The Response of Extracellular Polymeric Substances Production by Phototrophic Biofilms to a Sequential Disturbance Strongly Depends on Environmental Conditions

Microbial community and extracellular polymeric substance dynamics in arid-zone temporary pan ecosystems

Microbial extracellular polymeric substances (EPS) are an important component in sediment ecology. However, most research is highly skewed towards the northern hemisphere and in more permanent systems. This paper investigates EPS (i.e., carbohydrates and proteins) dynamics in arid Austral zone temporary pans sediments. Colorimetric methods and sequence-based metagenomics techniques were employed in a series of small temporary pan ecosystems characterised by alternating wet and dry hydroperiods. Microbial community patterns of distribution were evaluated between seasons (hot-wet and cool-dry) and across depths (and inferred inundation period) based on estimated elevation. Carbohydrates generally occurred in relatively higher proportions than proteins; the carbohydrate:protein ratio was 2.8:1 and 1.6:1 for the dry and wet season respectively, suggesting that EPS found in these systems was largely diatom produced. The wet- hydroperiods (Carbohydrate mean 102 μg g-1; Protein mean 65 μg g-1) supported more EPS production as compared to the dry- hydroperiods (Carbohydrate mean 73 μg g-1; Protein mean 26 μg g-1). A total of 15,042 Unique Amplicon Sequence Variants (ASVs) were allocated to 51 bacterial phyla and 1127 genera. The most abundant genera had commonality in high temperature tolerance, with Firmicutes, Actinobacteria and Proteobacteria in high abundances. Microbial communities were more distinct between seasons compared to within seasons which further suggested that the observed metagenome functions could be seasonally driven. This study's findings implied that there were high levels of denitrification by mostly nitric oxide reductase and nitrite reductase enzymes. EPS production was high in the hot-wet season as compared to relatively lower rates of nitrification in the cool-dry season by ammonia monooxygenases. Both EPS quantities and metagenome functions were highly associated with availability of water, with high rates being mainly associated with wet- hydroperiods compared to dry- hydroperiods. These data suggest that extended dry periods threaten microbially mediated processes in temporary wetlands, with implications to loss of biodiversity by desiccation.

Uncovering the role of algal organic matter biocoating on Navicula incerta cell deposition and biofilm formation

Spontaneous natural biofilm concentrates microalgal biomass on solid supports. However, the biofilm is frequently susceptible to exfoliation upon nutrient deficiency, particularly found in aged biofilm. Therefore, this study highlights a novel biofilm cultivation technique by pre-depositing the algal organic matters from marine diatom, Navicula incerta onto microporous polyvinylidene fluoride membrane to further strengthen the biofilm developed. Due to the improvement in membrane surface roughness and hydrophobicity, cells adhered most abundantly to soluble extrapolymeric substances-coated (sEPS) (76× 106± 16× 106 cells m-2), followed by bounded EPS-coated (57.67× 106± 0.33× 106 cells m-2), internally organic matter (IOM)-coated (39.00× 106± 5.19× 106 cells m-2), and pristine control the least (6.22× 106± 0.77× 106 cells m-2) at 24th h. Surprisingly, only bEPS-coated membrane demonstrated an increase in cell adhesion toward the end of the experiment at 72 h. The application of the bio-coating has successfully increased the rate of cell attachment by at least 45.3% upon inoculation and achieved as high as 89.9% faster attachment at 72 hours compared to the pristine control group. Soluble polysaccharides and proteins might be carried along by the cells adhering onto membranes hence resulting in a built up of EPS hydrophobicity (>70% in average on bio-coated membranes) over time as compared with pristine (control) that only recorded an average of approximately 50% hydrophobicity. Interestingly, cells grown on bio-coated membranes accumulated more internally bounded polysaccharides, though bio-coating had no discernible impact on the production of both externally and internally bounded protein. The collective findings of this study reveal the physiological alterations of microalgal biofilms cultured on bio-coated membranes.

Insights into effects of operating temperature on the removal of pharmaceuticals/pesticides/synthetic organic compounds by membrane bioreactor process

