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The cyanobacterium Trichodesmium is responsible for approximately half of the ocean's nitrogen input through nitrogen fixation. Although it was first recorded near Australia in the 18th century, the knowledge of where and when large quantity of Trichodesmium around Australia could be found is still lacking. Here, using multi‐band satellite imagery acquired between 2012 and 2021, we fill this knowledge gap through the use of deep learning, designed to recognize both the spectral shapes of individual pixels and spatial morphology of surface aggregations (scums) of Trichodesmium. Trichodesmium scums were found nearly everywhere around Australia, with a cumulative footprint (i.e., where the 10‐year average density is >0.001‰) exceeding 4.6 million km2. Strong seasonality was found, with peak months between September and November. Furthermore, temperature, iron‐rich dust and black carbon aerosols, with the latter being a result of frequent bushfires, play major roles in determining the spatial distributions and seasonality of Trichodesmium. Plain Language Summary: Responsible for half of the ocean's nitrogen input through nitrogen fixation, the saltwater cyanobacterium Trichodesmium is ubiquitous in global tropical and subtropical oceans but particularly abundant around Australia. However, although the earliest report goes back to the 18th century, the knowledge of where and when large quantities of Trichodesmium can be found around Australia is still incomplete. Based on satellite imagery and deep learning, we quantified relative abundance of Trichodesmium around Australia for the period of 2012–2021. Surface aggregations of Trichodesmium were found almost everywhere except the southern coast, with a cumulative footprint exceeding 4.6 million km2. Strong seasonality was found, with peak months between September and November. The spatial distributions and seasonality were found to correlate well with water temperature, iron‐rich dust from Australian desert, and black carbon aerosols from frequent bushfires. With the projected ocean warming in the coming century, Trichodesmium may expand further south, making the cumulative footprint even larger. Key Points: Deep learning was applied to multi‐band satellite images to detect and quantify Trichodesmium surface scums around AustraliaTrichodesmium scums were found nearly everywhere around Australia with a seasonality and a cumulative footprint exceeding 4.6 million km2Distribution and seasonality of Trichodesmium were driven by temperature, iron‐rich dust and black carbon from the mainland bushfires [ABSTRACT FROM AUTHOR]

The last several decades have witnessed dramatic advances in unfolding the diversity and commonality of oceanic diazotrophs and their N2-fixing potential. More recently, substantial progress in diazotrophic cell biology has provided a wealth of information on processes and mechanisms involved. The substantial contribution by the diazotrophic cyanobacterial genus Trichodesmium to the nitrogen influx of the global marine ecosystem is by now undisputable and of paramount ecological importance, while the underlying cellular and molecular regulatory physiology has only recently started to unfold. Here, we explore and summarize current knowledge, related to the optimization of its diazotrophic capacity, from genomics to ecophysiological processes, via, for example, cellular differentiation (diazocytes) and temporal regulations, and suggest cellular research avenues that now ought to be explored. [ABSTRACT FROM AUTHOR]

Primary production and standing crop, as chlorophyll-a (chl-a), of Trichodesmium spp., and other phytoplankton as well as the abundance and depth distribution of Trichodesmium were measured on three cruises to the tropical North Atlantic Ocean. Trichodesmium abundance was greatest on a cruise in May–June 1994, with average surface densities of 2250 trichomes l−1 and depth integrated abundance of 91×106 trichomes m−2. Average surface densities were 292 and 222 trichomes l−1 and depth integrated abundance 21 and 8.6×106 trichomes m−2 for the April 1996 and October 1996 cruises, respectively. Total (phytoplankton plus Trichodesmium) chl-a standing crop and the percentage as Trichodesmium averaged 47 (62%), 22 (13%) and 30 (11%) mg chl-a m−2 for May–June 1994 and April and October 1996. On the May–June 1994 and April and October 1996 cruises 89%, 93% and 92% of the trichomes were in colonies, and the remainder occurred as free trichomes. Peak abundances of Trichodesmium were generally in the upper water column, with an average biomass maximum at 12 m on the May–June 94 and October 96 cruises and at 40 m during the April 96 cruise. The average C:N ratio (atomic) of Trichodesmium was 6.5.Mean rates of total primary production (Trichodesmium and other phytoplankton together) for May–June 1994, and April and October 1996 were 1080, 932 and 804 mg C m−2 d−1, and Trichodesmium accounted for an average of 47%, 7.9% and 11%, respectively, of the total primary production for each cruise. These primary production rates exceed those typically reported at oligotrophic open ocean sites. Trichodesmium C assimilation numbers (mg C fixed mg chl-a−1 h−1) were highest at the surface and were always lower than those of other phytoplankton. Average nitrogen demand, as calculated from the mean Trichodesmium C fixation from all three cruises, was about 40 mg N m−2 d−1, about 10% of concurrently determined rates of N2 fixation. [Copyright &y& Elsevier]

