The importance of mass transfer relative to the intrinsic microbial activity was examined in a laboratory system using Mycobacterium sp. LB501T and poorly soluble anthracene as sole carbon source. M. sp. LB501T was grown on various amounts of solid anthracene in batch cultures, and microbial biomass formation was compared to independently determined dissolution fluxes. Provision of only a few anthracene crystals (< or = 2 g L(-1)) resulted in pseudolinear growth due to low dissolution fluxes, whereas exponential growth was only obtained when high amounts of solid anthracene (30 g L(-1)) were provided. The influence of substrate bioavailability on microbial growth was predicted successfully by a dynamic, flux-based approach (Best-Equation), which combines substrate dissolution from crystals into solution, substrate uptake by microorganisms from solution, and concurrent biomass formation.

Exposure of Escherichia coli MG1655 to environmental bacteriophages results in rapid selection for phage-tolerant subpopulations displaying increased biofilm formation. Analysis of one phage-tolerant strain revealed large amounts of the DNA-binding Dps protein in the outer membrane protein and production of fimbria-like structures. In dps and fimA mutant derivatives of MG1655, no selection of phage-tolerant bacteria upon exposure to bacteriophages occurred, suggesting a role for Dps and type I pili in bacteriophage tolerance.

The effects of exposure of Pseudomonas putida KT2442 to 2-chlorophenol as a model for the chemical stress response were examined by two-dimensional polyacrylamide gel electrophoresis. Individual protein concentrations were determined at 45, 65, and 95 min following the addition of 2-chlorophenol at a concentration of 1.63 mM to exponentially growing cultures of P. putida KT2442 by silver staining the separated proteins. The changes in the protein concentrations could be classified into four categories, namely those which increased continuously during exposure, those which decreased in concentration, those which showed a concentration peak at some point following exposure, and those which were essentially unaffected. Thirty proteins with isoelectric points between pH 4 and 6 increased in concentration, 27 decreased, and 90 had a concentration maximum or minimum between 45 and 95 min. Of those proteins with isoelectric points between 5.5 and 10, 68 increased in concentration, 39 decreased in concentration, and 47 showed a concentration peak in the middle of the sampling period. Thus, in the evaluation of the stress response, a functional description requires an understanding both of proteins which are required at higher concentrations and of those whose presence appears to be no longer essential.

Differences in expression of the Escherichia colistress protein HtpG were found following exposure of exponentially growing cells to heat or chemical shock when cells were grown under different environmental conditions. With anhtpG::lacZ reporter system, htpGexpression increased in cells grown in a complex medium (Luria-Bertani [LB] broth) following a temperature shock at 45°C. In contrast, no HtpG overexpression was detected in cells grown in a glucose minimal medium, despite a decrease in the growth rate. Similarly, in pyruvate-grown cells there was no heat shock induction of HtpG expression, eliminating the possibility that repression of HtpG in glucose-grown E. coli was due to catabolite repression. When 5 mM phenol was used as a chemical stress agent for cells growing in LB broth, expression of HtpG increased. However, when LB-grown cells were subjected to stress with 10 mM phenol and when both 5 and 10 mM phenol were added to glucose-grown cultures, repression ofhtpG expression was observed. 2-Chlorophenol stress resulted in overexpression of HtpG when cells were grown in complex medium but repression of HtpG synthesis when cells were grown in glucose. No induction of htpG expression was seen with 2,4-dichlorophenol in cells grown with either complex medium or glucose. The results suggest that, when a large pool of amino acids and proteins is available, as in complex medium, a much stronger stress response is observed. In contrast, when cells are grown in a simple glucose mineral medium, htpG expression either is unaffected or is even repressed by imposition of a stress condition. The results demonstrate the importance of considering differences in growth environment in order to better understand the nature of the response to an imposed stress condition.