Metabolic differences between attached and free-living marine bacteria: inadequacy of liquid cultures for describing in situ bacterial activity

Marinobacter sp. strain CAB was cultivated with or without porous glass bea ds as solid support. Two substrates were used: the hydrophilic sodium lacta te and a hydrophobic C-18-isoprenoid ketone (6,10, 14-trimethylpentadecan-2 -one (TMP)). The substrate adsorption onto the beads was measured. Bacteria l adhesion was determined by a direct count technique and amounted to 70% o f total cells. In the immobilised cell cultures (ICC), generation times wer e 1.5 and 1.8 times shorter than in the planktonic cultures (FCC) with sodi um lactate and with TMP, respectively. In ICC, the growth yields were lower (15.3(FCC) X 10(9) and 0.8(ICC) X 10(9) bacteria mg(-1) of sodium lactate; 50(FCC) X 10(9) and 35(ICC) X 10(9) bacteria mg(-1) of TMP). The mineralis ation of substrates was estimated after mass spectrometric determination of the CO2 production rates of both free and immobilised cell cultures. The r esults indicated a higher specific CO2 production rate in the ICC with sodi um lactate (3.1(FCC) +/- 0.2 and 3.5(ICC) +/- 0.3 nmol CO2 mg(-1) protein m in(-1)) but not in the ICC with TMP (1.9(FCC) +/- 0.7 and 0.5(ICC) +/- 0.3 nmol CO2 mg(-1) protein min(-1)). The affinities for the two substrates wer e lower in the presence of the solid support (K-m,K-ICC = 18.2 +/- 0.2 muM and 37.1 +/- 2.0 muM, for sodium lactate and TMP, respectively) than withou t support (K-m,K-FCC = 8.5 +/- 1.5 muM and 8.4 +/- 1.2 muM, for sodium lact ate and TMP, respectively). Moreover, the presence of a solid support showe d a lower inhibition by the TMP (K-i,K-FCC = 3.8 +/- 1.0 muM and K-i,K-ICC = 12.2 +/- 2.5 muM) which may explain why the immobilised cell cultures deg raded hydrophobic TMP more efficiently than the planktonic cultures. (C) 20 01 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.