Nitrogen-fixation by the cyanobacterial symbiont of the diatom genus Hemiaulus

Villareal, Tracy A.

doi:10.3354/meps076201

Cited by 100 publications

(67 citation statements)

References 11 publications

(18 reference statements)

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“…This is supported, at least circumstantially, by widespread isotopic and biomarker evidence for N-fixation by cyanobacteria in Upper Cretaceous sequences. The co-occurrence of several Hemiaulus species in the Cretaceous laminae is also consistent with observations of modern blooms where Hemiaulus hauckii is generally the dominant species but where other Hemiaulus species are present in subordinate amounts (Villareal, 1991;Scharek et al, 1999).…”

Section: Hemiaulus Ehrenbergsupporting

confidence: 72%

Late Cretaceous seasonal palaeoclimatology and diatom palaeoecology from laminated sediments

Davies

Kemp

2016

Cretaceous Research

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Laminated diatom-rich marine sediments from California and the Arctic Ocean provide a window into the seasonal climate and oceanography of the mid-and high-latitude Late Cretaceous. These remarkable shallow-buried sediments constitute palaeo-sediment traps that record exceptionally well-preserved sequential biogenic and lithogenic flux events. Many of the diatom laminae are composed of a few dominant taxa, and we use a species-based approach for palaeoecological interpretation. Contrary to many earlier interpretations, results indicate that both sites preserve a major flux of taxa adapted to exploit a strongly stratified ocean. The uppermost Maastrichtian Marca Shale of California records a seasonal cycle initiated with a spring bloom flux of diatom resting spores followed by a summer lithogenic sediment input likely driven by monsoonal storms providing river runoff and aeolian input. This is followed by a dominant diatom flux of species that thrived in the summer stratification in deep chlorophyll maxima and were sedimented in the fall when this stratification broke down. Dominant taxa comprising this group include Hemiaulus, Stephanopyxis, Stellarima and Rhizosolenia. The uppermost Campanian CESAR 6 core from the Arctic Alpha Ridge, records a spring bloom flux of resting spores followed by a more dominant summer and fall flux of diatom vegetative cells which were likely concentrated in subsurface summer blooms that generated a "summer export pulse" and by the breakdown of stratification in the fall that gave massive flux of deep chlorophyll maxima species in the fall dump. The dominance and diversity of Hemiaulus in the CESAR 6 core together with widespread evidence of N 2 -fixation may indicate that some diatom blooms were powered by intracellular N 2 -fixing cyanobacteria as in the modern oligotrophic ocean. Thin lenses of fine lithogenic sediment that occur mostly in the spring layer represent rafting by winter sea ice and support other evidence that suggests intermittent winter freezing in the Late Cretaceous Arctic.Keywords: Late Cretaceous; Diatom blooms; Paleoecology; California; Arctic; Sea Ice 3 1.Introduction Laminated pelagic and hemipelagic marine sediments often constitute "palaeosediment traps" that preserve sequential flux events from which the ancient seasonal flux cycle may be reconstructed. They commonly preserve both the biogenic flux events from surface ocean productivity and also the terrigenous sediment input common in hemipelagic or marginal settings. Within rare, exceptionally well-preserved Cretaceous sediments, fossil diatom algae record the seasonal cycle of marine production and flux to the sea bed. In the modern ocean diatom algae are the dominant, bloom-forming phytoplankton in many environments and are key players in the marine biological carbon pump. The relative contribution of diatoms to total primary production has been estimated to range from 35% in the oligotrophic oceans to 75% in the coastal zone and in the Antarctic (Nelson et al., 1995), while their contribution...

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Section: Hemiaulus Ehrenbergsupporting

confidence: 72%

Late Cretaceous seasonal palaeoclimatology and diatom palaeoecology from laminated sediments

Davies

Kemp

2016

Cretaceous Research

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“…The use of the Hemiaulus hauckii symbiont as the reference genome, and the high similarity between it and the Hemiaulus membranaceus symbiont genome (Hilton et al, 2013), place the symbionts of these two diatoms within the high percent identity range of the Amazon River plume HR-B population. The less similar HR-A population was likely made up of the symbionts of Hemiaulus indicus and/or Hemiaulus sinensis, each of which have also been observed harboring heterocyst-forming symbionts (Sundströ m, 1984;Villareal, 1991). Previous phylogenetic analysis has reported two distinct clades within the Hemiaulus symbionts, het2A and het2B, that exhibit a similar genetic distance as HR-A and HR-B (Janson et al, 1999b;Foster and Zehr, 2006).…”

