Molecular phylogeny of P rochlorococcus ecotYPes

Prochlorococczs is the dominant phototroph in the temperate oceans. It is found throughout the euphotic zonq at light intensities panning over four ;;";r ;i#gnitude. Thii growth range is larger than observed for any single culture of Piochlorororrui and is likely due to the co-existence of multiple ecotypes adapted for optimal grow_t! at different light intensities. Here we 6# tt" teS rDNA sequences of fou-r Proc-hlorococcus isolates from the paiific Ocean, MIT9201; MIT1202, MITg2ll and MIT9215, which have L""n pt ysiologically characterized as high or low B/A ecotypes b-ased on iniii int'Ut"rritios and light-dependent growth responses.-Ttt.l!1.9low B/A isolates are 6losely relatei and iluster together with other low B/A isolates in u pie"i""rfy ideniineO "high-light adapted" c.lade. The fourth Pacific isolate, " ti!f, gle "cotype, is not-a m"Imb"r oi this clade. Sequences specific to each ohviiolosical tvpe will be useful in probing field populations to determine the ipatiat uid te*po.ul distribution of the ecotypes of Prochlorococcus.