Biofilm Communities Research Articles

Enrichment of native plastic-associated biofilm communities to enhance polyester degrading activity.

Plastic pollution is an increasing worldwide problem urgently requiring a solution. While recycling rates are increasing globally, only 9% of all plastic waste has been recycled, and with the cost and limited downstream uses of recycled plastic, an alternative is needed. Here, we found that expanded polystyrene (EPS) promoted high levels of bacterial biofilm formation and sought out environmental EPS waste to characterize these native communities. We demonstrated that the EPS attached communities had limited plastic degrading activity. We then performed a long-term enrichment experiment where we placed a robust selection pressure on these communities by limiting carbon availability such that the waste plastic was the only carbon source. Seven of the resulting enriched bacterial communities had increased plastic degrading activity compared to the starting bacterial communities. Pseudomonas stutzeri was predominantly identified in six of the seven enriched communities as the strongest polyester degrader. Sequencing of one isolate of P. stutzeri revealed two putative polyesterases and one putative MHETase. This indicates that waste plastic-associated biofilms are a source for bacteria that have plastic-degrading potential, and that this potential can be unlocked through selective pressure and further in vitro enrichment experiments, resulting in biodegradative communities that are better than nature.

Spatio-temporal variation of bacterial community structure in two intertidal sediment types of Jiaozhou Bay

The intertidal sediment environment is dynamic and the biofilm bacterial community within it must constantly adapt, but an understanding of the differences in the biofilm bacterial community within sediments of different types is still relatively limited. The semi-enclosed Jiaozhou Bay has a temperate monsoon climate, with strong currents at the mouth of the bay. In this study, the structure of the bacterial community in Jiaozhou Bay sediment biofilms are described using high-throughput 16 S rRNA gene sequencing and the effects of temporal change and different sediment environment types are discussed. Alpha diversity was significantly higher in sandy samples than in muddy samples. Sandy sediments with increased heterogeneity promote bacterial aggregation. Beta diversity analysis showed significant differences between sediment types and between stations. Proteobacteria and Acidobacteria were significantly more abundant at ZQ, while Campilobacterota was significantly more abundant at LC. The relative abundances of Bacteroidetes, Campilobacterota, Firmicutes, and Chloroflexi were significantly higher in the muddy samples, while Actinobacteria and Proteobacteria were higher in the sandy samples. There were different phylum-level biomarkers between sediment types at different stations. There were also different patterns of functional enrichment in biogeochemical cycles between sediment types and stations with the former having more gene families that differed significantly, highlighting their greater role in determining bacterial function. Bacterial amplicon sequence variant variation between months was less than KEGG ortholog variation between months, presumably the temporal change had an impact on shaping the intertidal sediment bacterial community, although this was less clear at the gene family level. Random forest prediction yielded a combination of 43 family-level features that responded well to temporal change, reflecting the influence of temporal change on sediment biofilm bacteria.

Complete mineralization of 2,4-dichlorophenoxyacetic acid in a reduction and oxidation Synergistic Platform (ROSP)

Emissions of 2,4-dichlorophenoxyactic acid (2,4-D), one of the most widely used herbicides, pose serious risks to human and ecosystem health. Although biodegradation and abiotic chemical methods are available for 2,4-D removal, continuous treatment systems for 2,4-D removal are rare. We evaluated a Reduction and Oxidation Synergistic Platform (ROSP) that sequentially links an H2-based membrane catalyst-film reactor (H2-MCfR) and an O2-based membrane biofilm reactor (O2-MBfR). In continuous operation of the ROSP, 50 μM (or 11 ppm) of 2,4-D was completely mineralized with a total HRT of 12 h, yielding an effluent concentration < 0.2 μM 2,4-D (or < 44 ppb). In the H2-MCfR, over 80% of the influent 2,4-D was reductively hydrodechlorinated to phenoxyacetic acid (POA). The produced POA was the primary substrate supporting the co-oxidation of 2,4-D in the O2-MBfR. The biofilm community structure and genes encoding enzymes for POA and 2,4-D co-oxidation were identified through shallow metagenomic sequencing of the biofilm DNA samples. The dominant bacterial genus, Variovorax, and various mono-/dioxygenase-encoding genes related to aromatic ring hydrolysis, hydroxylation, and ring cleavage were associated with the removal of 2,4-D. In summary, reductive-dehalogenation products from the H2-MCfR become the primary substrate to enable the co-oxidation of the halogenated organic pollutants in the O2-MBfR, which does not require the addition of other organic materials. Therefore, the ROSP eliminates the need for an added organic substrate, which greatly reduces the demand for O2 and minimizes CO2 emissions.

