Harnessing selenium nanoparticles (SeNPs) for enhancing growth and germination, and mitigating oxidative stress in Pisum sativum L.

Selenium, an essential micronutrient for plants and animals, can cause selenium toxicity as an oxyanion or at elevated doses. However, the toxic selenite (SeO32-) oxyanion, can be converted into less harmful elemental nano-selenium (Se0), with various practical applications. This research aimed to investigate two methods for reducing SeO32-: abiotic reduction using cell-free extract from Enterococcus spp. (abiotic-SeNPs) and chemical reduction involving L-ascorbic acid (chemical-SeNPs). Analysis with XPS confirmed the presence of Se0, while FTIR analysis identified surface functional groups on all SeNPs. The study evaluated the effects of SeO32-, abiotic-SeNPs, and chemical-SeNPs at different concentrations on the growth and germination of Pisum sativum L. seeds. SeO32- demonstrated detrimental effects on germination at concentrations of 1 ppm (germination index (GI) = 0.3). Conversely, both abiotic- and chemical-SeNPs had positive impacts on germination, with GI > 120 at 10 ppm. Through the DPPH assay, it was discovered that SeNPs exhibited superior antioxidant capabilities at 80 ppm, achieving over 70% inhibition, compared to SeO32- (less than 20% inhibition), therefore evidencing significant antioxidant properties. This demonstrates that SeNPs have the potential to be utilized as an agricultural fertilizer additive, benefiting seedling germination and development, while also protecting against oxidative stress.

Cytotoxic-Ag-Modified Eggshell Membrane Nanocomposites as Bactericides in Concrete Mortar.

Against the backdrop of escalating infrastructure budgets worldwide, a notable portion-up to 45%-is allocated to maintenance endeavors rather than innovative infrastructure development. A substantial fraction of this maintenance commitment involves combatting concrete degradation due to microbial attacks. In response, this study endeavors to propose a remedial strategy employing nano metals and repurposed materials within cement mortar. The methodology entails the adsorption onto eggshell membranes (ESM) of silver nitrate (ESM/AgNO3) or silver nanoparticles (ESM/AgNPs) yielding silver-eggshell membrane composites. Subsequently, the resulting silver-eggshell membrane composites were introduced in different proportions to replace cement, resulting in the formulation of ten distinct mortar compositions. A thorough analysis encompassing a range of techniques, such as spectrophotometry, scanning electron microscopy, thermogravimetric analysis, X-ray fluorescence analysis, X-ray diffraction (XRD), and MTT assay, was performed on these composite blends. Additionally, evaluations of both compressive and tensile strengths were carried out. The mortar blends 3, 5, and 6, characterized by 2% ESM/AgNO3, 1% ESM/AgNPs, and 2% ESM/AgNPs cement replacement, respectively, exhibited remarkable antimicrobial efficacy, manifesting in substantial reduction in microbial cell viability (up to 50%) of typical waste activated sludge. Concurrently, a marginal reduction of approximately 10% in compressive strength was noted, juxtaposed with an insignificant change in tensile strength. This investigation sheds light on a promising avenue for addressing concrete deterioration while navigating the balance between material performance and structural integrity.

Recent Advances in Applications of Oxidases and Peroxidases Polymer-Based Enzyme Biocatalysts in Sensing and Wastewater Treatment: A Review.

Oxidase and peroxidase enzymes have attracted attention in various biotechnological industries due to their ease of synthesis, wide range of applications, and operation under mild conditions. Their applicability, however, is limited by their poor stability in harsher conditions and their non-reusability. As a result, several approaches such as enzyme engineering, medium engineering, and enzyme immobilization have been used to improve the enzyme properties. Several materials have been used as supports for these enzymes to increase their stability and reusability. This review focusses on the immobilization of oxidase and peroxidase enzymes on metal and metal oxide nanoparticle-polymer composite supports and the different methods used to achieve the immobilization. The application of the enzyme-metal/metal oxide-polymer biocatalysts in biosensing of hydrogen peroxide, glucose, pesticides, and herbicides as well as blood components such as cholesterol, urea, dopamine, and xanthine have been extensively reviewed. The application of the biocatalysts in wastewater treatment through degradation of dyes, pesticides, and other organic compounds has also been discussed.

