Bacterial community structure analyses to assess pollution of water and sediments in the Lake Shkodra/Skadar, Balkan Peninsula.

GOAL, SCOPE AND
BACKGROUND: Lake Skadar is the largest lake of the Balkan Peninsula, located along the Montenegro-Albanian border. The unique features of the lake and wide range of endemic, and rare or endangered plant and animal species, resulted in the classification of the Skadar as a wetland site of international significance. In spite of its importance, the lake is influenced by inflowing waters from the river Moraca and other regional rivers contaminated by the industry, municipal and agricultural activities in the area. Therefore, the lake has been the subject of various physical, chemical, biological and toxicological examinations. However, community-level analyses are most relevant to assess the effect of stressors on aquatic ecosystems. In the present study, bacterial community structure among differently polluted sites of the lake was compared using a genetic fingerprinting technique.
METHODS: Water and sediment samples were collected from five differently polluted sampling sites on the Lake Skadar in spring and autumn of the same year. The bacterial community structure in the samples was characterized and compared by temporal temperature gel electrophoresis (TTGE) analysis of polymerase chain reaction-amplified bacterial 16S rRNA genes. RESULTS AND DISCUSSION: The TTGE analysis resulted in many distinguishable and reproducible band patterns, allowing a reliable comparison of bacterial communities among sampling sites. Results on the bacterial community structure revealed that three of the selected locations can be considered as sites that have not shown any pollution degradation determined by our method, due to similar structure of a bacterial community in the sediment samples. On the other hand, significant shifts in the bacterial community structure in the mouth of the rivers Moraca and Plavnica were shown. Since the results coincide with some of the bioassays and chemical analysis performed previously, the changes in bacterial community structure are explained as an effect of antropogenic pollution on the lake ecosystem by waters of the river Moraca and the stream Plavnica.
CONCLUSION: The TTGE has proven to be an efficient and reliable method to monitor bacterial dynamics and community shifts in aquatic environments, especially in sediments. Within the variety of environmental quality assessments, the use of TTGE analyses from bacterial communities is strongly recommended, particularly as an initial investigation. However, in any conclusion on the state of the environment, the TTGE results should be combined to some other biological, chemical and hydrological data. RECOMMENDATION AND OUTLOOK: Since prokaryotes are a crucial group of organisms in the biosphere, the ecosystem function studies are largely based on bacterial communities. Therefore, bacterial community structure analysis should be a part of an integrated weight of evidence approach in pollution assessment. In case of Triad approach, consisting of chemical analyses, bioassays, and community studies in the field, the TTGE bacterial community structure analyses should be placed in the later Triad leg. In comparison to other community studies, based on various biotic indices, the TTGE bacterial community analysis has proven to be very sensitive, reliable and less time consuming.