In prokaryotes, only a few examples of differential gene expression in cell populations have been described. Colicin production in natural populations of Escherichia coli , while providing a competitive advantage in the natural habitat, also leads to lysis of the toxin-producing cell. Colicin K synthesis has been found to be induced due to an increase in ppGpp (I. Kuhar, J. P. van Putten, D. Žgur-Bertok, W. Gaastra, and B. J. Jordi, Mol. Microbiol. 41: 207-216). Using two transcriptional fusions, cka-gfp and cki-gfp , we show that at the single-cell level, the colicin K activity gene cka is expressed in only 3% of the bacterial population upon induction by nutrient starvation. In contrast, the immunity gene cki is expressed in the large majority of the cells. Expression of the cka-gfp fusion in a lexA -defective strain and in a relA spoT mutant strain indicates that differential expression of cka is established primarily at the level of transcription.

In caves microorganisms inhabit distinct habitats where they develop various interactions. As an evidence of microbial activ­ity several features can be identified. Microorganisms are in­volved bothin lithogenic and litholitic processes. Besides het­erotrophs in caves autotrophic organisms can be also expected. Some cyanobacteria and microalgae in caves can survive even at photon flux densities lower than their photosynthetic compen­sation point. In the paper up-to-date identified groups of mi­croorganisms (bacteria, cyanobacteria, microalgae, fungi and protozoa) withtheir localities in Slovenian caves are presented. Especially bacteria from caves, as the most diverse group, of­fer immense biotechnological and bioremediation potential. In caves microbial biomass can be considered a considerable food source for cave-dwelling higher organisms. Caves in Slovenia offer great chances to discover new species, as was fungus Mu­cor troglophilus discovered in association withthe cave cricket Troglophilus neglectus.

Water suppliers should provide safe drinking water following preventive measures. This is especially important for karst water sources, as they are among the most vulnerable. Recently, there has been a strong focus on the early warning system, which mainly involves monitoring proxy parameters, but does not consider drainage area conditions and other monitoring recommendations. Here, we present an innovative strategy for assessing contamination risk of karst water sources that covers spatio-temporal dimensions and can be integrated into management practices. It is based on event-based monitoring and risk mapping and has been tested in a well-known study area. The holistic early warning system provides accurate spatial hazard and risk assessment and operational monitoring guidelines, including locations, indicator parameters, and temporal resolution and duration. In the study area, the high contamination risk, representing 0.5 % of the area, was spatially delineated. The highest probability of source contamination occurs during recharge events when proxy parameters such as bacteria, ATP, Cl, and Ca/Mg ratio should be monitored in addition to continuous monitoring of turbidity, EC, and T. Monitoring of sinking streams should serve as a preventive measure, since water transfer from ponors to springs has been shown to take about one day, and poor quality water is present for at least another day. Therefore, intensive monitoring should be conducted at intervals of a few hours for at least a week. Although hydrologic systems vary, the proposed strategy is particularly useful in systems where water flows rapidly and where remediation is not feasible.