Rational redesign of the ferredoxin-NADP+-oxido-reductase/ferredoxin-interaction for photosynthesis-dependent H2-production.

Utilization of electrons from the photosynthetic water splitting reaction for the generation of biofuels, commodities as well as application in biotransformations requires a partial rerouting of the photosynthetic electron transport chain. Due to its rather negative redox potential and its bifurcational function, ferredoxin at the acceptor side of Photosystem 1 is one of the focal points for such an engineering. With hydrogen production as model system, we show here the impact and potential of redox partner design involving ferredoxin (Fd), ferredoxin-oxido-reductase (FNR) and [FeFe]­hydrogenase HydA1 on electron transport in a future cyanobacterial design cell of Synechocystis PCC 6803. X-ray-structure-based rational design and the allocation of specific interaction residues by NMR-analysis led to the construction of Fd- and FNR-mutants, which in appropriate combination enabled an about 18-fold enhanced electron flow from Fd to HydA1 (in competition with equimolar amounts of FNR) in in vitro assays. The negative impact of these mutations on the Fd-FNR electron transport which indirectly facilitates H2 production (with a contribution of ≤42% by FNR variants and ≤23% by Fd-variants) and the direct positive impact on the Fd-HydA1 electron transport (≤23% by Fd-mutants) provide an excellent basis for the construction of a hydrogen-producing design cell and the study of photosynthetic efficiency-optimization with cyanobacteria.

Carrying capacity in arid rangelands during droughts: the role of temporal and spatial thresholds.

Assessing the carrying capacity is of primary importance in arid rangelands. This becomes even more important during droughts, when rangelands exhibit non-equilibrium dynamics, and the dynamics of livestock conditions and forage resource are decoupled. Carrying capacity is usually conceived as an equilibrium concept, that is, the consumer density that can co-exist in long-term equilibrium with the resource. As one of the first, here we address the concept of carrying capacity in systems, where there is no feedback between consumer and resource in a limited period of time. To this end, we developed an individual-based model describing the basic characteristics of a rangeland during a drought. The model represents a rangeland composed by a single water point and forage distributed all around, with livestock units moving from water to forage and vice versa, for eating and drinking. For each livestock unit we implemented an energy balance and we accounted for the gut-filling effect (i.e. only a limited amount of forage can be ingested per unit time). Our results showed that there is a temporal threshold above which livestock begin to experience energy deficit and burn fat reserves. We demonstrated that such a temporal threshold increases with the number of animals and decreases with the rangeland conditions (amount of forage). The temporal threshold corresponded to the time livestock take to consume all the forage within a certain distance from water, so that the livestock can return to water for drinking without spending more energy than they gain within a day. In this study, we highlight the importance of a time threshold in the assessment of carrying capacity in non-equilibrium conditions. Considering this time threshold could explain contrasting observations about the influence of livestock number on livestock conditions. In case of private rangelands, the herd size should be chosen so that the spatial threshold equals (or exceeds) the length of the drought.

Robustness and management adaptability in tropical rangelands: a viability-based assessment under the non-equilibrium paradigm.

Rangelands provide the main forage resource for livestock in many parts of the world, but maintaining long-term productivity and providing sufficient income for the rancher remains a challenge. One key issue is to maintain the rangeland in conditions where the rancher has the greatest possibility to adapt his/her management choices to a highly fluctuating and uncertain environment. In this study, we address management robustness and adaptability, which increase the resilience of a rangeland. After reviewing how the concept of resilience evolved in parallel to modelling views on rangelands, we present a dynamic model of rangelands to which we applied the mathematical framework of viability theory to quantify the management adaptability of the system in a stochastic environment. This quantification is based on an index that combines the robustness of the system to rainfall variability and the ability of the rancher to adjust his/her management through time. We evaluated the adaptability for four possible scenarios combining two rainfall regimes (high or low) with two herding strategies (grazers only or mixed herd). Results show that pure grazing is viable only for high-rainfall regimes, and that the use of mixed-feeder herds increases the adaptability of the management. The management is the most adaptive with mixed herds and in rangelands composed of an intermediate density of trees and grasses. In such situations, grass provides high quantities of biomass and woody plants ensure robustness to droughts. Beyond the implications for management, our results illustrate the relevance of viability theory for addressing the issue of robustness and adaptability in non-equilibrium environments.

