PLANT MICROBE INTERACTIONS Endophytes of Grapevine Flowers, Berries, and Seeds: Identification of Cultivable Bacteria, Comparison with Other Plant Parts, and Visualization of Niches of Colonization Stéphane Compant & Birgit Mitter & Juan Gualberto Colli-Mull & Helmut Gangl & Angela Sessitsch Received: 5 January 2011 /Accepted: 14 May 2011 /Published online: 31 May 2011 # Springer Science+Business Media, LLC 2011 Abstract Endophytic bacteria can colonize various plants and organs. However, endophytes colonizing plant repro- ductive organs have been rarely analyzed. In this study, endophytes colonizing flowers as well as berries and seeds of grapevine plants grown under natural conditions were investigated by cultivation as well as by fluorescence in situ hybridization. For comparison, bacteria were additionally isolated from other plant parts and the rhizosphere and characterized. Flowers, fruits, and seeds hosted various endophytic bacteria. Some taxa were specifically isolated from plant reproductive organs, whereas others were also detected in the rhizosphere, endorhiza or grape inflo/ infructescence stalk at the flowering or berry harvest stage. Microscopic analysis by fluorescence in situ hybridization of resin-embedded samples confirmed the presence of the isolated taxa in plant reproductive organs and enabled us to localize them within the plant. Gammaproteobacteria (including Pseudomonas spp.) and Firmicutes (including Bacillus spp.) were visualized inside the epidermis and xylem of ovary and/or inside flower ovules. Firmicutes, mainly Bacillus spp. were additionally visualized inside berries, in the intercellular spaces of pulp cells and/or xylem of pulp, but also along some cell walls inside parts of seeds. Analysis of cultivable bacteria as well as microscop- ic results indicated that certain endophytic bacteria can colonize flowers, berries, or seeds. Our results also indicated that some specific taxa may not only derive from the root environment but also from other sources such as the anthosphere. Introduction In both managed and natural ecosystems, plants can interact with a wide range of bacteria, which can have pathogenic, neutral, or beneficial effects on their hosts. The majority of bacterial microsymbionts are epiphytic and are known to colonize the rhizosphere [9, 23]. A subset of the rhizo- sphere microflora can also enter and proliferate within plants as endophytes [17, 18]. Endophytes may also derive from other sources of colonization [8] and these kinds of microorganisms have been mostly isolated from endorhiza, stems and/or leaves [16, 29, 31]. Few studies have also demonstrated that part of the endophytic microflora can colonize plant reproductive organs [8, 10]. However, little S. Compant : B. Mitter : J. G. Colli-Mull : A. Sessitsch Bioresources Unit, AIT Austrian Institute of Technology GmbH, A-2444 Seibersdorf, Austria S. Compant (*) Départment Bioprocédés et Systèmes Microbiens, ENSAT-INP de Toulouse, Université de Toulouse, LGC UMR 5503 (CNRS/INPT/UPS), 1 Avenue de l′Agrobiopôle, B.P. 32607, F-31326 Castanet-Tolosan Cedex 1, France e-mail: scompant@ensat.fr S. Compant Centre de Viticulture-Œnologie de Midi Pyrénées, Université de Toulouse, Avenue de l’Agrobiopôle, Auzeville-Tolosane, BP 32607, F-31326 Castanet-Tolosan Cedex 1, France J. G. Colli-Mull Cinvestav-U. Irapuato, Km. 9.6 Libramiento Norte, Carretera Irapuato-León, Irapuato, Gto C.P. 36500, Mexico H. Gangl Bundesamt für Weinbau, Gölbeszeile 1, A-7000 Eisenstadt, Austria Microb Ecol (2011) 62:188–197 DOI 10.1007/s00248-011-9883-y