Tag Archives: algae

The trees have it…

Image: Stefan Laube/Wikimedia Commons.

Image: Stefan Laube/Wikimedia Commons.

Trees, those magnificent, organic, large – sometimes huge – woody constructions continue to fascinate and inspire all who stop, stand and stare up (and up, and up…) at them. So here’s a selection of tree-based items to maintain – or maybe even initiate? – the phenomenon of arborifascination. But first a question: why did the three-toed sloth come down from the trees?

Answer: to defecate! Sloths are considered to be amongst the most, well, er, slothful of animals that, anecdotally, spend most of their time in trees, doing ‘not a lot’, apart from eating tree leaves [they are arboreal herbivores, after all; Tree Use No. (TUN) 1]. However, not only is this descent to the ground energy-consuming, it also exposes the sloth to potential predators; so why would they risk it? Work by Jonathan Pauli et al. may have the answer to this otherwise inexplicable behaviour. Three-toed sloths* harbour moths, inorganic nitrogen (N) and algae (e.g. green algae Trichophilus spp.) within their fur. The lipid-rich algae are eaten by the sloths and presumably supplement their diet of leaves. By leaving the tree for defecation, the fur-residing moths are transported to their oviposition (egg-laying) sites in sloth dung, which subsequently facilitates further moth colonisation of sloth fur. Since those moths are ‘portals for nutrients’, levels of inorganic N (potentially from moth excreta) in sloth fur increase, which in turn fuels algal growth. As the researchers conclude, ‘these linked mutualisms between moths, sloths and algae appear to aid the sloth in overcoming a highly constrained lifestyle’. Wow! I will never look at a three-toed sloth in quite the same way again.

Also challenging perceived wisdom is work by Marc Ancrenaz et al. Traditionally, orangutans (the world’s largest arboreal mammal) are assumed to be obligate arborealists, swinging seemingly effortlessly from tree to tree (TUN 2) as they navigate their lofty aerial neighbourhood. However, observations of terrestrial activity by these primates in the wild begs the question, why? Hitherto this activity was considered to be a response to habitat disturbance, but Ancrenaz et al. found no difference in instances of this behaviour in disturbed versus non-disturbed areas. They therefore propose that terrestrial locomotion is part of the Bornean orangutan’s natural behavioural repertoire and may increase their ability to cope with at least smaller-scale forest fragmentation, and to cross moderately open spaces in mosaic landscapes. So, it seems that even orangutans can have a bit too much of the ‘high life’ at times.

Finally, a terrestrial–aquatic organism that’s going up in the world. Reviewing evidence of tree-climbing activity in extant crocodilians (crocodiles and alligators), Vladimir Dinets et al. suggest it is much more widespread than previously considered and ‘might have multiple functions’, e.g. as an alternative site for thermoregulation (TUN 4), or increased detectability of prey (TUN 5). So, there you have it, ‘tons’ of alternative tree uses! Trees, helping to make the world an even more amazing place.

 

* Two-toed sloths don’t go in for this more energetic activity – and have lower densities of moths, lower N levels and reduced algal biomass in their fur…

Half measures don’t work when restoring marine forests

Would you recognise a desert if it was covered in water? What I mean by that is if somewhere that should be covered in forest were barren and empty, would you notice? A paper in PLOS One outlines why it matters.

Seaweeds (macroalgae) are the “trees” of the oceans, providing habitat structure, food and shelter for other marine organisms…

Kelp forest

Forest-like kelp at San Diego aquarium. Photo Swandieve/sxc.hu

It’s easy to overlook the importance of marine plants if you’re not a scuba diver. From the shore one patch of sea looks much the same as another. Obviously if you’re underwater then things look different. Towards Restoration of Missing Underwater Forests by Campbell et al. is a paper looking at the missing forests of Phyllospora comosa, a brown algae that should be found of the coast of Sydney.

The seaweed disappeared with increasing pollution from the city but, despite an increase in water quality, the forests have not returned. Why?

Campbell and her team transplanted Phyllospora into sites at Long Bay and Cape Banks near Sydney. They observed the algae to see how they survived. They also watched plants at the donor sites for comparison. The results were mixed.

They did well at Long Bay. Better than well, in fact. They were reproducing better than the control sites, which suggests that the only reason there weren’t Phyllospora at Long Bay is that there weren’t any. That’s tautological, but obviously in nature you get new Phyllospora from older Phyllospora. A colonisation effort in Long Bay would get the re-establishment of the seaweed started.

