Brazilian Ironstone Plant Communities as Reservoirs of Culturable Bacteria With Diverse Biotechnological Potential

Selenium and Bacillus proteolyticus SES increased Cu-Cd-Cr uptake by ryegrass: highlighting the significance of key taxa and soil enzyme activity

Many studies have focused their attention on strategies to improve soil phytoremediation efficiency. In this study, a pot experiment was carried out to investigate whether Se and Bacillus proteolyticus SES promote Cu-Cd-Cr uptake by ryegrass. To explore the effect mechanism of Se and Bacillus proteolyticus SES, rhizosphere soil physiochemical properties and rhizosphere soil bacterial properties were determined further. The findings showed that Se and Bacillus proteolyticus SES reduced 23.04% Cu, 36.85% Cd, and 9.85% Cr from the rhizosphere soil of ryegrass. Further analysis revealed that soil pH, organic matter, soil enzyme activities, and soil microbial properties were changed with Se and Bacillus proteolyticus SES application. Notably, rhizosphere key taxa (Bacteroidetes, Actinobacteria, Firmicutes, Patescibacteria, Verrucomicrobia, Chloroflexi, etc.) were significantly enriched in rhizosphere soil of ryegrass, and those taxa abundance were positively correlated with soil heavy metal contents (P < 0.01). Our study also demonstrated that in terms of explaining variations of soil Cu-Cd-Cr content under Se and Bacillus proteolyticus SES treatment, soil enzyme activities (catalase and acid phosphatase) and soil microbe properties showed 42.5% and 12.2% contributions value, respectively. Overall, our study provided solid evidence again that Se and Bacillus proteolyticus SES facilitated phytoextraction of soil Cu-Cd-Cr, and elucidated the effect of soil key microorganism and chemical factor.

Does Organic Farming Increase Raspberry Quality, Aroma and Beneficial Bacterial Biodiversity?

Plant-associated microbes can shape plant phenotype, performance, and productivity. Cultivation methods can influence the plant microbiome structure and differences observed in the nutritional quality of differently grown fruits might be due to variations in the microbiome taxonomic and functional composition. Here, the influence of organic and integrated pest management (IPM) cultivation on quality, aroma and microbiome of raspberry (Rubus idaeus L.) fruits was evaluated. Differences in the fruit microbiome of organic and IPM raspberry were examined by next-generation sequencing and bacterial isolates characterization to highlight the potential contribution of the resident-microflora to fruit characteristics and aroma. The cultivation method strongly influenced fruit nutraceutical traits, aroma and epiphytic bacterial biocoenosis. Organic cultivation resulted in smaller fruits with a higher anthocyanidins content and lower titratable acidity content in comparison to IPM berries. Management practices also influenced the amounts of acids, ketones, aldehydes and monoterpenes, emitted by fruits. Our results suggest that the effects on fruit quality could be related to differences in the population of Gluconobacter, Sphingomonas, Rosenbergiella, Brevibacillus and Methylobacterium on fruit. Finally, changes in fruit aroma can be partly explained by volatile organic compounds (VOCs) emitted by key bacterial genera characterizing organic and IPM raspberry fruits.

Bacterial communities associated with sugarcane under different agricultural management exhibit a diversity of plant growth-promoting traits and evidence of synergistic effect

Plant-associated microbiomes have been a target of interest for the prospection of microorganisms, which may be acting as effectors to increase agricultural productivity. For years, the search for beneficial microorganisms has been carried out from the characterization of functional traits of growth-promotion using tests with a few isolates. However, eventually, the expectations with positive results may not be realized when the evaluation is performed in association with plants. In our study, we accessed the cultivable sugarcane microbiome under two conditions of agronomic management: organic and conventional. From the use of a new customized culture medium, we recovered 944 endophytic and epiphytic bacterial communities derived from plant roots, stalks, leaves, and rhizospheric soil. This could be accomplished by using a large-scale approach, initially performing an in planta (Cynodon dactylon) screening process of inoculation to avoid early incompatibility. The inoculation was performed using the bacterial communities, considering that in this way, they could act synergistically. This process resulted in 38 candidate communities, 17 of which had higher Indole-3-acetic acid (IAA) production and phosphate solubilization activity and, were submitted to a new in planta test using Brachiaria ruziziensis and quantification of functional traits for growth-promotion and physiological tests. Enrichment analysis of selected communities has shown that they derived mainly from epiphytic populations of sugarcane stalks under conventional management. The sequencing of the V3-V4 region of the 16S rRNA gene revealed 34 genera and 24 species distributed among the phylum Proteobacteria, Bacteroidetes, Firmicutes, and Actinobacteria. We also observed a network of genera in these communities where the genus Chryseobacterium stands out with a greater degree of interaction, indicating a possible direct or indirect role as a keystone taxon in communities with plant-growth promotion capacities. From the results achieved, we can conclude that the approach is useful in the recovery of a set of sugarcane bacterial communities and that there is, evidence of synergistic action providing benefits to plants, and that they are compatible with plants of the same family (Poaceae). Thus, we are reporting the beneficial bacterial communities identified as suitable candidates with rated potential to be exploited as bioinoculants for crops.

