Taxonomy and distribution of the genus Spartina

This investigation deals principally with the redetermination of the limits of and the variability within the species of Spartina, a genus of grasses. Results of the study show the genus to be composed of sixteen species and two minor forms. Only one minor nomenclatorial change is proposed. Because the genus had not, heretofore, been properly typified, Spartina cynosuroides (L.) Roth is selected as the type species;The sixteen species are placed in three complexes on the basis of morphological similarity. Species of the first complex possess hard, slender culms and spikelike panicles composed of numerous, short, closely imbricate, twisted spikes. Rhizomes are usually wanting; if present, they are short and knotty. Spartina arundinacea of several South Atlantic and Indian Ocean islands, S. ciliate of southern South America and S. spartinae of North and South America are members of the first complex;The second complex consists of species with soft, fleshy, succulent culms; pilose pubescence on parts of the spikelets; and soft, flaccid rhizomes with inflated scales. The plants are usually limited to the inter tidal zone of coastal marshes. Species admitted to this complex are S. alterniflora of North and South America and Europe, S. foliosa of the Pacific coast of North America, S. longispica of the region near the mouth of the River Plate in South America, S. maritima of Europe and Africa, S. neyrautii of southwestern France and S. townsendii of England and France;Plants of the third complex are characterized by hard culms; non-spikelike panicles; usually spreading non-twisted spikes; and hispid pubescence on the spikelets. Most of the species possess firm rhizomes; the scales are not inflated. Species of the third complex are S. bakeri of salt and fresh water habitats in Florida and Georgia, S. x caespitosa of disturbed ground in and around coastal marshes from Maine to Maryland, S. cynosuroides of coastal marshes of eastern United States, S. densiflora of South America, S. gracilis of the western plains and mountains of North America, S. patens of the salt marshes in eastern United States and S. pectinata of transcontinental distribution in northern North America;Within several of the species (S. alterniflora, S. cynosuroides, S. patens, S. pectinata and S. spartinae) at least two levels of polyploidy have been found. In none of these species have suitable means been found for identifying the various levels of polyploidy except by chromosome numbers. (Abstract shortened by UMI.

Carver Science Hall

Simpson College, Indianola, Iowa, will dedicate Carver Science Hall on the occasion ·of its third annual Christian Liberal Arts. Festival, October 6, 1956. This building venerates one of Simpson\u27s most distinguished former students, George Washington Carver. In paying homage to the memory of Dr. Carver, Simpson adds its name to the list of those who recognize the richness and warmth of this great and dedicated human spirit. The connection between Carver and Simpson is well known and there is no need to retell that chapter in his life -story here. But succinctly to emphasize that relationship, no words could be more appropriate than Carver\u27s own - At Simpson, I discovered that I was a human being.

Distribution of Spartina pectinata Link in Iowa

Earlier taxonomic studies in the genus Spartina of the Gramineae show the existence of but one of the sixteen species in Iowa, Spartina pectinata Link. That it is widely distributed throughout the state is evident from Figure 1. The counties identified by dots have yielded specimens presently accessioned into the herbaria of Iowa State College, State University of Iowa and Simpson College. In addition, the species has been observed in numerous other counties although records are not authenticated by specimens entered into institutional herbaria

Phenotypic responses to interspecies competition and commensalism in a naturally derived microbial co-culture

The fundamental question of whether different microbial species will co-exist or compete in a given environment depends on context, composition and environmental constraints. Model microbial systems can yield some general principles related to this question. In this study we employed a naturally occurring co-culture composed of heterotrophic bacteria, Halomonas sp. HL-48 and Marinobacter sp. HL- 58, to ask two fundamental scientific questions: 1) how do the phenotypes of two naturally co-existing species respond to partnership as compared to axenic growth? and 2) how do growth and molecular phenotypes of these species change with respect to competitive and commensal interactions? We hypothesized – and confirmed – that co-cultivation under glucose as the sole carbon source would result in competitive interactions. Similarly, when glucose was swapped with xylose, the interactions became commensal because Marinobacter HL-58 was supported by metabolites derived from Halomonas HL- 48. Each species responded to partnership by changing both its growth and molecular phenotype as assayed via batch growth kinetics and global transcriptomics. These phenotypic responses depended on nutrient availability and so the environment ultimately controlled how they responded to each other. This simplified model community revealed that microbial interactions are context-specific and different environmental conditions dictate how interspecies partnerships will unfold