Erratum to "Applications and immobilization strategies of the copper-centred laccase enzyme; a review"[Heliyon Volume 9, Issue 2, February 2023, Article e13156].

[This corrects the article DOI: 10.1016/j.heliyon.2023.e13156.].

A virally encoded GPCR drives glioblastoma through feed-forward activation of the SK1-S1P1 signaling axis.

The G protein-coupled receptor (GPCR) US28 encoded by the human cytomegalovirus (HCMV) is associated with accelerated progression of glioblastomas, aggressive brain tumors with a generally poor prognosis. Here, we showed that US28 increased the malignancy of U251 glioblastoma cells by enhancing signaling mediated by sphingosine-1-phosphate (S1P), a bioactive lipid that stimulates oncogenic pathways in glioblastoma. US28 expression increased the abundance of the key components of the S1P signaling axis, including an enzyme that generates S1P [sphingosine kinase 1 (SK1)], an S1P receptor [S1P receptor 1 (S1P1)], and S1P itself. Enhanced S1P signaling promoted glioblastoma cell proliferation and survival by activating the kinases AKT and CHK1 and the transcriptional regulators cMYC and STAT3 and by increasing the abundance of cancerous inhibitor of PP2A (CIP2A), driving several feed-forward signaling loops. Inhibition of S1P signaling abrogated the proliferative and anti-apoptotic effects of US28. US28 also activated the S1P signaling axis in HCMV-infected cells. This study uncovers central roles for S1P and CIP2A in feed-forward signaling that contributes to the US28-mediated exacerbation of glioblastoma.

Synthesis and Assessment of Antimicrobial Composites of Ag Nanoparticles or AgNO3 and Egg Shell Membranes.

Engineering research has been expanded by the advent of material fusion, which has led to the development of composites that are more reliable and cost-effective. This investigation aims to utilise this concept to promote a circular economy by maximizing the adsorption of silver nanoparticles and silver nitrate onto recycled chicken eggshell membranes, resulting in optimized antimicrobial silver/eggshell membrane composites. The pH, time, concentration, and adsorption temperatures were optimized. It was confirmed that these composites were excellent candidates for use in antimicrobial applications. The silver nanoparticles were produced through chemical synthesis using sodium borohydride as a reducing agent and through adsorption/surface reduction of silver nitrate on eggshell membranes. The composites were thoroughly characterized by various techniques, including spectrophotometry, atomic absorption spectrometry, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy, as well as agar well diffusion and MTT assay. The results indicate that silver/eggshell membrane composites with excellent antimicrobial properties were produced using both silver nanoparticles and silver nitrate at a pH of 6, 25 °C, and after 48 h of agitation. These materials exhibited remarkable antimicrobial activity against Pseudomonas aeruginosa and Bacillus subtilis, resulting in 27.77% and 15.34% cell death, respectively.

Applications and immobilization strategies of the copper-centred laccase enzyme; a review.

Laccase is a multi-copper enzyme widely expressed in fungi, higher plants, and bacteria which facilitates the direct reduction of molecular oxygen to water (without hydrogen peroxide production) accompanied by the oxidation of an electron donor. Laccase has attracted attention in biotechnological applications due to its non-specificity and use of molecular oxygen as secondary substrate. This review discusses different applications of laccase in various sectors of food, paper and pulp, waste water treatment, pharmaceuticals, sensors, and fuel cells. Despite the many advantages of laccase, challenges such as high cost due to its non-reusability, instability in harsh environmental conditions, and proteolysis are often encountered in its application. One of the approaches used to minimize these challenges is immobilization. The various methods used to immobilize laccase and the different supports used are further extensively discussed in this review.

Fusicoccin-A Targets Cancerous Inhibitor of Protein Phosphatase 2A by Stabilizing a C-Terminal Interaction with 14-3-3.

The cancerous inhibitor of protein phosphatase 2A (CIP2A) is an oncoprotein found overexpressed in many types of cancer. CIP2A has been shown to stabilize oncoproteins such as cMYC by shielding them from PP2A-mediated dephosphorylation. Here we report that the penultimate residue Ser904 in the C-terminus of CIP2A can be phosphorylated to create a binding site for the regulatory protein 14-3-3. We demonstrate that 14-3-3 is a new interaction partner of CIP2A. The 14-3-3/CIP2A C-terminal interaction complex can be targeted by the protein-protein interaction (PPI) stabilizer fusicoccin-A (FC-A), resulting in enhanced levels of phosphorylated Ser904. FC-A treatment of TNBC cells leads to the increased association of CIP2A with 14-3-3. We show that the composite interface between 14 and 3-3 and CIP2A's C-terminus can be targeted by the PPI stabilizer FC-A, providing a new interface that could potentially be exploited to modulate CIP2A's activity.

