Draft Genome Sequence of Frankia sp. Strain BCU110501, a Nitrogen-Fixing Actinobacterium Isolated from Nodules of Discaria trinevis.

Frankia forms a nitrogen-fixing symbiosis with actinorhizal plants. We report a draft genome sequence for Frankia sp. strain BCU110501, a nitrogen-fixing actinobacterium isolated from nodules of Discaria trinevis grown in the Patagonia region of Argentina.

Reproductive ecology of Ochetophila trinervis in Northwest Patagonia.

Native actinorhizal species Ochetophila trinervis (Gillies ex Hook. & Arn.) Poepp. ex Miers, also known as Discaria trinervis (Kellermann et al. 2005), grows along watercourses and distant from them, along a rainfall gradient in north-west Patagonia. We studied the reproductive ecology of this species under different macro- and micro-environmental conditions, in three zones in a rainfall gradient (western, intermediate and eastern) with two sites for each one, near and distant to a watercourse (riparian and dry-land). We performed field studies and germination trials. Plant size, reproductive effort (seed abundance per branch) and seed bank size of O. trinervis, were favoured by the proximity of streams in the drier environments of the gradient. The abundance of seedlings and saplings in the field was very low, which was in agreement with a lack of germination in the field, despite the good germination capacity of seeds. Sexual reproduction of O. trinervis was affected by the low abundance of seedlings. Lower rainfall, higher temperatures and a longer growing season along the gradient favour the potential regeneration of the species. Because of its nitrogen-fixing capacity and other features, O. trinervis has potential for reclamation of eroded lands in Patagonia. Patterns of seed biology and regeneration presented in this study will aid in the use of O. trinervis in the reclamation of disturbed lands.

Local adaptation of frankia to different Discaria (Rhamnaceae) host species growing in patagonia.

Frankia BCU110601 (Da) and Frankia BCU110345 (Dc) were isolated from root nodules of Discaria articulata and Discaria chacaye, respectively; Frankia BCU110501 (Dt) was previously isolated from Discaria trinervis. The strains were identical at the 16S sequence and after analysis of RFLP of 16S and 23S rDNA intergenic region. Diversity was revealed at the molecular level after fingerprint analysis by BOX-polymerase chain reaction. The strains were infective and effective on the original host plants. A cross-inoculation assay intra Discaria genus, including D. trinervis, D. articulata, and D. chacaye, with each of these isolated Frankia strains caused effective symbioses with a similar dry weight in each plant species regardless of the inoculated strain. Nevertheless, a differential degree of recognition was revealed: Homologous symbiotic pairs in the case of D. chacaye-Frankia BCU110345 (Dc), D. articulata-Frankia BCU110601 (Da), and D. trinervis-Frankia BCU110501 (Dt) had faster nodulation rates than heterologous pairs. The differences in nodulation rate would suggest the existence of a subspecific level of recognition within a certain cross-inoculation group, pointing to subspecific adaptation occurring in this actinorhizal symbiosis.

Infectivity of soilborne Frankia and mycorrhizae in Discaria trinervis along a vegetation gradient in Patagonian soil.

The infective capacities of the nitrogen fixing Actinomycete Frankia and arbuscular mycorrhizal fungi from soils near watercourses, along a vegetation gradient, were studied using plant bioassays. Frankia and arbuscular mycorrhizas capable of infecting Discaria trinervis were found at seventeen sites sampled. More specific enumeration of the infective capacities of both microorganisms in relation to environmental factors was performed in seven representative soils of the analysed vegetation zones (rainforest, xeric forest and steppe) using the most probable number method. The highest nodulation capacities ranged from 340 infective units g(-1 )soil, in a steppe marsh devoid of actinorhizas, to 61 in a coastal actinorhizal scrub (in xeric forest). The highest number of infective mycorrhizal units--also found in marsh--was 145. In general, rainforest soils had the lowest values for both microorganisms. Infective units of Frankia and arbuscular mycorrhizal fungi in soil were positively correlated (r = 0.89, P < 0.05). Both soilborne symbionts showed the highest infective capacity in semi-arid conditions nearby watercourse and at the valley bottom location. Tripartite symbiosis was effective in plants inoculated with steppe and xeric forest soils and plants inoculated with Frankia BCU110501 and Glomus mosseae. Interaction between both symbionts and influence of environmental conditions, in general, would contribute to define comparable trends of their infective capacities.