Significance of bacteria in urea dynamics in coastal surface waters

Abstract

Bacterial urea production and decomposition were studied in samples fromcoastal waters in the Southern California Bight (the Bight), USA, and anestuarine system of the Mankyung and Dongjin rivers (MD estuary) in Korea.Bacterial urea production ranged from undetectable to 139 nM d-1, and themean value of bacterial urea production (58 nM d-1, n = 6) was equivalentto 35-91% of the estimated phytoplankton N demand in the Bight. The rates ofbacterial production of urea were 2 orders of magnitude higher than thebacterial urea decomposition rates. Consequently, bacteria were consistentlynet producers of urea in the euphotic zone. The concentration-dependence ofurea decomposition showed the presence of a high affinity but low capacitysystem (K(l)+S(n): 26 to 33 nM, V(max): 3 to 11 nM d-1). The low K(m)values indicate that in typical seawater samples, which have >100 nM urea,the bacterial ureolysis system is always near-saturated. The significance ofbacteria as urea producers should be incorporated into models of nitrogenregeneration in surface waters.