We quantified the relationships among the specific growth rate, intracellular iron content, and steady state iron uptake rate for cultures of the marine diazotrophic cyanobacterium Trichodesmium (IMS 101) grown under differing conditions of Fe and N availability. The Fe quotas necessary to support a moderately Fe-limited growth rate (70% µmax) of 0.1 d[sup-1] under diazotrophy and ammonium were 38 and 8 µmol mol[sup-1], indicating a fivefold increased Fe cost for diazotrophy. This increased demand reflects the influences of both the ninefold lower marginal use efficiency and the greater maintenance Fe:C requirement at zero growth rate under diazotrophy (13.5 versus 5.2 µmol mol[sup-1]). For diazotrophic growth at µ = 0.1 d[sup-1], we estimate that 19%-53% of the cellular Fe is bound in nitrogenase. Trichodesmium is capable of luxury uptake of at least 13-fold greater amounts of Fe than needed for moderately Fe-limited growth. At least half of the populations sampled from the continental shelf of northern Australia had Fe:C ratios within the range of iron limitation of laboratory cultures. Bottle incubations showed that, after 3-4 d with added iron, a low Fe:C population (21 µmol mol[sup-1]) had higher N[sub2] fixation rates than controls, whereas a high Fe:C population (78 µmol mol[sup-1]) showed no response. The cellular N:P quotas and N[sub2] fixation rates were compared to those previously reported for the Atlantic Ocean. Empirically, these data suggest a critical N:P ratio ∼ 40-50 for... [ABSTRACT FROM AUTHOR]

Estimates of the iron use efficiency (IUE) for diazotrophic plant growth have been used to suggest iron limitation of marine N2 fixation. However, in the course of these inferences, neither the physiological complexity of these estimates nor the specific physiological parameters of marine diazotrophs were evaluated. Here, a semiempirical prediction of the IUE of diazotrophic growth for Trichodesmium was computed from considerations of the Fe content and reaction rates of the nitrogenase complex and PSI:PSII ratios, as well as field measurements of Mehler activity, cellular Fe-superoxide dismutase activity, and diel variability in C and N2 fixation. With a PSI:PSII ratio of 1 and 48% Mehler activity, the instantaneous IUE (0.33 mol C fixed·mol cellular Fe- 1 ·s- 1 ) was only 4-fold lower than that calculated for a phytoplankter growing on reduced N. We computed a range of daily integrated IUE values from 2900 to 7700 mol C·mol Fe- fixation as well as the uncertainties in cyanobacterial nitrogenase biochemistry and PSI:II ratios of field-collected Trichodesmium. The lowest observed Fe-superoxide dismutase:C quota of 2.9 (μmol:mol) suggests a maintenance requirement for this enzyme. The maintenance Fe:C requirement of 13.5 μmol:mol (derived from cultures of Trichodesmium IMS 101) and values of the IUE yielded an Fe requirement ranging from 27 to 48 Fe:C (μmol:mol) to achieve a diazotrophic growth rate of 0.1 d1 ·d- 1 , accounting for the diel variability in C and N2 fixation as well as the uncertainties in cyanobacterial nitrogenase biochemistry and PSI:II ratios of field-collected Trichodesmium. The lowest observed Fe-superoxide dismutase:C quota of 2.9 (μmol:mol) suggests a maintenance requirement for this enzyme. The maintenance Fe:C requirement of 13.5 μmol:mol (derived from cultures of Trichodesmium IMS 101) and values of the IUE yielded an Fe requirement ranging from 27 to 48 Fe:C (μmol:mol) to achieve a diazotrophic growth rate of 0.1 d- 1 . Based on these predicted requirements, the Fe:C contents of Caribbean Sea and most North Atlantic Ocean populations sampled thus far exceed that required to support the observed rates of N2 fixation. [ABSTRACT FROM AUTHOR]

