title: Visualizing aquatic bacteria by light and transmission electron microscopy.
abstract: The understanding of the functional role of aquatic bacteria in microbial food webs is largely dependent on methods applied to the direct visualization and enumeration of these organisms. While the ultrastructure of aquatic bacteria is still poorly known, routine observation of aquatic bacteria by light microscopy requires staining with fluorochromes, followed by filtration and direct counting on filter surfaces. Here, we used a new strategy to visualize and enumerate aquatic bacteria by light microscopy. By spinning water samples from varied tropical ecosystems in a cytocentrifuge, we found that bacteria firmly adhere to regular slides, can be stained by fluorochoromes with no background formation and fast enumerated. Significant correlations were found between the cytocentrifugation and filter-based methods. Moreover, preparations through cytocentrifugation were more adequate for bacterial viability evaluation than filter-based preparations. Transmission electron microscopic analyses revealed a morphological diversity of bacteria with different internal and external structures, such as large variation in the cell envelope and capsule thickness, and presence or not of thylakoid membranes. Our results demonstrate that aquatic bacteria represent an ultrastructurally diverse population and open avenues for easy handling/quantification and better visualization of bacteria by light microscopy without the need of filter membranes.
authors.affiliation: Laboratory of Cellular Biology, Department of Biology, Federal University of Juiz de Fora (UFJF), Juiz de Fora, MG, 36036-900, Brazil.
authors.forename: Thiago P
authors.initials: TP
authors.lastname: Silva
authors.forename: Natália P
authors.initials: NP
authors.lastname: Noyma
authors.forename: Thabata L A
authors.initials: TL
authors.lastname: Duque
authors.forename: Juliana P
authors.initials: JP
authors.lastname: Gamalier
authors.forename: Luciana O
authors.initials: LO
authors.lastname: Vidal
authors.forename: Lúcia M
authors.initials: LM
authors.lastname: Lobão
authors.forename: Hélio
authors.initials: H
authors.lastname: Chiarini-Garcia
authors.forename: Fábio
authors.initials: F
authors.lastname: Roland
authors.forename: Rossana C N
authors.initials: RC
authors.lastname: Melo
mesh_terms: D001419:Bacteria / Q000737:chemistry / Q000302:isolation & purification* / Q000648:ultrastructure*; D005618:Fresh Water / Q000382:microbiology*; D008853:Microscopy; D046529:Microscopy, Electron, Transmission; D013194:Staining and Labeling