Bridging the Gap: Type III Secretion Systems in Plant-Beneficial Bacteria

Type III secretion systems (T3SSs) are bacterial membrane-embedded nanomachines translocating effector proteins into the cytoplasm of eukaryotic cells. They have been intensively studied for their important roles in animal and plant bacterial diseases. Over the past two decades, genome sequencing has unveiled their ubiquitous distribution in many taxa of Gram-negative bacteria, including plant-beneficial ones. Here, we discuss the distribution and functions of the T3SS in two agronomically important bacterial groups: the symbiotic nodule-forming nitrogen-fixing rhizobia and the free-living plant-beneficial Pseudomonas spp. In legume-rhizobia symbiosis, T3SSs and their cognate effectors play important roles, including the modulation of the plant immune response and the initiation of the nodulation process in some cases. In plant-beneficial Pseudomonas spp., the roles of T3SSs are not fully understood, but pertain to plant immunity suppression, biocontrol against eukaryotic plant pathogens, mycorrhization facilitation, and possibly resistance against protist predation. The diversity of T3SSs in plant-beneficial bacteria points to their important roles in multifarious interkingdom interactions in the rhizosphere. We argue that the gap in research on T3SSs in plant-beneficial bacteria must be bridged to better understand bacteria/eukaryotes rhizosphere interactions and to support the development of efficient plant-growth promoting microbial inoculants.

Metagenomic Profiles of the Intestinal Virome of Long-Livers

The microbial community of the human intestine is important for maintaining human health. It has been reported that the gut microbiome changes with age, and it can be enrichedwith certain beneficial bacteria while also losing certain commensal bacteria.Little is known about the gut virome of long-livers. Our research aimed to extract, sequence and analyze the viral fraction of long-livers’ gut microbiota in comparison with those of young adults and the elderly. We were thereby able to characterize the gut virome profiles and viral diversity of three age groups. Keywords: aging, gut microbiome, viral metagenomics, bacteriophages

Superiority of Microencapsulated Essential Oils Compared With Common Essential Oils and Antibiotics: Effects on the Intestinal Health and Gut Microbiota of Weaning Piglet

Essential oils (EOs) have long been considered an alternative to antibiotics in the breeding industry. However, they are unstable and often present unpleasant odors, which hampers their application. Microencapsulation can protect the active gradients from oxidation and allow them to diffuse slowly in the gastrointestinal tract. The purpose of this study was to investigate the effect of microencapsulation technology on the biological function of EOs and the possibility of using microencapsulate EOs (MEEOs) as an alternative to antibiotics in weaning piglets. First, we prepared MEEOs and common EOs both containing 2% thymol, 5% carvacrol and 3% cinnamaldehyde (w/w/w). Then, a total of 48 weaning piglets were randomly allotted to six dietary treatments: (1) basal diet; (2) 75 mg/kg chlortetracycline; (3) 100 mg/kg common EOs; (4) 500 mg/kg common EOs; (5) 100 mg/kg MEEOs; and (6) 500 mg/kg MEEO. The trial lasted 28 days. The results showed that piglets in the 100 mg/kg MEEOs group had the lowest diarrhea index during days 15–28 (P < 0.05). In addition, 100 mg/kg MEEOs significantly alleviated intestinal oxidative stress and inflammation (P < 0.05), whereas 500 mg/kg common EOs caused intestinal oxidative stress (P < 0.05) and may lead to intestinal damage through activation of inflammatory cytokine response. MEEOs (100 mg/kg) significantly reduced the ratio of the relative abundance of potential pathogenic and beneficial bacteria in the cecum and colon (P < 0.05), thus contributing to the maintenance of intestinal health. On the other hand, chlortetracycline caused an increase in the ratio of the relative abundance of potential pathogenic and beneficial bacteria in the colon (P < 0.05), which could potentially have adverse effects on the intestine. The addition of a high dose of MEEOs may have adverse effects on the intestine and may lead to diarrhea by increasing the level of colonic acetic acid (P < 0.05). Collectively, the results suggest that microencapsulation technology significantly promotes the positive effect of EOs on the intestinal health of weaning piglets and reduces the adverse effect of EOs, and 100 mg/kg MEEOs are recommended as a health promoter in piglets during the weaning period.

Microbial Responses to the Reduction of Chemical Fertilizers in the Rhizosphere Soil of Flue-Cured Tobacco

