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.


AJ Cann. ORCID 0000-0002-9014-3720

Alan Cann is a Senior Lecturer in the School of Biological Sciences at the University of Leicester and Internet Consulting Editor for AoB.