New Type of Outer Membrane Vesicle Produced by the Gram-Negative Bacterium Shewanella vesiculosa M7T: Implications for DNA Content

Outer membrane vesicles (OMVs) from Gram-negative bacteria are known to be involved in lateral DNA transfer, but the presence of DNA in these vesicles has remained difficult to explain. An ultrastructural study of the Antarctic psychrotolerant bacterium Shewanella vesiculosa M7^T has revealed that this Gram-negative bacterium naturally releases conventional one-bilayer OMVs through a process in which the outer membrane is exfoliated and only the periplasm is entrapped, together with a more complex type of OMV, previously undescribed, which on formation drag along inner membrane and cytoplasmic content and can therefore also entrap DNA. These vesicles, with a double-bilayer structure and containing electron-dense material, were visualized by transmission electron microscopy (TEM) after high-pressure freezing and freeze-substitution (HPF-FS), and their DNA content was fluorometrically quantified as 1.8 ± 0.24 ng DNA/μg OMV protein. The new double-bilayer OMVs were estimated by cryo-TEM to represent 0.1% of total vesicles. The presence of DNA inside the vesicles was confirmed by gold DNA immunolabeling with a specific monoclonal IgM against double-stranded DNA. In addition, a proteomic study of purified membrane vesicles confirmed the presence of plasma membrane and cytoplasmic proteins in OMVs from this strain. Our data demonstrate the existence of a previously unobserved type of double-bilayer OMV in the Gram-negative bacterium Shewanella vesiculosa M7^T that can incorporate DNA, for which we propose the name outer-inner membrane vesicle (O-IMV).     

Cultured primate aortic smooth muscle cells express both the PDGF-A and PDGF-B genes but do not secrete mitogenic activity or dimeric platelet-derived growth factor protein

Proliferation of smooth muscle cells (SMC) in the arterial intima of man and experimental animals is important in the pathogenesis of atherosclerosis. Vascular SMC proliferation in vitro is stimulated by a number of agents, including the potent protein mitogen, platelet-derived growth factor (PDGF). Recent studies on rat arterial SMC indicate that these cells may, under certain circumstances, synthesize PDGF protein mitogens, suggesting that the regulation of SMC proliferation in vivo may have an autocrine or paracrine component. In this study we demonstrate that cultured nonhuman primate (baboon) aortic SMC transcribe both the PDGF-A and PDGF-B genes but do not secrete detectable mitogenic activity characteristic of native PDGF. The absence of this activity was not due to the presence in the cell conditioned medium of factors inhibitory for PDGF-mediated mitogenic activity. Metabolic labeling of the cells and immunoprecipitation with specific antibodies to human PDGF did not detect a dimeric (30 kDa) PDGF protein in either the intracellular or extracellular compartments, but instead identified PDGF-related proteins of molecular weight 12 kDa and 100 kDa. These data suggest the presence in vascular SMC of a mechanism regulating the translation of PDGF mRNA that may play an important role in the control of SMC proliferation in vivo.     

Response of Acala cotton to nitrogen rates in the San Joaquin Valley of California

The responses of Acala cotton (Gossypium hirsutum L.) in California to a range of applied nitrogen (N) treatments were investigated in a 5-year, multisite experiment. The experiment's goals were to identify crop growth and yield responses to applied N and provide information to better assess the utility of soil residual N estimates in improving fertilizer management. Baseline fertilizer application rates for the lowest applied N treatments were based on residual soil nitrate-N (NO3-N) levels determined on soil samples from the upper 0.6 m of the soil collected prior to spring N fertilization and within 1 week postplanting each year. Results have shown positive cotton lint yield responses to increases in applied N across the 56 to 224 kg N/ha range in only 41% (16 out of 39) of test sites. Soil NO3-N monitoring to a depth of 2.4 m in the spring (after planting) and fall (postharvest) indicate most changes in soil NO3- occur within the upper 1.2 m of soil. However, some sites (those most prone to leaching losses of soluble nutrients) also exhibited net increases in soil NO3-N in the 1.2- to 2.4-m depth zone when comparing planting time vs. postharvest data. The lack of yield responses and soil NO3-N accumulations at some sites indicate that more efforts should be put into identifying the amount of plant N requirements that can be met from residual soil N, rather than solely from fertilizer N applications.     

The protein tyrosine phosphatase SHP-1 modulates the suppressive activity of regulatory T cells

The importance of regulatory T cells (Tregs) for immune tolerance is well recognized, yet the signaling molecules influencing their suppressive activity are relatively poorly understood. In this article, through in vivo studies and complementary ex vivo studies, we make several important observations. First, we identify the cytoplasmic tyrosine phosphatase Src homology region 2 domain-containing phosphatase 1 (SHP-1) as an endogenous brake and modifier of the suppressive ability of Tregs; consistent with this notion, loss of SHP-1 expression strongly augments the ability of Tregs to suppress inflammation in a mouse model. Second, specific pharmacological inhibition of SHP-1 enzymatic activity via the cancer drug sodium stibogluconate potently augmented Treg suppressor activity both in vivo and ex vivo. Finally, through a quantitative imaging approach, we directly demonstrate that Tregs prevent the activation of conventional T cells and that SHP-1-deficient Tregs are more efficient suppressors. Collectively, our data reveal SHP-1 as a critical modifier of Treg function and a potential therapeutic target for augmenting Treg-mediated suppression in certain disease states.     