Microbial Precipitation of Pb(II) with Wild Strains of Paraclostridium bifermentans and Klebsiella pneumoniae Isolated from an Industrially Obtained Microbial Consortium.

The study focused on determining the microbial precipitation abilities of bacterial strains that were isolated from an industrially obtained Pb(II)-resistant microbial consortium. Previous research has demonstrated the effectiveness of the consortium on the bioprecipitation and adsorption of Pb(II) from solution. The bioremediation of Pb(II) using microbial precipitation provides an alternative option for Pb(II) removal from wastewater. Both strains, Klebsiella pneumoniae and Paraclostridium bifermentans, were successfully isolated from the consortium obtained from a battery recycling plant in South Africa. The experiments were conducted over both 30 h and 5 d, providing insight into the short- and long-term precipitation abilities of the bacteria. Various initial concentrations of Pb(II) were investigated, and it was found that P. bifermentans was able to remove 83.8% of Pb(II) from solution with an initial Pb(II) concentration of 80 mg L-1, while K. pneumoniae was able to remove 100% of Pb(II) with the same initial Pb(II) concentration after approximately 5 d. With the same initial Pb(II) concentration, P. bifermentans was able to remove 86.1% of Pb(II) from solution, and K. pneumoniae was able to remove 91.1% of Pb(II) from solution after 30 h. The identities of the precipitates obtained for each strain vary, with PbS and Pb0 being the main species precipitated by P. bifermentans and PbO with either PbCl or Pb3(PO4)2 precipitated by K. pneumoniae. Various factors were investigated in each experiment, such as metabolic activity, nitrate concentration, residual Pb(II) concentration, extracellular and intracellular Pb(II) concentration and the precipitate identity. These factors provide a greater understanding of the mechanisms utilised by the bacteria in the bioprecipitation and adsorption of Pb(II). These results can be used as a step towards applying the process on an industrial scale.

Non-Destructive Impedance Monitoring of Bacterial Metabolic Activity towards Continuous Lead Biorecovery.

The adverse health effects of the presence of lead in wastewater streams are well documented, with conventional methods of lead recovery and removal suffering from disadvantages such as high energy costs, the production of toxic sludge, and low lead selectivity. Klebsiella pneumoniae and Paraclostridium bifermentans have been identified as potential lead-precipitating species for use in a lead recovery bioreactor. Electrical impedance spectroscopy (EIS) on a low-cost device is used to determine the potential for the probe-free and label-free monitoring of cell growth in a bioreactor containing these bacteria. A complex polynomial is fit for several reactive equivalent circuit components. A direct correlation is found between the extracted supercapacitance and the plated colony-forming unit count during the exponential growth phase, and a qualitative correlation is found between all elements of the measured reactance outside the exponential growth phase. Strong evidence is found that Pb(II) ions act as an anaerobic respiration co-substrate for both cells observed, with changes in plated count qualitatively mirrored in the Pb(II) concentration. Guidance is given on the implementation of EIS devices for continuous impedance monitoring.

Online Control of Lemna minor L. Phytoremediation: Using pH to Minimize the Nitrogen Outlet Concentration.

Phytoremediation technologies are employed worldwide to remove nutrient pollutants from agricultural and industrial wastewater. Unlike in algae-based nutrient removal, control methodologies for plant-based remediation have not been standardized. Control systems that guarantee consistently low outlet concentrations of nitrogen and phosphorous often use expensive analytical instruments and are therefore rarely viable. In this study, pH measurement was used as the sole input to control the nitrate outlet concentration in a continuously operated Lemna minor (lesser duckweed) phytoremediation tank. When grown in 20 L batches of modified Hoagland's solution, it was found that a constant ratio exists between the amount of nitrate removed and the amount of acid dosed (required for pH control), which was equal to 1.25 mol N·(mol H+)-1. The nitrate uptake rates were determined by standard spetrophotometric method. At critically low nitrate concentrations, this ratio reduced slightly to 1.08 mol N·(mol H+)-1. Assuming a constant nitrogen content, the biomass growth rate could be predicted based on the acid dosing rate. A proportional-integral controller was used to maintain pH on 6.5 in a semi-continuously operated tank covered by L. minor. A nitrogen control strategy was developed which exploited this relationship between nitrate uptake and dosing and successfully removed upwards of 80% of the fed nitrogen from synthetic wastewater while a constant biomass layer was maintained. This study presents a clear illustration of how advanced chemical engineering control principles can be applied in phytoremediation processes.

