The genome of the choanoflagellate Monosiga brevicollis and the origin of metazoans.

Choanoflagellates are the closest known relatives of metazoans. To discover potential molecular mechanisms underlying the evolution of metazoan multicellularity, we sequenced and analysed the genome of the unicellular choanoflagellate Monosiga brevicollis. The genome contains approximately 9,200 intron-rich genes, including a number that encode cell adhesion and signalling protein domains that are otherwise restricted to metazoans. Here we show that the physical linkages among protein domains often differ between M. brevicollis and metazoans, suggesting that abundant domain shuffling followed the separation of the choanoflagellate and metazoan lineages. The completion of the M. brevicollis genome allows us to reconstruct with increasing resolution the genomic changes that accompanied the origin of metazoans.

Algoriphagus machipongonensis sp. nov., co-isolated with a colonial choanoflagellate.

A Gram-negative, non-motile, non-spore-forming bacterial strain, PR1(T), was isolated from a mud core sample containing colonial choanoflagellates near Hog Island, Virginia, USA. Strain PR1(T) grew optimally at 30 °C and with 3 % (w/v) NaCl. Strain PR1(T) contained MK-7 as the major menaquinone as well as carotenoids but lacked pigments of the flexirubin-type. The predominant fatty acids were iso-C(15 : 0) (29.4 %), iso-C(17 : 1)ω9c (18.5 %) and summed feature 3 (C(16 : 1)ω6c and/or C(16 : 1)ω7c; 11.3 %). The major polar lipids detected in strain PR1(T) were phosphatidylethanolamine, an unknown phospholipid, an aminophospholipid, an aminolipid and two lipids of unknown character. The DNA G+C content was 38.7 mol%. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain PR1(T) fell within the cluster comprising the genus Algoriphagus and was most closely related to Algoriphagus halophilus JC 2051(T) (95.4 % sequence similarity) and Algoriphagus lutimaris S1-3(T) (95.3 % sequence similarity). The 16S rRNA gene sequence similarity between strain PR1(T) and the type strains of other species of the genus Algoriphagus were in the range 91-95 %. Differential phenotypic properties and phylogenetic and genetic distinctiveness of strain PR1(T) demonstrated that this strain was distinct from other members of the genus Algoriphagus, including its closest relative, A. halophilus. Based on phenotypic, chemotaxonomic, phylogenetic and genomic data, strain PR1(T) should be placed in the genus Algoriphagus as a representative of a novel species, for which the name Algoriphagus machipongonensis sp. nov. is proposed. The type strain is PR1(T) (= ATCC BAA-2233(T) = DSM 24695(T)).

A bacterial sulfonolipid triggers multicellular development in the closest living relatives of animals.

Bacterially-produced small molecules exert profound influences on animal health, morphogenesis, and evolution through poorly understood mechanisms. In one of the closest living relatives of animals, the choanoflagellate Salpingoeca rosetta, we find that rosette colony development is induced by the prey bacterium Algoriphagus machipongonensis and its close relatives in the Bacteroidetes phylum. Here we show that a rosette inducing factor (RIF-1) produced by A. machipongonensis belongs to the small class of sulfonolipids, obscure relatives of the better known sphingolipids that play important roles in signal transmission in plants, animals, and fungi. RIF-1 has extraordinary potency (femtomolar, or 10(-15) M) and S. rosetta can respond to it over a broad dynamic range-nine orders of magnitude. This study provides a prototypical example of bacterial sulfonolipids triggering eukaryotic morphogenesis and suggests molecular mechanisms through which bacteria may have contributed to the evolution of animals.DOI:http://dx.doi.org/10.7554/eLife.00013.001.