Microencapsulation of Bacillus Strains for Improving Wheat (Triticum turgidum Subsp. durum) Growth and Development.

Bio-formulation technologies have a limited impact on agricultural productivity in developing countries, especially those based on plant growth-promoting rhizobacteria. Thus, calcium alginate microbeads were synthesized and used for the protection and delivery of three beneficial Bacillus strains for agricultural applications. The process of encapsulation had a high yield per gram for all bacteria and the microbeads protected the Bacillus strains, allowing their survival, after 12 months of storage at room temperature. Microbead analysis was carried out by observing the rate of swelling and biodegradation of the beads and the released-establishment of bacteria in the soil. These results showed that there is an increase of around 75% in bead swelling on average, which allows for larger pores, and the effective release and subsequent establishment of the bacteria in the soil. Biodegradation of microbeads in the soil was gradual: in the first week, they increased their weight (75%), which consistently results in the swelling ratio. The co-inoculation of the encapsulated strain TRQ8 with the other two encapsulated strains showed plant growth promotion. TRQ8 + TRQ65 and TRQ8 + TE3T bacteria showed increases in different biometric parameters of wheat plants, such as stem height, root length, dry weight, and chlorophyll content. Thus, here we demonstrated that the application of alginate microbeads containing the studied strains showed a positive effect on wheat plants.

Enrichment of Verrucomicrobia, Actinobacteria and Burkholderiales drives selection of bacterial community from soil by maize roots in a traditional milpa agroecosystem.

Milpas are rain-fed agroecosystems involving domesticated, semi-domesticated and tolerated plant species that combine maize with a large variety of other crop, tree or shrub species. Milpas are low input and low-tillage, yet highly productive agroecosystems, which have been maintained over millennia in indigenous communities in Mexico and other countries in Central America. Thus, milpas may retain ancient plant-microorganisms interactions, which could have been lost in modern high-tillage monocultures with large agrochemical input. In this work, we performed high-throughput 16S ribosomal DNA sequencing of soil adjacent to maize roots and bulk soil sampled at 30 cm from the base of the plants. We found that the bacterial communities of maize root soil had a lower alpha diversity, suggesting selection of microorganisms by maize-roots from the bulk-soil community. Beta diversity analysis confirmed that these environments harbor two distinct microbial communities; differences were driven by members of phyla Verrucomicrobia and Actinobacteria, as well as the order Burkholderiales (Betaproteobacteria), all of which had higher relative abundance in soil adjacent to the roots. Numerous studies have shown the influence of maize plants on bacterial communities found in soil attached tightly to the roots; here we further show that the influence of maize roots at milpas on bacterial communities is detectable even in plant-free soil collected nearby. We propose that members of Verrucomicrobia and other phyla found in the rhizosphere may establish beneficial plant-microbe interactions with maize roots in milpas, and propose to address their cultivation for future studies on ecology and potential use.

The RNPP family of quorum-sensing proteins in Gram-positive bacteria.

Quorum sensing is one of several mechanisms that bacterial cells use to interact with each other and coordinate certain physiological processes in response to cell density. This mechanism is mediated by extracellular signaling molecules; once a critical threshold concentration has been reached, a target sensor kinase or response regulator is activated (or repressed), facilitating the expression of quorum sensing-dependent genes. Gram-positive bacteria mostly use oligo-peptides as signaling molecules. These cells have a special kind of quorum-sensing systems in which the receptor protein interacts directly with its cognate signaling peptide. The receptors are either Rap phosphatases or transcriptional regulators and integrate the protein family RNPP, from Rap, Npr, PlcR, and PrgX. These quorum-sensing systems control several microbial processes, like sporulation, virulence, biofilm formation, conjugation, and production of extracellular enzymes. Insights of the mechanism of protein-signaling peptide binding as well as the molecular interaction among receptor protein, signaling peptide, and target DNA have changed some earlier perceptions. In spite of the increased knowledge and the potential biotechnological applications of these quorum-sensing systems, few examples on engineering for biotechnological applications have been published. Real applications will arise only when researchers working in applied microbiology and biotechnology are aware of the importance of quorum-sensing systems for health and bioprocess applications.