The chapter focuses on analysis of microbial communities of the plant rhizosphere, which has been driven by the greatly advanced DNA- or RNA-based molecular techniques. The application of these tools has allowed us to understand, at the phylogenetic level, which organisms occur together at the plant root. We can further infer, from the nucleic-acid-based data, which organisms may be positively or negatively selected by the plant root. On the other hand, using these very advanced tools, it has been difficult to discern the interactions that are a key to determining the intricacies of the life of root-associated microorganisms. The chapter examines the existing state of the art in this area, making use of case studies that illustrate the key achievements that have been made. Major points discussed are the intricacies of the use of environmental nucleic acids for the analyses, as well as the effects of plant physiology and plant type in shaping the plant-associated microbiota. In addition, we critically examine how to move forward in our examination of microbial interactions in the rhizosphere. It is vital that the emerging tools are now applied to dissect the interactions between microorganisms at the micrometer level, which is the scale at which microbial signals are perceived and obeyed.
COBISS.SI-ID: 4234360
In a social process called Quorum Sensing (QS) bacteria secrete and share signaling molecules that bind to specific receptors and induce adaptive responses within the population. We use the ComQXP QS system of Bacillus subtilis to study the intracellular co-dependence of two essential QS functions: signal production and signal response. We demonstrate that the QS signal-deficient mutants have an overly responsive QS system, disturbed balance between the primary and secondary metabolism and overproduce the secondary metabolite surfactin in the presence of exogenously provided signal. Such mutants fail to compete with the socially active signal producers due to surfactin-related mechanisms that discriminate the two populations. We believe that a constraint on signal production preserves QS functionality in the natural microbial populations. The work is also important becasue it adresses a Gram positive bacterium Bacillus subtilis, where QS is much less understood than in Gram negative bacteria, and also because B. subtilis is highly important industry, and for animal and plant health as probiotic and biopesticide. It also forms spores, the most resistant cells on our planet.
COBISS.SI-ID: 4358008
Exopolymeric substances (EPS) are important for biofilm formation and their chemical composition may influence the biofilm properties. To explore these relationships chemical composition of EPS from Bacillus subtilis biofilms grown in different media was studied. We observed marked differences in composition of EPS polymers isolated from biofilms grown in different media. The polysaccharide levan dominated the EPS in biofilms grown in sucrose rich media in addition to proteins and DNA. Biofilms also differed in thickness and the biofilm defective phenotypes of tasA and eps mutants were partially compensated in the sucrose rich medium. Since sucrose is essential for synthesis of levan and the presence of levan was confirmed in all biofilms grown in media containing sucrose, this study for the first time shows that levan, although not essential for biofilm formation, can be a structural and possibly stabilizing component of B. subtilis floating biofilms. In addition, we propose that this polysaccharide, when incorporated into the biofilm EPS, may also serve as a nutritional reserve.
COBISS.SI-ID: 4242040
This work explores the ecological context for evolution of quorum sensing diversity in bacteria, where social communication is limited to members of the same quorum sensing type (pherotype). We sampled isolates of Bacillus subtilis from soil on a microgeographical scale and identified three ecologically distinct phylogenetic groups (ecotypes) and three pherotypes. Each pherotype was strongly associated with a different ecotype. Each ecotype, however, contained one or more minority pherotypes shared with the other B. subtilis ecotypes and with more distantly related species taxa. The work published in an important journal (IF=5.7) is the first survey of pherotype diversity in relation to ecotypes proposing novel hypotheses for further testing the ecological drivers of social evolution. The work has been put forward as a significant scientific contribution in understanding the ecological role of diversity by FEMS microbiology ecology reviews. The importance of the work is also reflected in being selected as an oral presentation for the ISME congress in 2011 and 2013, among 1700 and 2000 contributed abstracts, respectively.
COBISS.SI-ID: 4044408
The chapter published by the eminent international publisher “Springer” focuses on diversity of aerobic spore-forming bacteria in soil. This was traditionally determined by physiological characterization of laboratory isolates indicating considerable physiological diversity, which reflects the wide variety of soil ecosystem functions carried out by these organisms. The application of cultivation-independent molecular techniques has now transformed studies of soil bacterial diversity and has uncovered much higher diversity in spore-formers than was previously anticipated. Aerobic spore-formers also provide excellent models for investigation of the mechanisms driving microbial diversity in soil. The article describes the insight that they are providing on biogeography of soil bacteria and the important roles of microbial communication, through signaling compounds, spatial scale and horizontal gene transfer on bacterial evolution, ecotype formation and speciation. This is the first comprehensive overview of the diversity of endospore-forming bacteria in soil. The chapter stresses their relevance as model organisms for ecological studies and their vast biotechnological potential. The chapter suggests new research directions in the field of diversity and evolution of spore-formers. It also brings out the importance of social interactions for understanding the ecology of these microorganisms.
COBISS.SI-ID: 3897720