MsmR1, a global transcription factor, regulates polymyxin synthesis and carbohydrate metabolism in Paenibacillus polymyxa SC2

Construction and characterization of stable multi-species biofilms formed by nine core gut bacteria on wheat fiber

Microbial aggregation mainly occurs on the intestinal epithelium, mucosal layer and undigested food particles in the gastrointestinal tract (GIT). Undigested food particles are usually insoluble dietary fiber (IDF), which can be easily obtained through daily diet, but there are few studies investigating whether the gut bacteria adhering to undigested food particles can form multi-species biofilms. In this study, we prepared mono- and multi-species biofilms using 18 core gut bacteria via a dynamic fermentation method, and it was found that multi-species composed of nine core gut bacteria (M9) showed the best biofilm formation ability. Cell counts of the nine bacteria in multi-species biofilms were 9.36, 11.85, 10.17, 9.93, 12.88, 11.39, 10.089, 9.06, and 13.21 Log10 CFU mL-1. M9 was tightly connected and regularly stacked on wheat fiber and had larger particle sizes than mono-species biofilms. M9 retained biofilm formation ability under pH and bile salt stresses. A human feces invasion experiment demonstrated that M9 can stably adhere to wheat fiber under the interference of complex gut bacteria, and the M9 multi-species biofilm had positions that can be filled by various gut bacteria. Metabolome results indicated that the M9 multi-species biofilm had more metabolic productions and more complex interspecies interactions than mono-species biofilms. This study provides a dynamic fermentation method to prepare multi-species biofilms on wheat fiber in vitro. It will also offer a research basis for clarifying whether gut bacteria can utilize IDF to form biofilm structures in vivo and the possible interspecific interactions and physiological functions of bacteria in biofilms.

Mechanisms on salt tolerant of Paenibacillus polymyxa SC2 and its growth-promoting effects on maize seedlings under saline conditions

Soil salinity negatively affects microbial communities, soil fertility, and agricultural productivity and has become a major agricultural problem worldwide. Plant growth-promoting rhizobacteria (PGPR) with salt tolerance can benefit plant growth under saline conditions and diminish the negative effects of salt stress on plants. In this study, we aimed to understand the salt-tolerance mechanism of Paenibacillus polymyxa at the genetic and metabolic levels and elucidate the mechanism of strain SC2 in promoting maize growth under saline conditions. Under salt stress, we found that strain SC2 promoted maize seedling growth, which was accompanied by a significant upregulation of genes encoding for the biosynthesis of peptidoglycan, polysaccharide, and fatty acid, the metabolism of purine and pyrimidine, and the transport of osmoprotectants such as trehalose, glycine betaine, and K+ in strain SC2. To further enhance the salt resistance of strain SC2, three mutants (SC2-11, SC2-13, and SC2-14) with higher capacities for salt resistance and exopolysaccharide synthesis were obtained via atmospheric and room-temperature plasma mutagenesis. In saline-alkaline soil, the mutants showed better promoting effect on maize seedlings than wild-type SC2. The fresh weight of maize seedlings was increased by 68.10% after treatment with SC2-11 compared with that of the control group. The transcriptome analysis of maize roots demonstrated that SC2 and SC2-11 could induce the upregulation of genes related to the plant hormone signal transduction, starch and sucrose metabolism, reactive oxygen species scavenging, and auxin and ethylene signaling under saline-alkaline stress. In addition, various transcription factors, such as zinc finger proteins, ethylene-responsive-element-binding protein, WRKY, myeloblastosis proteins, basic helix-loop-helix proteins, and NAC proteins, were up-regulated in response to abiotic stress. Moreover, the microbial community composition of maize rhizosphere soil after inoculating with strain SC2 was varied from the one after inoculating with mutant SC2-11. Our results provide new insights into the various genes involved in the salt resistance of strain SC2 and a theoretical basis for utilizing P. polymyxa in saline-alkaline environments.

