Library

Notes: Throughout the ages the undersides of earthenware vases have been the home for all manner of cryptic abbreviations and signs. The importance nowadays placed on such marks varies considerably according to the date and origin of the material, though generally it is greater when the signs refer in some manner to the potter, decorator, or producing factory, especially when considerations of the mark may affect the value of the piece.

Notes: The Rhizobium leguminosarum biovar viciae nodulation protein NodO is partially homologous to haemolysin of Escherichia coli and, like haemolysin, is secreted into the growth medium. The NodO protein can be secreted by a strain of E. coli carrying the cloned nodO gene plus the haemolysin secretion genes hlyBD, in a process that also requires the outer membrane protein encoded by tolC. The related protease secretion genes, prtDEF, from Erwinia chrysanthemi also enable E. coli to secrete NodO. The Rhizobium genes encoding the proteins required for NodO secretion are unlinked to nodO and are unlike other nod genes, since they do not require flavonoids or NodO for their expression. Although proteins similar to NodO were not found in rhizobia other than R. leguminosarum bv. viciae, several rhizobia and an Agrobacterium strain containing the cloned nodO gene were found to have the ability to secrete NodO. These observations indicate that a wide range of the Rhizobiaceae have a protein secretion mechanism analogous to that which secretes haemotysin and related toxins and proteases in the Enterobacteriaceae.

Notes: In a strain of Rhizobium leguminosarum biovar phaseoli, three copies of the regulatory nodulation gene nodD were identified on the Sym plasmid and sequenced. Two were closely linked to each other and the third was near, but not adjacent, to the nodABC genes. Each of these nodD genes could correct the Nod defect of a nodD mutant strain of R. leguminosarum biovar viciae on peas. A truncated form of nodD2 could also correct this mutant, indicating that the C-terminus of NodD2 is not needed for inducing activity. Upstream of nodD1 and in the same operon is a newly described gene, nolE, whose product appears to be exported into the periplasm. Close to nodD2 is another gene, nolP, with no known counterpart in other rhizobia. Both nolP and nolE-nodD1 are preceded by ‘nod-box’ sequences and, in the former case, there appear to be two tandemly repeated nod-box sequences. Mutations in each of the nodD genes and in the nolE and nolP genes did not abolish nodulation or nitrogen fixation on beans.

Notes: The three nodD genes of a strain of Rhizobium leguminosarum biovar phaseoli were cloned to study their effects on transcription of themselves and of the nodC genes of biovars phaseoli and viciae. Efficient transcription of nodD1 required nodD1 and was enhanced by exposure of the cells to bean exudate consistent with the presence of a nod-box preceding the nolE-nodD1 operon. Transcription of nodD2 and nodDZ was constitutive. nodC of R. leguminosarum biovar phaseoli was activated by each of the nodD genes of that biovar in the absence of inducers but expression was enhanced in cells grown with bean exudate or the flavonoids genistein or naringenin. A mutant of nodD2, tacking 60bp at its 3’end, activated nodC in the presence of inducer, but was defective in regulating certain of the nodD genes. The nodC gene of R. leguminosarum biovar viciae responded differently to the various nodD genes of R. leguminosarum biovar phaseoli than did the nodC of the latter biovar.

Notes: Translational fusions between a mutant phoA (lacking its promoter, ribosomal binding site and signal peptide sequence) and Rhizobium‘symbiotic’ genes were isolated. Since these fusions expressed alkaline phosphatase (AP), the product of phoA, the genes into which phoA was inserted apparently specify proteins located in the bacterial periplasm or cell membrane, the compartment in which AP has activity. These genes were psiA and genes upstream of psiA (psiA is required for normal nodule development and strains with multicopy psiA fall to make exopolysaccharide (EPS) and to nodulate). Fusions between phoA and pss (exo) genes, which are required for EPS production, also resulted in the expression of AP indicating that products of these pss genes were located at the cell surface. Using grus fusions to psiA and pssA, we found that the former was expressed in N2-fixing bean root nodules but the latter was not.

