Abstract
It is well known that the quality and quantity of bioactive metabolites in plants and microorganisms are affected by environmental factors. We applied heat stress as a promising approach to stimulate the production of antioxidants in four heat-tolerant bacterial strains (HT1 to HT4) isolated from Aushazia Lake, Qassim Region, Saudi Arabia. The phylogenetic analysis of the 16S rRNA sequences indicated that HT1, HT3 and HT4 belong to genus Bacillus. While HT2 is closely related to Pseudooceanicola marinus with 96.78% similarity. Heat stress differentially induced oxidative damage i.e., high lipid peroxidation, lipoxygenase and xanthine oxidase levels in HT strains. Subsequently, heat stress induced the levels of flavonoids and polyphenols in all strains and glutathione (GSH) in HT2. Heat stress also improved the antioxidant enzyme activities, namely, CAT, SOD and POX in all strains and thioredoxin activity in HT3 and HT4. While GSH cycle (GSH level and GPX, GR, Grx and GST activities) was only detectable and enhanced by heat stress in HT2. The hierarchical cluster analysis of the antioxidants also supported the strain-specific responses. In conclusion, heat stress is a promising approach to enhance antioxidant production in bacteria with potential applications in food quality improvement and health promotion.
Highlights
It is well known that the quality and quantity of bioactive metabolites in plants and microorganisms are affected by environmental factors
Out of 17 bacterial isolates recovered from Aushazia Lake at Qassim region of Saudi Arabia, four isolates demonstrated good growth ability and colonization under heat stress (56 °C)
The results indicated that the production of all forms of GSH at both control and heat stress conditions was very negligible by all heat tolerant (HT) isolates except HT2, as the latter showed a considerable production of all forms of GSH, as well as, the exposure to heat stress significantly enhanced this property in this isolate in case of reduced and total GSH
Summary
It is well known that the quality and quantity of bioactive metabolites in plants and microorganisms are affected by environmental factors. Heat stress differentially induced oxidative damage i.e., high lipid peroxidation, lipoxygenase and xanthine oxidase levels in HT strains. Heat stress is a promising approach to enhance antioxidant production in bacteria with potential applications in food quality improvement and health promotion. Antioxidants derived from small organisms such as bacteria and algae have recently been of growing interest to scientists in this field[12] In this vast range of different environments, living organisms are exposed to enormous changing environmental stressors including unfavorable temperature, salinity, adverse pH, high osmolarity, radiations and pollutants[13]. Heat stress can be defined as the rise in temperature beyond a threshold level for a period of time sufficient to cause irreversible damages to organisms This transient elevation in temperature is usually 10–15 °C above ambient, summer heat could reach temperature as high as 55 °C in places such as Arabian Desert. To our knowledge, the number of studies that investigated the physiological and biochemical responses of bacteria to extreme heat stress is negligible
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