Fragment Screening Yields a Small-Molecule Stabilizer of 14-3-3 Dimers That Modulates Client Protein Interactions.

The development of protein-protein interaction (PPI) inhibitors has been a successful strategy in drug development. However, the identification of PPI stabilizers has proven much more challenging. Here we report a fragment-based drug screening approach using the regulatory hub-protein 14-3-3 as a platform for identifying PPI stabilizers. A homogenous time-resolved FRET assay was used to monitor stabilization of 14-3-3/peptide binding using the known interaction partner estrogen receptor alpha. Screening of an in-house fragment library identified fragment 2 (VUF15640) as a putative PPI stabilizer capable of cooperatively stabilizing 14-3-3 PPIs in a cooperative fashion with Fusicoccin-A. Mechanistically, fragment 2 appears to enhance 14-3-3 dimerization leading to increased client-protein binding. Functionally, fragment 2 enhanced potency of 14-3-3 in a cell-free system inhibiting the enzyme activity of the nitrate reductase. In conclusion, we identified a general PPI stabilizer targeting 14-3-3, which could be used as a tool compound for investigating 14-3-3 client protein interactions.

Optimal Growth Conditions for Azolla pinnata R. Brown: Impacts of Light Intensity, Nitrogen Addition, pH Control, and Humidity.

Nitrogen pollution from agriculture is a major challenge facing our society today. Biological nitrogen fixation is key to combat the damage that is caused by synthetic nitrogen. Azolla spp. are ideal candidates for fast nitrogen fixation. This study aimed to investigate the optimal growth conditions for Azolla pinnata R. Brown. The growth conditions that were investigated included the growth medium type and strength, light intensity, the presence/absence of nitrogen in the medium, pH control, and humidity. Higher light intensities increased plant growth by 32%, on average. The highest humidity (90%) yielded higher growth rate values than lower humidity values (60% and 75%). The presence of nitrogen in the medium had no significant effect on the growth rate of the plants. pH control was critical under the fast growth conditions of high light intensity and high humidity, and it reduced algal growth (from visual observation). The optimal growth rate that was achieved was 0.321 day-1, with a doubling time of 2.16 days. This was achieved by using a 15% strength of the Hoagland solution, high light intensity (20,000 lx), nitrogen present in the medium, and pH control at 90% humidity. These optimised conditions could offer an improvement to the existing phytoremediation systems of Azolla pinnata and aid in the fight against synthetic nitrogen pollution.

One-Step Green Synthesis of Water-Soluble Fluorescent Carbon Dots and Its Application in the Detection of Cu2.

Renewable biowaste-derived carbon dots have garnered immense interest owing to their exceptional optical, fluorescence, chemical, and environmentally friendly attributes, which have been exploited for the detection of metals, non-metals, and organics in the environment. In the present study, water-soluble fluorescent carbon dots (CDs) were synthesized via facile green microwave pyrolysis of pine-cone biomass as precursors, without any chemical additives. The synthesized fluorescent pine-cone carbon dots (PC-CDs) were spherical in shape with a bimodal particle-size distribution (average diameters of 15.2 nm and 42.1 nm) and a broad absorption band of between 280 and 350 nm, attributed to a π-π* and n-π* transition. The synthesized PC-CDs exhibited the highest fluorescent (FL) intensity at an excitation wavelength of 360 nm, with maximum emission of 430 nm. The synthesized PC-CDs were an excellent fluorescent probe for the selective detection of Cu2+ in aqueous solution, amidst the presence of other metal ions. The FL intensity of PC-CDs was exceptionally quenched in the presence of Cu2+ ions, with a low detection limit of 0.005 µg/mL; this was largely ascribed to Cu2+ ion binding interactions with the enriched surface functional groups on the PC-CDs. As-synthesized PC-CDs are an excellent, cost effective, and sensitive probe for detecting and monitoring Cu2+ metal ions in wastewater.