The marine planktonic cyanobacterial genus Katagnymene was described by Lemmermann in 1900 and is found in oligotrophic tropical and subtropical oceans. The genus comprises two species, K. pelagica Lemmermann and K. spiralis Lemmermann, and both were observed in most stations sampled during a cruise in the southwest Pacific Ocean in 1998. Katagnymene is nonheterocystous and characterized by single ensheathed trichomes that do not form colonies. Acetylene reduction-GC demonstrated that natural populations of Katagnymene fixed nitrogen and that nitrogenase activity occurred exclusively in the light during a 12:12 light:dark cycle. Whole cell immunolocalization revealed that nitrogenase (the Fe protein) appeared in 7% of the total number of cells and that these were arranged in zones composed of consecutively arranged cells. At least one zone of nitrogenase-containing cells per trichome was found. Nitrogenase was present throughout both the day and night, as shown by Western blotting, and in the same percentage of cells. Ultrastructural immunolocalization on sectioned trichomes also confirmed the presence and localization of nitrogenase in Katagnymene. Cultures of Katagnymene are able to grow on nitrogen-free media and fix nitrogen only in the light. Finally, cloning and sequencing of nifH verified the diazotrophic nature of the genus Katagnymene and demonstrated a close relationship to members of the marine genus Trichodesmium. [ABSTRACT FROM AUTHOR]

Trichodesmium tenue Wille (1904) was examined using transmission electron microscopy to determine the role of carbohydrate, phosporus, and nitrogen storage in buoyancy regulation. Carbohydrate storage area (mean = 2.06 ± 0.61 [SE] μm[SUP2]; 6.62% of total cell area) in negatively buoyant colonies (NBCs) was significantly higher (P < 0.001) than in positively buoyant colonies (PBCs) (mean = 0.38 ± 0.06 μm[SUP2]; 0.73%). Distinct diel periodicity of carbohydrate content was found in NBCs, with a mean of 0.44 ± 0.10 μm[SUP2] (1.54%), as compared to PBCs, with a mean of 0.14 ± 0.05 μm[SUP2] (0.24%). Polyphosphate content increased in NBCs from morning to evening, and PBCs had a 10% decrease from morning to afternoon. Calculations indicated that averaged effects of polyphosphate on increased cell density is approximately 20% of that carbohydrate accumulation. Density contribution due to ballast weight of cabohydrate and polyphosphate indicated that NBCs were 12 times more dense than PBCs. Mean area of cyanophycin granules (N storage) was not significantly different between PBCs and NBCs. In conclusion, Trichodesmium tenue can regulate buoyancy by carbohydrate ballasting similar to that noted in limnetic cyanobacteria. Polyphosphate storage and possibly nitrogen storage products play a significant role in buoyancy regulation. [ABSTRACT FROM AUTHOR]

The DNA sequence of a fragment of nifH was compared to natural populations of the marine cyanobacteria Trichodesmium thiebautii and T. erythraeum from the Caribbean Sea and the unialgal culture Trichodesmum sp. NIBB 1067 and natural populations of T. erythraeum but were distinctly different in sequence form T. theirbautii. The data indicate that Trichodesmuim sp. NIBB 1067 is more closely related to T. erythraeum tham to T. thiebautii. [ABSTRACT FROM AUTHOR]

