Proteomic analysis reveals potential factors associated with enhanced EPS production in Streptococcus thermophilus ASCC 1275

Genomic and transcriptomic analysis of genes involved in exopolysaccharide biosynthesis by Streptococcus thermophilus IMAU20561 grown on different sources of nitrogen

Exopolysaccharides (EPSs), which are produced by lactic acid bacteria, have been found to improve the texture and functionality of fermented dairy products. In a previous study, four nitrogen sources were identified as affecting the yield, molecular weight and structure of EPSs produced by Streptococcus thermophilus IMAU20561 in M17 medium. In this genomic and transcriptomics study, a novel eps gene cluster responsible for assembly of repeating units of EPS is reported. This eps cluster (22.3 kb), consisting of 24 open reading frames, is located in the chromosomal DNA. To explore the biosynthetic mechanisms in EPS, we completed RNA-seq analysis of S. thermophilus IMAU20561 grown in four different nitrogen sources for 5 h (log phase) or 10 h (stationary phase). GO functional annotation showed that there was a significant enrichment of differentially expressed genes (DEGs) involved in: amino acid biosynthesis and metabolism; ribonucleotide biosynthesis and metabolism; IMP biosynthesis and metabolism; and phosphorus metabolism. KEGG functional annotation also indicated enrichment of DEGs involved in amino acid biosynthesis, glycolysis, phosphotransferase system, fructose, and mannose metabolism. Our findings provide a better understanding the genetic traits of S. thermophilus, the biosynthetic pathways needed for the production of EPS, and a theoretical basis for screening dairy starter cultures.

Enhanced electric field and charge polarity modulate the microencapsulation and stability of electrosprayed probiotic cells (Streptococcus thermophilus, ST44)

The effect of the polarity of the direct current electric field on the "organization" of Streptococcus thermophilus (ST44) probiotic cells within electrosprayed maltodextrin microcapsules was investigated. The generated electrostatic forces between the negatively surface-charged probiotic cells and the applied negative polarity on the electrospray nozzle, allowed to control the location of the cells towards the core of the electrosprayed microcapsules. This "organization" of the cells increased the evaporation of the solvent (water) and successively the glass transition temperature (Tg) of the electrosprayed microcapsules. Moreover, the utilization of auxiliary ring-shaped electrodes between the nozzle and the collector, enhanced the electric field strength and contributed further to the increase of the Tg. Numerical simulation, through Finite Element Method (FEM), shed light to the effects of the additional ring-electrode on the electric field strength, potential distribution, and controlled deposition of the capsules on the collector. Furthermore, when the cells were located at the core of the microcapsules their viability was significantly improved for up to 2 weeks of storage at 25 °C and 35% RH, compared to the case where the probiotics were distributed towards the surface. Overall, this study reports a method to manipulate the encapsulation of the surface charged probiotic cells within electrosprayed microcapsules, utilizing the polarity of the electric field and additional ring-electrodes.

Effects of galactosyltransferase on EPS biosynthesis and freeze-drying resistance of Lactobacillus acidophilus NCFM

Galactosyltransferase (GalT) is an important enzyme in synthesizing exopolysaccharide (EPS), the major polymer of biofilms protecting cells from severe conditions. However, the contribution to, and regulatory mechanism of GalT, in stressor resistance are still unclear. Herein, we successfully overexpressed GalT in Lactobacillus acidophilus NCFM by genetic engineering. The GalT activity and freeze-drying survival rate of the recombinant strain were significantly enhanced. The EPS yield also increased by 17.8%, indicating a positive relationship between freeze-drying resistance and EPS. RNA-Seq revealed that GalT could regulate the flux of the membrane transport system, pivotal sugar-related metabolic pathways, and promote quorum sensing to facilitate EPS biosynthesis, which enhanced freeze-drying resistance. The findings concretely prove that the mechanism of GalT regulating EPS biosynthesis plays an important role in protecting lactic acid bacteria from freeze-drying stress.

