The aim of this work was to determine the bacteriological status of water catchment, basin, which is used for water supply of the town of Krusevac, as well as the distribution of present bacteria morphotypes. The total count of bacteria ranged from 1.35x10**5/ml to 2.09x10**7/ml. The number of aerobic heterotrophs ranged from 415 CFU/ml to 64,500 CFU/ml. The differentiation of bacteria in three morphotypes (rods, cocci and curved) was made. Representation of rods ranged from 40.05% to 78.71%, cocci from 4.39% to 60.88% and curved from 1.54% to 17.20%. Seasonal and vertical distribution of morphotypes showed increased presence of rods and curved forms in terms of increased bacteriological load of water, while the presence of cocci increased in conditions of cleaner water.

Due to development in the science, especially in the area of biodegradation, it becomes clear that different species of aerobic and anaerobic bacteria are indigenous in the ground water. Due to changed condition in ground water, like infiltration of petroleum hydrocarbons, indigenous bacteria start to react and are involved in different processes of natural biodegradation. Also, great contribution of understanding how bacteria functionating in ground water is given from the field of well regeneration due to consequences of biofouling and biologically induced corrosion. In this article several natural processes related to bacteria are analyzed and its importance and distribution in ground water is shown.

The microbiological quality of the groundwater was monitored by determining relevant physiological groups of bacteria (organotrophic bacteria) which are indicators of water organic pollution. Standard high nutritive medium (Nutrient Agar) and low nutritive medium (R2A agar) were used. The enzymatic activity was also estimated based on IFA determination (index of phosphatase activity). According to the number of organotrophic bacteria and categorization by Kohl (Kohl, 1975) water is generally classified in category II. IFA showed variation of water quality, which varied from polluted to very pollute. The results showed organic pollution of groundwater and confirmed the sensitivity of enzymatic methods. In addition, cultivation methods confirmed superiority of low nutritive media.

Microthrix parvicella is dilamentous bacterium common present in the activated sludge on the plants with biological nutrient removal. Microthrix parvicella is described as a bacterium which present in a large numbers, has an extremely negative impact on the sludge settling, and its considered as the primary cause of bulking sludge on the WWTP-s with biological nutrient removal. Also, this bacterium considered as the primary foam-forming microorganisms in activated sludge, because those hydrophobic cells stabilized air bubbles or affected by the oil droplets in foam. Although there are numerous data regarding the growth of certain filamentous bacteria, as well as their impact on the waste waters treatment and deposition of sludge, they are often vague, and not always in clear correlation, especially when comparing data from different plants. The aim of this paper was toexamine the growth and population size of Microthrix parvicella in correlation to water temperature (seasonal dynamics of growth), and a correlation between population size of filamentous bactereia (filamentous sludge index-FI), especially M. parvicella growth and the sludge settlement (Imhoff 30 '), or the ratio of FI and the volume of sludge (sludge volume index – SVI) on WWTP of Subotica during 2011.