Adsorbent reinforced with bacterial-based compounds enhances the efficiency and selectivity of controlling harmful cyanobacteria, Microcystis aeruginosa.

In the present study, algicidal bacteria cultivated in an aqueous medium were utilized as a surface modification agent to develop an efficient adsorbent for the removal of Microcystis aeruginosa. The modification considerably enhanced M. aeruginosa cell removal efficiency. Moreover, the introduction of bio-compounds ensured specificity in the removal of M. aeruginosa. Additionally, the cyanotoxin release and acute toxicity tests demonstrated that the adsorption process using the developed adsorbent is environmentally safe. Furthermore, the practical feasibility of the adsorptive removal of M. aeruginosa was confirmed through cell removal tests performed using the developed adsorbent in a scaled-up reactor (50 L and 10 tons). In these tests, the effects of the adsorbent application type, water temperature, and initial cell concentration on the M. aeruginosa removal efficiency were evaluated. The results of this study provide novel insights into the valorization strategy of biological algicides repurposed as adsorbents, and provide practical operational data for effective M. aeruginosa removal in scaled-up conditions.

Exploring the insights and benefits of biomass-derived sulfuric acid activated carbon for selective recovery of gold from simulated waste streams.

The surging affluent in society, concomitant with increasing global demand for electrical and electronic devices, has led to a sharp rise in e-waste generation. E-wastes contain significant amounts of precious metals, such as gold, which can be recovered and reused, thus reducing the environmental impact of mining new metals. Selective recovery using sustainable and cost-effective materials and methods is therefore vital. This study undertook a detailed evaluation of low-cost biomass-derived activated carbon (AC) for selective recovery of Au from simulated e-waste streams. Utilizing high-performance synthesized H2SO4-AC, the adsorption mechanisms were explicated through a combination of characterization techniques, i.e., FE-SEM, BET, TGA, XRD, FTIR, XPS, and DFT simulations to conceptualize the atomic and molecular level interactions. Optimization of coordination geometries between model H2SO4-AC and anionic complexes revealed the most stable coordination for AuCl4- (binding energy, Eb = -4064.15 eV). The Au selectivity was further enhanced by reduction of Au(III) to Au(0), as determined by XRD and XPS. The adsorption reaction was relatively fast (∼5h), and maximum Au uptake reached 1679.74 ± 37.66 mg/g (among highest), achieved through adsorption isotherm experiments. Furthermore, a mixture of 0.5 M thiourea/1 M HCl could effectively elute the loaded Au and regenerate the spent AC. This study presents radical attempts to examine in detail, the synergistic effects of H2SO4 activation on biomass-derived ACs for selective recovery of Au from complex mixtures. The paper therefore describes a novel approach for the selective recovery of Au from e-wastes using multifunctional biomass-derived H2SO4-AC.

Chitosan-modified cotton fiber: An efficient and reusable adsorbent in removal of harmful cyanobacteria, Microcystis aeruginosa from aqueous phases.

In the present study, to remove harmful cyanobacterial species Microcystis aeruginosa from aqueous phases, adsorption-based strategy was utilized. For this strategy, the surface of cotton fiber was modified using chitosan molecules to develop a highly efficient and ecofriendly adsorbent in removal of Microcystis aeruginosa from aqueous solution. The pristine cotton fiber could not remove M. aeruginosa, while the chitosan-modified cotton (CS-m-Cotton) showed the 95% of cell removal efficiency within 12 h. The surface characteristics of chitosan-modified cotton compared to the pristine cotton fiber was examined by various surface analysis methods. In addition, the pre-treatment of pristine cotton using sodium hydroxide solution was an important factor for enhancement of chitosan modification efficiency on the cotton fiber. The developed chitosan-modified cotton fiber could be reusable for M. aeruginosa cell removal after the simple desorption treatment using ultrasonication in alkaline solution. During the repeated adsorbent regeneration and reuse, the chitosan-modified cotton maintained its M. aeruginosa removal efficiencies (>90%). From the acute toxicity assessment using the chitosan-modified cotton and, the measurements of chemical oxygen demand and microcystin level changes in the M. aeruginosa treatment process using the adsorbent, the environmental safety of the adsorption strategy using the developed adsorbent could be confirmed. Based on our results, the chitosan-modified cotton fiber could be proposed as an efficient and ecofriendly solution for remediation of harmful cyanobacterial species occurring water resources.

Polyethylenimine linked with chitosan improves astaxanthin production in Haematococcus pluvialis.

