Metabolic insights into how multifunctional microbial consortium enhances atrazine removal and phosphorus uptake at low temperature

Agricultural soils in the black soil region of northeast China often face negative stress due to low temperatures, pesticide contamination, and inadequate nutrient supply. In this study, a new cold-tolerant strain of Peribacillus simplex C1 (C1) was selectively isolated from atrazine contaminated soil. The artificially constructed microbial consortium (CPD) [C1, phosphorus-solubilizing bacterium Enterobacter sp. P1, and atrazine-degrading bacterium Acinetobacter lwoffii DNS32] demonstrated the most effective performance in enhancing atrazine degradation and phosphorus-solubilizing capacity when the initial inoculation ratio of 5:1:2 at 15 °C. CPD enhanced energy-related metabolic pathways and increased choline production to regulate bacterial adaptation to temperature decrease. Additionally, the strains could selectively utilize carbon sources (low molecular weight organic acids) or nitrogen sources (some metabolites of atrazine) provided by each other to enhance growth. Furthermore, strain C1 enhanced membrane fluidity through increased expression of the unsaturated fatty acids. Pot experiments demonstrated that CPD assisted soybean seedlings in resisting dual stresses of low temperature and atrazine contamination by inducing the expression of genes related to photosynthesis, membrane permeability, phosphorus response, and cold tolerance.

Negatively regulated aerobactin and desferrioxamine E by Fur in Pantoea ananatis are required for full siderophore production and antibacterial activity, but not for virulence

Pantoea ananatis is an emerging plant pathogen that causes disease in economically important crops such as rice, corn, onion, melon, and pineapple, and it also infects humans and insects. In this study, we identified biosynthetic gene clusters of aerobactin and desferrioxamine E (DFO-E) siderophores using the complete genome of P. ananatis PA13 isolated from rice sheath rot. P. ananatis PA13 exhibited the strongest antibacterial activity against Erwinia amylovora and Yersinia enterocolitica (Enterobacterales). Mutants of aerobactin or DFO-E maintained antibacterial activity against E. amylovora and Y. enterocolitica, as well as in a siderophore activity assay. However, double aerobactin- and DFO-E-gene-deletion mutants completely lost siderophore and antibacterial activity. These results reveal that both siderophore biosynthetic gene clusters are essential for siderophore production and antibacterial activity in P. ananatis PA13. A ferric uptake regulator protein (Fur) mutant exhibited a significant increase in siderophore production, and a Fur-overexpressing strain completely lost antibacterial activity. Expression of the iucA, dfoJ, and foxA genes was significantly increased in the Δfur mutant background, and expression of these genes returned to wild type levels after fur compensation. These results indicate that Fur negatively regulates aerobactin and DFO-E siderophores. However, siderophore production was not required for P. ananatis virulence in plants, but it appears to be involved in the microbial ecology surrounding the plant environment. This study is the first to report the regulation and functional characteristics of siderophore biosynthetic genes in P. ananatis. IMPORTANCE Pantoea ananatis is a bacterium that causes diseases in several economically important crops, as well as in insects and humans. This bacterium has been studied extensively as a potentially dangerous pathogen due to its saprophytic ability. Recently, the types, biosynthetic gene clusters, and origin of the siderophores in the Pantoea genus were determined using genome comparative analyses. However, few genetic studies have investigated the characteristics and functions of siderophores in P. ananatis. The results of this study revealed that the production of aerobactin and desferrioxamine E in the rice pathogen P. ananatis PA13 is negatively regulated by Fur, and that these siderophores are essential for antibacterial activity against Erwinia amylovora and Yersinia enterocolitica (Enterobacterales). However, siderophore production was not required for P. ananatis virulence in plants, but it appears to be involved in the microbial ecology surrounding the plant environment.

