Enumeration and biovolume determination of microbial cells – a methodological review and recommendations for applications in ecological research

A review of direct counts of micro-organisms is presented, which describes the evaluation of different techniques and applications of microscopic methods for enumeration, biovolume and biomass measurement. New staining techniques and their applications are discussed as well as methods to distinguish individual cell properties. Attention is paid to data analysis and error propagation, which is widely neglected during quantitative studies in microbial ecology. Comparisons to other methods are made in order to evaluate methods of direct microscopy with respect to their great importance for environmental descriptions and analyses.