Biology subjects

Brozel, V. S.

Publications and source records attributed to Brozel, V. S..

5 recordsLinked to original sources

bioRxiv2025

Fast-growing Bacillus sensu lato rhizosphere populations are constrained by antagonistic Pseudomonadota, Actinomycetota and other Bacillus sensu lato

Copiotrophic Bacillus and related taxa grow rapidly and are commonly isolated from soil. Despite their growth rate, Bacillus sensu lato (BSL) constitute less than one percent of soil bacterial communities, and the nutrient-enriched rhizosphere contains even fewer. Amendment of bulk soil with synthetic root exudate did not lead to increase in Bacillus culturable counts. We hypothesized that BSL populations in soil enriched with growth-supporting carbon are suppressed by various soil microbes. A screen using B. pseudomycoides as tester strain yielded 124 growth inhibiting isolates, aligning by 16S rRNA genes to 3 Alphaproteobacteria, 6 Betaproteobacteria, 5 Gammaproteobacteria, 3 Streptomyces, and 19 Bacillaceae. Most antagonists also suppressed four other BSL, and over 70% of the BSL isolates suppressed each other. The 11 sequenced BSL genomes encoded between 2 and 10 antibiotic biosynthetic gene clusters. Incubation of multiple isolates in artificial soil microcosms resulted in population growth restraint through a high percentage of endospores formed. This indicated that growth suppression by antagonists was due primarily to induction of sporulation. These results support our hypothesis that Bacillus populations in soil enriched with growth-supporting carbon are suppressed by various soil microbes.

microbiology↗

bioRxiv2024

Self-growth suppression in Bradyrhizobium diazoefficiens is caused by a diffusible antagonist

Microbes in soil navigate interactions by recognizing kin, forming social groups, exhibiting antagonistic behavior, and engaging in competitive kin rivalry. Here, we investigated a novel phenomenon of self-growth suppression (sibling rivalry) observed in Bradyrhizobium diazoefficiens USDA 110. Swimming colonies of USDA 110 developed a distinct demarcation line and inter-colony zone when inoculated adjacent to each other. In addition to self, USDA 110 suppressed growth of other Bradyrhizobium strains and several other soil bacteria. We demonstrated that the phenomenon of sibling rivalry is due to growth suppression but not cell death. The cells in the inter-colony zone were culturable but have reduced respiratory activity, ATP levels and motility. The observed growth suppression was due to the presence of a diffusible effector compound. This effector was labile, preventing extraction, and identification, but it is unlikely a protein or a strong acid or base. This counterintuitive phenomenon of self-growth suppression suggests a strategic adaptation for conserving energy and resources in competitive soil environments. Bradyrhizobiums utilization of antagonism including self-growth suppression likely provides a competitive advantage for long-term success in soil ecosystems.

microbiology↗

bioRxiv2024

Bradyrhizobium and the soybean rhizosphere: Species level bacterial population dynamics in established soybean fields, rhizosphere and nodules.

Bradyrhizobium fixes nitrogen symbiotically with soybean and is an agriculturally significant bacterium. Much is known about the Bradyrhizobium species that nodulate soybeans. Conversely, prevalence of Bradyrhizobium in soil and the rhizosphere is known only to the genus level as culture independent approaches have provided only partial 16S rRNA gene sequences, so that nodulating and non-nodulating species could not be distinguished. To track which species in bulk soil proliferate in the rhizosphere, and then nodulate, we sought to study population dynamics of Bradyrhizobium in soybean fields and rhizosphere at the species level. Recent advances in Oxford Nanopore Technologies provided us with higher fidelity and increased number of reads which enabled us to track Bradyrhizobium populations at the species level. We found evidence for 74 species of Bradyrhizobium within a community of 10,855 bacterial species in bulk soil and rhizosphere from three different soybean fields in South Dakota. The most predominant species in bulk soil and rhizosphere included B. liaoningense, B. americanum, and B. diversitatus, however none of these were isolated from nodules. Isolates from nodules included B. japonicum, B. elkanii and B. diazoefficiens. These nodulators also maintained populations in bulk soil and rhizosphere, although they were not the most prevalent Bradyrhizobium. Our findings reveal the rich diversity and community dynamics of Bradyrhizobium species in soybean field soil as well as in the rhizosphere. Our results showed that many species of the genus maintain populations in soybean field soil, even in the long-term absence of potential nodulating partners.