Sewage-derived substances and dead microbial cells cause gel biofilm formation in membrane bioreactors treating real sewage

Gel fouling is frequently reported as one of the biggest obstacles in membrane bioreactors (MBRs) and is observed under unstable conditions. However, the mechanism and the cause of gel fouling are unknown. In this study, gel fouling was induced and compared with normal fouling (cake fouling) in MBR to identify the source of the substances and microorganisms which form the basis of the gel biofilm. Two anoxic/oxic MBRs were operated under changing and stable sludge loading rate (SLR) to induce gel and cake fouling, respectively. As SLR increased from 0.07 to 0.11 kg-COD/kg-MLSS, transmembrane pressure increased rapidly, and a gel biofilm formed on the membrane surface. By contrast, a cake biofilm was developed under stable SLR of 0.07 kg-COD/kg-MLSS with slow transmembrane pressure increase. Excitation-emission matrix-parallel factor analysis indicated that simple aromatic proteins and soluble microbial byproduct-like substances in the filtered supernatant were efficiently removed in both reactors; however, proteins and polysaccharides accumulated in the supernatant with flocs. Scanning electron microscopy analysis revealed that the gel biofilm had a cloud-like structure, with aggregates of filamentous bacteria and microcolonies. The gel biofilm had a thick dead-cell layer and a small number of dispersed live cells, whereas the cake biofilm had a three-dimensional structure of live and dead cells. In the context of the microbial community in gel biofilms, sewage-derived bacteria, such as Campylobacteria and Clostridia, were highly dominant, and the microbial community resembled more sewage than activated sludge. These results indicate that the accumulation of sewage-derived substances and dead microorganisms might have formed gel biofilm in the MBR.

Diversity characterization of bacteria and fungi in water, sediments and biofilms from Songhua River in Northeast China

Water, sediments, and biofilms are the typical microbial carriers in natural water environments. However, comparative analysis of the distribution of bacterial and fungal communities in different carriers within the same habitat is relatively lacking. Therefore, this study employed 16 S and ITS rRNA gene sequencing to identify bacterial and fungal community structures in water, sediments, and biofilm. The results show that (1) the OTUs numbers revealed that the bacterial abundance, at the levels of species, genus, and family, followed the order of sediments > water > biofilms, while the fungal abundance order was water > sediments > biofilms. In addition, bacteria were mainly present in sediments, while fungi were mainly present in water. (2) The α diversity index (Shannon, ACE, Simpson, and Chao1) order, for bacteria was: sediments > water > biofilms, indicating that the diversity and homogeneity of bacteria in sediments were relatively higher; for fungi was: water > sediments > biofilms, indicating that the diversity and abundance of fungi in water were high. (3) The core phylum of bacterial in the water, sediments, and biofilms was Cyanobacteria (31.3–46.1%) and Actinobacteria (27.6–36.1%); Proteobacteria (35.0–41.8%), Cyanobacteria (14.7–36.6%); and Proteobacteria (63.3–69.2%), respectively. (4) The mainly colonized fungal phyla in biofilms in the water, sediments, and biofilms were Basidiomycota (29.3–38.7%) and Ascomycota (16.2–27.7%); Zygomycota (13.1–17.5%), Basidiomycota (5.6–17.6%); and Zygomycota (23.8–44.2%). (5) There were significant species differences in bacterial and fungal communities in water, sediments, and biofilm by NMDS analysis. Findings are useful for guiding significance for the Biogeochemical cycle of elements, the environmental fate of pollutants, and the study of water ecosystems.

Higher abundance of ammonia-oxidizing bacteria than ammonia-oxidizing archaea in biofilms and the microbial community composition of Kaiping Diaolou of China

We here investigated microbial biofilm communities on the surfaces of Linlu Villa, a villa built on a cultural heritage site known as Kaiping Diaolou and Villages located in southern China, by using next-generation sequencing technology. Then, 16S rRNA gene sequences revealed that the dominant bacterial groups in these biofilms were Cyanobacteria, Proteobacteria, Actinobacteria, Chloroflexi, Acidobacteria, Bacteroidetes, and Deinococcus-Thermus. The site survey revealed that the unique climatic conditions (ambient temperature and humidity), activities in the surroundings (farming and domestic pollution), and the rough surface of Diaolou buildings were the main factors promoting microbial colonization and development, and subsequent biofilm formation. In addition, we conducted inorganic nitrogen detecting on the surrounding environment of the Diaolou buildings and found that the inorganic nitrogen content was very high, with inorganic nitrogen NO3−-N reaching 8947.27 mg/kg; the NH4+-N content can reach 895.88 mg/kg qPCR quantification of AOA-amoA and AOB-amoA genes was performed at four sites and found that the abundance of ammonia-oxidizing bacteria (AOB) was far higher than that of ammonia-oxidizing archaea (AOA), reaching a maximum of 4–5 orders of magnitude, which is different from the current results on other cultural heritage sites. This may be due to the specific geographical location of Kaiping Diaolou and villages in the southern China with severe nitrogen deposition, as well as the surrounding residential areas and agricultural cultivation areas where nitrogen fertilizer is used in nearby agricultural cultivation. This will be worth further investigation, and the results are valuable for the protection for the protection of Kaiping Diaolou and Villages.

