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We report the complete genome sequence of Exiguobacterium profundum TSS-3, a strain isolated from the sediment of an extremely saline-alkaline spring located in Ixtapa, Chiapas-México (16° 47´ LN and 92° 54´ LO). Its genome is composed of a 2.8-Mb chromosome and a small 4.6-Kb plasmid.
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The implementation of bioreactor systems for the production of bacterial inoculants as biofertilizers has become very important in recent decades. However, it is essential to know the bacterial growth optimal conditions to optimize the production and efficiency of bioinoculants. The aim of this work was to identify the best nutriment and mixing conditions to improve the specific cell growth rates (µ) of two PGPB (plant growth-promoting bacteria) rhizobial strains at the bioreactor level. For this purpose, the strains Sinorhizobium mexicanum ITTG-R7T and Sinorhizobium chiapanecum ITTG-S70T were previously reactivated in a PY-Ca2+ (peptone casein, yeast extract, and calcium) culture medium. Afterward, a master cell bank (MCB) was made in order to maintain the viability and quality of the strains. The kinetic characterization of each bacterial strain was carried out in s shaken flask. Then, the effect of the carbon and nitrogen sources and mechanical agitation was evaluated through a factorial design and response surface methodology (RSM) for cell growth optimization, where µ was considered a response variable. The efficiency of biomass production was determined in a homemade bioreactor, taking into account the optimal conditions obtained during the experiment conducted at the shaken flask stage. In order to evaluate the biological quality of the product obtained in the bioreactor, the bacterial strains were inoculated in common bean (Phaseolus vulgaris var. Jamapa) plants under bioclimatic chamber conditions. The maximum cell growth rate in both PGPB strains was obtained using a Y-Ca2+ (yeast extract and calcium) medium and stirred at 200 and 300 rpm. Under these growth conditions, the Sinorhizobium strains exhibited a high nitrogen-fixing capacity, which had a significant (p < 0.05) impact on the growth of the test plants. The bioreactor system was found to be an efficient alternative for the large-scale production of PGPB rhizobial bacteria, which are intended for use as biofertilizers in agriculture.
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Introduction: The extensive use of chemical fertilizers has served as a response to the increasing need for crop production in recent decades. While it addresses the demand for food, it has resulted in a decline in crop productivity and a heightened negative environmental impact. In contrast, plant probiotic bacteria (PPB) offer a promising alternative to mitigate the negative consequences of chemical fertilizers. PPB can enhance nutrient availability, promote plant growth, and improve nutrient uptake efficiency, thereby reducing the reliance on chemical fertilizers. Methods: This study aimed to evaluate the impact of native Rhizobium strains, specifically Rhizobium calliandrae LBP2-1, Rhizobium mayense NSJP1-1, and Rhizobium jaguaris SJP1- 2, on the growth, quality, and rhizobacterial community of tomato crops. Various mechanisms promoting plant growth were investigated, including phosphate solubilization, siderophore production, indole acetic acid synthesis, and cellulose and cellulase production. Additionally, the study involved the assessment of biofilm formation and root colonization by GFP-tagged strains, conducted a microcosm experiment, and analyzed the microbial community using metagenomics of rhizospheric soil. Results: The results showed that the rhizobial strains LBP2-1, NSJP1-1 and SJP1-2 had the ability to solubilize dicalcium phosphate, produce siderophores, synthesize indole acetic acid, cellulose production, biofilm production, and root colonization. Inoculation of tomato plants with native Rhizobium strains influenced growth, fruit quality, and plant microbiome composition. Metagenomic analysis showed increased Proteobacteria abundance and altered alpha diversity indices, indicating changes in rhizospheric bacterial community. Discussion: Our findings demonstrate the potential that native Rhizobium strains have to be used as a plant probiotic in agricultural crops for the generation of safe food and high nutritional value.
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Microorganisms in extreme volcanic environments play an important role in the development of plants on newly exposed substrates. In this work, we studied the structure and diversity of a bacterial community associated to Andropogon glomeratus and Cheilanthes aemula at El Chichón volcano. The genetic diversity of the strains was revealed by genomic fingerprints and by 16S rDNA gene sequencing. Furthermore, a metagenomic analysis of the rhizosphere samples was carried out for pioneer plants growing inside and outside the volcano. Multifunctional biochemical tests and plant inoculation assays were evaluated to determine their potential as plant growth-promoting bacteria (PGPB). Through metagenomic analysis, a total of 33 bacterial phyla were identified from A. glomeratus and C. aemula rhizosphere samples collected inside the volcano, and outside the volcano 23 bacterial phyla were identified. For both rhizosphere samples, proteobacteria was the most abundant phylum. With a cultivable approach, 174 bacterial strains were isolated from the rhizosphere and tissue of plants growing outside the volcanic complex. Isolates were classified within the genera Acinetobacter, Arthrobacter, Bacillus, Burkholderia, Cupriavidus, Enterobacter, Klebsiella, Lysinibacillus, Pantoea, Pseudomonas, Serratia, Stenotrophomonas and Pandoraea. The evaluated strains were able to produce indole compounds, solubilize phosphate, synthesize siderophores, showed ACC deaminase and nitrogenase activity, and they had a positive effect on the growth and development of Capsicum chinense. The wide diversity of bacteria associated to pioneer plants at El Chichón volcano with PGPB qualities represent an alternative for the recovery of eroded environments, and they can be used efficiently as biofertilizers for agricultural crops growing under adverse conditions.
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We report the complete genome sequence of Ensifer mexicanus ITTG R7T, a nitrogen-fixing bacterium isolated from nodules of Acaciella angustissima plants growing naturally in Chiapas, Mexico. The genome is distributed in four replicons comprising one 4.31-Mbp chromosome, one 1,933-Kb chromid, and two plasmids of 436 and 455 Kb.