Things did not go so well at Cape Banks. Here Phyllospora did much worse than at Long Bay or the original populations. What this did see were that the transplanted algae were short and had a lot of bite marks from fish. What they suggest here is that the reason there isn’t Phyllospora on site is because there isn’t enough. Small colonies are suitable for snacking, but because they’re so small all the plants get damaged. A larger area might be so large that not all the plants suffer and that leaves enough for reproduction of the next generation.

They also found the new plants were concentrated in, or at the edge of the adult population. That suggests that the lone colonist plant will not flourish by itself, what matters isn’t just the plant but the whole community.

What I particularly liked about this paper is that there’s a classic example of scientists being scientists in it.

The disappearance of Phyllospora from reefs in Sydney coincided with a peak in high volume, near-shore sewage outfall discharges along the metropolitan coastline during the 1970s and 1980s (Coleman et al. 2008). Although causation has not been formally established, embryos of this species are particularly susceptible to pollutants commonly found in sewage, to the extent that they are used as a test species in standard ecotoxicological assessments.


They’re susceptible to pollutants. There were pollutants in the area, but that’s a correlation, not a proven causation. A causal link between pollution and the demise of the algae would be extremely convenient for anyone wanting to argue now is the time to restore the forests, and it’s not a ridiculous leap to make, but they still point out that it’s still not fully proven.

Correlation does not mean causation.

Image by Randall Munroe CC BY-NC.

What the paper shows is an example of discontinuity in ecosystems. The results show that it’s not simply a question of degree of forestation, but that you either have enough Phyllospora to make a viable forest system or you don’t. The amount you need might vary from place to place, but spending half the money isn’t going to give you half the result.

It’s also something that requires close examination. For plants that you don’t see from the shore, it’s easy not miss them when they’re gone. There are knock-on effects in how the loss of habitat affects other organisms. but that might appear a long way from the site where the root problem is.

Images

The Kelp Forest at an aquarium in San Diego. Photo © Swandieve/sxc.hu
Correlation. Image by Randall Munroe. This image licensed under a Creative Commons by-nc licence.

Mutualistic ants contribute to bromeliad nutrition

Mutualistic ants contribute to tank-bromeliad nutrition

Mutualistic ants contribute to tank-bromeliad nutrition

Epiphytes are keystone species in tropical rainforests because they provide food and/or habitat resources to different organisms not found elsewhere and because they play a major role in the nutrient cycles in canopy ecosystems. However, epiphytism imposes physiological constraints resulting from the lack of access to the nutrient sources available to ground-rooted plants. Hence, many epiphytes are characterized by morphological and functional adaptations – such as litter-trapping leaf arrangements (i.e. Asplenium ‘trash-baskets’); rainwater retention (e.g. tank-forming bromeliads); absorbent leaf trichomes (i.e. Tillandsia spp. bromeliads); velamen radicum in aerial roots (i.e. Orchidaceae); and slippery, waxy walls (e.g. insectivorous pitfall plants such as Brocchinia reducta and Catopsis berteroniana) – that facilitate access to nutrient acquisition. In addition, many epiphytes are involved in complex associations with animals, particularly ants, that provide them with nutritional benefits. You might expect that multiple associations with animals would result in higher nutrient acquisition compared with those with fewer interactions either through direct (i.e. animal mediated) or indirect (i.e. plant-trait mediated) interactions. This question is highly relevant to broadening our understanding of the mechanisms that foster biological diversity in the species-rich Tropics where plant–animal interactions are common.

Plants of the family Bromeliaceae, possessing both CAM and C3 photosynthetic pathways, dominate the vascular flora in Neotropical forests and most of them (i.e. all of the members of the Bromelioideae and Tillandsioideae subfamilies) absorb water and nutrients through specialized leaf trichomes. Their mechanical roots are used to maintain the plant’s position and do not play a significant role in plant nutrition. A conspicuous adaptation to improve nutrient acquisition by bromeliads is the phytotelm (‘plant-held water’). Bromeliad leaves are often tightly interlocking and form rosettes, creating tanks that collect rainwater and debris. These tanks provide a habitat for specialized aquatic organisms. Most major taxa are involved, including bacteria, algae, prokaryotes, protists, micro- and macro-invertebrates, and vertebrates. The detritus that enter the tank (mostly leaf litter) constitutes the main source of nutrients for the aquatic food web. Invertebrates reduce the incoming litter to fragments. Nitrogen and other nutrients are then made available to the plant through the bacterial decomposition of the small detritus and faecal pellets of aquatic metazoans. In sun-exposed areas, algae can grow in the phytotelm. They may then represent a higher trophic resource than leaf litter while constituting an important food source for filter-feeding invertebrates, algae may also compete with the plant for nitrogen. Other direct interactions with the terrestrial or amphibious animals inhabiting bromeliads may also constitute an important source of nutrients for tank-forming bromeliads. For example, bromeliad-associated spiders and treefrogs release faeces that are washed into the plant’s pools and collect at the leaf bases where they provide a source of nutrients for aquatic decomposers and for the bromeliad itself. In summary, tank-bromeliads can be considered ‘assisted saprophytes’. Mutualistic ants influence the vegetative traits of their associated bromeliads by determining the distribution of seedlings along gradients of incident light, thereby affecting the taxonomic composition and complexity of the aquatic food web contained in the phytotelmata, and, subsequently, the nitrogen flux to the plant’s leaves.

