A NEW IN-VIVO FLUOROMETRIC TECHNIQUE TO MEASURE GROWTH OF ADHERING PHOTOTROPHIC MICROORGANISMS

We developed a noninvasive rapid fluorimetric method for the investiga tion of growth of adhering (benthic) phototrophic microorganisms; The technique is based on the sensitive detection of the in vivo fluoresce nce of chlorophylls chlorophyll a and bacteriochlorophyll a and monito rs increases in signal over time as an indicator for growth, The growt h fluorimeter uses modulated excitation light of blue-light-emitting d iodes and a photodiode as the detector. The light-emitting diodes are mounted geometrically in an aluminum housing for efficient and uniform illumination of the bottoms of the growth containers, The fluorimeter was characterized with respect to detection limit and dynamic range. This system is capable of resolving in vivo chlorophyll a concentratio ns of 0.5 mu g liter(-1) in cyanobacteria and 0.03 mu g liter(-1) in d iatoms as well as in vivo bacteriochlorophyll a concentrations in phot otrophic bacteria of 0.3 mu g liter(-1), which points to an extremely high sensitivity compared with that of similar available techniques. T hus, the new fluorimeter allows the determination of growth at extreme ly low cell densities, The instrument was used successfully to measure the growth of several adhering isolates of the filamentous cyanobacte rium Microcoleus chthonoplastes from benthic microbial mats in seawate r of different salinities. The data obtained demonstrate broad growth responses for all strains, which thus can be characterized as euryhali ne organisms.