The response of structure and nitrogen removal function of the biofilm on submerged macrophytes to high ammonium in constructed wetlands

The ammonium exceedance discharge from sewage treatment plants has a great risk to the stable operation of subsequent constructed wetlands (CWs). The effects of high ammonium shocks on submerged macrophytes and epiphytic biofilms on the leaves of submerged macrophytes in CWs were rarely mentioned in previous studies. In this paper, the 16S rRNA sequencing method was used to investigate the variation of the microbial communities in biofilms on the leaves of Vallisneria natans plants while the growth characteristics of V. natans plants were measured at different initial ammonium concentrations. The results demonstrated that the total chlorophyll and soluble sugar synthesis of V. natans plants decreased by 51.45% and 57.16%, respectively, and malondialdehyde content increased threefold after 8 days if the initial NH4+-N concentration was more than 5 mg/L. Algal density, bacterial quantity, dissolved oxygen, and pH increased with high ammonium shocks. The average removal efficiencies of total nitrogen and NH4+-N reached 73.26% and 83.94%, respectively. The heat map and relative abundance analysis represented that the relative abundances of phyla Proteobacteria, Cyanobacteria, and Bacteroidetes increased. The numbers of autotrophic nitrifiers and heterotrophic nitrification aerobic denitrification (HNAD) bacteria expanded in biofilms. In particular, HNAD bacteria of Flavobacterium, Hydrogenophaga, Acidovorax, Acinetobacter, Pseudomonas, Aeromonas, and Azospira had higher abundances than autotrophic nitrifiers because there were organic matters secreted from declining leaves of V. natans plants. The analysis of the nitrogen metabolic pathway showed aerobic denitrification was the main nitrogen removal pathway. Thus, the nitrification and denitrification bacterial communities increased in epiphytic biofilms on submerged macrophytes in constructed wetlands while submerged macrophytes declined under ammonium shock loading.

Single and combined toxicity effects of microplastics and perfluorooctanoic acid on submerged macrophytes and biofilms

Microplastics (MPs) and Perfluorooctanoic acid (PFOA) have contaminated nearly all types of ecosystems, including marine, terrestrial and freshwater habitats, posing a severe threat to the ecological environment. However, their combined toxicity on aquatic organisms (e.g., macrophytes) remains unknown. This study investigated single and combined toxic effects of polypropylene (PP), polyethylene (PE), polyvinylchloride (PVC), polyethylene terephthalate (PET) and PFOA on Vallisneria natans (V. natans) and associated biofilms. Results showed that MPs and PFOA significantly affected plant growth, while the magnitude of the effect was associated with concentrations of PFOA and the types of MPs, and antagonistic effects were induced at combined MPs and PFOA exposure. In addition, antioxidant responses in plants, such as promoted activities of SOD and POD, as well as increased content of GSH and MDA, were triggered effectively by exposure to MPs and PFOA alone and in combination. Ultrastructural changes revealed the stress response of leaf cells and the damage to organelles. Moreover, single and combined exposure to MPs and PFOA altered the diversity and richness of the microbial community in the leaf biofilms. These results indicated that the coexistence of MPs and PFOA can induce effective defense mechanisms of V. natans and change the associated biofilms at given concentrations in the aquatic ecosystems.

New insights into the structure, microbial diversity and ecology of yellow biofilms in a Paleolithic rock art cave (Pindal Cave, Asturias, Spain)

In the absence of sunlight, caves harbor a great diversity of microbial colonies to extensive biofilms with different sizes and colors visible to the naked eye. One of the most widespread and visible types of biofilm are those with yellow hues that can constitute a serious problem for the conservation of cultural heritage in many caves, such as Pindal Cave (Asturias, Spain). This cave, declared a World Heritage Site by UNESCO for its Paleolithic parietal art, shows a high degree of development of yellow biofilms that represents a real threat to the conservation of painted and engraved figures. This study aims to: 1) identify the microbial structures and the most characteristic taxa composing the yellow biofilms, 2) seek the linked microbiome reservoir primarily contributing to their growth; 3) seed light on the driving vectors that contribute to their formation and determine the subsequent proliferation and spatial distribution. To achieve this goal, we used amplicon-based massive sequencing, in combination with other techniques such as microscopy, in situ hybridization and environmental monitoring, to compare the microbial communities of yellow biofilms with those of drip waters, cave sediments and exterior soil. The results revealed microbial structures related to the phylum Actinomycetota and the most characteristic bacteria in yellow biofilms, represented by the genera wb1-P19, Crossiella, Nitrospira, and Arenimonas. Our findings suggest that sediments serve as potential reservoirs and colonization sites for these bacteria that can develop into biofilms under favorable environmental and substrate conditions, with a particular affinity for speleothems and rugged-surfaced rocks found in condensation-prone areas. This study presents an exhaustive study of microbial communities of yellow biofilms in a cave, which could be used as a procedure for the identification of similar biofilms in other caves and to design effective conservation strategies in caves with valuable cultural heritage.

