Dissolved organic nitrogen hydrolysis rates in axenic cultures of Aureococcus anophagefferens (Pelagophyceae): comparison with heterotrophic bacteria

Abstract

The marine autotroph Aureococcus anophagefferens (Pelagophyceae) was rendered axenic in order to investigate hydrolysis rates of peptides, chitobiose, acetamide, and urea as indicators of the ability to support growth on dissolved organic nitrogen. Specific rates of hydrolysis varied between 8 and 700% of rates observed in associated heterotrophic marine bacteria.

FIG. 1.

Phylogenetic tree based on 1,617 nucleotide positions showing relationships of 7BT, 13BT, and 4BT to representative bacterial 16S rRNA genes. The tree was inferred from nearly-complete sequences by the neighbor-joining method. The numbers of bootstrap replicates that supported the branching order, from a total of 100 replicates, are shown above the internal segments. Values below 50% are not shown. Gene sequences from the SAR cluster were used as the outgroup. The scale bar shows numbers of substitutions per nucleotide position. CFB, Cytophaga-Flexibacter-Bacteroides.

FIG. 2.

Mean nitrogen hydrolysis rates (n = 3) and 95% confidence intervals. Urea and acetamide hydrolysis was measured on crude cell extracts of bacteria and CCMP 1982. Aminopeptide and chitobiose hydrolysis was measured in whole-cell suspensions, with the exception of hydrolysis of chitobiose by CCMP 1982, which was measured in crude cell extracts.