Survival of Escherichia coli O157:H7 in ground beef after sublethal heat shock and subsequent isothermal cooking.

Heat shock of Escherichia coli O157:H7 in broth media reportedly leads to enhanced survival during subsequent heating in broth medium or ground beef. Survival of E. coli O157:H7 during slow cooking thus may be enhanced by prior exposure to sublethal heat shock conditions, thereby jeopardizing the safety of slow-cooked products such as beef roasts. This study examined the effect of heat shocking E. coli O157:H7-inoculated lean (6 to 9% fat) ground beef on the survival of the pathogen in the same ground beef during a subsequent 4-h, 54.4 degrees C cooking process. Six different combinations of heat shock temperature (47.2, 48.3, or 49.4 degrees C) and time (5 or 30 min) were applied to a five-strain cocktail of microaerophilically grown cells in 25 g of prewarmed ground beef, which was followed by cooking at 54.4 degrees C. Temperature during a 30-min heat shock treatment did not significantly affect E. coli O157:H7 survival during subsequent isothermal cooking (P > 0.05). Survival after a 5-min heat shock was higher when the heat shock temperature was 48.3 or 49.4 degrees C (P < 0.05) than when it was 47.2 degrees C. The D-values at 54.4 degrees C (130 degrees F) (D54.4-value) of the process significantly increased only when cells were exposed to a heat shock combination of 5 min at 49.4 degrees C. Mean (n = 3 trials) reductions in E. coli O157:H7 during the 4-h, 54.4 degrees C isothermal cooking process ranged from 4.3 to 7.5 log CFU/g. Heating E. coli O157:H7-contaminated beef at the high end of the sublethal temperature range for 5 min could increase survival of E. coli O157:H7 during subsequent slow-cooking processes.

Radon in the workplace--a study of occupational exposure in BT underground structures.

During the period August 1993-October 1994 a study was undertaken throughout British Telecommunications plc to assess occupational exposure to radon. This paper is concerned only with that portion of the work concerned with underground structures. The results show that radon can build up to very high concentrations in manholes and implies a significant risk to those who need to work in them. For various reasons, which are explained, exposures are much less than predicted and in all but a very few cases the annual predicted radiation dose due to radon is expected to be below 5 milliSieverts (mSv). A safe system of work is described which seeks to ensure that no BT people receive an annual radiation dose of greater than 5 mSv as a result of occupational exposure to radon.

Zeolite A increases proliferation, differentiation, and transforming growth factor beta production in normal adult human osteoblast-like cells in vitro.

Silicon in trace amounts enhances bone formation, and the silicon-containing compound zeolite A (ZA) increases eggshell thickness in hens. In the studies reported here, treatment of nearly homogeneous strains of normal human osteoblast-like cells for 48 h with ZA at 0.1-100 micrograms/ml induced a dose-dependent increase (r = 0.35, P < 0.001) in DNA synthesis (n = 31) to 162 +/- 16% (mean +/- SEM) of control and in the proportion of cells in mitosis (n = 4) from 9.1 +/- 1.8 to 27.0 +/- 4.5% (r = 0.69, P < 0.005). ZA treatment also increased alkaline phosphatase activity (P < 0.05) and osteocalcin release (P < 0.05) but did not significantly affect collagen production per individual cell. The mitogenic action of ZA was dependent on cell seeding density over the range of 1250-40,000 cells per cm2, which is consistent with induction of an autocrine factor(s). TGF-beta is a potent mitogen for osteoblasts. ZA treatment increased the steady-state mRNA levels of transforming growth factor beta 1 (TGF-beta 1) and induced the release of the latent form of TGF-beta protein into the conditioned medium within 6 h. We conclude that ZA induces the proliferation and differentiation of cells of the osteoblast lineage.