Microbial community composition in sediments resists perturbation by nutrient enrichment

Functional redundancy in bacterial communities is expected to allow microbial assemblages to survive perturbation by allowing continuity in function despite compositional changes in communities. Recent evidence suggests, however, that microbial communities change both composition and function as a result of disturbance. We present evidence for a third response: resistance. We examined microbial community response to perturbation caused by nutrient enrichment in salt marsh sediments using deep pyrosequencing of 16S rRNA and functional gene microarrays targeting the nirS gene. Composition of the microbial community, as demonstrated by both genes, was unaffected by significant variations in external nutrient supply in our sampling locations, despite demonstrable and diverse nutrient-induced changes in many aspects of marsh ecology. The lack of response to external forcing demonstrates a remarkable uncoupling between microbial composition and ecosystem-level biogeochemical processes and suggests that sediment microbial communities are able to resist some forms of perturbation.     

Species composition of aphid vectors (Hemiptera: Aphididae) of barley yellow dwarf virus and cereal yellow dwarf virus in Alabama and western Florida

Yellow dwarf is a major disease problem of wheat, Triticum aestivum L., in Alabama and is estimated to cause yield loss of 21-42 bu/acre. The disease is caused by a complex of viruses comprising several virus species, including Barley yellow dwarf virus-PAV and Cereal yellow dwarf virus-RPV. Several other strains have not yet been classified into a specific species. The viruses are transmitted exclusively by aphids (Hemiptera:Aphididae). Between the 2005 and 2008 winter wheat seasons, aphids were surveyed in the beginning of each planting season in several wheat plots in Alabama and western Florida Collected aphids were identified and bioassayed for their yellow dwarf virus infectivity. This survey program was designed to identify the aphid species that serve as fall vectors of yellow dwarf virus into winter wheat plantings. From 2005 to 2008, bird cherry-oat aphid, Rhopalosiphum padi (L.); rice root aphid, Rhopalosiphum rufiabdominale (Sasaki); and greenbug, Schizaphis graminum (Rondani), were found consistently between October and December. The species of aphids and their timing of appearance in wheat plots were consistent with flight data collected in North Alabama between 1996 and 1999. Both R. padi and R. rufiabdominale were found to carry and transmit Barley yellow dwarf virus-PAV and Cereal yellow dwarf virus-RPV. The number of collected aphids and proportion of viruliferous aphids were low. Although this study has shown that both aphids are involved with introduction of yellow dwarf virus to winter wheat in Alabama and western Florida, no conclusions can be made as to which species may be the most important vector of yellow dwarf virus in the region.     

Primiparous females do not exhibit reduced maternal care in gray seals (Halichoerus grypus)

We compared the behaviors of primiparous and multiparous gray seal (Halichoerus grypus) females over the course of lactation to examine whether poorly developed maternal behaviors may play a role in the reduced lactation performance observed in primiparous females. Overall, primiparous females spent as much time interacting with their pups as multiparous females. The proportion of time spent nursing their pup increased significantly between early and peak lactation in both primiparous and multiparous females. Although there was no significant difference in the duration of nursing bouts as a function of reproductive status, primiparous females nursed significantly more frequently (bouts/hour) and, therefore, spent a significantly greater proportion of time nursing than multiparous females throughout lactation. Primiparous gray seal females were also significantly more active than multiparous females, however, the difference in activity represented only a small proportion of the overall time budget. We conclude that poorly developed maternal behaviors resulting from a lack of prior reproductive experience are unlikely to account for lower levels of milk energy transfer to pups in primiparous gray seals.     

Disruption of Sertoli-germ cell adhesion function in the seminiferous epithelium of the rat testis can be limited to adherens junctions without affecting the blood-testis barrier integrity: an in vivo study using an androgen suppression model

During spermatogenesis, both adherens junctions (AJ) (such as ectoplasmic specialization (ES), a testis-specific AJ type at the Sertoli cell-spermatid interface (apical ES) or Sertoli-Sertoli cell interface (basal ES) in the apical compartment and BTB, respectively) and tight junctions (TJ) undergo extensive restructuring to permit germ cells to move across the blood-testis barrier (BTB) as well as the seminiferous epithelium from the basal compartment to the luminal edge to permit fully developed spermatids (spermatozoa) to be sloughed at spermiation. However, the integrity of the BTB cannot be compromised throughout spermatogenesis so that postmeiotic germ cell-specific antigens can be sequestered from the systemic circulation at all times. We thus hypothesize that AJ disruption in the seminiferous epithelium unlike other epithelia, can occur without compromising the BTB-barrier, even though these junctions, namely TJ and basal ES, co-exist side-by-side in the BTB. Using an intratesticular androgen suppression-induced germ cell loss model, we have shown that the disruption of AJs indeed was limited to the Sertoli-germ cell interface without perturbing the BTB. The testis apparently is using a unique physiological mechanism to induce the production of both TJ- and AJ-integral membrane proteins and their associated adaptors to maintain BTB integrity yet permitting a transient loss of cell adhesion function by dissociating N-cadherin from beta-catenin at the apical and basal ES. The enhanced production of TJ proteins, such as occludin and ZO-1, at the BTB site can supersede the transient loss of cadherin-catenin function at the basal ES. This thus allows germ cell depletion from the epithelium without compromising BTB integrity. It is plausible that the testis is using this novel mechanism to facilitate the movement of preleptotene and leptotene spermatocytes across the BTB at late stage VIII through early stage IX of the epithelial cycle in the rat while maintaining the BTB immunological barrier function.     