In this study, the removal efficiency and mechanism of 8 kinds of typical micropollutants by membrane bioreactor (MBR) at different temperatures (i.e. 15, 25 and 35 °C) were investigated. MBR exhibited the high removal rate (>85%) for 3 kinds of industrial synthetic organic micropollutants (i.e. bisphenol A (BPA), 4-tert-octylphenol (TB) and 4-n-nonylphenol (NP)) with similar functional groups, structures and high hydrophobicity (Log D > 3.2). However, the removal rates of ibuprofen (IBU), carbamazepine (CBZ) and sulfamethoxazole (SMX) with pharmaceutical activity showed great discrepancy (i.e. 93%, 14.2% and 29%, respectively), while that of pesticides (i.e. acetochlor (Ac) and 2,4-dichlorophenoxy acetic acid (2,4-D) were both lower than 10%. The results showed that the operating temperature played a significant role in microbial growth and activities. High temperature (35 °C) led to a decreased removal efficiency for most of hydrophobic organic micropollutants, and was also not conducive for refractory CBZ due to the temperature sensitivity. At lower temperature (15 °C), a large amount of exopolysaccharides and proteins were released by microorganisms, which caused the inhibited microbial activity, poor flocculation and sedimentation, resulting in the polysaccharide-type membrane fouling. It was proved that dominant microbial degradation of 61.01%-92.73% and auxiliary adsorption of 5.29%-28.30% were the main mechanisms for micropollutant removal in MBR system except for pesticides due to the toxicity. Therefore, the removal rates of most micropollutants were highest at 25 °C due to the high activity sludge so as to enhance microbial adsorption and degradation.

Hospital and urban wastewaters shape the matrix and active resistome of environmental biofilms

Understanding the dynamics of antibiotic resistance gene (ARG) transfer and dissemination in natural environments remains challenging. Biofilms play a crucial role in bacterial survival and antimicrobial resistance (AMR) dissemination in natural environments, particularly in aquatic systems. This study focused on hospital and urban wastewater (WW) biofilms to investigate the potential for ARG dissemination through mobile genetic elements (MGEs). The analysis included assessing the biofilm extracellular polymeric substances (EPS), microbiota composition as well as metatranscriptomic profiling of the resistome and mobilome. We produced both in vitro and in situ biofilms and performed phenotypic and genomic analyses. In the in vitro setup, untreated urban and hospital WW was used to establish biofilm reactors, with ciprofloxacin added as a selective agent at minimal selective concentration. In the in situ setup, biofilms were developed directly in hospital and urban WW pipes. We first showed that a) the composition of EPS differed depending on the growth environment (in situ and in vitro) and the sampling origin (hospital vs urban WW) and that b) ciprofloxacin impacted the composition of the EPS. The metatranscriptomic approach showed that a) expression of several ARGs and MGEs increased upon adding ciprofloxacin for biofilms from hospital WW only and b) that the abundance and type of plasmids that carried individual or multiple ARGs varied depending on the WW origins of the biofilms. When the same plasmids were present in both, urban and hospital WW biofilms, they carried different ARGs.  We showed that hospital and urban wastewaters shaped the structure and active resistome of environmental biofilms, and we confirmed that hospital WW is an important hot spot for the dissemination and selection of antimicrobial resistance. Our study provides a comprehensive assessment of WW biofilms as crucial hotspots for ARG transfer. Hospital WW biofilms exhibited distinct characteristics, including higher eDNA abundance and expression levels of ARGs and MGEs, highlighting their role in antimicrobial resistance dissemination. These findings emphasize the importance of understanding the structural, ecological, functional, and genetic organization of biofilms in anthropized environments and their contribution to antibiotic resistance dynamics.

Biofilm Control in Flow-Through Systems Using Polyvalent Phages Delivered by Peptide-Modified M13 Coliphages with Enhanced Polysaccharide Affinity

Eradication of biofilms that may harbor pathogens in water distribution systems is an elusive goal due to limited penetration of residual disinfectants. Here, we explore the use of engineered filamentous coliphage M13 for enhanced biofilm affinity and precise delivery of lytic polyvalent phages (i.e., broad-host-range phages lysing multiple host strains after infection). To promote biofilm attachment, we modified the M13 major coat protein (pVIII) by inserting a peptide sequence with high affinity for Pseudomonas aeruginosa (P. aeruginosa) extracellular polysaccharides (commonly present on the surface of biofilms in natural and engineered systems). Additionally, we engineered the M13 tail fiber protein (pIII) to contain a peptide sequence capable of binding a specific polyvalent lytic phage. The modified M13 had 102- and 5-fold higher affinity for P. aeruginosa-dominated mixed-species biofilms than wildtype M13 and unconjugated polyvalent phage, respectively. When applied to a simulated water distribution system, the resulting phage conjugates achieved targeted phage delivery to the biofilm and were more effective than polyvalent phages alone in reducing live bacterial biomass (84 vs 34%) and biofilm surface coverage (81 vs 22%). Biofilm regrowth was also mitigated as high phage concentrations induced residual bacteria to downregulate genes associated with quorum sensing and extracellular polymeric substance secretion. Overall, we demonstrate that engineered M13 can enable more accurate delivery of polyvalent phages to biofilms in flow-through systems for enhanced biofilm control.