Exopolysaccharides of Paenibacillus polymyxa: A review

Paenibacillus polymyxa (P. polymyxa) is a member of the genus Paenibacillus, which is a rod-shaped, spore-forming gram-positive bacterium. P. polymyxa is a source of many metabolically active substances, including polypeptides, volatile organic compounds, phytohormone, hydrolytic enzymes, exopolysaccharide (EPS), etc. Due to the wide range of compounds that it produces, P. polymyxa has been extensively studied as a plant growth promoting bacterium which provides a direct benefit to plants through the improvement of N fixation from the atmosphere and enhancement of the solubilization of phosphorus and the uptake of iron in the soil, and phytohormones production. Among the metabolites from P. polymyxa, EPS exhibits many activities, for example, antioxidant, immunomodulating, anti-tumor and many others. EPS has various applications in food, agriculture, environmental protection. Particularly, in the field of sustainable agriculture, P. polymyxa EPS can be served as a biofilm to colonize microbes, and also can act as a nutrient sink on the roots of plants in the rhizosphere. Therefore, this paper would provide a comprehensive review of the advancements of diverse aspects of EPS from P. polymyxa, including the production, extraction, structure, biosynthesis, bioactivity and applications, etc. It would provide a direction for future research on P. polymyxa EPS.

Abh, AbrB3, and Spo0A play distinct regulatory roles during polymyxin synthesis in Paenibacillus polymyxa SC2

IMPORTANCE

Polymyxins are considered the last line of defense against multidrug-resistant bacteria. The regulatory mechanism of polymyxin synthesis is poorly studied in Paenibacillus polymyxa. In this study, we found that Abh and AbrB3 negatively regulated, whereas Spo0A positively regulated polymyxin synthesis in P. polymyxa SC2. In addition, a regulatory relationship between Abh, AbrB3, and Spo0A was revealed, which regulate polymyxin synthesis via multiple regulatory mechanisms in P. polymyxa.

Biofilms formation in plant growth-promoting bacteria for alleviating agro-environmental stress

Biofilm formation represents a pivotal and adaptable trait among microorganisms within natural environments. This attribute plays a multifaceted role across diverse contexts, including environmental, aquatic, industrial, and medical systems. While previous research has primarily focused on the adverse impacts of biofilms, harnessing their potential effectively could confer substantial advantages to humanity. In the face of escalating environmental pressures (e.g., drought, salinity, extreme temperatures, and heavy metal pollution), which jeopardize global crop yields, enhancing crop stress tolerance becomes a paramount endeavor for restoring sufficient food production. Recently, biofilm-forming plant growth-promoting bacteria (PGPB) have emerged as promising candidates for agricultural application. These biofilms are evidence of microorganism colonization on plant roots. Their remarkable stress resilience empowers crops to thrive and yield even in harsh conditions. This is accomplished through increased root colonization, improved soil properties, and the synthesis of valuable secondary metabolites (e.g., ACC deaminase, acetin, 2,3-butanediol, proline, etc.). This article elucidates the mechanisms underpinning the role of biofilm-forming PGPB in bolstering plant growth amidst environmental challenges. Furthermore, it explores the tangible applications of these biofilms in agriculture and delves into strategies for manipulating biofilm formation to extract maximal benefits in practical crop production scenarios.

Metabolic engineering of Paenibacillus polymyxa for effective production of 2,3-butanediol from poplar hydrolysate

2,3-Butanediol is an essential renewable fuel. The synthesis of 2,3-butanediol using Paenibacillus polymyxa has attracted increasing attention. In this study, the glucose-derived 2,3-butanediol pathway and its related genes were identified in P. polymyxa using combined transcriptome and metabolome analyses. The functions of two distinct genes ldh1 and ldh3 encoding lactate dehydrogenase, the gene bdh encoding butanediol dehydrogenase, and the spore-forming genes spo0A and spoIIE were studied and directly knocked out or overexpressed in the genome sequence to improve the production of 2,3-butanediol. A raw hydrolysate of poplar wood containing 27 g/L glucose and 15 g/L xylose was used to produce 2,3-butanediol with a maximum yield of 0.465 g/g and 93 % of the maximum theoretical value, and the total production of 2,3-butanediol and ethanol reached 21.7 g/L. This study provides a new scheme for engineered P. polymyxa to produce renewable fuels using raw poplar wood hydrolysates.