A brief history of research in campo rupestre: identifying research priorities and revisiting the geographical distribution of an ancient, widespread Neotropical biome

Few ecologists and evolutionary biologists are familiar with the ecology and evolution of the campo rupestre, an ancient azonal peinobiome characterized by a fire-prone, nutrient-impoverished, montane vegetation mosaic, home to thousands of endemics and climate refugia. With the goal of providing a synthetic view of the campo rupestre, we provide a brief historical account of the biological research, revisit its geographical distribution and identify knowledge gaps. The azonal campo rupestre is distributed as isolated and naturally fragmented sky islands, mostly in Central and Eastern Brazil and in the Guyana Shield, with significant areas across the Amazon, Cerrado, Atlantic Forest, Caatinga and Pantanal. Our proposal to elevate campo rupestre to the level of biome is expected to improve communication among scientists and consolidate the use of the term campo rupestre in the ecological and evolutionary literature, as is the case for analogous ecosystems, such as kwongan, fynbos, páramos and tepuis. Based on the identification of knowledge gaps, we propose a research programme comprising ten key topics that can foster our understanding of the ecology and evolution of campo rupestre and, potentially, support conservation strategies.

Bacterial endophytes from Lycoris radiata promote the accumulation of Amaryllidaceae alkaloids

Lycoris radiata is the major source of Amaryllidaceae alkaloids, having various medicinal activities. However, the low content of these alkaloids in planta limits their pharmaceutical development and utilization. In this study, the ability of bacterial endophytes to enhance the accumulation of five important Amaryllidaceae alkaloids was investigated. A total of 188 bacterial endophytes were isolated from L. radiata and their composition and diversity were analyzed. Fourteen ones were demonstrated to significantly increase the concentration of the alkaloids of interest in different organs, up to 11.1-fold over the control level, with no adverse influence on the plant growth. An additional 3 bacterial endophytes were found to significantly increase the dry weight of L. radiata with no adverse influence on the concentration of the alkaloids in planta, so the total yield of alkaloids in planta was increased up to 2.4-fold over the control level. Considering the plant growth-promoting abilities of these bacterial endophytes, it is speculated that the indole-3-acetic acid and siderophore secreted by them, combined with their nitrogen fixation ability, may contribute to the enhanced plant growth and the increased alkaloid accumulation in L. radiata. To our knowledge, this work is firstly defining the diversity of culturable bacterial endophytes in L. radiata and determining which species promoted the accumulation of Amaryllidaceae alkaloids. It provides several valuable bacterial inoculants that can be further applied to improve alkaloid production in L. radiata and broadens our understanding of the interactions between a medicinal plant and the bacterial endophytes.

Serratia liquefaciens FG3 isolated from a metallophyte plant sheds light on the evolution and mechanisms of adaptive traits in extreme environments

Serratia liquefaciens strain FG3 (SlFG3), isolated from the flower of Stachytarpheta glabra in the Brazilian ferruginous fields, has distinctive genomic, adaptive, and biotechnological potential. Herein, using a combination of genomics and molecular approaches, we unlocked the evolution of the adaptive traits acquired by S1FG3, which exhibits the second largest chromosome containing the largest conjugative plasmids described for Serratia. Comparative analysis revealed the presence of 18 genomic islands and 311 unique protein families involved in distinct adaptive features. S1FG3 has a diversified repertoire of genes associated with Nonribosomal peptides (NRPs/PKS), a complete and functional cluster related to cellulose synthesis, and an extensive and functional repertoire of oxidative metabolism genes. In addition, S1FG3 possesses a complete pathway related to protocatecuate and chloroaromatic degradation, and a complete repertoire of genes related to DNA repair and protection that includes mechanisms related to UV light tolerance, redox process resistance, and a laterally acquired capacity to protect DNA using phosphorothioation. These findings summarize that SlFG3 is well-adapted to different biotic and abiotic stress situations imposed by extreme conditions associated with ferruginous fields, unlocking the impact of the lateral gene transfer to adjust the genome for extreme environments, and providing insight into the evolution of prokaryotes.

Biotechnological potential of plant growth-promoting bacteria from the roots and rhizospheres of endemic plants in ironstone vegetation in southeastern Brazil

Microorganisms associated with plants have a great biotechnological potential, but investigations of these microorganisms associated with native plants in peculiar environments has been incipient. The objective of this study was to analyze the plant growth-promoting bacteria potential of cultivable bacteria associated with rare plants from the ferruginous rocky fields of the Brazilian Iron Quadrangle. The roots and rhizospheres of nine endemic plants species and samples of a root found in a lateritiric duricrust (canga) cave were collected, the culturable bacteria isolated and prospected for distinct biotechnological and ecological potentials. Out of the 148 isolates obtained, 8 (5.4%) showed potential to promote plant growth, whereas 4 (2.7%) isolates acted as biocontrol agents against Xanthomonas citri pathotype A (Xac306), reducing the cancrotic lesions by more than 60% when co-inoculated with this phytopathogen in Citrus sinensis plants. Moreover, other 4 (2.7%) isolates were classified as potential bioremediation agents, being able to withstand high concentrations of arsenite (5 mM As³⁺) and arsenate (800 mM As⁵⁺), by removing up to 35% and 15% of this metalloid in solution, respectively. These same four isolates had a positive influence on the growth of both the roots and the aerial parts when inoculated with tomato seeds in the soil contaminated with arsenic. This is the first time that an investigation highlights the potentialities of bacteria associated with rare plants of ferruginous rocky fields as a reservoir of microbiota of biotechnological and ecological interest, highlighting the importance of conservation of this area that is undergoing intense anthropic activity.