The ability of bacteria to use natural carbon sources greatly affects their growth and survival in the environment. Bacteria have evolved versatile abilities to use environmental carbon sources, but their diversity and assimilation pathways remain largely unexplored. Trans-aconitic acid, a geometric isomer of cis-aconitic acid involved in the tricarboxylic acid cycle, has long been considered a natural carbon source metabolizable by bacteria. However, its catabolism and ecological role in linking bacterial interactions with the environments remain unclear. Here, we identify a regulatory system in Bacillus velezensis FZB42 that is capable of sensing and catabolizing trans-aconitic acid. The system consists of a tar operon, an adjacent positive regulatory gene tarR, and a shared promoter. After receiving the trans-aconitic acid signal, the TarR protein interacts directly with the promoter, initiating the expression of the membrane transporter TarB and aconitate isomerase TarA encoded by the operon, which function in importing the trans-aconitic acid and isomerizing it into the central intermediate cis-aconitic acid. Subsequent soil colonization experiments reveal that trans-aconitic acid assimilating ability can give its coding bacteria a growth and competitive advantage. Bioinformatics analyses coupled with bacterial isolation experiments further show that the assimilation system of trans-aconitic acid is widely distributed in the bacterial domain, and its assimilating bacteria also extensively distributed in nature, indicating an important role of trans-aconitic acid metabolism in bacterial carbon acquisition. This work emphasizes the importance of metabolic adaptation to environmental carbon sources for bacterial survival and may provide inspiration for engineering microbes with enhanced environmental competitiveness.
Na Xue,Yunpeng Zhang,Zongxu Li,Yangge Zhu,Xuejing Liu,Hao Wang,Yimiao Nie,Long Wang
Fluorite commonly coexists with calcite, whilst the separation of these two minerals is a longstanding challenge due to their closely similar surface properties. In this work, froth flotation was adopted to remove calcite from fluorite with tara gum (TG) innovatively performed as the calcite depressant. Flotation experiment results showed that TG exhibited strong depression performance for calcite in a broad pH range (6–8) in sodium oleate (NaOL) system. Zeta potential results confirmed that TG trended to selectively react on the calcite and prevented the function of NaOL onto calcite surface. X-ray photoelectron spectroscopy (XPS) measurement found that TG chemisorbed onto calcite, while physically adsorbed on the fluorite. Atomic force microscopy (AFM) tests indicated that TG densely adhered onto calcite surface and greatly enhanced its hydrophilicity, whereas it adsorbed weakly on the fluorite surface. Molecular dynamics (MD) simulations further concluded that TG could abundantly adhere to the calcite surface with higher intensity and capacity. Therefore, TG exhibited effective depression impact on calcite and achieved the separation of fluorite from calcite successfully.
Na Xue,Yunpeng Zhang,Changfeng Chen,Yangge Zhu,Xuejing Liu,Ling Wang,Hao Wang,Yimiao Nie,Shuxian Liu,Long Wang
To address the challenges in selectively differentiating apatite from calcite via flotation, Tara gum (TG) functioned in the role of a calcite-selective inhibitor during this research. The micro-flotation tests indicated that apatite and calcite displayed comparable buoyancy characteristics when sodium oleate (NaOL) was utilized as the collector. Merely relying on NaOL alone made it extremely arduous to effectuate an efficient segregation of these two minerals. The addition of TG manifested potent and selective inhibitory effect on calcite floatability, while exerted no substantial influence on the flotation of apatite. The findings from the artificial mixed ore tests signified that employing TG in a suppressing role not only enhanced the P 2 O 5 grade within apatite but also had a relatively minor effect on the recovery rate. Surface wettability tests demonstrated that under the combined influence of TG and NaOL, the disparity in hydrophobicity between apatite and calcite was further augmented. Zeta potential measurements intimated TG being present in the system did not impinge on the adsorption of NaOL on the surface of apatite but severely impeded its adsorption on the surface of calcite. Experimental findings from adsorption capacity tests revealed the adsorption quantity of TG on the surface of calcite exhibited a significantly elevated magnitude compared to that on the surface of apatite. X-ray photoelectron spectroscopy (XPS) measurements analysis corroborated that TG was adsorbed on the surface of apatite via weak interactions, while atop the calcite surface, it underwent robust chemisorption with Ca through hydroxyl groups. The outcomes of simulation calculations further substantiated that TG had a greater propensity to attach across the surface of calcite relative to apatite. Based on these experimental revelations, TG held the promise of serving functioning as a discriminatory suppressing agent for the flotation separation of apatite from calcite.
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