Evolution of alkaline phosphatase in marine species of Vibrio

Biodiversity of vibrios

Vibrios are ubiquitous and abundant in the aquatic environment. A high abundance of vibrios is also detected in tissues and/or organs of various marine algae and animals, e.g., abalones, bivalves, corals, fish, shrimp, sponges, squid, and zooplankton. Vibrios harbour a wealth of diverse genomes as revealed by different genomic techniques including amplified fragment length polymorphism, multilocus sequence typing, repetetive extragenic palindrome PCR, ribotyping, and whole-genome sequencing. The 74 species of this group are distributed among four different families, i.e., Enterovibrionaceae, Photobacteriaceae, Salinivibrionaceae, and Vibrionaceae. Two new genera, i.e., Enterovibrio norvegicus and Grimontia hollisae, and 20 novel species, i.e., Enterovibrio coralii, Photobacterium eurosenbergii, V. brasiliensis, V. chagasii, V. coralliillyticus, V. crassostreae, V. fortis, V. gallicus, V. hepatarius, V. hispanicus, V. kanaloaei, V. neonatus, V. neptunius, V. pomeroyi, V. pacinii, V. rotiferianus, V. superstes, V. tasmaniensis, V. ezurae, and V. xuii, have been described in the last few years. Comparative genome analyses have already revealed a variety of genomic events, including mutations, chromosomal rearrangements, loss of genes by decay or deletion, and gene acquisitions through duplication or horizontal transfer (e.g., in the acquisition of bacteriophages, pathogenicity islands, and super-integrons), that are probably important driving forces in the evolution and speciation of vibrios. Whole-genome sequencing and comparative genomics through the application of, e.g., microarrays will facilitate the investigation of the gene repertoire at the species level. Based on such new genomic information, the taxonomy and the species concept for vibrios will be reviewed in the next years.

Heat-labile bacterial alkaline phosphatase from a marine Vibrio sp

Psychrophilic organisms have successfully adapted to various low-temperature environments such as cold ocean waters. Catalysts with increased catalytic efficiencies are produced, generally at the expense of thermal stability due to fewer non-covalent stabilizing interactions. A marine bacterial strain producing a particularly heat-labile alkaline phosphatase was selected from a total of 232 strains isolated from North-Atlantic coastal waters. From partial 16S rRNA sequences the strain was characterized as a Vibrio sp. An alkaline phosphatase was purified 151-fold with 54% yield from the culture medium using a single step affinity chromatography procedure on agarose-linked L-histidyldiazobenzylphosphonic acid. The active enzyme was a 55 +/- 6 kDa monomer. The enzyme had optimal activity at pH 10 and was strikingly heat-labile with a half-life of 6 min at 40 degrees C and 30 min at 32 degrees C. This enzyme from Vibrio sp. had a higher turnover number (k(cat)) and higher apparent Michaelis-Menten factor (K(m)) than the enzyme from Escherichia coli, a clear-indication of cold-adaptation. Inorganic phosphate was a competitive inhibitor with a relatively high K(i) value of 1.7 mM. Low affinity for phosphate may contribute to higher turnover rates due to more facile release of product.

Tryptophan biosynthesis in the marine luminous bacterium Vibrio harveyi

Tryptophan biosynthetic enzyme levels in wild-type Vibrio harveyi and a number of tryptophan auxotrophs of this species were coordinately regulated over a 100-fold range of specific activities. The tryptophan analog indoleacrylic acid evoked substantial derepression of the enzymes in wild-type cells. Even higher enzyme levels were attained in auxotrophs starved for tryptophan, regardless of the location of the block in the pathway. A derepressed mutant selected by resistance to 5-fluorotryptophan was found to have elevated basal levels of trp gene expression; these basal levels were increased only two- to threefold by tryptophan limitation. The taxonomic implications of these and other biochemical results support previous suggestions that the marine luminous bacteria are more closely related to enteric bacteria than to other gram-negative taxa.