A carbon source‐dependent antimetabolite sensitivity test in Bacillus megaterium B71 for isolation of ethionine resistant mutants

Abstract

Alteration of carbon sources significantly altered the analogue sensitivity of Bacillus megaterium B71. DL‐Ethionine (ETN) was highly inhibitory with glucose, mannitol, sucrose, citrate, glycerol and arabinose. DL‐Norleucine, L‐homoserine and S(2′‐aminoethyl)‐L‐cysteine were either highly inhibitory, slightly inhibitory or non‐inhibitory depending on the carbon sources used. Maltose markedly overcame the inhibitory effect of ETN in liquid culture. Uninhibited growth was poor on citrate and arabinose when compared with other carbon sources. Six carbon sources showing comparable growth were used to determine minimum inhibitory concentrations (MIC) of the analogues. The MIC of ETN was highest (450 μg/ml) with maltose and lowest (4 μg/ml) with mannitol. ETN sensitivity was inversely related to the endogenous L‐methionine pool size, and was relatively low with mannitol which was used to isolate ETN resistant mutants of B. megaterium B71. The best mutant BUE‐118 produced 435 μg/ml of L‐methionine.