Notes: Abstract Photosynthesis was studied in four species of red marine macroalgae: Palmaria palmata, Laurencia pinnatifida, Lomentaria articulata and Delesseria sanguinea. The rate of O2 evolution for submersed photosynthesis was measured as a function of incident photon flux density at normal pH and inorganic carbon concentration (pH 8.0, 2 mol m−3), and as a function of inorganic carbon concentration at pH 8.0 at saturating and at limiting photon flux density. The rate of CO2 uptake was measured for emersed photosynthesis as a function of CO2 partial pressure at saturating photon flux density. Previous pH-drift results suggest that Palmaria and Laurencia are able to use HCO inf3 sup− as well as CO2 whereas Lomentaria and Delesseria are restricted to CO2. None of the algae are saturated by 2 mol m−3 inorganic carbon at high light (400 μmol m−2 s−1) but are saturated at low light (35 μmol m−2 s−1). The inorganic C concentration at which half the light-saturated rate of O2 evolution is achieved is higher for Palmaria and Laurencia (1.51 and 1.85 mol m−3) than for Lomentaria and Delesseria (0.772 and 0.841 mol m−3). The lower values for the latter two species could reflect their putative restriction to CO2. If expressed in terms of CO2, the half-saturation values yield 7.2 and 7.8 mmol m−3 respectively, which are very similar to values obtained previously during pH-drift experiments but at lower concentrations of HCO inf3 sup− , consistent with restriction to CO2. The photosynthetic conductance (m s−1), calculated from the initial slope for photosynthesis at low concentrations of inorganic carbon, correlates with the suggested ability to extract inorganic carbon based on pH-drift results. Calculations made assuming that CO2 is the only species diffusing across the boundary layer are consistent with boundary layer thicknesses of 20 and 19 μm for Lomentaria and Delesseria respectively, which is feasible given the rapid water movement in the experiments. For Laurencia however, an unreasonably small boundary layer thickness of 6 μm is necessary to explain the flux, which indicates co-diffusion by HCO inf3 sup− . In the apparent absence of external carbonic anhydrase, direct uptake of HCO inf3 sup− , rather than external conversion to CO2 is indicated in this species. In air, the CO2 concentration at which photosynthesis is half-maximal increases in the same order as the ability to raise pH in drift experiments. At 21 kPa the CO2 compensation partial pressures for Palmaria and Laurencia at 0.56 and 1.3 Pa are low enough to suggest a carbon-concentrating mechanism is operating, while those of Lomentaria at 1.8 Pa and particularly that of Delesseria at 4.5 Pa could be explained without a carbon-concentrating mechanism. The algae tested (all except Delesseria) showed more O2 evolution than could be accounted for with a photosynthetic quotient of 1.0 and uncatalysed conversion of HCO inf3 sup− to CO2 outside the cell in high light at pH 8.0 when high algal fresh weight per unit medium was used. These results are concordant with other data suggesting use of HCO inf3 sup− by Palmaria and Laurencia, but discordant with the rest of the available information in indicating use of HCO inf3 sup− by Lomentaria. The reason for this is unclear. The lightsaturated rate of O2 evolution on an algal area basis and the photon flux density needed to saturate photosynthesis were related partly to the habitat from which the seaweeds were collected, but more strongly to the ability to use HCO inf3 sup− . Values for the two users of HCO inf3 sup− , Palmaria (population used was intertidal; also occurs subtidally) and Laurencia (intertidal/shaded intertidal), were greater than for Lomentaria (shaded intertidal), which was greater than Delesseria (subtidal), both of which are believed to be restricted to CO2. In accordance with earlier δ13C data and, for Delesseria, estimates of the achieved growth rates in situ, carbon is likely to be saturating and use of HCO inf3 sup− is unlikely to occur in the normal low-light habitats of Lomentaria and Delesseria. Analysis of N-use efficiencies show that they are closer to the low-CO2-affinity Laminariales than the high-CO2-affinity Fucaceae.