Bidirectional C and N transfer and a potential role for sulfur in an epiphytic diazotrophic mutualism

In nitrogen-limited boreal forests, associations between feathermoss and diazotrophic cyanobacteria control nitrogen inputs and thus carbon cycling, but little is known about the molecular regulators required for initiation and maintenance of these associations. Specifically, a benefit to the cyanobacteria is not known, challenging whether the association is a nutritional mutualism. Targeted mutagenesis of the cyanobacterial alkane sulfonate monooxygenase results in an inability to colonize feathermosses by the cyanobacterium Nostoc punctiforme, suggesting a role for organic sulfur in communication or nutrition. Isotope probing paired with high-resolution imaging mass spectrometry (NanoSIMS) demonstrated bidirectional elemental transfer between partners, with carbon and sulfur both being transferred to the cyanobacteria, and nitrogen transferred to the moss. These results support the hypothesis that moss and cyanobacteria enter a mutualistic exosymbiosis with substantial bidirectional material exchange of carbon and nitrogen and potential signaling through sulfur compounds.Subject terms: Microbial ecology, Plant ecology, Biogeochemistry, Stable isotope analysis     

Use of membrane filters for soil algal bioassays

A culture technique for eucaryotic and procaryotic soil algae involving the use of membrane filters superimposed on the surface of inorganic nutrient agar is described. Nostoc commune grew exponentially when cultured in this manner. No significant differences in biomass production or nitrogenase activity were detected among culture subsets within replicate experiments run under standard conditions. Estimates of daily growth rates (0.340), culture doubling time (48.9 h), and nitrogenase activity (14.54 nM C₂H₂ reduced μg⁻¹ chl a h⁻¹) were consistent with laboratory and field estimates reported for several planktonic species of Anabaena and strains of Nostoc commune isolated from diverse terrestrial habitats. Therefore, the filter-culture technique is an alternative which may be superior to traditional liquid culture methodology for studies involving certain soil procaryotic and eucaryotic algae.     

The influence of winter temperatures on the annual radial growth of six northern range margin tree species

This study explores the influence of temperature on the growth of six northern range margin (NRM) tree species in the Hudson River Valley (HRV). The HRV has excellent geographic and floristic qualities to study the influence of climate change on forested ecosystems. Indices of radial growth for three populations per species are developed and correlated against average minimum and maximum monthly temperatures from 1897 to 1994. Only positive correlations to temperature are considered for this analysis. Principal component analysis (PCA) is performed on chronologies over the entire HRV and at four subregions. PCA reveals a strong common signal among populations at subregional and regional scales. January temperatures most limit growth at the ecosystem level, supporting the hypothesis that winter temperatures may control vegetational ecotones. Surprisingly, growth of the oak–hickory ecosystem is most limited by January temperatures only in the southern half of the study region. Chestnut and white oak are the primary species driving the geographic pattern. As winter xylem embolism is a constant factor for ring-porous species, snow cover and its interaction on fine root mortality may be the leading factors of the pattern of temperature sensitivity. Species-specific differences in temperature sensitivity are apparent. Atlantic white-cedar (AWC) and pitch pine are more sensitive to the entire winter season (December–March) while oak and hickory are most sensitive to January temperatures. AWC is most sensitive species to temperature. Chestnut and white oak in the HRV are more sensitive to winter temperature than red oak. Pignut hickory has the most unique response with significant relations to late growing season temperatures. Interestingly, AWC and pitch pine are sensitive to winter temperatures at their NRM while oak and hickory are not. Our results suggest that temperature limitations of growth may be species and phylogenetically specific. They also indicate that the influence of temperature on radial growth at species and ecosystem levels may operate differently at varying geographic scales. If these results apply broadly to other temperate regions, winter temperatures may play an important role in the terrestrial carbon cycle.     

Isozymes of alpha-galactosidase from Bacillus stearothermophilus

Two molecular forms of alpha-galactosidase (EC 3.2.1.22) synthesized constitutively by Bacillus stearothermophilus, strain AT-7, have been purified. alpha-Galactosidase I (with the substrate p-nitrophenyl alpha-D-galactopyranoside (PNPG)) has a pH optimum of 6 and half-life at 65 degrees C of > 2 h at low protein concentration. alpha-Galactosidase II has a pH optimum of 7 with PNPG and a half-life at 65 degrees C of about 3 min. The isozymes also differ with respect to their Km with PNPG and melibiose. Both enzymes are inhibited competitively by D-galactose, melibiose, and Tris. With the beta-glycosides cellobiose and lactose either noncompetitive or mixed-type inhibition is observed, with the pattern dependent on both the pH and the isozyme. The two isozymes have similar Arrhenius activation energies (about 20 kcal/mol, 1 kcal = 4.184 kJ). Their molecular weights, estimated by disc gel electrophoresis, are alpha-galactosidase I, 280 000 +/- 30 000 and alpha-galactosidase II, 325 000 +/- 15 000. Dodecyl sulfate gel electrophoresis gave a single band for each enzyme. The respective molecular weights, 81 000 +/- 500 for alpha-galactosidase I and 84 000 +/- 500 for alpha-galactosidase II, suggest that both enzymes consist of four subunits.