microbiology↗

bioRxiv2020

Unique Proteomes Implicate Functional Specialization across Heterocysts, Akinetes, and Vegetative Cells in Anabaena cylindrica

In response to environmental changes, vegetative cells of Anabaena cylindrica can differentiate into two other cell types: a heterocyst for oxic N2-fixation, and an enlarged spore called akinete for stress survival. Akinetes normally differentiate from vegetative cells adjacent to heterocysts. Heterocysts inhibit nearby cells from differentiating into heterocysts but can induce adjacent cells to become akinetes, a rare embryogenetic induction in prokaryotes. The mechanism for a patterned differentiation in A. cylindrica has been little studied. Here, we isolated three types of cells from A. cylindrica to identify their proteomes using LC-MS/MS. A total of 1395 proteins were identified, including 664 proteins from akinetes, 751 proteins from heterocysts, and 1236 proteins from vegetative cells. There were 45 proteins (33 novel proteins) found exclusive to akinetes, 57 heterocyst-specific proteins (33 novel proteins), including nif gene products, and 485 proteins exclusively in vegetative cells. Our proteomic data suggest that akinetes, unlike the typical spores of bacteria, perform unique biochemical functions that collaborate with both heterocysts and vegetative cells. A HAVe model for collaboration among heterocysts, akinetes and vegetative cells is proposed to illustrate the metabolic network of cyanophycin and carbohydrates based on the distribution of their biosynthesis related proteins in three types of cells. Interestingly, cell division proteins, DNA replication proteins, some carboxysomal proteins including RuBisCO and proteins in photosystems I, II were found abundant in heterocysts, the non-dividing cells dedicated exclusively to oxic N2-fixation. The identification of the akinete and heterocyst proteomes enables the pursuit of genetic studies into the patterned differentiation of akinetes and heterocysts.

microbiology↗

bioRxiv2017

Growth and extended survival of Escherichia coli O157:H7 in soil organic matter

Enterohaemorrhagic Escherichia coli such as serotype O157:H7 are a leading cause of food-associated outbreaks. While the primary reservoir is associated with cattle, plant foods have been associated as sources of human infection. E. coli is able to grow in the tissue of food plants such as spinach. While fecal contamination is the primary suspect, soil has been underestimated as a potential reservoir. Persistence of bacterial populations in open systems is the product of growth, death, predation, and competition. Here we report that E. coli O157:H7 can grow using the soluble compounds in soil, and characterize the effect of soil growth in the stationary phase proteome. E. coli 933D (stxII-) was cultured in Soil Extracted Soluble Organic Matter (SESOM) and the culturable count determined for 24 d. The proteomes of exponential and stationary phase populations were characterized by 2D gel electrophoresis and protein spots were identified by MALDI-TOF mass spectrometry. While LB controls displayed a death phase, SESOM grown population remained culturable for 24 d, indicating an altered physiological state with superior longevity. This was not due to decreased cell density on entry to stationary phase as 24h SESOM populations concentrated 10-fold retained their longevity. Principal component analysis showed that stationary phase proteomes from SESOM and LB were different. Differences included proteins involved in stress response, motility, membrane and wall composition, nutrient uptake, translation and protein turnover, and anabolic and catabolic pathways, indicating an altered physiological state of soil-grown cells entering stationary phase. The results suggest that E. coli may be a soil commensal that in absence of predation and competition maintains stable populations in soil.

microbiology↗