Astaxanthin is receiving increasing interest as an antioxidant and high value-added secondary metabolite. Haematococcus pluvialis is the main source for astaxanthin production, and many studies are being conducted to increase the production of astaxanthin. In this study, we linked polyethylenimine (PEI) with chitosan to maintain astaxanthin-inducing ability while securing the recyclability of the inducer. Astaxanthin accumulation in H. pluvialis was induced to 86.4 pg cell-1 with the PEI-chitosan fiber (PCF) treatment prepared by cross-linking of 10 µM PEI and low molecular weight (MW) chitosan via epichlorohydrin. PEI concentration affected the astaxanthin accumulation, whereas the MW of chitosan did not. In addition, the PCF treatment in H. pluvialis increased the reactive oxygen species (ROS) content in cells, thereby upregulating the transcription of enzymes involved in astaxanthin biosynthesis. PCF can be reused multiple times with the maintenance of over 90% of the astaxanthin production efficiency. This study offers a reusable PCF stimulation strategy for enhancing natural astaxanthin content, and PCF treatment will easily increase the production scale or reduce production costs by using recyclability that is not available in current methods. KEY POINTS: • Polyethylenimine-chitosan fiber (PCF) was applied to Haematococcus pluvialis • PCF promotes astaxanthin accumulation by enhancing oxidative stress in H. pluvialis • PCF can be reused multiple times with maintaining over 90% production efficiency.

Strategies to control the growth of cyanobacteria and recovery using adsorption and desorption.

In this study, adsorption strategy using diethylenetriamine-modified cotton fiber (DETA-cotton) was investigated to control the target cells in aqueous phase. Adsorptive removal of M. aeruginosa using the DETA-cotton showed decrease in cell concentration from (100 ± 4.0) × 104 cells/mL to (32.1 ± 0.7) × 104 cells/mL in 24 h, and the concentration of microcystin did not increase during the removal process. Also, an increase in the amine groups on the surface was confirmed through the surface characterization by FT-IR and XPS. Desorption process was performed to analyze total lipid and fatty acid contents for potential use as bio-energy resources. About 90 % of the adsorbed cells were recovered through desorption, and the lipid content and composition were more suitable for use as biodiesel raw materials. Our adsorption-based approach might provide feasible solution not only to counteract environmental issue HABs but also to recover energy-resources from the harmful cyanobacterial species.

Amination of Non-Functional Polyvinyl Chloride Polymer Using Polyethyleneimine for Removal of Phosphorus from Aqueous Solution.

The eutrophication of freshwater environments caused by an excess inflow of phosphorus has become a serious environmental issue because it is a crucial factor for the occurrence of harmful algal blooms (HABs) in essential water resources. The adsorptive removal of phosphorus from discharged phosphorus containing effluents has been recognized as one of the most promising solutions in the prevention of eutrophication. In the present study, a polyvinyl chloride (PVC)-polyethyleneimine (PEI) composite fiber (PEI-PVC) was suggested as a stable and recoverable adsorbent for the removal of phosphorus from aqueous phases. The newly introduced amine groups of the PEI-PVC were confirmed by a comparison between the FT-IR and XPS results of the PVC and PEI-PVC. The phosphorus sorption on the PEI-PVC was pH dependent. At the optimum pH for phosphorus adsorption (pH 5), the maximum adsorption capacity of the PEI-PVC fiber was estimated to be 11.2 times higher (19.66 ± 0.82 mg/g) than that of conventional activated carbon (1.75 ± 0.4 mg/g) using the Langmuir isotherm model. The phosphorus adsorption equilibrium of the PEI-PVC was reached within 30 min at pH 5. From the phosphorus-loaded PEI-PVC, 97.4% of the adsorbed amount of phosphorus on the PEI-PVC could be recovered by employing a desorption process using 1M HCl solution without sorbent destruction. The regenerated PEI-PVC through the desorption process maintained a phosphorus sorption capacity almost equal to that of the first use. In addition, consistently with the PVC fiber, the PEI-PVC fiber did not elute any toxic chlorines into the solution during light irradiation. Based on these results, the PEI-PVC fiber can be suggested as a feasible and stable adsorbent for phosphorus removal.

Microalgal secondary metabolite productions as a component of biorefinery: A review.

