Vertical and horizontal distribution patterns of the giant sea anemone Heteractis crispa with symbiotic anemonefish on a fringing coral reef

The distribution patterns of the leathery sea anemone, Heteractis crispa, which contains an algal endosymbiont (zooxanthellae) and anemonefish, were investigated in relation to size distribution on a shallow fringing reef (3.2 ha, 0–4 m depth) in Okinawa, Japan. Individual growth and movements were also examined. Large individuals (>1,000 cm²) inhabited reef edges up to a depth of 4 m, while small anemone (<500 cm²) inhabited shallow reefs including inner reef flats. Individuals rarely moved, and their sizes were significantly correlated with their water depths. Growth of small anemones was negatively correlated with their distance from the reef edge, suggesting that reef edges provide more prey and lower levels of physiological stress. This study suggested that deep reef edges are suitable habitats for H. crispa. Large anemones were inhabited by large Amphiprion perideraion or large Amphiprion clarkii, both of which are effective defenders against anemone predators. Anemones that settle in deep reef edges may enjoy a higher survival rate and attain a large size because of their symbiotic relationship with anemonefish. However, early settlers do not harbor anemonefish. Their mortality rate would be higher in the deep edges than in shallow edges, the complicated topography of which provides refuge.     

Biochemical and physiological characteristics of Xenorhabdus species,symbiotically associated with entomopathogenic nematodes including Steinernema kushidai and their pathogenicity against Spodoptera litura (Lepidoptera: Noctuidae)

The symbiotic bacterium strain, SK-1 isolated from Steinernema kushidai, a new species of entomopathogenic nematode, was compared with other strains of Xenorhabdus species. Like other Xenorhabdus nematophilus strains, this new strain is gram-negative, facultatively anaerobic, peritrichously flagellated rod and negative for catalase and nitrate reduction. It can be distinguished from the other Xenorhabdus spp. by differences in reactions to phenylalanine deaminase, no acid production from myo-inositol and utilizations of inosine, dl-malate, formate and methanol. Intra-haemocoelic injection of actual cells or liquid culture supernatant into sixth instar larvae of Spodoptera litura for either Phase I or II variants were not pathogenic. Other strains of X. nematophilus showed pathogenicity for whole cell injections. The supernatants of strain D-1 and ATCC 19061, which are symbionts of Steinernema carpocapsae were pathogenic, however pathogenicity decreased and then terminated by increases in temperature.     

Molecular organisation of the malate synthase genes of Aspergillus nidulans and Neurospora crassa

Summary A soybean nodulin cDNA clone (E41) hybrid-selected mRNA for three in vitro translation products with apparent molecular weights of 26 kDa, 25 kDa and 24 kDa. Based on Southern analysis of soybean genomic DNA, combined with mapping and sequencing of genomic clones, we identified four genes that are related to E41, one of which was identified to be the previously characterized N-20 gene. Our data indicate the linkage of three of the genes, of which one is a truncated version and suggest that they originated by gene duplication combined with deletion and conversion. The genes are highly expressed and we postulate that the sequence conservation in the 5 and 3 flanking regions of all four genes, has a functional role in their expression. Hybrid-selected translation products of E41 are not immunoprecipitable with antibody to the soluble fraction of nodules suggesting that they are membrane associated. The N-20 gene, which is a member of this gene subfamily, showed sequence similarity to four previously characterized nodulin genes and a phylogenetic tree is proposed based on the extent of sequence similarity.     

Lichens toGunnera — with emphasis onAzolla

Summary N₂-fixing cyanobacteria occur in symbiotic associations with fungi (ascomycetes) as lichens and with a few green plants. The associated cyanobacterium is always a species ofNostoc orAnabaena. Only a small number of plant genera are involved but there is a remarkable range of host diversity. Associations occur with several bryophytes (e.g.Anthoceros, Blasia, Cavicularia), a pteridophyte (Azolla), cycads (nine genera includingMacrozamia andEncephalartos) and an angiosperm (Gunnera). Except forGunnera, where the cyanobacterium penetrates the plant cells, the cyanobacteria are extracellular with specialized morphological modifications and/or structures of the host plant organs providing an environment which facilitates interaction with the prokaryote.Salient aspects of current knowledge pertaining to the establishment, perpetuation, and functioning of the individual symbioses are summarized. Where possible this includes information concerning recognition and specificity, mode(s) of infection, morphological modifications/adaptations of the host plant and a synopsis of morphological, physiological and biochemical changes common to the symbiotic cyanobacteria. The latter encompasses heterocyst frequencies, enzymes involved in ammonia assimilation, photosynthetic capability and metabolic interaction with the host.TheAzolla-Anabaena symbioses, which have potential agronomic significance as an alternative nitrogen source and maintain continuity with the endophyte through the sexual cycle, are emphasized.     

