Activity and diversity of bacterial cells with high and low nucleic acid content

Abstract

ABSTRACT: In most aquatic environments, at least 2 subpopulations of bacterial cells can be dis-criminated by flow cytometry based on their nucleic acid content. Recent investigations have shownthat the cells with a high nucleic acid (HNA) content have a higher cell-specific activity (CSA) cellthan those with a low nucleic acid (LNA) content. In this study, the CSA and biomass-specific activi-ties (BSA) of HNA and LNA cells from different aquatic ecosystems, including marine, brackish andfreshwater, were investigated using radioactive leucine incorporation and cell sorting by flow cytom-etry. The genetic diversity of natural assemblages, HNA and LNA cells was investigated using theSSCP (PCR single-strand conformation polymorphism) method. Data showed that both CSA and BSAof HNA cells were always significantly higher than CSA and BSA of LNA cells. In addition, HNA cellshad a dominant contribution to the production of the total community (77 to 98%). For the differentsamples, the SSCP fingerprints from the natural assemblage and from the 2 sorted fractions were notsignificantly different. This clearly suggests that HNA and LNA subpopulations were composed bythe same dominant species and, thus, confirms an important heterogeneity of physiological stateswithin most natural populations.