The overuse of chemical fertilizers has resulted in the degradation of the physicochemical properties and negative changes in the microbial profiles of agricultural soil. These changes have disequilibrated the balance in agricultural ecology, which has resulted in overloaded land with low fertility and planting obstacles. To protect the agricultural soil from the effects of unsustainable fertilization strategies, experiments of the reduction of nitrogen fertilization at 10, 20, and 30% were implemented. In this study, the bacterial responses to the reduction of nitrogen fertilizer were investigated. The bacterial communities of the fertilizer-reducing treatments (D10F, D20F, and D30F) were different from those of the control group (CK). The alpha diversity was significantly increased in D20F compared to that of the CK. The analysis of beta diversity revealed variation of the bacterial communities between fertilizer-reducing treatments and CK, when the clusters of D10F, D20F, and D30F were separated. Chemical fertilizers played dominant roles in changing the bacterial community of D20F. Meanwhile, pH, soil organic matter, and six enzymes (soil sucrase, catalase, polyphenol oxidase, urease, acid phosphatase, and nitrite reductase) were responsible for the variation of the bacterial communities in fertilizer-reducing treatments. Moreover, four of the top 20 genera (unidentified JG30-KF-AS9, JG30-KF-CM45, Streptomyces, and Elsterales) were considered as key bacteria, which contributed to the variation of bacterial communities between fertilizer-reducing treatments and CK. These findings provide a theoretical basis for a fertilizer-reducing strategy in sustainable agriculture, and potentially contribute to the utilization of agricultural resources through screening plant beneficial bacteria from native low-fertility soil.

Mutation of Bacillus velezensis Using Corona Discharge

Bacillus velezensis is a kind of beneficial bacteria that is widely used in agriculture industry. Bacillus velezensis was irradiated with corona discharge generated by a needle-array high-voltage electrode. The results showed an improvement of activity of Bacillus velezensis by the corona discharge treatment was confirmed at an optimum input energy. Mutation of the Bacillus velezensis by the corona discharge treatment was also confirmed through an rRNA sequence alignment analysis. The enzyme activity of the mutated bacteria was greatly improved, which was a positive effect that can meet the production demand.

Effects of Etlingera elatior inflorescence extract on beneficial bacteria of the healthy human gut

Background: Etlingera species is an enduring plant in the Zingiberaceae family, with more than 100 species local to many countries. It has been utilized commonly as a culinary spice or eaten crude for its therapeutic impacts. This research is intended to study the effects of E. elatior inflorescence, which is commonly known as bunga kantan in Peninsular Malaysia, upon the microbiota of healthy human gut. Material and methods: The closed bud E. elatior inflorescence was cleaned and dried in the hot air oven and grounded into fine powder. The extract from the E. elatior inflorescence was obtained using hot water extraction method. The effects of the inflorescence extract on L. rhamnosus and L. acidophilus were studied through micro-broth dilution process where different concentration of sample was incorporated into a broth medium followed by the application of a standardized volume of Lactobacillus sp. into the medium of the 96 well plate. Results: Growth was seen in both L. rhamnosus and L. acidophilus, indicating that E. elatior inflorescence acted like a prebiotic towards L. acidophilus and L. rhamnosus Conclusion: E. elatior inflorescence concentrate acts like a prebiotic towards L. acidophilus incomparable to L. rhamnosus

THE COMPOST, A SOURCE OF PLANT BENEFICIAL BACTERIA WITH BIOCONTROL POTENTIAL

Recycling the sewage sludge from treatment plants is a common activity. The resulting compost is usually rich in plant nutrients and beneficial microorganisms. However, compost properties greatly differ depending on the nature of the fermented biomass and fermentation processes. The aim of this study was to analyze the microbial load of three different composts, in order to detect new bacterial strains with plant protection properties. Isolated bacteria were microbiologically characterized and evaluated for their potential to reduce soil-borne phytopathogenic fungi. Results showed a microbial load of approximately 106 CFU/g of compost. In the analyzed samples it was revealed that as bacterial load increases, the fungal amount decreases. Analyzing some newly isolated bacteria obtained from these composts, a good biocontrol potential against soil-borne pathogenic fungi was revealed. Some of the isolated bacterial strains revealed antifungal activity against Rhizoctonia solani and Sclerotinia sclerotiorum. These bacteria showed good colonization capacity and lytic enzymes production, correlated to antimicrobial activity. These compost-originated bacteria reveal high potential in pathogens inhibition. Therefore, the analyzed composts are recommended not only as soil fertility improvers, but also as potential suppressors of soil-borne pathogens. Results revealed these composts as source of plant beneficial bacteria with biological control potential.

Polyphenols—Gut Microbiota Interrelationship: A Transition to a New Generation of Prebiotics

The present review summarizes the studies carried out on this topic in the last five years. According to the new definitions, among all the compounds included in the group of prebiotics, polyphenols are probably the most important secondary metabolites produced by the plant kingdom. Many of these types of polyphenols have low bioavailability, therefore reaching the colon in unaltered form. Once in the colon, these compounds interact with the intestinal microbes bidirectionally by modulating them and, consequently, releasing metabolites. Despite much research on various metabolites, little is known about the chemistry of the metabolic routes used by different bacteria species. In this context, this review aims to investigate the prebiotic effect of polyphenols in preclinical and clinical studies, highlighting that the consumption of polyphenols leads to an increase in beneficial bacteria, as well as an increase in the production of valuable metabolites. In conclusion, there is much evidence in preclinical studies supporting the prebiotic effect of polyphenols, but further clinical studies are needed to investigate this effect in humans.