6:15 PM - 7:30 PM
[MIS26-P04] Aerobic methane production by planktonic microbes under nitrogen and phosphorus starved conditions in a lake
We performed the batch-culture experiments to identify the effects of cell starvation on the rate of aerobic methane production under nitrogen and phosphorus limited conditions. Planktonic microbes collected from well-oxygenated water of Lake Saiko (Yamanashi Prefecture) were incubated with a growth medium (BG-11) for several months and used for the starvation experiment to make their cells N-starved or P-starved conditions by removing either element from the BG-11 medium. Then, we added MPn and/or inorganic nitrogen (N_) and inorganic phosphorus (P_) to confirm the response of N-starved or P-starved microbes to such experimental additions.
The results showed that although the cell nutritional conditions did not affect the production of CH4, nutrient balance of lake water (N excess or P excess) greatly influenced the aerobic methane production. First, we confirmed aerobic CH4 production in the MPn addition treatment, suggesting the active C-P lyase catalysis that converts MPn to methane and inorganic phosphate. Moreover, we found that MPn + N_ addition accelerated the aerobic CH4 production. This is due probably to the fact that N_ addition promoted the biosynthesis of C-P lyase and/or made lake water more P-limited condition (increase of N/P ratio); both may contribute to increasing the MPn utilization by microbes. However, MPn + P_ addition did not increase the CH4 production, indicating the opportunistic utilization of MPn alternative to P_ under phosphorus limited conditions. The present results suggest that the input of excess N into lake ecosystems promotes the metabolism of MPn by planktonic microorganisms, which leads to increase of aerobic methane production in phosphorus-limited oligotrophic lakes.