Optimization of temperature and pH of the transconjugant produced by genus Lactobacillus and genus Lactococcus

Abstract

Probiotics are live microorganisms known to improve gut health which has become more evident in recent times. The present study aimed to optimize a trans-conjugant made via conjugation of two probiotic strains, genus Lactobacillus and genus Lactococcus. As Lactobacillus is a probiotic strain that shows slow growth in milk due to its inability to metabolize lactose and casein, the novel trans-conjugant was expected to possess improved growth rates by conjugating recipient bacterium Lactobacillus and donor bacterium Lactococcus for faster growth of Lactobacillus in milk for probiotic production. Lactobacillus and Lactococcus strains were isolated from curd and cheese respectively, confirmed with biochemical tests including Gram staining, catalase test, sugar fermentation test, Arginine hydrolysis tests and Arginine dihydrolase test, sub-cultured and then conjugated. Growth curves of the trans-conjugant at varied temperatures and pH were generated using spectrophotometry to determine optimum conditions for the growth of trans-conjugant. The results confirmed the presence and growth of trans-conjugant through selective growth in modified De Man Rogosa and Sharpe Agar (MRS) which indicated a color change from purple to yellow. Analysis of growth of Lactobacillus and trans-conjugant in MRS indicated a shorter lag phase in trans-conjugant by 2h when compared to that of Lactobacillus. Spectrophotometric analysis of trans-conjugant at varying temperatures indicated a significant difference (p = 0.0389) in growth rate at 30⁰C when compared to 4⁰C and 37⁰C whereas trans-conjugant at varying pH indicated the highest yield and best growth rate reaching stationary phases within 28h at pH 6 when compared to pH 4 and 5 with a log phase longer than 54h and pH 7 which reached stationary phase within 2h. The growth condition optimization of trans-conjugant with a significantly (p = 0.0304) higher growth rate by 2h compared to Lactobacillus revealed an optimum pH 6 and 30°C for faster microbial biomass production needed for probiotics.