Cultivation of microorganisms in micro-volumes of culture media

Studies on the cultivation of aerobic microorganisms in microdrops of growth medium, immobilized in a layer of highly dispersed disconnector (Aerosil), were carried out. The dispersion of the growth medium and its immobilization in a layer of Aerosil was found to produce no influence on the morphological, cultural and biochemical properties of Serratia marcescens cells, determined both immediately after treatment with the field and some time after storage of the treated suspensions. On the contrary, the duration of the action of ferromagnetic bodies produced essential influence on the viability of the microorganisms in dispersed growth medium and on the accumulation of cells in the course of subsequent cultivation. The development of cells grown in the microdrops of the nutriuent medium was similar to that of cells grown in submerged cultivation, following the S-shaped curve. With the increase of the seed dose a drop in the initial growth rate occurred and the accumulation of microbial cells increased by the end of the process. The greatest increase of biomass was observed with minimal seed doses. With a rise in the concentration of amino nitrogen in the growth medium the yield of cells increased only till this concentration reached 320 mg%. Under these conditions the specific growth rate also increased. The accumulation of cells was greater and occurred earlier when microorganisms were cultivated in immobilized state in powder.     

A note on yeast growth in media used for the cultivation of lactobacilli

Yeast species found in mayonnaise-based salads are capable of growth in media used for the isolation of lactobacilli. Many counts of lactobacilli from such products may, therefore, inadvertently include counts of yeasts. A method is presented whereby the use of media with and without chloramphenicol makes it possible to deduce a differential count of bacteria. It was not possible to prevent yeast growth in de Man, Rogosa and Sharpe agar by the addition of cycloheximide since many isolates were resistant to it.     

Continuous cultivation of microorganisms

This review presents selected studies on continuous cultivation including the genetics and selection of microorganisms, production of biomass, liquid fuels and other products, published in 1982-1984 and bearing a relationship to biotechnology.     

High-cell-density cultivation of microorganisms

High-cell-density cultivation (HCDC) is required to improve microbial biomass and product formation substantially. An overview of HCDC is given for microorganisms including bacteria, archae and eukarya (yeasts). Problems encountered by HCDC and their possible solutions are discussed. Improvements of strains, different types of bioreactors and cultivation strategies for successful HCDC are described. Stirred-tank reactors with and without cell retention, a dialysis-membrane reactor, a gas-lift reactor and a membrane cyclone reactor used for HCDC are outlined. Recently modified traditional feeding strategies and new ones are included, in particular those for unlimited growth to very dense cultures. Emphasis is placed on robust fermentation control because of the growing industrial interest in this field. Therefore, developments in the application of multivariate statistical control, artificial neural networks, fuzzy control and knowledge-based supervision (expert systems) are summarized. Recent advances using Escherichia coli– the pioneer organism for HCDC – are outlined. Received: 20 October 1998 / Received revision: 18 December 1998 / Accepted: 21 December 1998