Evolutionary instability of symbiotic function in Bradyrhizobium japonicum

Bacterial mutualists are often acquired from the environment by eukaryotic hosts. However, both theory and empirical work suggest that this bacterial lifestyle is evolutionarily unstable. Bacterial evolution outside of the host is predicted to favor traits that promote an independent lifestyle in the environment at a cost to symbiotic function. Consistent with these predictions, environmentally-acquired bacterial mutualists often lose symbiotic function over evolutionary time. Here, we investigate the evolutionary erosion of symbiotic traits in Bradyrhizobium japonicum, a nodulating root symbiont of legumes. Building on a previous published phylogeny we infer loss events of nodulation capability in a natural population of Bradyrhizobium, potentially driven by mutation or deletion of symbiosis loci. Subsequently, we experimentally evolved representative strains from the symbiont population under host-free in vitro conditions to examine potential drivers of these loss events. Among Bradyrhizobium genotypes that evolved significant increases in fitness in vitro, two exhibited reduced symbiotic quality, but no experimentally evolved strain lost nodulation capability or evolved any fixed changes at six sequenced loci. Our results are consistent with trade-offs between symbiotic quality and fitness in a host free environment. However, the drivers of loss-of-nodulation events in natural Bradyrhizobium populations remain unknown.     

Estimating the effect of moving meat-free products to the meat aisle on sales of meat and meat-free products: A non-randomised controlled intervention study in a large UK supermarket chain

BackgroundReducing meat consumption could bring health and environmental benefits, but there is little research to date on effective interventions to achieve this. A non-randomised controlled intervention study was used to evaluate whether prominent positioning of meat-free products in the meat aisle was associated with a change in weekly mean sales of meat and meat-free products.Methods and findingsWeekly sales data were obtained from 108 stores: 20 intervention stores that moved a selection of 26 meat-free products into a newly created meat-free bay within the meat aisle and 88 matched control stores. The primary outcome analysis used a hierarchical negative binomial model to compare changes in weekly sales (units) of meat products sold in intervention versus control stores during the main intervention period (Phase I: February 2019 to April 2019). Interrupted time series analysis was also used to evaluate the effects of the Phase I intervention. Moreover, 8 of the 20 stores enhanced the intervention from August 2019 onwards (Phase II intervention) by adding a second bay of meat-free products into the meat aisle, which was evaluated following the same analytical methods.During the Phase I intervention, sales of meat products (units/store/week) decreased in intervention (approximately −6%) and control stores (−5%) without significant differences (incidence rate ratio [IRR] 1.01 [95% CI 0.95–1.07]. Sales of meat-free products increased significantly more in the intervention (+31%) compared to the control stores (+6%; IRR 1.43 [95% CI 1.30–1.57]), mostly due to increased sales of meat-free burgers, mince, and sausages. Consistent results were observed in interrupted time series analyses where the effect of the Phase II intervention was significant in intervention versus control stores.ConclusionsProminent positioning of meat-free products into the meat aisle in a supermarket was not effective in reducing sales of meat products, but successfully increased sales of meat-free alternatives in the longer term.A preregistered protocol (https://osf.io/qmz3a/) was completed and fully available before data analysis.

Carmen Piernas and co-workers study positioning and marketing of meat-free products in supermarkets.     

Basis for the Exclusion of Escherichia coli from the Rumen Ecosystem

The possible causes for the exclusion of Escherichia coli from the rumen ecosystem were investigated. Evidence presented indicates that oxidation-reduction potential, temperature, pH, CO₂, volatile fatty acids, traces of heavy metals, and bacteriophage are not environmental factors which select against E. coli in the rumen ecosystem. The feeding of nutrients utilizable by E. coli to an artificially inoculated continuous-culture rumen ecosystem did not prevent the washout of the E. coli from the continuous cultures. The presence of an inhibitor of E. coli growth was demonstrated. High concentrations of rumen fluid (50 to 100%) were necessary to inhibit growth in Antibiotic Medium 3. The inhibitor may operate to control the growth of E. coli in the rumen ecosystem. Because of the presence of an inhibitor, the possibility that rumen fluid is deficient in nutrients to support the growth of E. coli cannot be eliminated.     

