Protistan microbial observatory in the Cariaco Basin,Caribbean. I. Pyrosequencing vs Sanger insights into species richness

Microbial diversity and distribution are topics of intensive research. In two companion papers in this issue, we describe the results of the Cariaco Microbial Observatory (Caribbean Sea, Venezuela). The Basin contains the largest body of marine anoxic water, and presents an opportunity to study protistan communities across biogeochemical gradients. In the first paper, we survey 18S ribosomal RNA (rRNA) gene sequence diversity using both Sanger- and pyrosequencing-based approaches, employing multiple PCR primers, and state-of-the-art statistical analyses to estimate microbial richness missed by the survey. Sampling the Basin at three stations, in two seasons, and at four depths with distinct biogeochemical regimes, we obtained the largest, and arguably the least biased collection of over 6000 nearly full-length protistan rRNA gene sequences from a given oceanographic regime to date, and over 80 000 pyrosequencing tags. These represent all major and many minor protistan taxa, at frequencies globally similar between the two sequence collections. This large data set provided, via the recently developed parametric modeling, the first statistically sound prediction of the total size of protistan richness in a large and varied environment, such as the Cariaco Basin: over 36 000 species, defined as almost full-length 18S rRNA gene sequence clusters sharing over 99% sequence homology. This richness is a small fraction of the grand total of known protists (over 100 000–500 000 species), suggesting a degree of protistan endemism.     

Improving the clinical efficiency of T2 mapping of ligament integrity

Current MR methods use T₂^? relaxation time as a surrogate measure of ligament strength. Currently, a multi-echo voxel-wise least squares fit is the gold standard to create T₂^? maps; however, the post-processing is time-intensive and serves as a stopgap for clinical use. The study objective was to determine if an alternative method could improve post-processing time without sacrificing fidelity of T₂^? values for eventual translational use in the clinic. Using a 6 echo FLASH sequence, three different methods were used to determine intact posterior cruciate ligament (PCL) median T₂^? Two of these methods utilized a voxel-wise method to establish T₂^? maps: (1) a current “gold standard” method using a voxel-wise 6 echo least-squares fit (6LS) and (2) a voxel-wise 2 echo point T₂^? determination (2MM). The third method used median ligament signal intensity and a single nonlinear least-squares fit (6LS_ROI) instead of a voxel-wise basis. The resulting median T₂^? values of the PCL and computational time were compared. The median T₂^? values were 42% higher using the 2MM compared to the 6LS method (p<0.0001). However, a strong correlation was found for the median T₂^? values between the 2MM and 6LS methods (R²=0.80). The median T₂^? values were not significantly different between the 6LS and 6LS_ROI methods (p=0.519). Using the 2MM (which provides a regional map) and the 6LS_ROI (which efficiently provides the median T₂^? value) methods in tandem would take only minutes of post-processing computational time compared to the 6LS method (~540 min), and hence would facilitate clinical application of T₂^? maps to predict ligament structural properties as a patient outcome measure.     

Enzymatic Protein Carboxyl Methylation in Rat Posterior Pituitary: Neurophysins in Rapid-Turnover Pool Determine Methyl Accepting Capacity

In vitro stimulation of intact rat posterior pituitary by either veratridine or K+ depolarization results in the concomitant release of neurophysins and in a decrease (70-80%) in their carboxyl methylation as measured either with L-[methyl-3H]methionine in the intact lobes after stimulation or in their homogenates with [methyl-3H]S-adenosyl-L-methionine and purified protein carboxyl methyltransferase. A similar reduction in neurophysin methylation (60%) was observed when the arrival of newly synthesized neurophysins at the posterior pituitary was blocked by colchicine. Experimental data indicate that the reduction in neurophysin content of the lobes after 12 h of colchicine treatment (less than 7%) or after in vitro stimulation (about 10%) cannot account for the marked reduction in neurophysin methylation. The results suggest that the granule pool characterized by rapid turnover of neurophysins probably represents the major source of methyl acceptor proteins in the lobe. In spite of the marked reduction in neurophysin methyl accepting capacity observed after stimulation, there was no parallel increase in methyl accepting capacity of the released neurophysins. We propose that a neurophysin subfraction that might be associated with the membrane of releasable granules participates in the methylation reaction in situ.     

Multiline varieties and disease control

Summary A general model for the evolution of pathogen populations on mixtures or multilines is developed. This model is used to extend previous analyses of the effects of the widespread cultivation of multilines on the evolution of virulence in obligate parasites to mixtures of lines carrying different numbers of resistance genes. It is concluded that the composition of an equilibrium pathogen population growing on a multiline may vary within wide limits and the prinicipal determinant of its composition is the number of components in the multiline and the resistance genes they carry. Other factors of importance are (i) the relative contribution made by each host class (with different numbers of resistance genes) to the pathogen spore pool each generation; (ii) the levels of stabilizing selection against unnecessary virulence genes; and (iii) the way in which unnecessary genes for virulence combine to reduce pathogen fitness. Conditions for the fixation of avirulent biotypes in the pathogen population and the evolution of a pathogen superrace are given for multilines of various compositions.Paper No. 9246 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh, North Carolina. This investigation was supported in part by NIH Research Grant No. GM 11546 from the National Institute of General Medical Sciences     

Linkage analysis for 18 enzyme loci in Pinus rigida Mill.

Summary Estimates of recombination frequency among enzyme loci of pitch pine revealed two new linkages, Mdh3:Pgm2 (=0.01) and Pep1:Mdh4 (=0.38), and confirmed two previously established linkages. Tighter linkage (=0.30) was ruled out for nearly all gene pairs examined. In general, the Bayesian approach used in this study to test for linkage performed better than alternative methods.This work was supported by the School of Natural Resources, College of Agricultural and Life Sciences, University of Wisconsin, Madison, WI, and by McIntyre-Stennis, project no. 142-C385     

Multiline varieties and disease control

Summary Existing theoretical models have led to conflicting predictions concerning the likely effect of the widespread use of dirty crop multilines on the evolution of virulence in pathogen populations. Here we attempt to clarify these problems by extending existing models to include selection against unnecessary genes for virulence at two different stages in the life cycle of the pathogen. The results of these studies indicate that the stage of the life cycle at which selection occurs can significantly influence the evolution of virulence in pathogen populations growing on multiline varieties.     

伤害性刺激和非伤害性刺激对大鼠丘脑后核神经元电活动的影响

用微电极细胞外记录的方法,观察内脏痛、躯体痛和触觉刺激对大鼠丘脑后核(PO)中770个神经元电活动的影响,其中305(38.3％)个对伤害性刺激起反应,103(13.4％)个对触觉刺激起反应。对伤害性刺激反应的神经元中多数对躯体痛和内脏痛刺激均起反应且反应形式相同,少数反应不同或相反,对触觉刺激反应的神经元中多数也对两种伤害性刺激均起反应,只对触觉刺激反应的神经元很少。