A new paper in Annals of Botany studies eight tank- and one tankless-bromeliad species and finds that leaf nitrogen concentrations are positively correlated with the presence of mutualistic ants, with the scale of the benefit depending on the identity of the associated ant species. A protocarnivorous tank-bromeliad not associated with mutualistic ants appears to obtain nitrogen from ant carcasses, but the results suggest that it is more advantageous for a bromeliad to obtain ant-derived nutrients (e.g. faeces, insect remains) via its roots than to use carnivory via its tank.

This study suggests that the contribution of phytotelm communities to bromeliad nutrition is more complex than previously thought. It also highlights a gap in our knowledge of the reciprocal interactions between bromeliads and the various trophic levels (from bacteria to large metazoan predators) that intervene in reservoir-assisted nutrition.

 

Is pink your favourite colour? How about gold?

Flamingos Partying by Pedro Szekely How do you like your salmon – nice and pink, or do you prefer a whiter shade of pale? And when you go to the zoo, do you like your flamingoes off-white or a nice rosy shade? If you prefer pink, you should know that farmed salmon and captive flamingoes only go that colour when the diets they are fed are supplemented with astaxanthin, a red ketocarotenoid pigment. More recently, astaxanthin has started to be used for human consumption because of antioxidant, anti-ageing, anti-inflammatory and immune-stimulating properties.

At present, the global demand for this pigment is satisfied mainly by synthetic astaxanthin produced by chemical companies. The global market for astaxanthin is worth more than US$200 million per year. The estimated production cost of synthetic astaxanthin is approximately US$1000 per kilo, and the market price is approximately US$2000 a kilo. That makes astaxanthin nearly as expensive as gold. So if you could get algae to grow gold for you on the cheap, would you do it?

Haematococcus pluvialis is a unicellular green alga able to accumulate large amounts of astaxanthin (4 % dry weight) under stress conditions. The life cycle of H. pluvialis is complex and involves at least four types of cells. Under stress conditions, astaxanthin biosynthesis is accompanied by morphological changes of the motile vegetative (green) cells into non-motile cysts (red), which represent a resting stage with a heavy resistant cellulose cell wall. Astaxanthin is accumulated in the cytoplasm of cyst cells, providing protection against photo-inhibition and oxidative stress. Although H. pluvialis is one of the richest sources of astaxanthin, its massive culture for commercial purposes has been little exploited because of its slow growth rate and complex life cycle.

A recent paper in AoB PLANTS sets out to standardize and apply a genetic improvement programme to H. pluvialis in order to improve its carotenogenic capacity and to evaluate the performance of a selected strain in large commercial-sized open ponds. Improved astaxanthin productivity of the selected strain was maintained even when grown on a large scale and holds promise as the basis for viable commercial production of this valuable biochemical by natural means.

 