The interest in developing microalgae for industrial use has been increasing because of concerns about the depletion of petroleum resources and securing sustainable energy sources. Microalgae have high biomass productivity and short culture periods. However, despite these advantages, various barriers need to be overcome for industrial applications. Microalgal cultivation has a high unit price, thus rendering industrial application difficult. It is indispensably necessary to co-produce their primary and secondary metabolites to compensate for these shortcomings. In this regard, this article reviews the following aspects, (1) co-production of primary and secondary metabolites in microalgae, (2) induction methods for the promotion of the biosynthesis of secondary metabolites, and (3) perspectives on the co-production and co-extraction of primary and secondary metabolites. This paper presents various approaches for producing useful metabolites from microalgae and suggests strategies that can be utilized for the co-production of primary and secondary metabolites.

The Ripple Effect of Graphite Nanofilm on Stretchable Polydimethylsiloxane for Optical Sensing.

Graphene-based optical sensing devices have been widely studied for their broad band absorption, high carrier mobility, and mechanical flexibility. Due to graphene's weak light absorption, studies on graphene-based optical sensing thus far have focused on hybrid heterostructure devices to enhance photo-absorption. Such hybrid devices need a complicated integration process and lead to deteriorating carrier mobility as a result of heterogeneous interfaces. Rippled or wrinkled graphene has been studied in electronic and optoelectronic devices. However, concrete demonstrations of the impact of the morphology of nanofilms (e.g., graphite and graphene) associated with light absorption in optical sensing devices have not been fully examined. This study explored the optical sensing potential of a graphite nanofilm surface with ripples induced by a stretchable polydimethylsiloxane (PDMS) supporting layer under different stretch:release ratios and then transferred onto silicon, both under experimental conditions and via simulation. The optical sensing potential of the rippled graphite nanofilm was significantly enhanced (260 mA/W at the stretch-release state of 30%), as compared to the pristine graphite/PDMS (20 mA/W at the stretch-release state of 0%) under laser illumination at a wavelength of 532 nm. In addition, the results of our simulated computation also confirmed the improved light absorption of rippled graphite nanofilm surface-based optical sensing devices, which was comparable with the results found in the experiment.

Semi-continuous immobilized cultivation of Porphyridium cruentum for sulfated polysaccharides production.

In this study, semi-continuous immobilized cultivation of Porphyridium cruentum through calcium alginate beads was performed for sulfated polysaccharides (SPs) production. The cell biomass and daily SPs productivity in the calcium alginate bead immobilized culture were increased by up to 79 ± 3.4% and 45.6 ± 3.2%, compared to those in the control, respectively. Furthermore, simultaneous application of immobilization and blue wavelength illumination further increased the phycobiliproteins content by 260 ± 9%, compared to those in the control. Similarly, nutrient deficiencies in combination with immobilization increased daily SPs productivity by about twice that of the control. The chemical composition and biological activity of the extracellular polymeric substances produced through immobilization were similar to those of the control. This study suggests the potential application of calcium alginate beads-based immobilization for continuous and high-efficiency SPs production using P. cruentum.

Amination of cotton fiber using polyethyleneimine and its application as an adsorbent to directly remove a harmful cyanobacterial species, Microcystis aeruginosa, from an aqueous medium.

In the present study, we applied an adsorption-based strategy for the removal of a harmful cyanobacterial species, Microcystis aeruginosa, using cotton fiber. Considering the negatively charged surface properties of M. aeruginosa cells in aqueous phases, aminated cotton fibers were prepared through polyethyleneimine (PEI) modification on the pristine cotton fibers. The aminated surface properties of PEI-modified cotton fiber (PEI-cotton) were confirmed by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and potentiometric titration analyses. The pristine cotton fiber could not remove the M. aeruginosa cells, but the PEI-cotton could efficiently remove 98.7% of M. aeruginosa cells from the aqueous medium. In addition, removed cells could be observed on the sorbent surface by field emission scanning electron microscopy (FE-SEM) analysis. PEI-cotton fabricated in 3% PEI solution could remove M. aeruginosa cells (97.9%) more efficiently compared to that fabricated in 1% (82.1%) and 2% (86.2%) of PEI solutions. From the toxicity assessment of the PEI-cotton using Daphnia magna, negligible toxicity of PEI-cotton was confirmed. Our results indicate that the application of PEI-cotton fibers for the removal of M. aeruginosa cells could be suggested as a feasible, effective, and eco-friendly method of harmful algal bloom (HAB) control in water resources.

Fe(III) loaded chitosan-biochar composite fibers for the removal of phosphate from water.

