Similar bacterial growth on dissolved organic matter in anoxic and oxic lake water

Anoxic metabolism yields less energy per unit substrate utilized than oxic respiration. In addition, substrate availability is believed to be reduced under anoxic conditions since oxygenases cannot be used. Consequently, it is generally assumed that bacteria grow slower in anoxic environments than in oxic environments. The results of the present study challenge this view. We compared the growth of bacterial assemblages under carbon-limited conditions in lake water under anoxic and oxic conditions. Bioassay experiments were performed with water from 3 lakes differing in nutrient concentrations and organic matter content. Among bacteria using the same source of organic matter, median anoxic growth rates were 84 to 110% of oxic growth rates. The total biomass yield during the experiments did not differ between anoxic and oxic treatments. We suggest that anoxic bacterial growth was regulated by substrate availability rather than by metabolic energy yield and that availability of organic matter under anoxic conditions was equal to or even greater than that in oxic treatments. This implies that anoxic decomposition rates may actually have been faster than oxic rates.