Within the endemic invertebrate faunas of hydrothermal vents, five biogeographic provinces are recognized. Invertebrates at two Indian Ocean vent fields (Kairei and Edmond) belong to a sixth province, despite ecological settings and invertebrate-bacterial symbioses similar to those of both western Pacific and Atlantic vents. Most organisms found at these Indian Ocean vent fields have evolutionary affinities with western Pacific vent faunas, but a shrimp that ecologically dominates Indian Ocean vents closely resembles its Mid-Atlantic counterpart. These findings contribute to a global assessment of the biogeography of chemosynthetic faunas and indicate that the Indian Ocean vent community follows asymmetric assembly rules biased toward Pacific evolutionary alliances.

Presented here is the complete genome sequence of Thiomicrospira crunogena XCL-2, representative of ubiquitous chemolithoautotrophic sulfur-oxidizing bacteria isolated from deep-sea hydrothermal vents. This gammaproteobacterium has a single chromosome (2,427,734 base pairs), and its genome illustrates many of the adaptations that have enabled it to thrive at vents globally. It has 14 methyl-accepting chemotaxis protein genes, including four that may assist in positioning it in the redoxcline. A relative abundance of coding sequences (CDSs) encoding regulatory proteins likely control the expression of genes encoding carboxysomes, multiple dissolved inorganic nitrogen and phosphate transporters, as well as a phosphonate operon, which provide this species with a variety of options for acquiring these substrates from the environment. Thiom. crunogena XCL-2 is unusual among obligate sulfur-oxidizing bacteria in relying on the Sox system for the oxidation of reduced sulfur compounds. The genome has characteristics consistent with an obligately chemolithoautotrophic lifestyle, including few transporters predicted to have organic allocrits, and Calvin-Benson-Bassham cycle CDSs scattered throughout the genome.

We applied two experiments useful in the study of ligandregulated DNA binding proteins to AraC, the dimeric regulator of the Escherichia coli L-arabinose operon. In the absence of arabinose, AraC prefers to loop DNA by binding to two half-sites that are separated by 210 base pairs, and in the presence of arabinose it prefers to bind to adjacently located half-sites. The basis for this ligand-regulated shift in binding appears to result from a shift in the rigidity of the system, where rigidity both in AraC protein in the absence of arabinose, and in the DNA are required to generate the free energy differences that produce the binding preferences. Eliminating the dimerization domains and connecting the two DNA binding domains of AraC by a flexible peptide linker should provide a protein whose behavior mimics that of AraC when there is no interaction between its dimerization and DNA binding domains. The resulting protein bound to adjacent half-sites on the DNA, like AraC protein in the presence of arabinose. When the two double-stranded DNA half-sites were connected by 24 bases of single-stranded, flexible DNA, wild-type AraC protein bound to the DNA in the presence and absence of arabinose with equal affinity, showing that AraC modulates its DNA binding affinity in response to arabinose by shifting the relative positions of its DNA binding domains. These results are consistent with the light switch mechanism for the action of AraC, refine the model, and extend the range of experimental tests to which it has been subjected.

Recent evidence suggests that deep-sea vestimentiferan tube worms acquire their endosymbiotic bacteria from the environment each generation; thus, free-living symbionts should exist. Here, free-living tube worm symbiont phylotypes were detected in vent seawater and in biofilms at multiple deep-sea vent habitats by PCR amplification, DNA sequence analysis, and fluorescence in situ hybridization. These findings support environmental transmission as a means of symbiont acquisition for deep-sea tube worms.

In an effort to better understand the factors influencing carbon fixation by Prochlorococcus, and to elucidate the effects of these cyanobacteria on the ocean carbon cycle, the kinetic parameters and isotopic discrimination of form IA ribulose 1,5-bisphosphate carboxylase/oxygenase (RubisCO) from Prochlorococcus marinus MIT 9313 were determined. The RubisCO genes (cbbL and cbbS) were cloned and expressed in Escherichia coli. Enzyme was purified via ammonium sulfate precipitation, and the optimum pH and temperature, as well as Michaelis-Menton constants, were determined radiometrically. The degree to which this RubisCO discriminates against 13 CO 2 during fixation was determined by the high-precision substrate depletion method. Purified enzyme had a pH optimum of 7.5, was most active between 20uC and 30uC, had a moderate V max (0.41 mmol min 21 mg protein 21 ), and had the highest K CO2 value (0.75 mmol L 21 ) for a form I RubisCO characterized to date. The e value, e 5 1,000[(k 12 /k 13 ) 2 1], for the enzyme was determined to be 24.0% (95% C.I. 5 22.2-25.6%), within the range observed for other form I RubisCOs. This e value is a critical baseline for interpreting the d 13 C values of marine environmental samples, particularly those collected from the open ocean, where P. marinus is responsible for a substantial fraction of carbon fixation.