Excess phosphorous (P) in aquatic systems causes adverse environmental impacts including eutrophication. This study fabricated Fe(III) loaded chitosan-biochar composite fibers (FBC-N and FBC-C) from paper mill sludge biochar produced under N2 (BC-N) and CO2 (BC-C) conditions at 600 °C for adsorptive removal of phosphate from water. Investigations using SEM/EDX, XPS, Raman spectroscopy, and specific surface area measurement revealed the morphological and physico-chemical characteristics of the adsorbent. The Freundlich isotherm model well described the phosphate adsorption on BC-N, while the Redlich-Peterson model best fitted the data of three other adsorbents. The maximum adsorption capacities were 9.63, 8.56, 16.43, and 19.24 mg P g-1 for BC-N, BC-C, FBC-N, and FBC-C, respectively, indicating better adsorption by Fe(III) loaded chitosan-biochar composite fibers (FBCs) than pristine biochars. The pseudo-first-order kinetic model suitably explained the phosphate adsorption on BC-C and BC-N, while data of FBC-N and FBC-C followed the pseudo-second-order and Elovich model, respectively. Molecular level observations of the P K-edge XANES spectra confirmed that phosphate associated with iron (Fe) minerals (Fe-P) were the primary species in all the adsorbents. This study suggests that FBCs hold high potential as inexpensive and green adsorbents for remediating phosphate in contaminated water, and encourage resource recovery via bio-based management of hazardous waste.

Utilization of extracellular fungal melanin as an eco-friendly biosorbent for treatment of metal-contaminated effluents.

Fungal melanins have been considered as potential biosorbents due to their metal-binding properties, stability, and scalability. Previous studies established scalable fungal melanin production methods with promising strains, however, their applicability for metal-contaminated effluents treatment has not been sufficiently reported. Herein, melanin pigment derived from Amorphotheca resinae was produced and characterized using microscopy and spectroscopy techniques. Adsorptive properties towards Cu(II), Pb(II), Cd(II), and Zn(II) were evaluated using batch tests. Melanin pigment was composed of aggregates of nanosized particles with indole-based constituents. Adsorption capacities increased with the pH of solution, especially at pH > 4.0. Maximum binding capacities of Cu(II), Pb(II), Cd(II), and Zn(II) on melanin were 69.18, 103.23, 24.31, and 13.57 mg/g, respectively. The competitive adsorption experiments elucidated affinity as Cu(II)>Pb(II)≫Cd(II)>Zn(II). Adsorption time generally required <2.5 h to reach equilibrium; the pseudo-second-order kinetic model well described the kinetics. Chelating ability of free radicals in pigment was considered as a possible mechanism for adsorption. Initial adsorption capacities remained almost intact even after 5 consecutive adsorption-desorption cycles. Complete removal of Cu(II), Pb(II), and Cd(II) from metal-contaminated effluent was confirmed. Consequently, melanin pigment derived from A. resinae can be used as a biosorbent suitable for the treatment of metal-contaminated aqueous solutions.

Alternative pathways utilize or circumvent putrescine for biosynthesis of putrescine-containing rhizoferrin.

The siderophore rhizoferrin (N1,N4-dicitrylputrescine) is produced in fungi and bacteria to scavenge iron. Putrescine-producing bacterium Ralstonia pickettii synthesizes rhizoferrin and encodes a single nonribosomal peptide synthetase-independent siderophore (NIS) synthetase. From biosynthetic logic, we hypothesized that this single enzyme is sufficient for rhizoferrin biosynthesis. We confirmed this by expression of R. pickettii NIS synthetase in Escherichia coli, resulting in rhizoferrin production. This was further confirmed in vitro using the recombinant NIS synthetase, synthesizing rhizoferrin from putrescine and citrate. Heterologous expression of homologous lbtA from Legionella pneumophila, required for rhizoferrin biosynthesis in that species, produced siderophore activity in E. coli. Rhizoferrin is also synthesized by Francisella tularensis and Francisella novicida, but unlike R. pickettii or L. pneumophila, Francisella species lack putrescine biosynthetic pathways because of genomic decay. Francisella encodes a NIS synthetase FslA/FigA and an ornithine decarboxylase homolog FslC/FigC, required for rhizoferrin biosynthesis. Ornithine decarboxylase produces putrescine from ornithine, but we show here in vitro that FigA synthesizes N-citrylornithine, and FigC is an N-citrylornithine decarboxylase that together synthesize rhizoferrin without using putrescine. We co-expressed F. novicida figA and figC in E. coli and produced rhizoferrin. A 2.1 Å X-ray crystal structure of the FigC N-citrylornithine decarboxylase reveals how the larger substrate is accommodated and how active site residues have changed to recognize N-citrylornithine. FigC belongs to a new subfamily of alanine racemase-fold PLP-dependent decarboxylases that are not involved in polyamine biosynthesis. These data reveal a natural product biosynthetic workaround that evolved to bypass a missing precursor and re-establish it in the final structure.

