Flow cytometry in the marine environment

Abstract

The first special issue published by Cytometry in the field of Aquatic Sciences was edited by Clarice Yentsch and Paul Horan in 1989 (Cytometry 1989;10:5). Eleven years later, with the help of the Association Française de Cytométrie (AFC), the International Society for Analytical Cytology largely opened the ISAC XX Congress in Montpellier (20-25 May 2000; France) to numerous researchers and laboratories involved in cytometry techniques to analyse microorganisms such as phytoplankton, bacteria, viruses and small protozoa living in aquatic environments. The number of applications in the field of Aquatic Sciences, and especially in marine biology, is clearly growing (Legendre et al., this issue). A frontier's conference in Marine Science, given during the Opening Day by Professor Louis Legendre, summarised the main oceanographic environmental questions and related discoveries and progress due to flow cytometry during the last decade. This conference well introduced two parallel sessions on microorganisms living in aquatic environments. The first one was mainly dedicated to the analysis of phytoplankton in marine and lake habitats with new perspectives in terms of in situ on-line acquisitions and multivariate data analysis to identify populations. The second parallel session dealing with cytometric applications to environmental microbiology showed the important progress made during the last decade to detect, count, sort and then identify free bacteria in order to understand their role in ecosystems. The Congress also allowed biotechnology specialists to present FCM applications in the field of microbiology. A third microbiology session, previously introduced by a scientific tutorial “Bugs in the Beam–Cytometric Measurement of Microorganisms” was more devoted to bacterial detection and characterisation in peculiar industrial environments. Lastly, illustrating the large interest of applications using flow and image analysis in these research fields, no less than thirty posters were exhibited during the Congress week. What are the reasons of flow cytometry (FCM) success in oceanographic applications and especially in marine microbiology? Besides the well known methodological advantages of FCM which are specific to oceanographic applications (phytoplankton autofluorescences) or not (high speed multiparametric measurements), the most challenging and attractive advantage was that FCM appeared to be a preferential tool to open the microbial “black-boxes”. In fact, due to their major global contribution in both geochemical and trophodynamical roles, small planktonic cells (particularly picoplankton, < 2μm) have been the privileged targets of FCM investigation. As anticipated by Platt (Cytometry 1989;10:5), FCM based studies have brought a significant contribution to building the bridge between the global oceanographic knowledge and the biological heterogeneity of the real microbial world. The diversity of FCM application fields is also growing. Papers compiled in this issue well illustrate this point: from the simultaneous monitoring of different kinds of marine microorganisms (e.g. Li., this issue) to the estimation of their growth parameters (Gomez et al., this issue) or their response to toxic contaminants (Lage et al., this issue). Thus, FCM can be considered as a tool involved in the study of the most important environmental questions which can affect marine ecosystems. That is not to say that we don't need improvements in this methodology. In this issue, some papers showed that different methodological aspects in FCM applications need to be addressed: from very basic but crucial aspects of cellular measurements (Cucci and Sieracki, this issue) to very sophisticated numerical methods to analyse the large amounts of data delivered by FCM (e.g. Boddy et al., this issue). Unfortunately, very promising extensions of FCM which are presently under development and application in the field of aquatic microbiology and which were discussed during the congress are not reported in this issue. At least two of these developments can be cited: sorting facilities which offered new ways to link different properties of marine microorganisms and laser scanning cytometry which appeared well suited for the detection of rare events. People interested in these specific points can read either the recent reviews of Reckermann (Sci Mar 2000;64:235-246) and of Vives-Rego et al. (FEMS Microbiol Rev 2000;685:1-20). The editors would like to thank the ISAC Council and the Scientific Advisory Committee, and the Association Française de Cytométrie which allowed the Congress to be held in Montpellier and who facilitate the existence of specific sessions on microorganisms. We also thank the Editorial Board of Cytometry which offered to publish this special issue. All the participants in sessions devoted to the ecology of microorganisms were invited to submit papers to Cytometry. All the manuscripts received were reviewed according to the procedure in place in Cytometry before their publication in the issue. For us, Montpellier also represented a symbolic place for such a Congress, since, Ostreococcus tauri (Chlorophyta, Prasinophyceae), which is the smallest free eucaryote known today and which is acquiring the status of a new biological model, was discovered using flow cytometry in the Mediterranean Thau lagoon located near the town.