valuable fauna with high endemism and ancient phylogenetic lineages, fostered by long‐term climatic stability and complex microclimates. Despite numerous studies on southern African vegetation cover, the current state of knowledge about the natural extension of indigenous forests is rather fragmentary. We use an integrated approach of population‐level phylogeography and climatic niche modeling of forest‐associated chafer species to assess connectivity and extent of forest habitats since the last glacial maximum. Current and past species distribution models ascertained potential fluctuations of forest distribution and supported a much wider potential current extension of forests based on climatic data. Considerable genetic admixture of mitochondrial and nuclear DNA among many populations and an increase in mean population mutation rate in Extended Bayesian Skyline Plots of all species indicated more extended or better connected forests in the recent past (<5 kya). Genetic isolation of certain populations, as revealed by population differentiation statistics (), as well as landscape connectivity statistics and habitat succession scenarios suggests considerable loss of habitat connectivity. As major anthropogenic influence is likely, conservational actions need to be considered.     

Assessing the ecological risk posed by a recently established invasive alien predator: <Emphasis Type="Italic">Harmonia axyridis</Emphasis> as a case study

Invasive alien predators are a serious threat to biodiversity worldwide. However, there is no generic method for assessing which local species are most at risk following the invasion of a new predator. The harlequin ladybird, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae), is an alien in Europe and many other parts of the world where it affects other species of ladybirds through competition for food and intra-guild predation (IGP). Here, we describe a method developed to assess which European ladybird species are most at risk following the invasion of H. axyridis. The three components of the risk assessment are: the likelihood that the assessed native species encounters H. axyridis in the field, the hazard of competition for food, and the IGP hazard. Thirty native European ladybird species were assessed through data obtained from field observations, laboratory experiments and literature reviews. The species that are considered most at risk are found on deciduous trees, have immature stages which are highly vulnerable to IGP by H. axyridis, and are primarily aphidophagous. These species should be the focus of specific studies and possibly conservation actions. The risk assessment method proposed here could be applied to other alien predators which are considered a threat to native species through competition and predation.     

The tunable pReX expression vector enables optimizing the T7-based production of membrane and secretory proteins in <Emphasis Type="Italic">E. coli</Emphasis>

Background

To optimize the production of membrane and secretory proteins in Escherichia coli, it is critical to harmonize the expression rates of the genes encoding these proteins with the capacity of their biogenesis machineries. Therefore, we engineered the Lemo21(DE3) strain, which is derived from the T7 RNA polymerase-based BL21(DE3) protein production strain. In Lemo21(DE3), the T7 RNA polymerase activity can be modulated by the controlled co-production of its natural inhibitor T7 lysozyme. This setup enables to precisely tune target gene expression rates in Lemo21(DE3). The t7lys gene is expressed from the pLemo plasmid using the titratable rhamnose promoter. A disadvantage of the Lemo21(DE3) setup is that the system is based on two plasmids, a T7 expression vector and pLemo. The aim of this study was to simplify the Lemo21(DE3) setup by incorporating the key elements of pLemo in a standard T7-based expression vector.

Results

By incorporating the gene encoding the T7 lysozyme under control of the rhamnose promoter in a standard T7-based expression vector, pReX was created (ReX stands for Regulated gene eXpression). For two model membrane proteins and a model secretory protein we show that the optimized production yields obtained with the pReX expression vector in BL21(DE3) are similar to the ones obtained with Lemo21(DE3) using a standard T7 expression vector. For another secretory protein, a c-type cytochrome, we show that pReX, in contrast to Lemo21(DE3), enables the use of a helper plasmid that is required for the maturation and hence the production of this heme c protein.

Conclusions

Here, we created pReX, a T7-based expression vector that contains the gene encoding the T7 lysozyme under control of the rhamnose promoter. pReX enables regulated T7-based target gene expression using only one plasmid. We show that with pReX the production of membrane and secretory proteins can be readily optimized. Importantly, pReX facilitates the use of helper plasmids. Furthermore, the use of pReX is not restricted to BL21(DE3), but it can in principle be used in any T7 RNAP-based strain. Thus, pReX is a versatile alternative to Lemo21(DE3).