Trichodesmium thiebautii Gomont, a marine planktonic diazotrophic cycanobacaterium, has an unusual sub-cellular arrangement. To identify subcellular structures related to photosynthesis, antibodies against phycoerythrin, phycocyanin, and ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) were used together with an immunogold labeling technique and electron microscopy. Thylakoid membranes, identified by transmission electron microscopy and phycobiliprotein labeling, arranged as a loose network throughout all cells. Rubisco showed a particularly intense localization in medium electron-dense polyhedral bodies, therefore identified as carboxysomes. The average density of the carboxysomal Rubisco label was about five times higher than that in the cytoplasm. The carboxysomes (4-11 per cell section) were scattered throughout the cytoplasm. These data, together with those obtained from double immunolabeling experiments using nitrogenase (Fe-protein) and Rubisce antibodies,revealed that Trichodesmium contains both N [sub2[sub-]] and Co[sub2[sub-]] fixing proteins within the same cell. This is in contrast to the previous concept of a spatial segregation of the two processes in Trichodesmium and demonstrate that nitrogenase containing cells are not comparable to heterocysts in this context. [ABSTRACT FROM AUTHOR]

Nitrogenase reductase (Fe-protein) was detected in the marine planktonic cyanobacterium Trichodemium. The molecular weight was about 38kD, as shown by western blotting using anti-Rhodospirillum rubrum nitrogenase reductase antiserum. The enzyme was confined to a limited number (ca. 10-40%) of randomly distributed trichomes in the Trichodesmium colonies, as shown by immunogold localization and transmission electron microscopy. Associated microorganisms had little or no nitrogenase. Nitrogenase showed a diel cycle in localization: present throughout the cytoplasm of cells in N[SUB2]-fixing (daytime) colonies but at the periphery of non-N[SUB2]-fixing (nighttime) colonies. This structural arrangement of N[SUB2]-fixing trichomes and nitrogenase is novel and different from the previously held paradigm for this and other diazotrophic cyanobacteria. [ABSTRACT FROM AUTHOR]

Examines the utility of several biogeochemical tracers for following the fate of the planktonic diazotrophic cyanobacterium Trichodesmium in the sea. Culture of the cyanobacterium; Major hydrocarbon identified; Relative distribution of fatty acids as their methyl esters in field collected colonies of Trichodesmium and unialgal culture.

Trichodesmium Ehrenberg species were collected in the Caribbean Sea, Sargasso Sea, and coastal areas of Tanzania (Indian Ocean). The specimens were divided into five species on the basis of morphometric characters such as cell dimensions and colony formation: T. tenue Wille, T. erythraeum Ehrenberg, T. thiebautii Gomont, T. hildebrandtii Gomont, and T. contortum Wille. In addition, Trichodesmium sp., a spherical colony of uncertain taxonomic position was examined. The cell structure of each species was investigated by means of light, scanning electron, and transmission electron microscopy. Particular attention was paid to the presence and ultrastructural arrangement of gas vacuoles and glycogen fiber clusters (GFCs). This resulted in identification of two major groups of species: 1) T. tenue, Trichodesmium sp. with spherical-shaped colonies, and T. erythraeum with GFCs and more or less localized gas vacuoles; and 2) T. thiebautii, T. hildebrandtii, and T. contortum lacking GFCs and with gas vacuoles spread at random. The specie, within each grop were further characterized with respect to the dimesion of the gas veside, cylindrical bodies, scroll bodies, and a new cellular inlusion body. Differnces in colony formation and cell dimesions correlated with specific ultraatructural character in five of the six forms. This is the first ultrstrucrural study comparing different forms of Trichodesmium sampled at grographically remote areas and shows that one species appears identical rrgarless of the sampling site. Some of the species had lint been investigated earlier, and probably more species are to be identified and analyzed. [ABSTRACT FROM AUTHOR]

