Cell growth and production of recombinant proteins in stationary phase cultures of Escherichia coli recover concomitantly with spontaneous lysis of a fraction of the ageing cell population. Further exploration of this event has indicated that sonic cell disruption stimulates both cell growth and synthesis of plasmid-encoded recombinant proteins, even in exponentially growing cultures. These observations indicate an efficient cell utilisation of released intracellular material and also that this capability is not restricted to extreme nutrient-starving conditions. In addition, the efficient re-conversion of waste cell material can be viewed as a potential strategy for an extreme exploitation of carbon sources and cell metabolites in production processes of both recombinant and non-recombinant microbial products.

The transition from the exponential to the stationary phase of Escherichia coli cultures has been investigated regarding nutrient availability. This analysis strongly suggests that the declining of the cell division rate is not caused by mere nutrient limitation but also by an immediate sensing of cell concentration. In addition, both the growth rate and the final biomass achieved by a batch culture can be manipulated by altering its density during the early exponential phase. This result, which has been confirmed by using different experimental approaches, supports the hypothesis that the E. coli quorum sensing is not only determined by the release of soluble cell-to-cell communicators. Cell-associated sensing elements might also be involved in modulating the bacterial growth even in the presence of non-limiting (although declining) nutrient concentrations, thus promoting their economical utilisation in dense populations.

Peat moss is gradually being replaced by other materials as a growing medium in forest nurseries due to economic and ecological constraints. In this study, six different mixtures were tested, mixing peat moss (P) and pine bark (B) with digested sewage sludge (S) activated sewage sludge (A) and paper mill sludge (M), as growing media for Pinus halepensis seedlings; three different waste doses were applied. Seed germination percentage, seedling growth and foliar nutrient content after 1 year in a greenhouse and percentage survival after transplanting were recorded. The influence of base substrate (P or B) on germination percentage changed in different ways according the type of waste. The order of the different applied mixtures by suitability (germination rate and seedling growth) from best to worst was as follows: activated sludge with peat, activated sludge with pine bark, sewage sludge with peat, sewage sludge with pine bark, paper mill sludge with pine bark and finally paper mill sludge with peat.

The effect of ammonium as a medium supplement on plasmid-encoded recombinant beta-galactosidase synthesis was explored in Escherichia coli cells during aerobic growth in complex medium. After induction, only doses of ammonium chloride below 1 g/L are able to transiently enhance the yield. However, the presence of nontoxic ammonium chloride concentrations of up to 10 g/L results in lower values of beta-galactosidase in a concentration-dependent fashion. A significant reduction in plasmid DNA content explains the decrease in the yield by a gene-dosage-involving mechanism.

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