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A met cell could become met bio thr leu thi by a (rare) double mutation that converts the met bio- genetic material into bio . Likewise, a met bio thr leu- thi cell could become met bio thr leu thi by three mutations that convert the thi genetic material into leu . From the results, how do you know that the occurrence of thi colonies is not due to these types of rare double or triple mutations?
Solution
VerifiedEach bacterium got different nutritional requirements to survive. That's why in-vitro, different media are prepared for different microorganisms. Organic compounds, like vitamins play an important role in cellular functions. Most of vitamins are often synthesized by bacteria. Due to mutation, this property of synthesizing vitamins is hampered. As a result, certain vitamin, which bacteria cannot produce, is supplemented into growing media. Such bacterium that cannot survive on minimal media is known as auxotroph. In an experiment, two bacteria with double (met- bio- tbr+ leu+ thi+) and triple (met+ bio+ thr- leu- thi-) mutations has taken. When grown individually on media lacking methionine and biotin for double mutated bacteria and threonine, leucin and thiamine lacking media for triple mutated bacteria, it was observed that there are no bacterial colonies formed on the plate. When bacterial mixture is mixed well, it was observed that bacterial colonies are formed indicating that bacteria that are grown, had the ability to synthesize methione (met+), biotin (b/o+). threonine (thr+), leucine (leu+)r and thiamine (thi+). This explains that there is an exchange of genetic material between these bacteria. As a result, mutated bacteria became normal by acquiring characters from other bacteria. Later on this experiment explained the phenomenon of conjugation. In this, genetic material between bacteria is exchanged through physical contact by forming sex pili or conjugating bridge.
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