First estimates of productivity in Lessonia trabeculata and Lessonia nigrescens (Phaeophyceae, Laminariales) from the southeast Pacific

Lessonia is the main Laminariales found along the southeast Pacific coast. Lessonia nigrescens Bory de Saint‐Vincent in the intertidal and Lessonia trabeculata Villouta et Santelices in the subtidal, are the most important habitat constructors in rocky coastal communities in northern and central Chile. In both species, the seasonal production and erosion of distal tissue were estimated in biomass units using the Area of Constant Biomass Model that combined the individual blade elongation, obtained with the traditional hole‐punching method, with the blade length and biomass distribution along the blade. In austral late spring (December 96) and autumn (May 97), blade production and erosion were transformed to the level of population from standing stock measurements (number and biomass of blades and plants per substrate area), considering that previous blade weight analysis showed the highest and lowest values at these times, as well as the population parameter extremes that were expected to occur. Both species displayed a seasonal pattern, with a production increase in later winter and spring and decrease towards the end of summer that coincided with higher distal tissue erosion. At the level of individual blades, Lessonia trabeculata showed higher mean production (0.026 g dw d⁻¹) and erosion (0.01 g dw d⁻¹) than L. nigrescens (production 0.01 g dw d⁻¹ and loss 0.002 g dw d⁻¹). The standing stocks, with respect to density and biomass, were similar in spring and autumn for both populations. Nevertheless, the net productivity (production minus erosion) of the intertidal L. nigrescens showed greater values due to the greater density of blades (2112 ± 1360 (SE) blades m⁻²) compared with the subtidal L. trabeculata (527 ± 151 (SE) blades m⁻²). Spring net productivities of 42 g dw m⁻²d⁻¹ (254 g ww m⁻²d⁻¹; 11.46 gC m⁻²d⁻¹) for L. nigrescens and 11 g dw m⁻² d⁻¹ (64 g ww m⁻² d⁻¹; 2.46 gC m⁻²d⁻¹) for L. trabeculata were estimated. A preliminary model of production and biomass fate for Lessonia populations is proposed.     

Alginic acids in Lessonia vadosa: Partial hydrolysis and elicitor properties of the polymannuronic acid fraction

Extraction of Lessonia vadosa(Laminariales, Phaeophyta) collectedin three different localities near PuntaArenas in the south of Chile, with 3%aqueous sodium carbonate solutions gave asodium alginate yield in the range3.0–17.7% dry weight. There were markeddifferences in the mannuronic acid toguluronic acid ratio (M/G) (0.21–1.69) inthe alginic acids, samples collected inPuerto del Hambre in winter were composedmainly of mannuronic acid residues. Thealginate samples were characterized bypartial hydrolysis and FT-IR spectroscopy.No relationship was found between tissuetype and polyguluronic acid content. Theelicitor activity of the polymannuronicacid enriched fraction from alginic acid ofblades from Puerto del Hambre was assayedin wheat plants. The polymannuronic acidenriched fraction induced substancialelicitation of phenylalanine ammonia-lyase(PAL) and peroxidase (POD) activities.     

Development and characterization of nine polymorphic microsatellite markers in the Chilean kelp Lessonia nigrescens

A total of nine microsatellite loci were isolated and characterized in the Chilean kelp Lessonia nigrescens Bory. Using two different enriched libraries, we observed 1-14 alleles per locus in two samples of 21 kelp individuals each. The observed heterozygosities ranged from 0.05 to 0.80 and all loci are in Hardy-Weinberg equilibrium for one or both samples. Seventeen samples collected from different sites showed high allele diversity along the species distribution. The variation detected at these markers is currently being used for the study of populations of Lessonia nigrescens at different geographical scales.     

Population dynamics of two Scottish Ultramafic (serpentine) rarities with contrasting life histories

Summary

The paper reports demographic studies of the endemic Cerastium nigrescens and the very rare Arenaria norvegica ssp. norvegica on the Keen of Hamar ultramafic outcrop on Unst, Shetland from June 1994 to November 1996. Plants of Cerastium nigrescens showed a Deevey type II curve and mature plants had a half-life of 3.8 years. Plants of Arenaria norvegica ssp. norvegica showed a Deevey type I curve with high mortality after flowering in the second year. There was some evidence of increased mortality during droughts but this had little impact on the total population. Seed production and seedling recruitment for both species was good throughout the study period. Seed bank measurements ranged from 12–13 m² for Cerastium nigrescens and 24–43 m^-2 for Arenaria norvegica ssp. norvegica. The study showed that there was no immediate threat to the populations of the two species but because of their isolated occurrence they are susceptible to extinction and should be carefully monitored.     

The gene coding for nigrescin produced by Prevotella nigrescens ATCC 25261

Aim:  To identify the gene that encodes nigrescin, a bacteriocin produced by Prevotella nigrescens ATCC 25261.
Methods and Results:  Each open reading frame (ORF) of the nig gene cluster ( nigA, nigB, nigC and nigD ) was transferred into an expression vector. The recombinant proteins encoded by nigA, nigB, nigC and nigD were purified and assayed for bacteriocin activity against Porphyromonas gingivalis . The ORFs of the nig gene cluster in Pr. nigrescens ATCC 25261 were re-analysed. It revealed that the position of nig ORFs was similar to previously designated locations, except that the start codon of nigC was reassigned. The new nigC gene started at the nucleotide base position 2454 and stopped at position 3608 (the position designated is relative to the first nucleotide base of the nig locus) and putatively encoded a protein with a predicted molecular mass of 41·9 kDa. The N-terminal 6xHistidine-tag recombinant proteins of NigA, NigB, NigC and NigD were overexpressed in Escherichia coli BL21 star (DE3) and were purified using Ni-NTA resins. Only recombinant NigC showed inhibitory activity against P. gingivalis A244 with minimal inhibition concentration (MIC) of 40 μg ml⁻¹.
Conclusion:  These results indicate that nigC is the gene that encodes nigrescin.
Significance and Impact of the study:  This is the first report that indicates that the gene nigC codes for nigrescin, a bacteriocin produced by Pr. nigrescens ATCC 25261.