Rhizosolenia

Belt, S.T. Allard, W.G. Masse, G. Robert, J.-M. Owland, S.J. (2001) Structural charactaisation of Cjo highly branched isoprenoid alkenes (rhizenes) in the marine diatom Rhizosolenia setigera. Tarahedron Lett., 42, 5583-5. 

Adverse effects, most sensitive species Brown algae, Fucus serratus Copepod, Tisbe holothuriae Pacific oyster, Crassostrea gigas, larvae Alga, Rhizosolenia spp. 

Nagasaki K, Tomaru Y, Katanozaka N, Shirai Y, Nishida K, Itakura S, Yamaguchi M (2004) Isolation and characterization of a novel single-stranded RNA virus infecting the bloom-forming diatom Rhizosolenia seti-gera. Appl Environ Microbiol 70 704-711... 

Photic zone I Cyanobacteria E Endosymbiont/ diatom Calothrix rhizosoleniae Janson et al., 1999a,b Foster and Zehr, 2006... 

Diztom/Richelia intracellularis associations can be spatially extensive and contribute intensive input of N through N2 fixation in the upper water column. For instance, a Hemiaulus hauckii/Richelia bloom encountered by Carpenter et al. (1999) off the northeast coast of South America in Oct 1996 was observed over a linear cruise track of 2500 km and accounted for very substantial levels of N2 fixation (see below). The symbionts for individual diatoms such as Hemiaulus and Rhizosolenia while morphologically similar are genetically distinct and discrete probes for each association have been developed and applied in the Amazon River plume to enumerate the relative densites of these two associations (Foster et al., 2007). 

Singler, H., and Villareal, T. A. (2005). Nitrogen inputs into the euphotic zone by vertically migrating Rhizosolenia mats. J. Plankton Res. 27, 545—556. 

Eucalanus pileatus Rhizosolenia alata (100 pgC 1-1, C N = 5) 15 Paffenhofer and Knowles, 1979... 

Some of the earliest reports of planktonic symbiosis describe the association of a heterocystous cyanobacterium, Richelia intracellularis, with various diatoms, including Rhizosolenia (Ostenfeld and Schmidt, 1901), Hemiaulus spp. and Guinardia cylindms (Siindstrom, 1984 Taylor, 1982 ViUareal, 1992). Up to 13 different species of Rhizosolenia have been reported with Richelia symbionts however some authors (Soumia, 1970 Siindstrom, 1984) questioned the host identity, argued that many were misidentified, and proposed that most of the Rhizosolenia species were just varieties of R. clevei. 

Two of the most common Hemiaulus species reported with symbiotic R. intracellularis are H. hauckii and H. membranaceus. A third symbioses, occurs between Richelia and H. sinensis. In Hemiaulus host diatoms, it is not known where the symbiotic Richelia reside, whereas in Rhizosolenia spp. hosts, the Richelia remains as an extracellular endosymbiont residing between the plasmalemma and silica wall of the diatom host (Janson et ai, 1995 Taylor, 1982 ViUareal, 1990). In Hemiaulus diatoms, typically there are two trichomes (series of cells comprised of a few vegetative cells and one terminal heterocyst) per host cell, and in Rhizosolenia species occasionally 1-32 Richelia trichomes have been observed (Siindstrom, 1984 Villareal, 1990). 

Lemmerman (1905) was one of the first to depict the unique association of another heterocystous cyanobacterium, Calothrix rhizosoleniae, attached to the spines of a Chaetocoeros compressus diatom. Norris (1961) noted that the cyanobionts only attach transversely to the intercellular spaces of the diatom with the heterocyst closest to the host diatom. Others report the same symbiont as R. intracellularis (G6mez et al., 2005 Janson et ai, 1999 Karsten, 1907 Norris, 1961), thus there is... 

Few have attempted to isolate and cultivate these consortia, and to the best of our knowledge only T. Villareal (1989) was successful for several months in culturing a Rhizosolenia-Richelia symbiosis. The division cycles of the host Rhizosolenia and Richelia were asynchronous in culture, and as such several asymbiotic hosts were observed (Villareal, 1989). Transmission from host to daughter cell is typically vertical, however asymbiotic hosts and free-living Richelia observed in the field and culture suggest horizontal transmission as well. 

In a micro-autography study, field collected Rhizosolenia-Richelia symbioses were incubated with C-labeUed bi-carbonate. Higher density of silver grains localized on the symbiotic Richelia trichomes than on the host Rhizosolenia filaments, suggesting that the Richelia were actively photosynthesizing and the host diatom were inactive (Weare et al., 1974). An equally plausible explanation for less silver grains on the Rhizosolenia host is that some of the fixed and labeled photosynthetic products were transferred to the host from the symbiont. Similar scenarios of carbon, and nitrogen transfer, are well documented in terrestrial... 

Although the Calothrix cyanobionts of Chaetoceros are attached to the diatom spines, the cyanobionts are only located at the interceUular spaces and attached transversely at the heterocyst (Norris, 1961), which could be seen as a morphological adaptation for nitrogen transfer. Others (e.g., ViUareal, 1990) have suggested that the extraceUular location of the Richelia symbionts with Rhizosolenia clevei is mechanistic for nitrogen transfer. 

Some of the highest numbers for the Hemiaulus-Richelia symbioses were reported in the western tropical North Atlantic (WTNA). Carpenter et al. (1999) observed an extensive bloom off the NE coast of South America in autumn of 1996. They reported cell densities from 10 to 10 Richelia Recently, in the same vicinity as the study of Carpenter et al. (1999), Foster et al. (2007) reported extremely high niJH gene copy (>10 copies L ) abundances (proxy for cell abundances) for Richelia associated H. hauckii and Rhizosolenia clevei. In addition, they found within the plume waters of the Amazon River runoff a positive correlation between salinity and the abundance of the H. hauckii-Richelia abundance (Foster et al, 2007). 

In her 9-year field study in the North Pacific central gyre, Venrick (1974) reported that for most of the years Richelia associated with Rhizosolenia were relatively low (0.1-1 Richelia ceU ml ) in abundance, however, in summer months when the upper water column stratified and nutrients were measurably low, symbiotic populations increased 1-2 orders of magnitude. Environmental parameters, i.e., nutrient concentrations, during bloom and non-bloom summers in the upper 45 m were indistinguishable, suggesting little evidence for a condition to initiate and perpetuate the blooms. Venrick (1974) proposed that the blooms were a localized phenomena occurring independently at various locations within the central Pacific... 

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