Annulus-pore relationship in Gramineae (Poaceae) pollen: the pore margin of Pariana

Pariana, a primitive bamboo, is the only genus in the Gramineae (Poaceae) to have pollen grains without an annulus as part of its single aperture (porate) system. In contrast, the markedly thickened exine layer underlying the pore margin is similar to counterparts in all grass genera. Components of the future annulus in Gramineae pollen develop toward the cytoplasm (proximally) and begin to be pressed outward by an increase in the cytoplasm during the microspore vacuolate stage, culminating in an annulus by maturity. However, in some species of Pariana these components are either not sufficiently developed or the cytoplasmic expansion is not sufficient to press the components into an annular ring around the pore. The structural relationship of exine layering in this type of pollen grain in Gramineae and other families with similar apertures has not hitherto been extensively studied. A critical examination of the apertures in bambusoid grasses may clarify their systematic position within the Gramineae.     

Actions of the juvenile hormone, 20-hydroxy-ecdysone,and the oöstatic hormone during oögenesis in the flies Phormia regina and Sarcophaga bullata

Application of juvenile hormone (JH) to sugar-fed Phormia flies leads to full ovarian development, i.e. the flies become autogenous. Application of JH to sugar + liver-fed Phormia leads to the simultaneous development of primary, secondary and tertiary oöcytes, suggesting the role of the oöstatic hormone is to shut off the action of the JH. This is consistent with the notion that the oöstatic hormone may act on the corpus allatum either directly or through the neurosecretory system. Application of 20-hydroxy-ecdysone to Phormia or Sarcophaga, when primary oöcytes have started to develop (stage 4A), causes the primary oöcytes to degenerate, with concomitant development of the secondary oöcytes.     

Efficiency of partner choice and sanctions in Lotus is not altered by nitrogen fertilization

Eukaryotic hosts must exhibit control mechanisms to select against ineffective bacterial symbionts. Hosts can minimize infection by less-effective symbionts (partner choice) and can divest of uncooperative bacteria after infection (sanctions). Yet, such host-control traits are predicted to be context dependent, especially if they are costly for hosts to express or maintain. Legumes form symbiosis with rhizobia that vary in symbiotic effectiveness (nitrogen fixation) and can enforce partner choice as well as sanctions. In nature, legumes acquire fixed nitrogen from both rhizobia and soils, and nitrogen deposition is rapidly enriching soils globally. If soil nitrogen is abundant, we predict host control to be downregulated, potentially allowing invasion of ineffective symbionts. We experimentally manipulated soil nitrogen to examine context dependence in host control. We co-inoculated Lotus strigosus from nitrogen depauperate soils with pairs of Bradyrhizobium strains that vary in symbiotic effectiveness and fertilized plants with either zero nitrogen or growth maximizing nitrogen. We found efficient partner choice and sanctions regardless of nitrogen fertilization, symbiotic partner combination or growth season. Strikingly, host control was efficient even when L. strigosus gained no significant benefit from rhizobial infection, suggesting that these traits are resilient to short-term changes in extrinsic nitrogen, whether natural or anthropogenic.     

Human mannose 6-phosphate-uncovering enzyme is synthesized as a proenzyme that is activated by the endoprotease furin

N-Acetylglucosamine-1-phosphodiester alpha-N-acetylglucosaminidase, also known as "uncovering" enzyme (UCE), is localized in the trans-Golgi network, where it removes a covering N-acetylglucosamine from the mannose 6-phosphate recognition marker on lysosomal acid hydrolases. Here we show that UCE is synthesized as an inactive proenzyme that is activated by the endoprotease furin, which cleaves an RARLPR/D sequence to release a 24-amino acid propiece. As furin is localized in the trans-Golgi network, newly synthesized UCE is inactive until it reaches this terminal Golgi compartment. LoVo cells (derived from a human colon adenocarcinoma) lack furin activity and have extremely low UCE activity. Addition of furin to LoVo cell extracts restores UCE activity to normal levels, demonstrating that the UCE proenzyme is stable in this cell type. LoVo cells secrete acid hydrolases with phosphomannose diesters as a consequence of the deficient UCE activity. This demonstrates for the first time that UCE is the only enzyme in these cells capable of efficiently uncovering phosphomannose diesters. UCE also hydrolyzes UDP-GlcNAc, a sugar donor for Golgi N-acetylglucosaminyltransferases. The fact that UCE is not activated until it reaches the trans-Golgi network may ensure that the pool of UDP-GlcNAc in the Golgi stack is not depleted, thereby maintaining proper oligosaccharide assembly.