Phosphorus adsorption behavior of industrial waste biomass-based adsorbent, esterified polyethylenimine-coated polysulfone-Escherichia coli biomass composite fibers in aqueous solution.

This study sought to develop a highly efficient adsorbent material for phosphorus (P) removal via valorization of industrial Escherichia coli biomass waste. To ensure an easy and fast recovery after the sorption process, the E. coli biomass waste was immobilized into polysulfone matrix. Additionally, to improve P sorption capacity, the sorbent surface was coated with polyethylenimine (PEI) and further chemically modified. The P uptakes of the developed sorbent (decarboxylated PEI-modified polysulfone-biomass composite fiber, DC-PEI-PEF) were significantly affected by pH. Moreover, the maximum sorption capacity (qmax) of DC-PEI-PEF was estimated as 30.46 ± 1.09 mg/g at neutral pH, as determined by a Langmuir isotherm model. Furthermore, DC-PEI-PEF could reach sorption equilibrium within 5 min and exhibited reusability potential. The partition coefficient of the newly developed material (DC-PEI-PEF) was calculated as 0.387 mg/g⋅µM at 4 mg/L of initial P concentration and decreased as initial P concentrations increased. Therefore, DC-PEI-PEF could be suggested as a promising adsorbent for application in direct phosphorus removal from natural aquatic environments.

Application of a polyethylenimine-modified polyacrylonitrile-biomass waste composite fiber sorbent for the removal of a harmful cyanobacterial species from an aqueous solution.

Cyanobacterial harmful algal blooms (Cyano-HABs) in water resources involving algal species such as Microcystis aeruginosa have become a serious environmental issue due to their severely negative effects. In the present study, an adsorption-based strategy was employed to control M. aeruginosa, with industrial waste-derived Escherichia coli biomass valorized to produce polyethylenimine-modified polyacrylonitrile-E. coli biomass composite fiber (PEI-PANBF). PEI-PANBF removed approximately 80% of M. aeruginosa cells from an aqueous solution without causing any cell damage. Interestingly, the thickness of PEI-PANBF had a strong influence on the efficiency of M. aeruginosa cell removal. In addition, PEI-PANBF simultaneously removed M. aeruginosa cells and their toxic secondary metabolite, microcystin-LR, from aqueous media. Thus, our proposed fiber represents a feasible utilization method of industrial waste biomass as a biosorbent for the control of Cyano-HABs.

Astaxanthin biosynthesis promotion with pH shock in the green microalga, Haematococcus lacustris.

In this study, the use of pH shock to improve astaxanthin synthesis in Haematococcus lacustris was investigated. It has been found that pH shock (pH = 4.5, 60 s) imposes stress in the cells and induces physiological changes, which result in astaxanthin accumulation. The optimal acid-base combination of pH shock was H2SO4-KOH, which increased the astaxanthin content per cell to 39 ± 6.92% than those of the control. In addition, pH shock can be applied simultaneously with the other inductive strategies such as high irradiance and carbon source supply. When high irradiance was applied simultaneously with pH shock, astaxanthin yield was increased 65 ± 0.541% than control. In addition, astaxanthin content per cell was increased 105 ± 6.66% than those of the control, with the concomitant application of carbon source addition with pH shock. Herein, these novel findings provide a useful technique for producing astaxanthin using H. lacustris.

Effect of Pseudoalteromonas sp. MEBiC 03485 on biomass production and sulfated polysaccharide biosynthesis in Porphyridium cruentum UTEX 161.

The effect of co-cultivation of Porphyridium cruentum UTEX 161 with Pseudoalteromonas sp. MEBiC 03485 on P. cruentum growth and its sulfated polysaccharide (EPS) production were examined. The strain MEBiC 03485 had beneficial effects on P. cruentum growth, EPS production, and EPS quality. These effects were due to a compound secreted by the strain MEBiC 03485. Notably, secretory compound treatment also increased intracellular phycoerythrin and phycocyanin content by 89.4% and 161%, respectively. In addition, the biological activities of EPS extracted from MEBiC 03485 treatment tended to be higher than the control without treatment. Our results suggest a novel approach for potentially enhancing the growth of P. cruentum and its EPS production and quality by co-culturing with the symbiotic strain MEBiC 03485.