Effects of trace PFOA on microbial community and metabolisms: Microbial selectivity, regulations and risks

Perfluorooctanoic acid (PFOA), a "forever chemical", is continuously discharged and mitigated in the environment despite its production and use being severely restricted globally. Due to the transformation, attachment, and adsorption of PFOA in aquatic environments, PFOA accumulates in the porous media of sediments, soils, and vadose regions. However, the impact of trace PFOA in the porous media on interstitial water and water safety is not clear. In this work, we simulated a porous media layer using a sand column and explored the effects of µg-level PFOA migration on microbial community alternation, microbial function regulation, and the generation and spread of microbial risks. After 60 days of PFOA stimulation, Proteobacteria became the dominant phylum with an abundance of 91.8%, since it carried 71% of the antibiotic resistance genes (ARGs). Meanwhile, the halogen-related Dechloromonas abundance increased from 0.4% to 10.6%. In addition, PFOA significantly stimulated protein (more than 1288%) and polysaccharides (more than 4417%) production by up-regulating amino acid metabolism (p< 0.001) and membrane transport (p < 0.001) to accelerate the microbial aggregation. More importantly, the rapidly forming biofilm immobilized and blocked PFOA. The more active antioxidant system repaired the damaged cell membrane by significantly up-regulating glycerophospholipid metabolism and peptidoglycan biosynthesis. It is worth noting that PFOA increased the abundance of antibiotic resistance genes (ARGs) and human bacterial pathogens (HBPs) in porous media by 30% and 106%. PFOA increased the proportion of vertical transmission ARGs (vARGs), and co-occurrence network analysis (r ≥ 0.8, p ≤ 0.01) verified that vARGs were mainly mediated by HBPs. A comprehensive understanding of PFOA interactions with its microecological environment is provided.

Comparative transcriptome analysis for the biosynthesis of antioxidant exopolysaccharide in Streptococcus thermophilus CS6

BACKGROUND

Food grade Streptococcus thermophilus produces biological exopolysaccharides (EPSs) with great potential with respect to catering for higher health-promoting demands; however, how S. thermophilus regulates the biosynthesis of EPS is not completely understood, decelerating the application of these polymers. In our previous study, maltose, soy peptone and initial pH were three key factors of enhancing EPS yield in S. thermophilus CS6. Therefore, we aimed to investigate the regulating mechanisms of EPS biosynthesis in S. thermophilus CS6 via the method of comparative transcriptome and differential carbohydrate metabolism.

RESULTS

Soy peptone addition (58.6 g L^-1 ) and a moderate pH (6.5) contributed to a high bacterial biomass and a high EPS yield (407 mg L^-1 ). Maltose, soy peptone and initial pH greatly influenced lactose utilization in CS6. Soy peptone addition induced a high accumulation of mannose and arabinose in intracellular CS6, differential monosaccharide composition (mannose, glucose and arabinose) in EPS and high radical [2,2-diphenyl-1-picrylhydrazyl, superoxide and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)] scavenging activities. Carbohydrate transportation, sugar activation and eps cluster-associated genes were differentially expressed to regulate EPS biosynthesis. Correlation analysis indicated high production of EPSs depended on high expression of lacS, galPMKUTE, pgm, gt2-5&4-1 and epsLM.

CONCLUSION

The production of antioxidant EPS in S. thermophilus CS6 depended on the regulation of galactose metabolism cluster and eps cluster. The present study recommends a new approach for enhancing EPS production by transcriptomic regulation for further food and health application of EPS. © 2022 Society of Chemical Industry.

Proteomic perspectives on thermotolerant microbes: an updated review

INTRODUCTION

Thermotolerant microbes are a group of microorganisms that survive in elevated temperatures. The thermotolerant microbes, which are found in geothermal heat zones, grow at temperatures of or above 45°C. The proteins present in such microbes are optimally active at these elevated temperatures. Hence, therefore, serves as an advantage in various biotechnological applications. In the last few years, scientists have tried to understand the molecular mechanisms behind the maintenance of the structural integrity of the cell and to study the stability of various thermotolerant proteins at extreme temperatures. Proteomic analysis is the solution for this search. Applying novel proteomic tools determines the proteins involved in the thermostability of microbes at elevated temperatures.

METHODS

Advanced proteomic techniques like Mass spectrometry, nano-LC-MS, protein microarray, ICAT, iTRAQ, and SILAC could enable the screening and identification of novel thermostable proteins.

RESULTS

This review provides up-to-date details on the protein signature of various thermotolerant microbes analyzed through advanced proteomic tools concerning relevant research articles. The protein complex composition from various thermotolerant microbes cultured at different temperatures, their structural arrangement, and functional efficiency of the protein was reviewed and reported.

CONCLUSION

This review provides an overview of thermotolerant microbes, their enzymes, and the proteomic tools implemented to characterize them. This article also reviewed a comprehensive view of the current proteomic approaches for protein profiling in thermotolerant microbes.