Contribution of oxygen radicals to altered NO-dependent pulmonary vasodilation in acute and chronic hypoxia

Chronic hypoxia (CH) increases pulmonary arterial endothelial nitric oxide (NO) synthase (NOS) expression and augments endothelium-derived nitric oxide (EDNO)-dependent vasodilation, whereas vasodilatory responses to exogenous NO are attenuated in CH rat lungs. We hypothesized that reactive oxygen species (ROS) inhibit NO-dependent pulmonary vasodilation following CH. To test this hypothesis, we examined responses to the EDNO-dependent vasodilator endothelin-1 (ET-1) and the NO donor S-nitroso-N-acetyl penicillamine (SNAP) in isolated lungs from control and CH rats in the presence or absence of ROS scavengers under normoxic or hypoxic ventilation. NOS was inhibited in lungs used for SNAP experiments to eliminate influences of endogenously produced NO. Additionally, dichlorofluorescein (DCF) fluorescence was measured as an index of ROS levels in isolated pressurized small pulmonary arteries from each group. We found that acute hypoxia increased DCF fluorescence and attenuated vasodilatory responses to ET-1 in lungs from control rats. The addition of ROS scavengers augmented ET-1-induced vasodilation in lungs from both groups during hypoxic ventilation. In contrast, upon NOS inhibition, DCF fluorescence was elevated and SNAP-induced vasodilation diminished in arteries from CH rats during normoxia, whereas acute hypoxia decreased DCF fluorescence, which correlated with augmented reactivity to SNAP in both groups. ROS scavengers enhanced SNAP-induced vasodilation in normoxia-ventilated lungs from CH rats similar to effects of hypoxic ventilation. We conclude that inhibition of NOS during normoxia leads to greater ROS generation in lungs from both control and CH rats. Furthermore, NOS inhibition reveals an effect of acute hypoxia to diminish ROS levels and augment NO-mediated pulmonary vasodilation.     

Mechanistic insight into human ether-à-go-go-related gene (hERG) K+ channel deactivation gating from the solution structure of the EAG domain

Human ether-à-go-go-related gene (hERG) K(+) channels have a critical role in cardiac repolarization. hERG channels close (deactivate) very slowly, and this is vital for regulating the time course and amplitude of repolarizing current during the cardiac action potential. Accelerated deactivation is one mechanism by which inherited mutations cause long QT syndrome and potentially lethal arrhythmias. hERG deactivation is highly dependent upon an intact EAG domain (the first 135 amino acids of the N terminus). Importantly, deletion of residues 2-26 accelerates deactivation to a similar extent as removing the entire EAG domain. These and other experiments suggest the first 26 residues (NT1-26) contain structural elements required to slow deactivation by stabilizing the open conformation of the pore. Residues 26-135 form a Per-Arnt-Sim domain, but a structure for NT1-26 has not been forthcoming, and little is known about its site of interaction on the channel. In this study, we present an NMR structure for the entire EAG domain, which reveals that NT1-26 is structurally independent from the Per-Arnt-Sim domain and contains a stable amphipathic helix with one face being positively charged. Mutagenesis and electrophysiological studies indicate that neutralizing basic residues and breaking the amphipathic helix dramatically accelerate deactivation. Furthermore, scanning mutagenesis and molecular modeling studies of the cyclic nucleotide binding domain suggest that negatively charged patches on its cytoplasmic surface form an interface with the NT1-26 domain. We propose a model in which NT1-26 obstructs gating motions of the cyclic nucleotide binding domain to allosterically stabilize the open conformation of the pore.     

Changes in gene expression in Arabidopsis shoots during phosphate starvation and the potential for developing smart plants

Our aim was to generate and prove the concept of "smart" plants to monitor plant phosphorus (P) status in Arabidopsis. Smart plants can be genetically engineered by transformation with a construct containing the promoter of a gene up-regulated specifically by P starvation in an accessible tissue upstream of a marker gene such as beta-glucuronidase (GUS). First, using microarrays, we identified genes whose expression changed more than 2.5-fold in shoots of plants growing hydroponically when P, but not N or K, was withheld from the nutrient solution. The transient changes in gene expression occurring immediately (4 h) after P withdrawal were highly variable, and many nonspecific, shock-induced genes were up-regulated during this period. However, two common putative cis-regulatory elements (a PHO-like element and a TATA box-like element) were present significantly more often in the promoters of genes whose expression increased 4 h after the withdrawal of P compared with their general occurrence in the promoters of all genes represented on the microarray. Surprisingly, the expression of only four genes differed between shoots of P-starved and -replete plants 28 h after P was withdrawn. This lull in differential gene expression preceded the differential expression of a new group of 61 genes 100 h after withdrawing P. A literature survey indicated that the expression of many of these "late" genes responded specifically to P starvation. Shoots had reduced P after 100 h, but growth was unaffected. The expression of SQD1, a gene involved in the synthesis of sulfolipids, responded specifically to P starvation and was increased 100 h after withdrawing P. Leaves of Arabidopsis bearing a SQD1::GUS construct showed increased GUS activity after P withdrawal, which was detectable before P starvation limited growth. Hence, smart plants can monitor plant P status. Transferring this technology to crops would allow precision management of P fertilization, thereby maintaining yields while reducing costs, conserving natural resources, and preventing pollution.