Growth patterns of giant deep sea Beggiatoaceae from a Guaymas Basin vent site

We studied the growth of giant filamentous sulfur oxidizing bacteria of the family Beggiatoaceae collected from a hydrothermal seep area in the Guaymas Basin. We measured the incorporation of 14C-bicarbonate tracer into individual filaments using a microimager that allows quantitative determination of the distribution of radioisotopes with 20 µm resolution. Filaments incorporated label along their entire length; thus growth occurred uniformly throughout these whole filaments and not only at their tips. Uptake of 14C-bicarbonate was strongly stimulated by reducing the pH from 8.2, the value near the sediment surface, to 7.05, as found within 1–2 mm below the surface; the presence of oxygen or sulfide had no effect. Thus, Beggiatoaceae strongly prefer assimilation of CO2 over other DIC species. In consequence, migration of these motile filaments into deeper sediments, where sharply decreasing pH increases the availability of CO2, will favor cell growth. Genomic evidence was found for periplasmic carbonic anhydrases, indicative of the carbon concentration mechanism.