From genetic improvement to commercial-scale mass culture of a Chilean strain of the green microalga Haematococcus pluvialis with enhanced productivity of the red ketocarotenoid astaxanthin. (2013) AoB PLANTS 5: plt026 doi: 10.1093/aobpla/plt026
Astaxanthin is a red ketocarotenoid, widely used as a natural red colourant in marine fish aquaculture and poultry and, recently, as an antioxidant supplement for humans and animals. The green microalga Haematococcus pluvialis is one of the richest natural sources of this pigment. However, its slow growth rate and complex life cycle make mass culture difficult for commercial purposes. The aims of this research were (i) to standardize and apply a genetic improvement programme to a Chilean strain of H. pluvialis in order to improve its carotenogenic capacity and (ii) to evaluate the performance of a selected mutant strain in commercial-sized (125 000 L) open ponds in the north of Chile. Haematococcus pluvialis strain 114 was mutated by ethyl methanesulfonate. The level of mutagen dose (exposure time and concentration) was one that induced at least 90% mortality. Surviving colonies were screened for resistance to the carotenoid biosynthesis inhibitor diphenylamine (25 µM). Resistant mutants were grown in a 30-mL volume for 30 days, after which the total carotenoid content was determined by spectrophotometry. Tens of mutants with improved carotenogenic capacity compared with the wild-type strain were isolated by the application of these standardized protocols. Some mutants exhibited curious morphological features such as spontaneous release of astaxanthin and loss of flagella. One of the mutants was grown outdoors in commercial-sized open ponds of 125 000 L in the north of Chile. Grown under similar conditions, the mutant strain accumulated 30% more astaxanthin than the wild-type strain on a per dry weight basis and 72% more on a per culture volume basis. We show that random mutagenesis/selection is an effective strategy for genetically improving strains of H. pluvialis and that improved carotenogenic capacity is maintained when the volume of the cultures is scaled up to a commercial size.

 

Algae found under teenager’s bed…

Image: Wikimedia Commons.

Image: Wikimedia Commons.

Shock, horror! But no surprises there you might think. After all, teenagers’ bedrooms are notorious ‘no-go’ areas for their parents – and others of a sensitive nature – and anything can develop (even new life forms!) in the insalubrious environment contained therein. But this is no ordinary tale of teenage grot. Rather, it is a carefully planned experiment carried out by 17-year old Sara Volz who was trying ‘to use guided evolution, so artificial selection, to isolate populations of algae cells with abnormally high oil content’.

Entitled ‘Optimizing algae biofuels: artificial selection to improve lipid synthesis’, her investigation used the herbicide sethoxydim to kill algae with low levels of acetyl-CoA carboxylase (ACCase), an enzyme crucial to lipid synthesis. Under this strong environmental pressure, the remaining artificially selected algae cells revealed significant increases in lipid accumulation. If those cells can be sustained, artificial selection could be used to increase microalgal oil yields and make algae biofuel viable. Well, her inquisitiveness within an imaginative laboratory setting(!) earned Sara (representing Cheyenne Mountain High School, Colorado Springs, USA) top prize in the Intel Science Talent Search (Intel STS), ‘the nation’s [i.e. USA’s] most prestigious science research competition for high school seniors’. The US$100 000 scholarship should go a long way to funding her studies at Massachusetts Institute of Technology (USA) where she is destined this autumn. As will what remains of the US$50 000 Davidsons Fellowship Scholarship Sara won in 2012 for a project entitled, ‘Enhancing algae biofuels: investigation of the environmental and enzymatic factors effecting algal lipid synthesis’. More usually employed as a post-emergence herbicide to control grass weeds in broad-leaved crops, sethoxydim apparently also has ‘indoor uses’. However, one imagines that the good people at Cornell didn’t envisage such an indoor use!

[Now, I don’t want to be picky, but to subject these claims to proper scrutiny, etc, we do need to know what the algae were. So, I did my own research, and eventually managed to find that Sara has ‘worked with several different strains – the ones I use currently are Chlorella vulgaris and Nannochloropsis salina…‘. But that information seems to predate the 2013 Intel STS project. So, we’re still uncertain of the species. Nevertheless, this young scientist is definitely one to watch! And not just because she was listed as one of the top 10 teen inventors in the USA by Popular Science magazine as far back as September 2011 – Ed.].

 

Because they’re not red(!)

Image: Franz Eugen Köhler, Köhler’s Medizinal-Pflanzen. Gera-Untermhaus, 1897.

Image: Franz Eugen Köhler, Köhler’s Medizinal-Pflanzen. Gera-Untermhaus, 1897.

Although this may appear to be a smart-arse answer to the question ‘Why are plants green?’, it’s probably not too wide of the mark. Many interested parties have wrestled with the question and several suggestions have been made as to why most plants – by which commentators tend to mean the principal photosynthetic parts, the leaves – are predominantly green in colour. Most of these dwell on the preponderance of green-coloured chlorophylls (yes, plural – a and b) in land plants. See MinuteEarth’s charming video about this here, or ResearchGate’s academically-contributed thread on the issue here, or the undergraduate-student-targeted item by Mark McGinley (an Associate Professor in the Honors College and Department of Biological Sciences at Texas Tech University in Lubbock, USA) here. However, it seems that the ‘real’ answer rests with the evolutionary heritage of the land flora, as deduced by Jonas Collén et al. and their announcement of the sequencing of the genome of Chondrus crispus, a red alga/seaweed commonly called Irish moss.