Effective Adsorption of Congo Red from Aqueous Solution Using Fe/Al Di-Metal Nanostructured Composite Synthesised from Fe(III) and Al(III) Recovered from Real Acid Mine Drainage.

This study presents the first known exploration of Congo red dye (CR) adsorption by a polycationic Fe/Al Di-metal nanostructured composite (PDFe/Al) synthesised using Fe(III) and Al(III) recovered from authentic acid mine drainage (AMD). The PDFe/Al successfully removed CR from the aqueous solution. The mineralogical, microstructural, and chemical properties of the synthesised PDFe/Al adsorbent (before and after adsorption) were studied using state-of-the-art analytical instruments. The optimum conditions were observed to be 100 mg·L-1 CR, 1 g of the PDFe/Al in 500 mL adsorbate solution, 20 min of shaking, pH = 3-8, and a temperature of 35 °C. At optimised conditions, the PDFe/Al showed ≥99% removal efficacy for CR dye and an exceptionally high Langmuir adsorption capacity of 411 mg·g-1. Furthermore, a diffusion-limited adsorption mechanism was observed, with two distinct surfaces involved in the adsorption of CR from an aqueous solution. It was determined that the adsorption of CR induced internal strain and deformation within the matrices and interlayers of the PDFe/Al which resulted in a marked increase in the adsorbent pore surface area and pore volume. The remarkably high adsorption capacity could be attributed to the high surface area. A regeneration study showed that the adsorbent could be reused more than four times for the adsorption of CR. The findings from this study demonstrated the feasibility of recovering valuable minerals from toxic and hazardous AMD and demonstrated their potential for the treatment of industrial wastewaters.

Enterococcus spp. Cell-Free Extract: An Abiotic Route for Synthesis of Selenium Nanoparticles (SeNPs), Their Characterisation and Inhibition of Escherichia coli.

Selenite (SeO32-), the most toxic and most reactive selenium (Se) oxyanion, can be reduced to elemental selenium (Se0) nanoparticles by a variety of bacteria, including Enterococcus spp. Previously, the orthodox view held that the reduction of SeO32- to Se0 by a wide range of bacteria was solely accomplished by biological processes; however, recent studies have shown that various bacterial strains secrete metal-reducing metabolites, thereby indirectly catalysing the reduction of these metal species. In the current study, selenium nanoparticles were synthesised from the abiotic reduction of selenite with the use of Enterococcus spp. cell-free extract. Once separated from the cell-free extract, the particles were analysed using Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), Transmission electron microscopy (TEM) and a Zetasizer. The results revealed that the SeNPs were spherical in shape, containing both amorphous and crystalline properties, and the sizes with the highest frequency ranged close to 200 nm. Additionally, the obtained nanoparticles exhibited antimicrobial properties by directly inhibiting the viability of an E. coli bacterial strain. The results demonstrate not only the potential of abiotic production of SeNPs, but also the potential for these particles as microbial inhibitors in medical or similar fields.

Metallic nickel nanoparticles supported polyaniline nanotubes as heterogeneous Fenton-like catalyst for the degradation of brilliant green dye in aqueous solution.

Metallic nanoparticles supported on porous matrices are promising heterogeneous catalysts for Fenton-like reaction towards the degradation of organic contaminants in water. Herein, novel magnetic nanocomposites (NCs) of metallic nickel (Ni0) nanoparticles and nanotubular polyaniline matrix (PANI/Ni0 NCs) were fabricated by simple reductive formation of Ni0 nanoparticles upon the pre-synthesized PANI nanotubes (NTs) surface and applied as heterogeneous Fenton-like catalyst in degrading cationic brilliant green dye (BG) in aqueous solution. Various physico-chemical characterization techniques revealed effective supporting of soft ferromagnetic well dispersed nano-dimensional Ni0 particles onto the PANI NTs matrix. Heterogeneous Fenton-like catalytic performance of PANI/Ni0 NCs for BG degradation in the presence of hydrogen peroxide (H2O2) oxidant demonstrated their superiority when compared with unsupported Ni0 nanoparticles counterpart. Experiments with a minimum 0.1 g/L of NCs and 10 mM of H2O2 displayed complete degradation of 100 mg/L BG within 120 min reaction time. Improved BG degradation was observed with increase in the dose of PANI/Ni0, H2O2 concentration and temperature, whereas it reduced with rise in initial concentration of BG. The rate of degradation was well described by the pseudo-first- order kinetic model. Six consecutive BG degradation experiments confirmed NCs reusability without loss of original (∼100%) degradation efficiency up to the fifth cycle. Finally, liquid chromatography-mass spectrometric (LC-MS) analyses of the BG samples after 120 min degradation time exposed the formation of N,N-diethylaniline as degradation product along with partial mineralization of the other end products via the attack of reactive hydroxyl radicals (HO•) produced in the catalytic system.

