Abstract
Stress physiology of lactic acid bacteria (LAB) is crucial to their ecological fitness and applicational implications. As a self-imposed stress, lactic acid is the major final metabolic product of LAB and its accumulation can be detrimental to bacterial cells. However, the relationship between LAB carbohydrate metabolism, the primary energy supplying bioactivities, and lactic acid stress responses is not fully understood. Pediococcus pentosaceus has been recognized as an important cell factory and demonstrated probiotic activities. This study investigated behavior of P. pentosaceus under lactic and acetic acid stresses, particularly with supplementations of metabolizable carbohydrates. Lactic and acetic acid retain similar growth stagnation effect, and both resulted in cell death in P. pentosaceus. All metabolizable carbohydrates improved bacterial survival compared to lactic acid control, while xylooligosaccharides (XOS) exerted the highest viability protective efficacy, 0.82 log CFU/mL higher population survived than other carbohydrates after 30 h of incubation. RNA-seq pipeline showcased the intensive global transcriptional responses of P. pentosaceus to lactic acid, which caused significant regulations (more than 2 Log2 fold) of 16.5% of total mRNA coding genes. Glucose mainly led to gene suppressions (83 genes) while XOS led to gene up-regulations (19 genes) under lactic acid stress. RT-qPCR study found that RNA polymerase-centered transcriptional regulation is the primary regulatory approach in evaluated culture conditions. The synergy between lactic acid stress and carbohydrate metabolism should be attentively contemplated in future studies and applications.
Highlights
The applications of lactic acid bacteria (LAB) have been primarily associated with the production of fermented foods, such as vegetables, meats, dairies, and beverages (Zannini et al, 2016)
Different carbohydrates were supplemented in modified mMRS broth and the culture pHs were adjusted using sterilized LA or acetic acid (AA)
After inoculation of P. pentosaceus CGMCC 1.7665, optical density was monitored at optical density values at 595 nm wavelength (OD595) during the 30 h incubation (Figure 1)
Summary
The applications of lactic acid bacteria (LAB) have been primarily associated with the production of fermented foods, such as vegetables, meats, dairies, and beverages (Zannini et al, 2016). As a self-imposed stress, acidic stress is often gradually introduced to the bacterial culture in company with the proliferation of LAB and the accumulation of lactic acid (LA). These altered culture environments are likely harmful to LAB and could eventually stagnate culture growth and related bacterial activities (Liu et al, 2015; Papadimitriou et al, 2016). The utilization of LAB in both fermented food production and engineered industrial fermentation requires robust acid tolerance in featured bacteria strains (Wu et al, 2014). Acid tolerance of LAB is of great importance to their applications
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