Digital image analysis for microscope characterisation of the critical parameters involved in the fermentative production of secondary metabolites

Secondary metabolites, particularly antibiotics, are among the most relevant pharmaceutical compounds worldwide and they are generally produced by submerged cultivation of filamentous fungi. From the hydrodynamical point of view, these processes deal with the dispersion of up to four different phases: water-oil-air-fungi. It is well recognized that hydrodynamics has a significant influence on the global performance of the fermentation process; however, very little is understood about the relationships between hydrodynamics-dispersion-physiology-productivity. This poor understanding is partially due to the lack of precise methodologies to assess fungal viability (determining both the yield and productivity of the metabolite) and the size of the air bubbles and oil drops (related to the nutrient transport efficiency like oxygen and fatty acids). In this work, the published developments of our group, regarding image analysis-based methodologies for the study of Trichoderma harzianum cultivation for antimycotics production (v.g. 6-pentyl-alpha-pyrone) have been summarized and revised. The application of such methodologies resulted in the improvement of basic knowledge of the phenomena occurring within the fermenter as well as in the development of strategies for increasing the productivity of these processes. Key words: micelial cultures; hydrodynamics; multiphasic dispersión; microbial physiology; productivity; image analysis