Control of a toxic cyanobacterial bloom species, Microcystis aeruginosa, using the peptide HPA3NT3-A2.

Microcystis aeruginosa, a species of freshwater cyanobacteria, is known to be one of the dominant species causing cyanobacterial harmful algal blooms (CyanoHABs). M. aeruginosa blooms have the potential to produce neurotoxins and peptide hepatotoxins, such as microcystins and lipopolysaccharides (LPSs). Currently, technologies for CyanoHAB control do not provide any ultimate solution because of the secondary pollution associated with the control measures. In this study, we attempted to use the peptide HPA3NT3-A2, which has been reported to be nontoxic and has antimicrobial properties, for the development of an eco-friendly control against CyanoHABs. HPA3NT3-A2 displayed significant algicidal effects against M. aeruginosa cells. HPA3NT3-A2 induced cell aggregation and flotation (thereby facilitating harvest), inhibited cell growth through sedimentation, and eventually destroyed the cells. HPA3NT3-A2 had no algicidal effect on other microalgal species such as Haematococcus pluvialis and Chlorella vulgaris. Additionally, HPA3NT3-A2 was not toxic to Daphnia magna. The algicidal mechanism of HPA3NT3-A2 was intracellular penetration. The results of this study suggest the novel possibility of controlling CyanoHABs using HPA3NT3-A2.

A polyamine-independent role for S-adenosylmethionine decarboxylase.

The only known function of S-adenosylmethionine decarboxylase (AdoMetDC) is to supply, with its partner aminopropyltransferase enzymes such as spermidine synthase (SpdSyn), the aminopropyl donor for polyamine biosynthesis. Polyamine spermidine is probably essential for the growth of all eukaryotes, most archaea and many bacteria. Two classes of AdoMetDC exist, the prokaryotic class 1a and 1b forms, and the eukaryotic class 2 enzyme, which is derived from an ancient fusion of two prokaryotic class 1b genes. Herein, we show that 'eukaryotic' class 2 AdoMetDCs are found in bacteria and are enzymatically functional. However, the bacterial AdoMetDC class 2 genes are phylogenetically limited and were likely acquired from a eukaryotic source via transdomain horizontal gene transfer, consistent with the class 2 form of AdoMetDC being a eukaryotic invention. We found that some class 2 and thousands of class 1b AdoMetDC homologues are present in bacterial genomes that also encode a gene fusion of an N-terminal membrane protein of the Major Facilitator Superfamily (MFS) class of transporters and a C-terminal SpdSyn-like domain. Although these AdoMetDCs are enzymatically functional, spermidine is absent, and an entire fusion protein or its SpdSyn-like domain only, does not biochemically complement a SpdSyn deletion strain of E. coli This suggests that the fusion protein aminopropylates a substrate other than putrescine, and has a role outside of polyamine biosynthesis. Another integral membrane protein found clustered with these genes is DUF350, which is also found in other gene clusters containing a homologue of the glutathionylspermidine synthetase family and occasionally other polyamine biosynthetic enzymes.

Polyamine-independent growth and biofilm formation, and functional spermidine/spermine N-acetyltransferases in Staphylococcus aureus and Enterococcus faecalis.

Polyamines such as spermidine and spermine are primordial polycations that are ubiquitously present in the three domains of life. We have found that Gram-positive bacteria Staphylococcus aureus and Enterococcus faecalis have lost either all or most polyamine biosynthetic genes, respectively, and are devoid of any polyamine when grown in polyamine-free media. In contrast to bacteria such as Pseudomonas aeruginosa, Campylobacter jejuni and Agrobacterium tumefaciens, which absolutely require polyamines for growth, S. aureus and E. faecalis grow normally over multiple subcultures in the absence of polyamines. Furthermore, S. aureus and E. faecalis form biofilms normally without polyamines, and exogenous polyamines do not stimulate growth or biofilm formation. High levels of external polyamines, including norspermidine, eventually inhibit biofilm formation through inhibition of planktonic growth. We show that spermidine/spermine N-acetyltransferase (SSAT) homologues encoded by S. aureus USA300 and E. faecalis acetylate spermidine, spermine and norspermidine, that spermine is the more preferred substrate, and that E. faecalis SSAT is almost as efficient as human SSAT with spermine as substrate. The polyamine auxotrophy, polyamine-independent growth and biofilm formation, and presence of functional polyamine N-acetyltransferases in S. aureus and E. faecalis represent a new paradigm for bacterial polyamine biology.