Coccolithophores are a major group of phytoplankton and play a significant role in the carbon cycle, as their calcareous exoskeletons comprise half the carbonate in deep-sea sediments. The bloom species Emiliania huxleyi is globally distributed with multiple strains isolated from around the world. A model for coccolithophore biology, it has been the object of numerous morphological, physiological, and transcriptomic studies, and it is now the first coccolithophore to have its genome sequenced. The reference genome provides an opportunity for us to address an outstanding issue of E. huxleyi biology: its remarkable morphological, physiological, and genomic variation between isolates. Variability suggests that E. huxleyi may have a ?pan-genome?, where different strains of a single species possess a heterogeneous gene complement. We use the JGI Annotation Pipeline and the JGI EST Pipeline to exploit the reference genome in combination with transcriptomic data from two other strains and discover potentially strain-specific genes. Such genes provide evidence of inter-strain heterogeneity, though they do not fully characterize the E. huxleyi pan-genome.

We report the draft genome sequences of Bacillus glennii V44-8, Bacillus saganii V47-23a, and Bacillus sp. strain V59.32b, isolated from the Viking spacecraft assembly cleanroom, and Bacillus sp. strain MER_TA_151 and Paenibacillus sp. strain MER_111, isolated from the Mars Exploration Rover (MER) assembly cleanroom.

Coccolithophores have influenced the global climate for over 200million years1. These marine phytoplankton can account for 20 percent of total carbon fixation in some systems2. They form bloomsthat can occupy hundreds of thousands of square kilometres andare distinguished by their elegantly sculpted calcium carbonate exoskeletons(coccoliths), rendering themvisible fromspace3.Althoughcoccolithophores export carbon in the form of organic matter andcalcite to the sea floor, they also release CO2 in the calcificationprocess. Hence, they have a complex influence on the carbon cycle,driving either CO2 production or uptake, sequestration and exportto the deep ocean4. Here we report the first haptophyte referencegenome, from the coccolithophore Emiliania huxleyi strainCCMP1516, and sequences from 13 additional isolates. Our analysesreveal a pan genome (core genes plus genes distributed variablybetween strains) probably supported by an atypical complementof repetitive sequence in the genome. Comparisons across strainsdemonstrate thatE. huxleyi, which has long been considered a singlespecies, harbours extensive genome variability reflected in differentmetabolic repertoires. Genome variability within this speciescomplex seems to underpin its capacity both to thrive in habitatsranging from the equator to the subarctic and to form large-scaleepisodic blooms under a wide variety of environmental conditions.