W.C.Dule el1 Methods42(2007)358-376 OH gae w the volume of the holobiont [44]that can be accommo in( Ocri ubaend and syechoc inp to the rial symo ya by fime important microalgal-inverte opnyta)of demn 1(3) Dinoflagellate endosymbionts of the genusS (often referred to as zooxanthellae)are common in corals some mollusks (especially the giant P sunlight to provide their hosts with photoautotrophic met- HO丫 5.Biomedicinally significant phytochemicals from marine symbioses lymgbyabellin A (24)and B (25 abunda gA tha led to the the Nobel and vered as nat 1mctaS0. is noteworthy that commercial production of Ara-A was d he ajusculamide C(27刀 sal or endosymbiotic microorganisms.Among the>18.000 marine natural prod ucts(MNPs)d bed to date,recent 4.Phytobionts of invertebrate symbioses dates are in trials for anti-cancer treatment(68%)with the tuni commensal microorganisms that include heterotrophic cer treatment target a broad spectrum of molecular S N MeO O O O O S N OH OH O Cl Cl dollabellin (22) H N O O N O O N O H N O N N S symplostatin 1 (23) O N O S HN O HN S N HO O O Cl Cl O H O N O S HN O HN S N HO O O Cl Cl O lyngbyabellin A (24) and B (25) O O O O OH O Br OH O OMe OH aplysiatoxin (26) MeO NH NH NH O O O O O O N N NH N NH O O O O O H3C majusculamide C (27) 4. Phytobionts of invertebrate symbioses Marine invertebrates, including sponges, cnidarians and tunicates, often harbor dense and diverse populations of commensal microorganisms that include heterotrophic and chemoautotrophic bacteria, cyanobacteria, fungi, and eukaryotic algae within host tissues where they reside as extra- and intra-cellular symbionts. In some sponges, microbial symbionts may constitute more than 40% of the volume of the holobiont [44] that can be accommo￾dated within specialist bacteriocyte host cells [45]. Single￾cell and filamentous cyanobacterial symbionts, belonging to the genera Aphanocapsa, Synochocystis, Phormidium (Oscillatoria), Anabaena and Synechococcus, inhabit the light-exposed pinacoderm (ectosome) of sponges, whereas cyanobacteria found in the mesohyl interior (endosome) are likely concentrated from surrounding seawater by filter feeding. Other important groupings of microalgal-inverte￾brate symbioses include the obligate Prochloron cyano￾phytes (Prochlorophyta) of didemnid ascidians (tunicates) and the dinoflagellate-anthozoan symbioses of corals. Dinoflagellate endosymbionts of the genus Symbiodinium (often referred to as zooxanthellae) are common in corals, anemones, jellyfish, some mollusks (especially the giant Tridacna clams) and foraminifera. These remarkable phy￾tobionts drive the formation of coral reefs by capturing sunlight to provide their hosts with photoautotrophic met￾abolic energy while enhancing skeletal-carbonate deposi￾tion by photosynthetic uptake of CO2 [46]. 5. Biomedicinally significant phytochemicals from marine symbioses Marine invertebrates are an abundant source of struc￾turally unique secondary metabolites having proven thera￾peutic potential, of which a small number are advancing through clinical trials [7,8]. The earliest example was the discovery of arabinose-containing spongouridine (28) and spongothymidine (29) from the Caribbean sponge Cryptot￾heca (Tethya) crypta [47–49]. These natural products served as a template for the synthesis of the nucleoside antiviral drug Ara-A (Vidarabine) (30) that led to the development of acyclovir (Zovirax) (31), which is active against the her￾pes virus, and the anti-AIDS drug azidothymidine (AZT) (32) for which Hitchens and Elion were jointly awarded the Nobel Prize in 1988 [8]. Interestingly, Ara-A and spongouridine were later discovered as natural metabolites of the Mediterranean gorgonian Euniicella cavolinin [50]. It is noteworthy that commercial production of Ara-A was obtained by fermentation of Streptomyces griseus [51], pro￾viding an early hint that bioactive natural products of mar￾ine invertebrates could be of microbial origin (albeit bacterial in this case) accumulated from dietary, commen￾sal or endosymbiotic microorganisms. Among the >18,000 marine natural products (MNPs) described to date, recent reviews give 22 MNPs, or chemically derived analogues, to be in clinical trials [7,52]. The majority of these drug candi￾dates are in trials for anti-cancer treatment (68%) with the remainder in therapeutic areas of inflammation, pain, and asthma, and one candidate for treatment of Alzheimer’s disease. Marine-derived agents under examination for can￾cer treatment target a broad spectrum of molecular W.C. Dunlap et al. / Methods 42 (2007) 358–376 363