Numerical taxonomic analysis of cross-inoculation patterns of legumes and Rhizobium

Summary A survey was made of published results of tests of the capacity of Rhizobium derived from one legume genus to nodulate plants from other genera. The data were derived from more than 14,000 separate cross-inoculation trials involving species from 165 genera of legumes. Numerical taxonomic techniques were applied to 113 of the genera for which results of substantial cross-infection tests were available. The data were examined using mean character difference coefficients re-expressed as total and positive-only similarity coefficients. The resulting similarity matrices were clustered by the unweighted pair-group method using arithmetic averages. Eighteen affinity groups were defined at the 70% similarity level. With few exceptions, the physiological and cultural behavior of the rhizobia was consistent within the defined groups. Two broad categories were suggested in the numerical taxonomic analysis, and their validity is discussed in regard to the geographic, physiological and cultural characteristics of the legumes and their Rhizobium microsymbionts. The taxonomic and agronomic value of this approach and the new groupings are discussed.     

大豆-根瘤菌共生体系光合与固氮关系研究

水培大豆和田间生长的大豆,接种根瘤菌 Rhizobium B16-11C 后植株全氮含量、叶片叶绿素含量和净光合速率及种子产量都明显增加。比较 Clark 大豆的结瘤品系和不结瘤品系获类似结果。摘除根瘤后3天内叶片净光合速率无明显变化。大豆植株遮阴、去叶或切掉地上部导致根瘤活性明显下降。但去豆荚不能提高根瘤固氮的比活性。根瘤活性的日变化不能用根瘤蔗糖、淀粉含量或周围温度的变化来解释,其控制因子尚待深入研究。     

Enhanced N2-fixing ability of a deletion mutant of arctic rhizobia with sainfoin (Onobrychis viciifolia)

Summary Mutagenesis provoked by exposure at elevated temperature of the cold-adapted, arctic Rhizobium strain N31 resulted in the generation of five deletion mutants, which exhibited loss of their smaller plasmid (200 kb), whereas the larger plasmid (> 500 kb) was still present in all mutants. Deletion mutants did not show differences from the wild type in the antibiotic resistance pattern, the carbohydrates and organic acids utilization, and the growth rate at low temperature. However, deletion mutants differed from the wild type and among themselves in the ex planta nitrogenase activity, the nodulation index, and the symbiotic effectiveness. The deletion mutant N31.6rif ^r showed higher nodulation index and exhibited higher nitrogenase activity and symbiotic efficiency than the other deletion mutants and the wild type. The process of deletion mutation resulted in the improvement of an arctic Rhizobium strain having an earlier and higher symbiotic nitrogen fixation efficiency than the wild type.     

Negative effects of agrocin 84-encoding Agrobacterium plasmids on symbiotic properties of Rhizobium meliloti

Two plasmids, pAgK84::Tn5-Mob from Agrobacterium radiobacter carrying genes for the production of agrocin 84, and RP4-4 from E. coli were inserted either separately or together into a strain of Rhizobium meliloti. Each of these plasmid-containing R. meliloti transconjugants was less effective than the wild type strain in their ability to fix nitrogen in Medicago tornata. The pAgK84::Tn5-Mob-containing transconjugant was significantly less effective than that containing RP4-4. The transconjugant strains were inferior to the wild type strain in their ability to nodulate seedlings and to compete for nodulation.     

The large mimosoid genus Inga Mill. (tribe Ingeae,Caesalpinioideae) is nodulated by diverse Bradyrhizobium strains in its main centers of diversity in Brazil

Inga (Caesalpinioideae) is the type genus of the Ingeae tribe in the mimosoid clade. It comprises about 300 species, all trees or treelets, and has an exclusively neotropical distribution, with Brazil as its main center of diversity. In this study, we analyzed the diversity of 40 strains of rhizobia isolated from root nodules collected from ten species of Inga belonging to different types of vegetation in Brazil. Sequences of their housekeeping genes (dnaK, recA, rpoB, gyrB and glnII), 16S rRNA genes, internal transcribed spacer (ITS) regions, as well as their symbiosis-essential genes (nodC and nifH) were used to characterize them genetically. The ability of the rhizobia to form nodules on Inga spp., and on the promiscuous legume siratro (Macroptilium atropurpureum) was also evaluated. A multilocus sequence analysis (MLSA) combined with an analysis of the ITS region showed that the isolates were distributed into four main groups (A-D) within the large genus Bradyrhizobium. Analysis of the nodC and nifH genes showed that the isolates formed a separate branch from all described species of Bradyrhizobium, except for B. ingae. Most of the tested isolates formed nodules on siratro and all isolates tested nodulated Inga spp. Our results suggest a unique co-evolutionary history of Bradyrhizobium and Inga and demonstrate the existence of potential new species of microsymbionts nodulating this important and representative genus of leguminous tree from the Caesalpinioideae mimosoid clade.