Water level and fish-mediated cascading effects on the microbial community in eutrophic warm shallow lakes: a mesocosm experiment

Information on the effects of water level changes on microbial planktonic communities in lakes is limited but vital for understanding ecosystem dynamics in Mediterranean lakes subjected to major intra- and inter-annual variations in water level. We performed an in situ mesocosm experiment in an eutrophic Turkish lake at two different depths crossed with presence/absence of fish in order to explore the effects of water level variations and the role of top-down regulation at contrasting depths. Strong effects of fish were found on zooplankton, weakening through the food chain to ciliates, HNF and bacterioplankton, whereas the effect of water level variations was overall modest. Presence of fish resulted in lower biomass of zooplankton and higher biomasses of phytoplankton, ciliates and total plankton. The cascading effects of fish were strongest in the shallow mesocosms as evidenced by a lower zooplankton contribution to total plankton biomass and lower zooplankton:ciliate and HNF:bacteria biomass ratios. Our results suggest that a lowering of the water level in warm shallow lakes will enhance the contribution of bacteria, HNF and ciliates to the plankton biomass, likely due to increased density of submerged macrophytes (less phytoplankton); this effect will, however, be less pronounced in the presence of fish.     

Persistent directional cell migration requires ion transport proteins as direction sensors and membrane potential differences in order to maintain directedness

Background  

Ion transport proteins generate small electric fields that can induce directional cell motility; however, little is known about their mechanisms that lead to directedness. We investigated Na, K-ATPase (NaKA) and Na+/H+ exchanger isoforms (NHE1 and 3) in SaOS-2 and Calvarial osteoblasts, which present anode- and cathode- directed motility, during electrotaxis.     

Evaluation of increased proportion of cells with unusually high sister chromatid exchange counts as a cytogenetic biomarker for lead exposure

Sister chromatid exchange (SCE) frequency and high-frequency cells (HFCs) were analyzed in 50 storage battery plant workers with mean blood lead level (BLL) of 40.14±9.99 μg/dL. The mean BLL in the control group (n=30) was 9.77±1.67 μg/dL. This difference in mean BLLs between control and exposed group was statistically significant (p<0.05) and reflects clearly the lead exposure in the workers. Urinary aminolevulinic acid (U-ALA) was also determined in both control (3.37±0.89 mg ALA/g creatinine) and exposed groups (12.39±6.18 mg ALA/g creatinine) and U-ALA excretion was statistically higher (p<0.05) in lead-exposed workers. The relationship between biomarkers of lead exposure/effect and HFC percentage was higher than the relationship between biomarkers of lead exposure/effect and SCE frequency. Accordingly, HFC analysis seemed to be more sensitive than the SCE analysis as a cytogenetic biomarker for lead exposure. Additionally, the statistically significant correlation (r ²=0.880, p<0.01) between U-ALA excretion and HFC percentage in lead-exposed workers supported the probability of ALA mediated indirect mechanism for lead genotoxicity.     

Pressure-related Increase of Asymmetric Dimethylarginine Caused by Hyperbaric Oxygen in the Rat Brain: A Possible Neuroprotective Mechanism

A decrease in nitric oxide availability in the brain tissue due to the inhibition of nitric oxide synthase (NOS) activity during the early phases of hyperbaric oxygen (HBO) exposure was found to be involved in hyperoxic vasoconstriction leading to reduced regional cerebral blood flow. We hypothesized that the concentration of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase (NOS), may be an important factor during this hyperoxic vasoconstriction state. Rats were exposed to 1, 2 and 3 atmospheres pure oxygen for two hours. A fourth group of animals served as control. Asymmetric dimethylarginine, L-Arginine and nitrite/nitrate (NO_x) concentrations were measured from deproteinized rat brain cytosols. In rat brains exposed to 3 atmospheres O₂, ADMA and L-Arginine levels were found to be significantly higher and NO_x significantly lower than control levels. Additionally, statistically significant correlations between ADMA and L-Arginine, and ADMA and NO_x concentrations were detected. In conclusion, this is the first study indicating increased ADMA levels in rat brains exposed to HBO. The simultaneously decreased NO_x values suggest that ADMA elevation resulted in NOS inhibition and therefore may be responsible for the early phase hyperoxic vasoconstriction.