Flavobacterium johnsoniae as a Model Organism for Characterizing Biopolymer Utilization in Oligotrophic Freshwater Environments

Abstract

ABSTRACTBiopolymers are important substrates for heterotrophic bacteria in oligotrophic freshwater environments, but information on bacterial growth kinetics with biopolymers is scarce. The objective of this study was to characterize bacterial biopolymer utilization in these environments by assessing the growth kinetics ofFlavobacterium johnsoniaestrain A3, which is specialized in utilizing biopolymers at μg liter−1levels. Growth of strain A3 with amylopectin, xyloglucan, gelatin, maltose, or fructose at 0 to 200 μg C liter−1in tap water followed Monod or Teissier kinetics, whereas growth with laminarin followed Teissier kinetics. Classification of the specific affinity of strain A3 for the tested substrates resulted in the following affinity order: laminarin (7.9 × 10−2liter·μg−1of C·h−1) ≫ maltose > amylopectin ≈ gelatin ≈ xyloglucan > fructose (0.69 × 10−2liter·μg−1of C·h−1). No specific affinity could be determined for proline, but it appeared to be high. Extracellular degradation controlled growth with amylopectin, xyloglucan, or gelatin but not with laminarin, which could explain the higher affinity for laminarin. The main degradation products were oligosaccharides or oligopeptides, because only some individual monosaccharides and amino acids promoted growth. A higher yield and a lower ATP cell−1level was achieved at ≤10 μg C liter−1than at >10 μg C liter−1with every substrate except gelatin. The high specific affinities of strain A3 for different biopolymers confirm that some representatives of the classesCytophagia-Flavobacteriaare highly adapted to growth with these compounds at μg liter−1levels and support the hypothesis thatCytophagia-Flavobacteriaplay an important role in biopolymer degradation in (ultra)oligotrophic freshwater environments.