Insight into the Metabolic Profiles of Pb(II) Removing Microorganisms.

The objective of the study was to gather insight into the metabolism of lead-removing microorganisms, coupled with Pb(II) removal, biomass viability and nitrate concentrations for Pb(II) bioremoval using an industrially obtained microbial consortium. The consortium used for study has proven to be highly effective at removing aqueous Pb(II) from solution. Anaerobic batch experiments were conducted with Luria-Bertani broth as rich growth medium over a period of 33 h, comparing a lower concentration of Pb(II) with a higher concentration at two different nutrient concentrations. Metabolite profiling and quantification were conducted with the aid of both liquid chromatography coupled with tandem mass spectroscopy (UPLC-HDMS) in a "non-targeted" fashion and high-performance liquid chromatography (HPLC) in a "targeted" fashion. Four main compounds were identified, and a metabolic study was conducted on each to establish their possible significance for Pb(II) bioremoval. The study investigates the first metabolic profile to date for Pb(II) bioremoval, which in turn can result in a clarified understanding for development on an industrial and microbial level.

Effect of shear on morphology, viability and metabolic activity of succinic acid-producing Actinobacillus succinogenes biofilms.

Two custom-designed bioreactors were used to evaluate the effect of shear on biofilms of a succinic acid producer, Actinobacillus succinogenes. The first bioreactor allowed for in situ removal of small biofilm samples used for microscopic imaging. The second bioreactor allowed for complete removal of all biofilm and was used to analyse biofilm composition and productivity. The smooth, low porosity biofilms obtained under high shear conditions had an average cell viability of 79% compared to 57% at the lowest shear used. The maximum cell-based succinic acid productivity for high shear biofilm was 2.4 g g-1DCW h-1 compared to the 0.8 g g-1DCW h-1 of the low shear biofilm. Furthermore, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assays confirmed higher cell metabolic activities for high shear developed biofilm compared to biofilm developed at low shear conditions. Results clearly indicated that high shear biofilm cultivation has beneficial morphological, viability, and cell-based productivity characteristics.

Impact of metabolite accumulation on the structure, viability and development of succinic acid-producing biofilms of Actinobacillus succinogenes.

Biofilms of Actinobacillus succinogenes have demonstrated exceptional capabilities as biocatalysts for high productivity, titre and yield production of succinic acid (SA). The paper presents a microscopic analysis of A. succinogenes biofilms developed under varied fermenter conditions. The concentration of excretion metabolites is controlled by operating the fermenter in a continuous mode where the liquid throughput is adjusted. It is clearly illustrated how the accumulation of excreted metabolites (concomitant with the sodium build-up due to base dosing) has a severe effect on the biofilm structure and physiology. Under high accumulation (HA) conditions, some cells exhibit severe elongation while maintaining a cross-sectional diameter like the rod/cocci-shaped cells predominantly found in low accumulation (LA) conditions. The elongated cells formed at high accumulation conditions were found to be more viable than the clusters of rod/cocci-shaped cells and appear to form connections between the clusters. The global microscopic structure of the HA biofilms also differed significantly from the LA biofilms. Although both exhibited shedding after 4 days of growth, the LA biofilms were more homogenous (less patchy), thicker and with high viability throughout the biofilm depth. The viability of the HA biofilms was threefold lower than the corresponding LA biofilms towards the end of the fermentation. Visual observations were supported by quantitative analysis of multiple biofilm samples and strengthened the main observations. The work presents valuable insights on the effect of metabolite accumulation on biofilm structure and growth.