Irfan Türetgen

Role of single-celled organisms in mucilage formation on the shores of Büyükada Island (the Marmara Sea)

This study was implemented to determine the environmental factors and causative organisms of the recent mucilage formation in the Marmara Sea. Samples were taken during the study from 7 different depths (0.5―30 m) of one sampling point of the Buyukada Island shore between January and June 2008. As a result, 6 2 phytoplankton species belonging to 5 different groups were identified. Dinofiagellates were dominant in terms of species number, and diatoms in terms of cell number. In January and February, mucilage formation was very dense, where 5 phytoplankton species (Clindrotheca closterium, Pseudo-nitzschia sp., Skeletonema costatum, Thalassiosira rotula (Bacillariophyceae) and Gonyaulax fragilis (Dinophyceae)) were reported as dominant organisms. Among them, Gonyaulax fragilis has never been reported in the Marmara Sea previously, thus that organism appeared firstly with the formation of dense mucilage and then when the mucilage decayed in May and June 2008, G. fragilis disappeared. Autofluorescent single-celled organisms were classified in three groups depending on their cell sizes (>20 μm, >2 μm, >o.2 μm) by membrane filtration and total count of bacteria were determined by epifluorescence microscope after dying with DAPI. The highest total bacteria was recorded in April at 25 m depth (66 55 ± 44 . 4 cells ml ―1 ) while the lowest count was in June at 0 . 5 m depth ( 1077 ± 2 6. 1 cells ml ―1 ). The seawater temperature ranged between 7.0 and 21.5°C, salinity between 20 . 9 and 37 . 4 ppt and dissolved oxygen amount between 2 . 75 and 12 . 75 mg l ―1 . The chlorophyll-a amount ranged between 0.10 and 6. 35 μg l ―2 , the higher values were recorded in January at 15 m depth (6.35 μg l ―1 ) and in April at 10 m depth ( 4 .8 9 μg l ―1 ). Among the nutrients, the amounts of nitrite + nitrate-N varied between 0 . 02 and 7 .6 7 μg-at N l ―1 , phosphate-P between 0.11 and 0.96 μg-at P l ―1 and silicate-Si between 0.37 and 8. 93 μg-at Si l ―1 . The highest values were determined at a deeper layer where nutrients are accumulated. On the other hand, the N:P ratio interval was found as 0.1―11.3, Si:P ratio as 2.92―52.33 and N:Si ratio as 0.01―1.10 during the sampling period. Nitrogen was the limiting nutrient and the silica amount was enough to enable the development of diatoms.

Induction of Viable but Nonculturable (VBNC) state and the effect of multiple subculturing on the survival ofLegionella pneumophila strains in the presence of monochloramine

The aim of the study was to evaluate the response of two differentLegionella pneumophila strains with their 20 times subcultured passages, regarding VBNC induction and to test the effect of multiple subculturing on cell vulnerability in the presence of monochloramine. A freshly opened ofL. pneumophila ATCC 33152, a first subculture of environmental isolate ofL. pneumophila and the 20th subcultures of both strains were tested for survival in the presence of different doses of monochloramine (24 hours). Besides culture method, live-dead cells were visualised. It was found that multiple subcultured strains were significantly more susceptible to monochloramine and not capable of entering to VBNC state in comparison with freshly opened/isolated strains. Environmental isolate was survived at 2 ppm dose of monochloramine after 24 h, whereas 20th subculture of this strain failed to survive. Multiple subculturedL. pneumophila strains were lost their culturability and viability significantly. This phenomenon should be considered while working with laboratory strains. After monochloramine disinfection,L. pneumophila bacteria can completely lose their cultivability but do not lose viability, which remains responsible for serious outbreaks worldwide. Even after completely loosing cultivability, it is possible to find live cells in network water in the VBNC state.The aim of the study was to evaluate the response of two differentLegionella pneumophila strains with their 20 times subcultured passages, regarding VBNC induction and to test the effect of multiple subculturing on cell vulnerability in the presence of monochloramine. A freshly opened ofL. pneumophila ATCC 33152, a first subculture of environmental isolate ofL. pneumophila and the 20th subcultures of both strains were tested for survival in the presence of different doses of monochloramine (24 hours). Besides culture method, live-dead cells were visualised. It was found that multiple subcultured strains were significantly more susceptible to monochloramine and not capable of entering to VBNC state in comparison with freshly opened/isolated strains. Environmental isolate was survived at 2 ppm dose of monochloramine after 24 h, whereas 20th subculture of this strain failed to survive. Multiple subculturedL. pneumophila strains were lost their culturability and viability significantly. This phenomenon should be considered while working with laboratory strains. After monochloramine disinfection,L. pneumophila bacteria can completely lose their cultivability but do not lose viability, which remains responsible for serious outbreaks worldwide. Even after completely loosing cultivability, it is possible to find live cells in network water in the VBNC state.

Effects of short-time drying on biofilm-associated bacteria

Microorganisms tend to form biofilms consisting of cells embedded in a highly hydrated extracellular polymeric matrix. The biofilm protects its inhabitants from antimicrobial agents, pH alterations, and confers protection against drying. It is known that biofilm-associated bacteria can survive for a while in the absence of water. When rehydrated, metabolic processes are quickly restored and microorganisms resume life. The aim of this study is to evaluate the survival of heterotrophic bacteria, sulphate-reducing bacteria and amoeba against short-time drying. Biofilms were allowed to grow for 30 and 60 days on stainless steel (316, 2B) coupons in annular biofilm reactor, which was fed with drinking water network under constant, non-turbulent shear stress and temperature. The results presented in this study indicate a role for biofilm layer in protecting biofilm-associated microorganisms from drying. The current study has provided that short-time (24 h) absence of water could not affect biofilm-associated heterotrophic microorganisms significantly, in terms of cell viability.