Karakterizacija aktivnih profagov izolatov Bacillus subtilis iz talnega mikrohabitata

This master’s thesis investigates the presence, diversity and activity of prophages in microscale Bacillus subtilis PS soil isolates. Prophages are viral genomes integrated into bacterial chromosomes that can remain dormant or be induced to produce phage particles. Their activation affects bacterial physiology, gene exchange and competition, yet their role in natural B. subtilis isolates remains poorly understood. To address this, 40 sympatric PS isolates were experimentally screened for phage activity, titers and variety of plaques. Prophage induction was carried out both spontaneously (SPI) and chemically with mitomycin C (MitC). Filtered supernatants were analyzed for phages using spotting and confluent plaque assays on the prophage-free indicator strain B. subtilis Δ6. This was followed by phage isolation from plaques, enrichment on liquid and solid medium, precipitation, DNA extraction, PCR (plaque and genomic PCR) and transmission electron microscopy (TEM). A swarm boundary assay was also performed to test whether phage release occurs during social interactions. Active prophages were detected in six strains (PS-11, PS-24, PS-25, PS-233, PS-237, PS-261), which is 15% of all isolates. The plaques showed a broad range of morphologies, including large ringed plaques, numerous small plaques, and two different plaque types from one supernatant. MitC was consistently more effective than SPI, producing higher titers. In some samples plaques co-occurred with inhibition zones