Effect of aeration on the growth and metabolism of lactobacillus acidophilus farr

Abstract

The influence of aerobic culture conditions on the growth of Lactobacillus acidophilus Farr was studied. This organism was cultured on modified-MRS media having limited amount of glucose aerobically or an nonaeration culture condition. Under the non-aeration culture conditions, these cells which have long been known as homofermentative lactic acid bacteria showed their typical character. But under the aerobic conditions, this strain abnormally produced considerable amount of acetic acid besides formic acid and ethanol, indicating heterofermentative nature. The value of Y glucose and YATP also varied within the range of 18.3 to 70.0 and 8.34 to 19.39 depending upon the culture conditions. The specific growth rate, $\mu$, also increased spharply from 0.23 to 0.98 hr$^{-1}$. These deviation from homofermentative character is shown to have a close interaction with the action of NADH-oxidase, of which activity is highly increased by the presense of oxygen. The high NADH-oxidase synthesis together with the participation of phosphoroclastic split under the aerobic culture conditions can make an explanation on the shift from homolactic to heterolactic fermentation of L. acidophilus Farr. In addition, morphological change is occurred by aeration, namely chain form converting to individual bacillus form. It is also examined that L. acidophilus showed colonial alteration on solid media. These rough(R) and smooth(S) colonial variants are stable up to 30 generations on continuous culture conditions, and showed a similar growth characteristics.