In silico mutagenesis of human ACE2 with S protein and translational efficiency explain SARS-CoV-2 infectivity in different species

The coronavirus disease COVID-19 constitutes the most severe pandemic of the last decades having caused more than 1 million deaths worldwide. The SARS-CoV-2 virus recognizes the angiotensin converting enzyme 2 (ACE2) on the surface of human cells through its spike protein. It has been reported that the coronavirus can mildly infect cats, and ferrets, and perhaps dogs while not pigs, mice, chicken and ducks. Differences in viral infectivity among different species or individuals could be due to amino acid differences at key positions of the host proteins that interact with the virus, the immune response, expression levels of host proteins and translation efficiency of the viral proteins among other factors. Here, first we have addressed the importance that sequence variants of different animal species, human individuals and virus isolates have on the interaction between the RBD domain of the SARS-CoV-2 spike S protein and human angiotensin converting enzyme 2 (ACE2). Second, we have looked at viral translation efficiency by using the tRNA adaptation index. We find that integration of both interaction energy with ACE2 and translational efficiency explains animal infectivity. Humans are the top species in which SARS-CoV-2 is both efficiently translated as well as optimally interacting with ACE2. We have found some viral mutations that increase affinity for hACE and some hACE2 variants affecting ACE2 stability and virus binding. These variants suggest that different sensitivities to coronavirus infection in humans could arise in some cases from allelic variability affecting ACE2 stability and virus binding.     

Ethanol production from native cassava starch by a mixed culture of Endomycopsis fibuligera and Zymomonas mobilis

The conversion of starch from unhydrolyzed cassava flour to ethanol by a pure culture of Endomycopsis fibuligera and by a co-culture of this amylolytic yeast and the bacterium Zymomonas mobilis was studied. The best overall results were obtained using the mixed culture. After 96 h of fermentation of a medium containing 150 g/l initial cassava starch, an ethanol concentration of 31.4 g/l, a productivity of 0.33 g ethanol/l × h and a yield of 0.21 g ethanol/g initial starch were reached. The highest yield (0.37 g/g) was obtained after 48 h when using a medium containing 50 g/l initial starch.     

Effects of climate legacies on above‐ and belowground community assembly

The role of climatic legacies in regulating community assembly of above‐ and belowground species in terrestrial ecosystems remains largely unexplored and poorly understood. Here, we report on two separate regional and continental empirical studies, including >500 locations, aiming to identify the relative importance of climatic legacies (climatic anomaly over the last 20,000 years) compared to current climates in predicting the relative abundance of ecological clusters formed by species strongly co‐occurring within two independent above‐ and belowground networks. Climatic legacies explained a significant portion of the variation in the current community assembly of terrestrial ecosystems (up to 15.4%) that could not be accounted for by current climate, soil properties, and management. Changes in the relative abundance of ecological clusters linked to climatic legacies (e.g., past temperature) showed the potential to indirectly alter other clusters, suggesting cascading effects. Our work illustrates the role of climatic legacies in regulating ecosystem community assembly and provides further insights into possible winner and loser community assemblies under global change scenarios.     

Photosynthetic electron transport interaction of xanthorrhizol isolated from Iostephane heterophylla and its derivatives

A bioactivity-guided chemical study of Iostephane heterophylla (Asteraceae) led to the isolation of xanthorrhizol (1) as the compound that causes inhibition of ATP synthesis, H⁺-uptake and electron flow from water to methylviologen (basal, phosphorylating and uncoupled) in freshly lysed spinach chloroplasts, thus acting as an inhibitor of the Hill reaction. Acetyl (2), dihydro (3) and acetyl-dihydro (4) derivatives were synthesized. It was found that 4 was less active than 1 and 2 in ATP synthesis, whereas 3 was the most potent inhibitor of the Hill reaction and was also an inhibitor of H⁺-ATPase. Studies of the photosynthetic partial redox reactions from PQ to MV indicated that 1 partially inhibited the PQ pool, but that 3 did not. However, both inhibited the uncoupled electron transport in PSII from water to DCBQ. Uncoupled electron flow from water to silicomolybdate was completely inhibited by 3 and partially by 1. The reaction from DPC to DCPIP was inhibited by both 1 and 3. These results indicate that the inhibition site is located within PSII for 1 and 3 as was corroborated by fluorescence decay data.     

Capitalizing on an ecological process to aid coral reef ecosystem restoration: Can gastropod trophodynamics enhance coral survival?

Coral Reefs - Coral reefs in the Florida Keys have degraded in recent decades, prompting efforts to re-establish populations of staghorn coral, Acropora cervicornis, to restore structure and...