One, no one and one hundred thousand Planktothrix species: is lateral gene transfer a neglected source of genetic diversity

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Intemational Conference

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GENOMICS ANO GENETIC OIVERSITY OF HABS

ONE, NO ONE ANO ONE HUNOREO THOUSANO

PLANKTOTHR/XSPECIES:

IS LATERAL GENE TRANSFER

A NEGLECTED

SOURCE OF GENETIC DIVERSITY?

Domenico D'Alelio, Andrea Gandolfi, Nico Salmaso

/ASMA Research and /nnovation Centre, Fondazione Edmund Mach, Environment and Natura/ Resources Area, Via

E.

Mach l, /-38010 S. Miche/e e/Adiqe (Trento), Italy. E-mail: domenico.dalelio@iasma.it

The systematics of the genus P/anktothrix (cyanobaeteria) basically relies on phenotypic and ecological traits. In faet, atlempts towards the definition of species by means of morphological, genetic and biochemical analyses are scanty and have been carried out using few sympatric strains which probably under-represent the adual diversity. On the other hand, the idea that the whole genus could be meno-specific is stili supported. We isolated about 300 strains of P/anktothrixfrom eight lakes in Northern Italy and analyzed their morphology and genetics (i.e. for rpoC1 and rbcLX coding-genes). The rpoC1 gene was highly polymorphic, with about 30 single nucleotide poly-morphisms, resulting in an overall diversity of -6%; differences in rbcLX were less abundant. The strains clustered into two main geno-type-groups: one was associated to the "species"

P.

rubescens, whose red-water blooms are reported in rneso/olqotrophic lakes; the other included sequences recombinant between P. rubescens and P. agardhii, the latter bemq a green-water bloom "species" reported In eutrophic lakes. Furtherrnore, even sequences published on GenBank by previous authors and referring to strans putatively identifled as either P. rubescens or P. agardhli'clustered in the "recombinant clade". Our study, stili in progress, points out the faet that recornbination, orobably as lateral gene transfer, could potentially limit the forrnation of stable species within the genus P/anktothrix; a potente cense-quence of this phenomenon might be that different scientists could atlain distind ideas of a single biological entity, dependnq on the nature of each observer's observation (i.e. a sort of "Pirandellian syndrome").

179

COMPREHENSIVE TRANSCRIPTOME

AN AL

YSIS OF

ALEXAN-OR/UM TAMARENSEREVEALS INDEPENDENT ORIGIN OF

SAXI-TOXIN SYNTHESIS IN CYANOBACTERIAAND DINOFLAGELLATES

Jeremiah D. Hackettl, Jennifer H. Wisecaverl, Dave M. Kulis-, Donald M. Anderson", Debashish Bhattacharva", F. Gerald Plumley4, Deana l. Erdner?

Oepartment of Ec%gy and Evo/utionary Bidoqy, University of Arizona, P.

o.

Box 210088, Tucson, AZ 85721, USA. E-mail: hackettj@email.arizona.edu.

Biology Oepartment Woods Ho/e Oceanographic /nstitution, Woods Ho/e, MA 02543, USA

. Oepartment of Ec%gy, Evo/ution, and Natura/ Resources, /nstitute of Marine and Coasta/ Sciences, Rutgers

Untversity,

New Brunswick, NJ 0890 l, USA

- Bermuda /nstitute of Ocean Sciences, St. George 's GEO l, Bermuda

=Oepartment of Marine Science, University of Texes, 750 Channe/ View Dr., Port Aransas, TX 78373, USA

.Ve assembled a comprehensive transcriptome dataset for the saxitoxin-produdng dinoflagellate Alexandriumfamarensecombinlng over 10 giganases d expressed sequence tag, 454 and Illumina pyrosequencing data. The resulting assembly comprises 112,383 contigs with an average coverage of l00X. :"om vvhich 56,578 proteins were predicted. We also generated 454

transcrpìore

data for three additional toxic dinoflagellates: A. famarenseSPE 10-03.

=Yrodiniumbahamense,and Gymnafiniumcatenatum.Searching these data,

we

identified 274 potential homologs of 14 cyanobacterial saxitoXlngenes 1CIuding ali of the genes directiy invofved in toxin synthesis. We used these candidate proteins in phylogenetic analyses to determine thelr evolu1Jonal,/ '1lstOry.Four dinoflagellate candidate proteins group cbsey

with

cyanobacterial saxitoxin genes in phylogenetic analyses and are like~ the homologs of sxiA, sxt8 and sxtG in dinoflagellates, SxtA is split into

two

proteins in the dinoflagellates with sxtA 1 corresponding to the N-terminai portion with methyltransferase

ard

acyl carrier protein domains and sxtA2 corresponding to the C-terminai portion

with

the aminotransferase domain. Phylogenetic analyses of sxtA, sxtB 3J1dsxtG homologs suggest that they were acquired independentiy in cyanobacteria and dinoflagellates from similar bacterial sources. The A. famarense :ranscriptome does not contai n phylogenetically related homologs for the remaining saxitoxin genes. Hooever,

we

identifìed candidate functional homologs for ali of the remaining saxitoxin synthesis genes that were acquired from a variety of sources. These results indicate that the saxitoxin synthesis pathways