Probiotics are microorganisms that have many health benefits to their host, such as promoting normal intestinal microflora, inhibiting the growth of pathogenic microorganisms, improving digestion and stimulation of gastrointestinal immunity. Probiotic microorganisms include bacteria, fungi and yeast, and they are highly desirable to be used as animal feed supplements. For this application, Bacillus species are preferred since they are resistant to extreme environmental conditions due to their spore-forming capacity in addition to having other important probiotic characteristics. In the first chapter of this study, 84 independent bacterial colonies were obtained from different bovine chyme samples and among them 29 were determined as belonging to genus Bacillus. These isolates were principally screened for their antimicrobial activity against a group of selected bacteria including pathogenic organisms such as Salmonella enterica, Klebsiella pneumoniae, Pseudomonas aeruginosa and Staphylococcus aureus. 7 strains (STF4, STF8, STF9, STF10, STF15, STF25 and STF26) with highest antimicrobial activity were further tested for other probiotic properties. They were resistant to the gastrointestinal conditions and most of the antibiotics tested. In addition, they were checked for the presence of plasmids and performed cytotoxicity tests. We propose novel Bacillus strains that have potential to be used as probiotic organisms. TNT is a hazardous nitroaromatic compound that can be found in soil, sediment and water due to extensive contamination from military munitions after the World War II. It has many negative health effects on almost all of the living organisms (e.g. bacteria, fungi, algae, animal and human). So far, bacteria, fungi and plants are commonly used for biodegradation process but only a little is known about effect of algae on this issue. However, algae can be used as a good alternative for bioremediation and biosensor purposes as they do not require advance technology and are effective in terms of cost. 5 different microalgae strains (STA1, STA2, STA3, STA4 and STA5) were tested in terms of survival in different TNT concentration and biodegradation capability of TNT. These strains were isolated from water contaminated with TNT obtained from the Brass Factory affiliated with Mechanical and Chemical Industry Corporation (MKE) located in Kırıkkale, Turkey. Even though these strains did not use TNT as carbon source for growth; they utilize it at different degrees for other metabolic activities. Moreover, the growth of STA2 strain was not inhibited by high TNT concentrations (up to 50 mg/L TNT).