Indigenous and Environmental Modulation of Frequencies of Mutation in Lactobacillus plantarum

Abstract

Reliability of microbial (starter) strains in terms of quality, functional properties, growth performance, and robustness is essential for industrial applications. In an industrial fermentation process, the bacterium should be able to successfully withstand various adverse conditions during processing, such as acid, osmotic, temperature, and oxidative stresses. Besides the evolved defense mechanisms, stress-induced mutations participate in adaptive evolution for survival under stress conditions. However, this may lead to accumulation of mutant strains, which may be accompanied by loss of desired functional properties. Defining the effects of specific fermentation or processing conditions on the mutation frequency is an important step toward preventing loss of genome integrity and maintaining the productivity of industrial strains. Therefore, a set of Lactobacillus plantarum mutator reporter strains suitable for qualitative and quantitative analysis of lowfrequency mutation events was developed. The mutation reporter system constructed was validated by using chemical mutagenesis (N-methyl-N-nitro-N-nitrosoguanidine) and by controlled expression of endogenous candidate mutator genes (e.g., a truncated derivative of the L. plantarum hexA gene). Growth at different temperatures, under low-pH conditions, at high salt concentrations, or under starvation conditions did not have a significant effect on the mutation frequency. However, incubation with sublethal levels of hydrogen peroxide resulted in a 100-fold increase in the mutation frequency compared to the background mutation frequency. Importantly, when cells of L. plantarum were adapted to 42°C prior to treatment with sublethal levels of hydrogen peroxide, there was a 10-fold increase in survival after peroxide treatment, and there was a concomitant 50-fold decrease in the mutation frequency. These results show that specific environmental conditions encountered by bacteria may significantly influence the genetic stability of strains, while protection against mutagenic conditions may be obtained by pretreatment of cultures with other, nonmutagenic stress conditions.

Probiotic Properties and Bile Salt Hydrolase Activity of Some Isolated Lactic Acid Bacteria

“…Maximum growth (214%) at 0.05% H 2 O 2 was observed for isolate NMP47633. These results agreed with the results of Machielsen et al (2010), who found that exposure to 0.1% hydrogen peroxide caused a notable reduction in the viability of most tested Lactobacillus isolates. These authors also indicated that all strains tolerant to heat stress were also tolerant to oxidative stress.…”

The Evolution of Stress-Induced Hypermutation in Asexual Populations

“…As mutation is the ultimate source for novel adaptations, these results are relevant to broad aspects of biology. Emergence of drug resistance in bacteria (Cirz et al 2005; Cirz and Romesberg 2006, 2007); evolution of cancer cells and the emergence of chemotherapeutic resistance (Huang et al 2007; Bristow and Hill 2008; Ruan et al 2009); evolution of pesticide resistance in commercial crops (Gressel 2010); industrial applications using bacteria in stressful environments (Machielsen et al 2010); host–parasite coevolution (Pal et al 2007; Morgan et al 2010; Racey et al 2010); and evolution of pathogen virulence (Oliver et al 2000; Mérino et al 2002; Boshoff et al 2003; Gibson et al 2010).…”

Genome Instability in Lactobacillus rhamnosus GG

“…In addition, it might be worthwhile to avoid exposure to stress conditions that might activate transposons (7). However, pretreatment of cells under nonmutagenic conditions (42°C) appeared to protect them against subsequent increases in the mutation frequency due to oxidative stress, showing that sequential exposure to certain stresses may also be used to protect industrial strains against elevated mutation rates and in this way potentially enhance the stability of these strains (22).…”