Systematic and Applied Microbiology 38 (2015) 358–367 Contents lists available at ScienceDirect Systematic and Applied Microbiology j ourna l ho mepage: www.elsevier.de/syapm Spatially uniform but temporally variable bacterioplankton in a semi-enclosed coastal area Alexandra Meziti a , Konstantinos A. Kormas b , Maria Moustaka-Gouni c , Hera Karayanni a,∗ a Department of Biological Applications and Technology, University of Ioannina, 45110 Ioannina, Greece b Department of Ichthyology and Aquatic Environment, University of Thessaly, 38446 Volos, Greece c Department of Botany, School of Biology, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece a r t i c l e i n f o Article history: Received 20 November 2014 Received in revised form 10 April 2015 Accepted 13 April 2015 Keywords: Diversity Pyrosequencing 16S rRNA gene Bacteria SAR11 Temporal/spatial variations a b s t r a c t Studies focusing on the temporal and spatial dynamics of bacterioplankton communities within littoral areas undergoing direct influences from the coast are quite limited. In addition, they are more compli- cated to resolve compared to communities in the open ocean. In order to elucidate the effects of spatial vs. temporal variability on bacterial communities in a highly land-influenced semi-enclosed gulf, surface bacterioplankton communities from five coastal sites in Igoumenitsa Gulf (Ionian Sea, Greece) were ana- lyzed over a nine-month period using 16S rDNA 454-pyrosequencing. Temporal differences were more pronounced than spatial ones, with lower diversity indices observed during the summer months. During winter and early spring, bacterial communities were dominated by SAR11 representatives, while this pat- tern changed in May when they were abruptly replaced by members of Flavobacteriales, Pseudomonadales, and Alteromonadales. Additionally, correlation analysis showed high negative correlations between the presence of SAR11 OTUs in relation to temperature and sunlight that might have driven, directly or indi- rectly, the disappearance of these OTUs in the summer months. The dominance of SAR11 during the winter months further supported the global distribution of the clade, not only in the open-sea, but also in coastal systems. This study revealed that specific bacteria exhibited distinct succession patterns in an anthropogenic-impacted coastal system. The major bacterioplankton component was represented by commonly found marine bacteria exhibiting seasonal dynamics, while freshwater and terrestrial-related phylotypes were absent. © 2015 Elsevier GmbH. All rights reserved. Introduction Studies into the temporal and spatial changes of marine micro- bial assemblages constitute a challenging and still evolving field, which aims to elucidate the procedures that shape microbial diversity and community structure [29]. Species diversity and its variability in space and time is a key feature of all biological com- munities, and relates to their functions and dynamics [20,25]. These procedures are ecologically important, since microorganisms are the major players of global biogeochemical cycles [6]. The recent introduction of next-generation sequencing (NGS) techniques has significantly advanced our knowledge in this field of research as it has allowed more-detailed studies of microbial communities in marine environments [40]. To date, most studies using NGS ∗ Corresponding author. Tel.: +30 265 100 7324. E-mail addresses: hkaray@cc.uoi.gr, hera06@gmail.com (H. Karayanni). techniques have focused on the changes in bacterial diversity related to depth [9,19,34], time [5,15,28,49], or space [19,32,35,53] in oceanic and offshore waters. Similar studies of coastal environ- ments close to and directly impacted by land masses are limited [14], while those investigating the temporal shifts of bacterio- plankton in these dynamic ecosystems are even less common [52]. Consequently, this study was designed in order to investigate whether location (space) or time (season) were more important in shaping bacterial diversity in a coastal ecosystem under high anthropogenic pressure. The area chosen for this study was the Igoumenitsa Gulf in the Ionian Sea (NW Greece). The gulf is under constant impact from anthropogenic activities originating from the adjacent city of Igoumenitsa (25,000 inhabitants) and is connected to the open Ionian Sea. The gulf’s depth ranges from 2 m (northwest area) to more than 22 m at its center and close to the new harbor (east). Related to shipping, it accommodates up to 11,000 commer- cial and passenger vessels combined per year (Igoumenitsa Port http://dx.doi.org/10.1016/j.syapm.2015.04.003 0723-2020/© 2015 Elsevier GmbH. All rights reserved.