ORIGINAL ARTICLE Proteomic response of Escherichia coli to the alkaloid extract of Papaver polychaetum Çağakan Ozbalci & Çağlayan Unsal & Dilek Kazan & Berna Sariyar-Akbulut Received: 2 March 2010 / Accepted: 30 July 2010 # Springer-Verlag and the University of Milan 2010 Abstract The cellular response of Escherichia coli exposed to alkaloids extracted from a biennial endemic plant, Papaver polychaetum, was explored using proteome analy- sis. Following determination of the minimum inhibitory concentration of the berberine-containing plant extract as 1,250 μg/mL, E. coli cells were grown in the presence of 750 μg/mL extract. The response of the bacteria to the extract, with berberine found as the major alkaloid, was analyzed on two-dimensional gels. The differentially expressed proteins in the presence of 750 μg/mL extract were identified by matrix-assisted laser desorption/ionization-time of flight mass spectrometry. These proteins included those that play vital roles for maintenance such as protein synthesis (elongation factor-Ts), transport (oligopeptide-binding protein A, uncharacterized amino-acid ABC transporter ATP binding protein YECC), energy metabolism (alpha-subunit of ATP synthase, pyridine nucleotide transhydrogenase STHA) and regulation. These results provide clues for understanding the mechanism of the alkaloid extract-induced stress and cytotox- icity on E. coli. The altered proteins can serve as potential targets for development of innovative therapeutic agents. Keywords Proteomics . Antimicrobial . Escherichia coli . Papaver polychaetum . Berberine Introduction Widespread bacterial drug resistance to current cheap and effective first-choice drugs raises the number of untreat- able bacterial infections and adds urgency to the search for new infection-fighting strategies (World Health Orga- nization 2002; Vlieghe et al. 2009). In addition to careful use of existing antimicrobials and better hygiene condi- tions, development of novel therapeuticals is the key to fighting the remarkable adaptability of microorganisms. The challenge in the search for new antimicrobial classes lies in the timely knowledge of the molecular mechanism of action of the drug and the related bacterial response (Bandow et al. 2003). Use of plants for medicinal purposes has been practised for many centuries (Summer 2000; Hanson 2005; van Wyk and Wink 2005). Due to their unmatched availability of chemical diversity, plant extracts, either as pure compounds or as standardized extracts, provide unlimited opportunities for new drugs to counter multi-resistant microorganisms (Cos et al. 2006). Papaver polychaetum, belonging to the plant kingdom Papaveraceae, is a biennial endemic species (southern Turkey) possessing antimicrobial activity (Ünsal et al. 2007, 2009). The alkaloid found in P. polychaetum is berberine (Sariyar 2002) that is commonly used for various Electronic supplementary material The online version of this article (doi:10.1007/s13213-010-0118-0) contains supplementary material, which is available to authorized users. Ç. Ozbalci : D. Kazan : B. Sariyar-Akbulut (*) Department of Bioengineering, Faculty of Engineering, Marmara University, Göztepe Campus, Kadiköy, 34722 Istanbul, Turkey e-mail: berna.akbulut@marmara.edu.tr Ç. Unsal Department of Pharmacognosy, Faculty of Pharmacy, Istanbul University, 34116 Beyazıt, Istanbul, Turkey D. Kazan TUBITAK-MAM, Research Institute for Genetic Engineering and Biotechnology, PK: 21, 41470 Gebze-Kocaeli, Turkey Ann Microbiol DOI 10.1007/s13213-010-0118-0