Cryptic growth within a binary microbial culture

The ability of viable cells of the species Pseudomonas putida and Hyphomicrobium sp. to metabolize the particulate and soluble cellular organic constituents of both species was studied in a series of batch experiments. Both P. putida and Hyphomicrobium sp. were grown in individual batch reactors on either the ¹⁴C-labelled soluble or the particulate debris of sonicated cells of each species derived from steady-state chemostat cultures. Cell generation times (t_g)observed for P. putida cultivated on soluble organic material originating from either sonicated P. putida or Hyphomicrobium sp. cells, were t_g= 2.0 h and t_g= 6.3 h, respectively. Corresponding t_gvalues of Hyphomicrobium sp. on soluble organic material originating from sonicated P. putida and Hyphomicrobium so. were, respectively, 11.6 h and 4.3 h. While particulate debris originating from either species was solubilized by both P. putida and Hyphomicrobium sp., no increases in cell numbers were observed for either species. The data indicate that bacteria are capable of scavenging soluble material released upon cell lysis at near maximal rates; solubilization of debris also occurred but at much slower overall rates with no observable cell replication. The results reaffirm that cryptic growth and turnover of cellular biomass can be significant under situations of low substrate flux or starvation conditions.