Xanthomonas citri pv. aurantifolii Genomes in pathogenicity-related subsystems. These subsystems, the Types I and IV Secretion Systems, and the Type IV pilus, therefore emerge as important ones in helping explain the aggressiveness of the A type of citrus canker and the apparent dominance in the field of the corresponding strain over the B and C strains.
The ferruginous rupestrian grasslands (FRG) in the Iron Quadrangle (IQ) are ecosystems characterized by rocky soils with reduced availability of water and nutrients, but high levels of metals. In order to comprehend the interference of microorganisms on the adaptive process of endemic plant Mimosa calodendrum (Fabaceae), bacteria associated with its roots and rhizosphere were isolated. Fourteen isolates were obtained and subsequently grown in the presence of different concentrations of arsenic (As) species. The isolate Mc250, an Alcaligenes faecalis strain, resisted to 10 mM of As (III) and 800 mM of As (V). In the presence of this strain, atomic spectrometer detected a reduction of 55% for As (III) and 72% for As (V) respectively in 10 mM and 500 mM solution. Scanning electron microscopy of this isolate demonstrated morphological modification and EDX spectroscopy revealed the presence of both As species adsorbed on the membrane, justifying the removal observed in the in vitro assays. To validate this potential removal of As in vivo, tomato plants were used as grown model in the presence and absence of A. faecalis in soil previously contaminated with 5 mM of As (III). After 14 days, plants from contaminated soil had their growth improved when compared to untreated control plants. All these results suggest for the first time that plant-associated bacteria from FRG-IQ present potential for soil rhizoremediation and may benefit the adaptive processes of plants in extreme environments including application in recovering degraded areas.
Background In Citrus cultures, three species of Xanthomonas are known to cause distinct diseases. X. citri subsp. citri patothype A, X. fuscans subsp. aurantifolii pathotypes B and C, and X. alfalfae subsp. citrumelonis, are the causative agents of cancrosis A, B, C, and citrus bacterial spots, respectively. Although these species exhibit different levels of virulence and aggressiveness, only limited alternatives are currently available for proper and early detection of these diseases in the fields. The present study aimed to develop a new molecular diagnostic method based on genomic sequences derived from the four species of Xanthomonas. Results Using comparative genomics approaches, primers were synthesized for the identification of the four causative agents of citrus diseases. These primers were validated for their specificity to their target DNA by both conventional and multiplex PCR. Upon evaluation, their sensitivity was found to be 0.02 ng/µl in vitro and 1.5 × 104 CFU ml−1 in infected leaves. Additionally, none of the primers were able to generate amplicons in 19 other genomes of Xanthomonas not associated with Citrus and one species of Xylella, the causal agent of citrus variegated chlorosis (CVC). This denotes strong specificity of the primers for the different species of Xanthomonas investigated in this study. Conclusions We demonstrated that these markers can be used as potential candidates for performing in vivo molecular diagnosis exclusively for citrus-associated Xanthomonas. The bioinformatics pipeline developed in this study to design specific genomic regions is capable of generating specific primers. It is freely available and can be utilized for any other model organism.
Extensive mineral extractivism in the Brazilian Iron Quadrangle (IQ) region has destroyed large areas of land, decimating plant species, and their associated microbiota. Very little is known about the microbiota of the region; hence, cultivable bacteria associated with plants of its soils were investigated for their biotechnological potential. Samples were collected from nine plant species and six soils, and 65 cultivable bacterial isolates were obtained. These represent predominantly gram-positive bacilli (70%) capable of producing amylases (55%), proteases (63%), cellulases (47%), indole acetic acid (IAA) (46%), siderophores (26%), and to solubilize phosphate (9%). In addition, 65% of these were resistant to ampicillin, 100% were sensitive to tetracycline, and 97% were tolerant to high arsenic concentrations. Three isolates were studied further: the isolate FOB3 (Rosenbergiella sp.) produced high concentrations of IAA in vitro in the absence of tryptophan – shown by the significant improvement in plant germination and growth rate where the isolate was present. For isolates C25 (Acinetobacter sp.) and FG3 (Serratia sp.), plasmids were purified and inserted into Escherichia coli cells where they modified the physiological profile of the transformed strains. The E. coli::pFG3B strain showed the highest capacity for biofilm production, as well as an increase in the replication rate, arsenic tolerance and catalase activity. Moreover, this strain increased DNA integrity in the presence of arsenic, compared to the wild-type strain. These results help to explain the importance of bacteria in maintaining plant survival in ferruginous, rocky soils, acting as plant growth promoters, and to highlight the biotechnological potential of these bacteria.IMPORTANCE The Iron Quadrangle region is responsible for ∼60% of all Brazilian iron production and, at the same time, is responsible for housing a wide diversity of landscapes, and consequently, a series of endemic plant species and dozens of rare species – all of which have been poorly studied. Studies exploring the microbiota associated with these plant species are limited and in the face of the continuous pressure of extractive action, some species along with their microbiota are being decimated. To understand the potential of this microbiota, we discovered that cultivable bacterial isolates obtained from plants in the ferruginous rocky soil of the Iron Quadrangle region have diverse biotechnological potential, revealing a genetic ancestry still unknown.
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