The initial inoculation ratio regulates bacterial coculture interactions and metabolic capacity

Coculture is an important model system in microbial ecology studies. As a key experimental parameter, the initial inoculation ratio has a crucial impact on the results of the coculture system. However, such an effect has never been investigated under multiple niche conditions. In this study, we established a simple coculture system with two model bacteria in various carbon sources and investigated the influence of initial inoculum ratios of 1:1000 to 1000:1 on community structure, function, and bacterial interaction. We found that the final ratio of the cocultures with different initial inoculum ratios differed in approximately five-sixths of the carbon sources, suggesting that the final ratio is highly dependent on the initial inoculum ratio, while the carbon source preferences of bacteria could not predict the final ratio of cocultures. Furthermore, we found that the initial ratio could regulate the metabolic capacity of the coculture, as only cocultures with initial ratios of 1:1 and 1000:1 gained high capacity on 14 specific carbon sources. The underlying reason may be that the pattern of species interaction is changed by the initial ratio. In conclusion, we showed that the initial ratio can induce emergent properties in coculture. These findings suggest that the initial ratio not only impacts the reproducibility of coculture experiments but also can influence our understanding of generic microbial ecology.

Inhibitors of Bacterial Swarming Behavior

Bacteria can migrate in groups of flagella-driven cells over semisolid surfaces. This coordinated form of motility is called swarming behavior. Swarming is associated with enhanced virulence and antibiotic resistance of various human pathogens and may be considered as favorable adaptation to the diverse challenges that microbes face in rapidly changing environments. Consequently, the differentiation of motile swarmer cells is tightly regulated and involves multi-layered signaling networks. Controlling swarming behavior is of major interest for the development of novel anti-infective strategies. In addition, compounds that block swarming represent important tools for more detailed insights into the molecular mechanisms of the coordination of bacterial population behavior. Over the past decades, there has been major progress in the discovery of small-molecule modulators and mechanisms that allow selective inhibition of swarming behavior. Herein, an overview of the achievements in the field and future directions and challenges will be presented.

Fluorinated Analogues of Desferrioxamine B from Precursor-Directed Biosynthesis Provide New Insight into the Capacity of DesBCD

The siderophore desferrioxamine B (DFOB, 1) native to Streptomyces pilosus is biosynthesized by the DesABCD enzyme cluster. DesA-mediated decarboxylation of l-lysine gives 1,5-diaminopentane (DP) for processing by DesBCD. S. pilosus culture medium was supplemented with rac-1,4-diamino-2-fluorobutane ( rac-FDB) to compete against DP to generate fluorinated analogues of DFOB, as agents of potential clinical interest. LC-MS/MS analysis identified fluorinated analogues of DFOB with one, two, or three DP units (binary notation: 0) exchanged for one (DFOA-F₁[001] (2), DFOA-F₁[010] (3), DFOA-F₁[100] (4)), two (DFOA-F₂[011] (5), DFOA-F₂[110] (6), DFOA-F₂[101] (7)), or three (DFOA-F₃[111] (8)) rac-FDB units (binary notation: 1). The two sets of constitutional isomers 2-4 and 5-7 arose from the position of the substrates in the N-acetyl, internal, or amine-containing regions of the DFOB trimer. N-Acetylated fluorinated DFOB analogues were formed where the rac-FDB substrate was positioned in the amine region ( e.g., N-Ac-DFOA-F₁[001] (2a)). Other analogues contained two hydroxamic acid groups and three amide bonds. Experiments using rac-FDB, R-FDB, or S-FDB showed a similar species profile between rac-FDB and R-FDB. These data are consistent with the following. (i) DesB can act on rac-FDB. (ii) DesC can act directly on rac-FDB. (iii) The products of DesBC or DesC catalysis of rac-FDB can undergo a second round of DesC catalysis at the free amine. (iv) DesD catalysis of these products gives N, N'-diacetylated compounds. (v) A minimum of two hydroxamic acid groups is required to form a viable DesD-substrate(s) precomplex. (vi) One or more DesBCD-catalyzed steps in DFOB biosynthesis is enantioselective. This work has provided a potential path to access fluorinated analogues of DFOB and new insight into its biosynthesis.