Estimates of the iron use efficiency (IUE) for diazotrophic plant growth have been used to suggest iron limitation of marine N2 fixation. However, in the course of these inferences, neither the physiological complexity of these estimates nor the specific physiological parameters of marine diazotrophs were evaluated. Here, a semiempirical prediction of the IUE of diazotrophic growth for Trichodesmium was computed from considerations of the Fe content and reaction rates of the nitrogenase complex and PSI:PSII ratios, as well as field measurements of Mehler activity, cellular Fe-superoxide dismutase activity, and diel variability in C and N2 fixation. With a PSI:PSII ratio of 1 and 48% Mehler activity, the instantaneous IUE (0.33 mol C fixed·mol cellular Fe- 1 ·s- 1 ) was only 4-fold lower than that calculated for a phytoplankter growing on reduced N. We computed a range of daily integrated IUE values from 2900 to 7700 mol C·mol Fe- 1 ·d- 1 , accounting for the diel variability in C and N2 fixation as well as the uncertainties in cyanobacterial nitrogenase biochemistry and PSI:II ratios of field-collected Trichodesmium. The lowest observed Fe-superoxide dismutase:C quota of 2.9 (μmol:mol) suggests a maintenance requirement for this enzyme. The maintenance Fe:C requirement of 13.5 μmol:mol (derived from cultures of Trichodesmium IMS 101) and values of the IUE yielded an Fe requirement ranging from 27 to 48 Fe:C (μmol:mol) to achieve a diazotrophic growth rate of 0.1 d- 1 . Based on these predicted requirements, the Fe:C contents of Caribbean Sea and most North Atlantic Ocean populations sampled thus far exceed that required to support the observed rates of N2 fixation. [ABSTRACT FROM AUTHOR]

Abstract: We analyzed flavodoxin gene sequences and transcription patterns in the marine nitrogen-fixing cyanobacterium Trichodesmium Ehrenberg ex Gomont 1892. While a typical cyanobacterial flavodoxin ortholog (fld1) was identified from cultured (strain IMS101) and environmental Trichodesmium by PCR and Southern blot hybridization, a second flavodoxin (fld2) was identified in the genome sequence. BLAST and phylogenetic analyses indicated that the two fld genes were highly divergent: fld1 was most closely related to fld common in cyanobacteria, wheras fld2 formed a distinct cluster with a fld so far only found in the unicellular diazotrophic cyanobacteria Cyanothece and Crocosphaera (in which fld2 was the only fld). The fld2 cluster was more closely allied with a fld in non-cyanobacterial diazotrophs such as Azotobacter and Azoarcus than fld1 in other cyanobacteria. This result suggests different evolutionary history of these two genes. Real-Time RT–PCR analysis on iron-replete and iron-deplete Trichodesmium cultures revealed remarkable diel dynamics in transcription of both flds but surprisingly failed to show induction under iron stress. Addition of nitrate to these cultures depressed nifH and fld2 transcription while elevating the transcription of fld1 in iron-stressed cultures. A positive correlation between fld and nifH transcript abundances was found, which was stronger in the case of fld2 than fld1. Our data suggest that these two flavodoxins in Trichodesmium may be functionally diversified and that use of flavodoxin as an iron stress indicator needs to be validated for each organism with consideration of diel dynamics of gene expression. [Copyright &y& Elsevier]

Presents a study which described a model to calculate nitrogen fixation rate for remote estimates of Trichodesmium biomass. Modeling approach; Model parameterization and sensitivity; Application of the model in the South Atlantic Bight.

Presents a study which developed a multispectral classification scheme to detect the cyanobacteria Trichodesmium spp. in satellite data from the sea-viewing wide field-of-view sensor. Sources of the spectral characteristics used to establish the criteria for the classification scheme; Results; Discussion.