ORIGINAL ARTICLE Effect of a transient perturbation on marine bacterial communities with contrasting history O. Zemb 1,2 , N. West 1,2 , M. Bourrain 1,2 , J.J. Godon 3 and P. Lebaron 1,2 1 Universite ´ Pierre et Marie Curie-Paris 6, Laboratoire ARAGO, Banyuls-sur-Mer, France 2 CNRS, UMR7621, Laboratoire d’Oce ´ anographie Biologique de Banyuls, Banyuls-sur-Mer, France 3 INRA, UR050, Laboratoire de Biotechnologie de l’Environnement, Narbonne, France Introduction The oceans play a major role in the global carbon cycle by the important exchange of carbon dioxide between the ocean and the atmosphere. Marine heterotrophic bacteria participate in the carbon cycle by the production of biomass from dissolved organic carbon (DOC) which then becomes available to their predators (Azam 1998). In this context the carbon flow from the DOC to the rest of the food chain is related to the rate of protein synthe- sis. In the event of a perturbation affecting the bacteria, the stability of the ecosystem could be assured by a short functional resilience of the heterotrophic bacteria (i.e. time required to recover their function after a perturba- tion) [see Botton et al. (2006)]. Various factors are sus- pected to affect the functional resilience of bacteria, such as the diversity of the community (Griffiths et al. 2000; Wertz et al. 2007), the productivity of the system (Moore et al. 1993) or the prior exposure to perturbations (Tobor-Kaplon et al. 2006). For example some rare popu- lations were crucial in microbial mats in a hypersaline lagoon where a major population shift was concomitant with the resilience of nitrogen fixation and photosynthesis abilities after a hurricane (Yannarell et al. 2007), showing that functional resilience can occur even without resilience of the initial populations. Functional resilience Keywords bacterial production, chemical perturbation, marine bacteria, resilience, single strand conformation polymorphism. Correspondence Philippe Lebaron, Universite ´ Pierre et Marie Curie-Paris 6, Laboratoire ARAGO, Avenue Fontaule ´ , BP44, F66650 Banyuls-sur-Mer, France. E-mail: lebaron@obs-banyuls.fr 2009 ⁄ 1865: received 24 October 2009, revised 5 January 2010 and accepted 3 February 2010 doi:10.1111/j.1365-2672.2010.04706.x Abstract Aims: To evaluate the importance of the bacterial composition on the resilience of the organic matter assimilation in the sea. Methods and Results: Chemostats were inoculated with coastal and offshore bacterial communities. Bacterial density and protein synthesis increased before stabilizing, and this response to confinement was more marked in the offshore chemostats. Before the toluene perturbation the community structure in the coastal chemostats remained complex whereas the offshore chemostats became dominated by Alteromonas sp. After the perturbation, bacterial protein synthe- sis was inhibited before peaking briefly at a level fivefold to that observed before the perturbation and then stabilizing at a level comparable to that before the perturbation. Alteromonas dominated both the coastal and the offshore communities immediately after the perturbation and the coastal communities did not recover their initial complexity. Conclusions: Cell lysis induced by the toluene perturbation favoured the growth of Alteromonas which could initiate growth rapidly in response to the nutrient pulse. Despite their different community structure in situ, the resilience of pro- tein synthesis of coastal and offshore bacterial communities was dependent on Alteromonas, which dominated in the chemostats. Significance and Impact of the Study: Here we show that although Alteromonas sp. dominated in artificial offshore and coastal communities in chemostats, their response time to the shock was different. This suggests that future pertur- bation studies on resilience in the marine environment should take account of ecosystem history. Journal of Applied Microbiology ISSN 1364-5072 ª 2010 The Authors Journal compilation ª 2010 The Society for Applied Microbiology, Journal of Applied Microbiology 109 (2010) 751–762 751