Section: Discussionmentioning

confidence: 99%

Metatranscriptomics of N2-fixing cyanobacteria in the Amazon River plume

et al. 2014

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Biological N 2 fixation is an important nitrogen source for surface ocean microbial communities. However, nearly all information on the diversity and gene expression of organisms responsible for oceanic N 2 fixation in the environment has come from targeted approaches that assay only a small number of genes and organisms. Using genomes of diazotrophic cyanobacteria to extract reads from extensive meta-genomic and -transcriptomic libraries, we examined diazotroph diversity and gene expression from the Amazon River plume, an area characterized by salinity and nutrient gradients. Diazotroph genome and transcript sequences were most abundant in the transitional waters compared with lower salinity or oceanic water masses. We were able to distinguish two genetically divergent phylotypes within the Hemiaulus-associated Richelia sequences, which were the most abundant diazotroph sequences in the data set. Photosystem (PS)-II transcripts in Richelia populations were much less abundant than those in Trichodesmium, and transcripts from several Richelia PS-II genes were absent, indicating a prominent role for cyclic electron transport in Richelia. In addition, there were several abundant regulatory transcripts, including one that targets a gene involved in PS-I cyclic electron transport in Richelia. High sequence coverage of the Richelia transcripts, as well as those from Trichodesmium populations, allowed us to identify expressed regions of the genomes that had been overlooked by genome annotations. High-coverage genomic and transcription analysis enabled the characterization of distinct phylotypes within diazotrophic populations, revealed a distinction in a core process between dominant populations and provided evidence for a prominent role for noncoding RNAs in microbial communities.

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“…The high chlorophyll autofluorescence of the diatom masked the chlorophyll contained in the cyanobiont vegetative cells. R. intracellularis was located in the diatom intercellular space (Villareal, 1991;Rai et al, 2000). The physical proximity between the cyanobiont and the diatom's chloroplasts may be due to the cyanobionts' high demand for carbohydrates (Wolk et al, 1994) required for the energetic costs of nitrogen fixation (Villareal, 1992;Janson et al, 1995a;Rai et al, 2000).…”

Section: Identification and Characterization Of The Diatomdiazotroph mentioning

confidence: 99%

Seasonal dynamics of the endosymbiotic, nitrogen-fixing cyanobacterium Richelia intracellularis in the eastern Mediterranean Sea

et al. 2008

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Biological nitrogen fixation has been suggested as an important source of nitrogen for the ultraoligotrophic waters of the Levantine Basin of the Mediterranean Sea. In this study, we identify and characterize the spatial and temporal distribution of the N-fixing (diazotrophic) cyanobacterium Richelia intracellularis. R. intracellularis is usually found as an endosymbiont within diatoms such as Rhizosolenia spp and Hemiaulus spp. and is an important diazotroph in marine tropical oceans. In this study, two stations off the Mediterranean coast of Israel were sampled monthly during 2005-2007. R. intracellularis was identified by microscopy and by reverse transcribed-PCR which confirmed a 98.8% identity with known nifH sequences of R. intracellularis from around the world. The diatom-diazotroph associations were found throughout the year peaking during autumn (October-November) at both stations. Abundance of R. intracellularis ranged from 10 to 55 heterocysts l À1 and correlated positively with the dissolved Si(OH) 4 /(NO 3 þ NO 2 ) ratio in surface waters. Although the rates of nitrogen fixation were very low, averaging B1.1 nmol N l À1 day À1 for the R. intracellularis size fraction (410 lm) from surface waters, they correlated positively with heterocyst counts during thermal stratification. The lack of large-scale diatom-diazotroph blooms and the low rates of nitrogen fixation by these diazotrophs may result from the P-starved conditions affecting the Levantine basin.

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Nitrogen-fixation by the cyanobacterial symbiont of the diatom genus Hemiaulus

Cited by 100 publications

References 11 publications

Late Cretaceous seasonal palaeoclimatology and diatom palaeoecology from laminated sediments

Late Cretaceous seasonal palaeoclimatology and diatom palaeoecology from laminated sediments

Metatranscriptomics of N2-fixing cyanobacteria in the Amazon River plume

Seasonal dynamics of the endosymbiotic, nitrogen-fixing cyanobacterium Richelia intracellularis in the eastern Mediterranean Sea

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