Although red algae contain green chlorophyll, their red coloration is a result of large amounts of non-green pigments such as phycoerythrin. During the inferred course of its evolution, C. crispus lost many genes (its compact genome of 9606 genes compares with the unicellular green alga Chlamydomonas reinhardtii with 14 516 genes, and Arabidopsis thaliana’s 27 416). And this genetic reductionism would have had evolutionary knock-on effects. In particular, the loss of flagellar genes, needed for the motility of certain cells – especially the gametes during sexual reproduction in so-called ‘lower’ land plants  – may have been enough to have given ‘rival’ flagellate green algae the evolutionary ‘leg-up’ needed to allow them to claim the land as their own, and ultimately to beget the land flora. Or, as the paper’s press release puts it: ‘Had this massive gene loss never occurred, red algae might have extensively colonized the terrestrial environment, in the same way as green algae, which are the ancestors of all land plants’. And that’s why plants are green/aren’t red. ‘Just so!’, an exceedingly well-informed Mr Kipling is reported to have said.

Algal cell walls and their diversity: a PhD position

The green alga Penium under white light (top) and labelled with monoclonal antibody

The green alga Penium under white light (top) and labelled with a monoclonal antibody

Zoë Popper, an Annals of Botany Editor, has a funded  PhD position to characterise algal cell walls and make cell wall-directed monoclonal antibodies, using biochemical analysis and immunocytochemistry. The project will also generate and investigate cell wall mutants of the putative model charophycean green alga, Penium margaritaceum.

As Zoe and co-authors* wrote in their review earlier this year, Penium margaritceum (a charophycean green alga) is rapidly emerging as a model organism, and several characteristics make it a particularly appropriate tool for investigating all cell-wall biochemistry. It is a unicellular organism in the CGA, and it produces only a primary cell wall. Additionally, it has a cell-wall polymer constituency similar to land plants. It also is amenable to live-cell labeling with monoclonal antibodies and carbohydrate-binding modules for developmental studies. Finally, there is relative ease in its experimental manipulation, and genomic libraries will be available soon. A polysaccharide-rich cell wall is a shared feature of plants and algae, and is involved in their growth, cell-cell interactions, and defence responses. Additionally, many wall components have a commercial value. Therefore, better understanding of wall structure, composition and biosynthesis may facilitate their exploitation.

*Co-authors are Gurvan Michel, Cecilé Hervé, David Domozych, William Willats, Maria Tuohy, Bernard Kloareg and Dagmar Stengel

Relevant publications include: Popper ZA et al. 2011. Annual Review of Plant Biology 62:doi: 10.1146/annurev-arplant-042110-103809

and Domozych DS et al. 2011. Journal of Botany doi:10.1155/2011/632165, Pathathil S, et al. 2010. Plant Physiol. 153: 514–525, Popper ZA and Tuohy MG, 2010. Plant Physiol. 153: 373–383, Sørensen I et al. 2010. Plant Physiol. 153: 366–372, Popper ZA. 2008. Current Opinion in Plant Biology 11: 286–292.

Working at National University of Ireland, Galway, Zoe is seeking an enthusiastic and highly motivated student for a 4-year, SFI-funded (Research Frontiers Programme), PhD project. The project is in collaboration with Professor David Domozych (Skidmore College, USA, http://www.skidmore.edu/academics/biology/plant_bio/d_domo.html) Professor Michael Hahn (Complex Carbohydrate Research Center, USA, http://www.ccrc.uga.edu/) and Professor Jocelyn Rose (Cornell University, USA, http://www.plantbio.cornell.edu/) and will include 2 (4-month) research placements in collaborator laboratories. The student will be based full-time at NUI Galway and will be registered for the new School of Natural Sciences structured PhD programme.

Project skill set: The student will be trained in polysaccharide extraction, fractionation and biochemical characterisation, chromatography, immunocytochemistry, histology, microscopy (light, fluorescence, confocal), mutagenisation, ELISA. The student will also have opportunity to learn electron tomography at Skidmore College.

Qualifications: The project is suited to applicants who have an interest in plant biochemistry and evolution and a background in plant science/biology, botany, biochemistry, molecular biology, genetics, or chemistry but other cognate disciplines may be considered. Applicants should possess a minimum of a B.Sc. Honours degree graded at 2.1, or higher. Proficiency in English language (both written and spoken), an aptitude for critical inquiry and problem solving, are essential.

For further information, informal enquiries, and applications please e-mail: zoe.popper@nuigalway.ie