Laysan Water Chemistry

Temperature and salinity in Lake Laysan varied little around 23ºC and 80 ppt, respectively (See Fig. A). Chlorophyll a concentrations did not exceed 1 mg/L (See Fig. B). Hydrogen sulfide concentrations were low throughout the water column, and decreased with depth (See Fig. B). DON comprised much of the ~550 mM total nitrogen pool (See Fig. C), while NO₃^- and NH₄⁺ concentrations were each only fractions of total N (See Fig. D). Total phosphorus increased from 8 to ~12 mM between 0.3 and 7.5 m, mirroring increases in SNP with depth; SRP varied little around 3 mM through the water column (See Fig. E). SRSi concentrations varied 5-fold between 0.3 and 4 m (See Fig. F).

Laysan water chemistry figure

Forty-two pure bacterial cultures derived from Lake Laysan. On the basis of 16S rRNA homologies these cultures affiliated with 27 taxonomically distinct strains in 13 families or unclassified taxa in the a-, g-, and e-Proteobacteria, Firmicutes, Bacteroidetes, and the Chlorobiaceae (Table 1). Cultures from the g-Proteobacteria belonged in the Vibrionaceae, Alteromonadaceae, Halomonadaceae, and the Xanthomonas group. Representatives of four a-Proteobacteria families were cultivated, three of which were not represented in clone libraries from the same sample.

Eight bacteria cultivated from Laysan shared <97% 16S rRNA sequence identity with bacteria in the public domain. Five of the eight are a-Proteobacteria. Two cultures belong in the Bacteroidetes; the closest neighbors of one of these cultures is Psychroflexus torquis, an obligate psychrophile from Antarctic sea-ice. Phenotypic data including fatty acid and substrate assimilation support placement of this strain as a new, mesophilic species in the genus Psychroflexus (Donachie et al, in press). The only e-Proteobacterium cultivated from Laysan shares <96% 16S rRNA identity with an Arcobacter sp., its nearest cultivated neighbor based on 16S rDNA sequence identity. All strains considered potentially novel in terms of 16S rRNA identities have been characterized on the basis of whole cell fatty acid profiles, substrate utilization, and other phenotypic properties. These data support our contention that they are new species and in some cases new genera.