STUDENTS:NENA KOUKOUGELI
                        DIMITRA-IOLI SKOUROLIAKOU
UNIVERSITY OF IOANNINA GREECE
BIOLOGICAL APLICATIONS AND TECHNOLOGY
AQUATIC MICROORGANISMS

WEEK: 4th

LEFT: control

RIGHT: warmth-exposed

From the 3^rd to the  4th week, we observed some differences. Firstly, we can clearly see that in both columns the water is not as clear as it used to be, due to the bacteria and the nutrients from the sediment. Also, a notable difference is the growth of a brown film on the surface of the bottles. This structure is consisted of microorganisms attaching to surfaces and developing biofilms. A biofilm is an assemblage of  microbial cells that is irreversibly associated. Biofilm-associated cells can be differentiated from their suspended counterparts by the generation of an extracellular polymeric substance (EPS) matrix, reduced growth rates, and the up- and down- regulation of specific genes.  The plastic material of our bottles is a great environment for microorganisms to growth. (Donlan et al, 2002) It is also important to mention  that water system biofilm is highly complex, containing corrosion product, clay material and filamentous bacteria. As we can see in the pictures, the concentration of the biofilm in first column is greater from the second one, even though biofilms can grow in very low and high temperatures. Thus, we can assume that in the 2^nd column, the rapid fluctuation of temperature affects the bacteria not only directly by limiting the growth of the no-resistant at high temperatures, bacteria, but also it affects them indirectly by the overheating of the plastic bottle, that excretes damaging chemicals. This fact, can reduce even more the growth rates of biofilm. Also, in both columns the sludge is darker from the previous week, due to the anoxic conditions. Finally, it is remarkable that after 4 weeks, we can still observe some Annelida even in the warmth exposed bottle. This fact indicates the toughness of some organisms on the ecosystem of Lake Vrellis.

 In conclusion, the most noticeable difference from the 3rd week, is the growth of biofilms in both columns and the effect of rapid fluctuation of the temperature.

Hypothesis: The rapid fluctuation of the temperature on daily basis, reduces the growth rate of the microorganisms in the 2^nd Winogradsky column.