Zhen Jiao

Expression of PprI from Deinococcus radiodurans Improves Lactic Acid Production and Stress Tolerance in Lactococcus lactis.

PprI is a general switch protein that regulates the expression of certain proteins involved in pathways of cellular resistance in the extremophilic bacterium Deinococcus radiodurans. In this study, we transformed pprI into Lactococcus lactis strain MG1363 using the lactococcal shuttle vector pMG36e and investigated its effects on the tolerance and lactic acid production of L. lactis while under stress. PprI was stably expressed in L. lactis as confirmed by western blot assays. L. lactis expressing PprI exhibited significantly improved resistance to oxidative stress and high osmotic pressure. This enhanced cellular tolerance to stressors might be due to the regulation of resistance-related genes (e.g., recA, recO, sodA, and nah) by pprI. Moreover, transformed L. lactis demonstrated increased lactic acid production, attributed to enhanced lactate dehydrogenase activity. These results suggest that pprI can improve the tolerance of L. lactis to environmental stresses, and this transformed bacterial strain is a promising candidate for industrial applications of lactic acid production.

Improving the fermentation quality of wheat straw silage stored at low temperature by psychrotrophic lactic acid bacteria.

This study aimed to explore the feasible approaches to develop a silage production technique in regions with low temperatures. An effective low-temperature silage technology system was constructed and two frigostable Lactobacillus (L.) strains isolated from alpine pastures were selected and proved to be available for wheat straw silage at 5°C. The strains QZ227 and QZ887 were both identified as L. plantarum according to the phenotype, 16S rRNA, and RecA gene analysis. QZ227, QZ887 and a commercial inoculant FG1 consisting of L. plantarum were effective for improving the fermentation quality of wheat straws silage at 5°C for 30 days as indicated by the higher content of lactic acid and for 60 days by lower pH values, while the control with sterile water instead conferred reduced benefits. Additionally, silages fermented at low temperature proved to be acceptable for feeding livestock after being placed in a simulated environmental temperature of 20°C for 14 days to detect its edibility during the early spring when the temperature begins to rise. Both QZ227 and QZ887 showed potential applications of silage making in frigid areas and were effective inoculants in a low-temperature silage technology system.

Screening of Probiotic Activities of Lactobacilli Strains Isolated from Traditional Tibetan Qula, A Raw Yak Milk Cheese

In this study, 69 lactobacilli isolated from Tibetan Qula, a raw yak milk cheese, were screened for their potential use as probiotics. The isolates were tested in terms of: Their ability to survive at pH 2.0, pH 3.0, and in the presence of 0.3% bile salts; tolerance of simulated gastric and intestinal juices; antimicrobial activity; sensitivity against 11 specific antibiotics; and their cell surface hydrophobicity. The results show that out of the 69 strains, 29 strains (42%) had survival rates above 90% after 2 h of incubation at pH values of 2.0 or 3.0. Of these 29 strains, 21 strains showed a tolerance for 0.3% bile salt. Incubation of these 21 isolates in simulated gastrointestinal fluid for 3 h revealed survival rates above 90%; the survival rate for 20 of these isolates remained above 90% after 4 h of incubation in simulated intestinal fluid. The viable counts of bacteria after incubation in simulated gastric fluid for 3 h and simulated intestinal fluid for 4 h were both significantly different compared with the counts at 0 h (p<0.001). Further screening performed on the above 20 isolates indicated that all 20 lactobacilli strains exhibited inhibitory activity against Micrococcus luteus ATCC 4698, Bacillus subtilis ATCC 6633, Listeria monocytogenes ATCC 19115, and Salmonella enterica ATCC 43971. Moreover, all of the strains were resistant to vancomycin and streptomycin. Of the 20 strains, three were resistant to all 11 elected antibiotics (ciprofloxacin, erythromycin, tetracycline, penicillin G, ampicillin, streptomycin, polymyxin B, vancomycin, chloramphenicol, rifampicin, and gentamicin) in this study, and five were sensitive to more than half of the antibiotics. Additionally, the cell surface hydrophobicity of seven of the 20 lactobacilli strains was above 70%, including strains Lactobacillus casei 1,133 (92%), Lactobacillus plantarum 1086-1 (82%), Lactobacillus casei 1089 (81%), Lactobacillus casei 1138 (79%), Lactobacillus buchneri 1059 (78%), Lactobacillus plantarum1141 (75%), and Lactobacillus plantarum 1197 (71%). Together, these results suggest that these seven strains are good probiotic candidates, and that tolerance against bile acid, simulated gastric and intestinal juices, antimicrobial activity, antibiotic resistance, and cell surface hydrophobicity could be adopted for preliminary screening of potentially probiotic lactobacilli.

Ensilage of oats and wheatgrass under natural alpine climatic conditions by indigenous lactic acid bacteria species isolated from high-cold areas

Five different species of selected broad-spectrum antibiotic lactic acid bacteria isolated from extremely high–cold areas were used as starters to ferment indigenous forage oats and wheatgrass under rigid alpine climatic conditions. The five isolates were Lactobacillus plantarum QZ227, Enterococcus mundtii QZ251, Pediococcus cellicola QZ311, Leuconostoc mesenteroides QZ1137 and Lactococcus lactis QZ613, and commercial Lactobacillus plantarum FG1 was used as the positive control and sterile water as the negative control. The minimum and maximum temperatures were −22°C and 23°C during the fermentation process, respectively. The pH of wheatgrass silage fermented by the QZ227 and FG1 inocula reached the expected values (≤4.15) although the pathogens detected in the silage should be further investigated. All of the inocula additives used in this study were effective in improving the fermentation quality of oat silage as indicated by the higher content of lactic acid, lower pH values (≤4.17) and significant inhibition of pathogens. QZ227 exhibited a fermentation ability that was comparable with the commercial inoculum FG1 for the whole process, and the deterioration rate was significantly lower than for FG1 after storage for 7 months. The pathogens Escherichia coli, mold and yeast were counted and isolated from the deteriorated silage. E. coli were the main NH3-N producer while F. fungi and yeast produced very little.

Ar+ beam implantation causes enhancement of salt stress tolerance in highland barley

This study examines the effects of ionizing radiation (control, 4 × 1016, 6 × 1016, 9.5 × 1016, and 15 × 1016 Ar+/cm2) on some physio-biochemical and molecular responses of highland barley (Hordeum vulgare L. ssp. vulgare) under salt stress for 0, 24, 48, and 96 h. The growth parameters of highland barley were the highest at the dose of 9.5 × 1016 Ar+/cm2, but the lowest at 15 × 1016 Ar+/cm2 dose. The malondialdehyde (MDA) content increased with increasing irradiation dose and peaked at 15 × 1016 Ar+/cm2 during stress treatments. The activities of antioxidant enzymes and proline accumulation showed different changes than MDA following ion beam irradiation toward stress conditions, at the dose of 15 × 1016 Ar+/cm2, antioxidant enzyme activities and proline content were the lowest compared with their corresponding controls, while at the dose of 9.5 × 1016 Ar+/cm2 antioxidant enzyme activities and proline content were the highest. Moreover, the expression of salt-related gene followed the same pattern as that of the antioxidant enzymes. Our results suggest that the dose of 9.5 × 1016 Ar+/cm2 alleviates salt stress by modulating the physio-biochemical responses and eliciting the stress signal transduction in plants.