Phenotypic responses to interspecies competition and commensalism in a naturally derived microbial co-culture

The fundamental question of whether different microbial species will co-exist or compete in a given environment depends on context, composition and environmental constraints. Model microbial systems can yield some general principles related to this question. In this study we employed a naturally occurring co-culture composed of heterotrophic bacteria, Halomonas sp. HL-48 and Marinobacter sp. HL- 58, to ask two fundamental scientific questions: 1) how do the phenotypes of two naturally co-existing species respond to partnership as compared to axenic growth? and 2) how do growth and molecular phenotypes of these species change with respect to competitive and commensal interactions? We hypothesized – and confirmed – that co-cultivation under glucose as the sole carbon source would result in competitive interactions. Similarly, when glucose was swapped with xylose, the interactions became commensal because Marinobacter HL-58 was supported by metabolites derived from Halomonas HL- 48. Each species responded to partnership by changing both its growth and molecular phenotype as assayed via batch growth kinetics and global transcriptomics. These phenotypic responses depended on nutrient availability and so the environment ultimately controlled how they responded to each other. This simplified model community revealed that microbial interactions are context-specific and different environmental conditions dictate how interspecies partnerships will unfold

SN 2008S: an electron capture SN from a super-AGB progenitor?

We present comprehensive photometric and spectroscopic observations of the faint transient SN 2008S discovered in NGC 6946. SN 2008S exhibited slow photometric evolution and almost no spectral variability during the first nine months, implying a high density CS medium. The light curve is similar in shape to that of SN 1998S and SN 1979C, although significantly fainter at maximum light. Our quasi-bolometric lightcurve extends to 300 days and shows a tail phase decay rate consistent with that of ^{56}Co. We propose that this is evidence for an explosion and formation of ^{56}Ni (0.0015 +/- 0.0004 M_Sun). The large MIR flux detected shortly after explosion can be explained by a light echo from pre-exisiting dust. The late NIR flux excess is plausibly due to a combination of warm newly-formed ejecta dust together with shock-heated dust in the CS environment. We reassess the progenitor object detected previously in Spitzer archive images, supplementing this discussion with a model of the MIR spectral energy distribution. This supports the idea of a dusty, optically thick shell around SN 2008S with an inner radius of nearly 90AU and outer radius of 450AU, and an inferred heating source of 3000 K and luminosity of L ~ 10^{4.6} L_Sun. The combination of our monitoring data and the evidence from the progenitor analysis leads us to support the scenario of a weak electron capture supernova explosion in a super-AGB progenitor star (of initial mass 6-8 M_sun) embedded within a thick CS gaseous envelope. We suggest that all of main properties of the electron capture SN phenomenon are observed in SN 2008S and future observations may allow a definitive answer.Comment: accepted for publication in MNRAS (2009 May 7

Characterization of an unusual bipolar helicase encoded by bacteriophage T5

Bacteriophage T5 has a 120 kb double-stranded linear DNA genome encoding most of the genes required for its own replication. This lytic bacteriophage has a burst size of ∼500 new phage particles per infected cell, demonstrating that it is able to turn each infected bacterium into a highly efficient DNA manufacturing machine. To begin to understand DNA replication in this prodigious bacteriophage, we have characterized a putative helicase encoded by gene D2. We show that bacteriophage T5 D2 protein is the first viral helicase to be described with bipolar DNA unwinding activities that require the same core catalytic residues for unwinding in either direction. However, unwinding of partially single- and double-stranded DNA test substrates in the 3′–5′ direction is more robust and can be distinguished from the 5′–3′ activity by a number of features including helicase complex stability, salt sensitivity and the length of single-stranded DNA overhang required for initiation of helicase action. The presence of D2 in an early gene cluster, the identification of a putative helix-turn-helix DNA-binding motif outside the helicase core and homology with known eukaryotic and prokaryotic replication initiators suggest an involvement for this unusual helicase in DNA replication initiation