Let's Talk about Slime; or Why Biofouling Needs More Attention in Sensor Science.

Although there is a growing demand for new sensors for environmental monitoring, biofouling continues to plague current sensors and sensing networks. As soon as a sensor is placed in water, the formation of a biofilm begins. Once a biofilm is established, reliable measurements are often no longer possible. Although current biofouling mitigation strategies can slow the biofouling process, a biofilm will eventually develop on or near the sensing surface. While antibiofouling strategies are being continuously developed, the complexity of the biofilm community structure and the surrounding environment means that there is unlikely to be a single solution that will minimize biofilms on all environmental sensors. Thus, antibiofouling research often focuses on optimizing a specific biofilm mitigation approach for a given sensor, application, and environmental condition. While this is practical from the standpoint of a sensor developer, it makes the comparison of different mitigation strategies difficult. In this Perspective, we discuss the application of different biofouling mitigation strategies to sensing and then explore the need for the sensor community to adopt standard protocols to increase the comparability of the biofouling mitigation approaches and help sensor developers identify the most appropriate strategy for their system.

Multichannel Microfluidic Platform for Temporal-Spatial Investigation of Niche Roles of Pseudomonas aeruginosa and Escherichia coli within a Dual-Species Biofilm.

In natural or man-made environments, microorganisms exist predominantly as biofilms forming surface-associated bacterial communities embedded in extracellular polymeric substances (EPSs). Often, biofilm reactors used for endpoint and disruptive analyses of biofilm are not suitable for periodic observation of biofilm formation and development. In this study, a microfluidic device designed with multiple channels and a gradient generator was used for high-throughput analysis and real-time monitoring of dual-species biofilm formation and development. We compared the structural parameters of monospecies and dual-species biofilms containing Pseudomonas aeruginosa (expressing mCherry) and Escherichia coli (expressing green fluorescent protein [GFP]) to understand the interactions in the biofilm. The rate of biovolume increase of each species in monospecies biofilm (2.7 × 105 μm3) was higher than those in a dual-species biofilm (9.68 × 104 μm3); however, synergism was still observed in the dual-species biofilm due to overall increases in biovolume for both species. Synergism was also observed in a dual-species biofilm, where P. aeruginosa forms a "blanket" over E. coli, providing a physical barrier against shear stress in the environment. The microfluidic chip was useful for monitoring the dual-species biofilm in the microenvironment, indicating that different species in a multispecies biofilm exhibit different niches for the survival of the biofilm community. Finally, we demonstrated that the nucleic acids can be extracted from the dual-species biofilm in situ after biofilm imaging analysis. In addition, gene expression supported that the activation and suppression of different quorum sensing genes resulted in the different phenotype seen in the biofilm. This study showed that the integration of microfluidic device with microscopy analysis and molecular techniques could be a promising tool for studying biofilm structure and gene quantification and expression simultaneously. IMPORTANCE In natural or man-made environments, microorganisms exist predominantly as biofilms forming surface-associated bacterial communities embedded in extracellular polymeric substances (EPSs). Often, biofilm reactors used for endpoint and disruptive analyses of biofilm are not suitable for periodic observation of biofilm formation and development. Here, we demonstrate that a microfluidic device with multiple channels and a gradient generator can be useful for high-throughput analysis and real-time monitoring of dual-species biofilm formation and development. Our study revealed synergism in the dual-species biofilm, where P. aeruginosa forms a "blanket" over E. coli, providing a physical barrier against shear stress in the environment. Furthermore, different species in a multispecies biofilm exhibit different niches for the survival of the biofilm community. This study showed that the integration of microfluidic device with microscopy analysis and molecular techniques could be a promising tool for studying biofilm structure and gene quantification and expression simultaneously.

Microbial Biofilm Colonizing Plastic Substrates in the Ross Sea (Antarctica): First Overview of Community-Level Physiological Profiles

The microbial colonization of plastic substrates made of polyvinylchloride (PVC) and polyethylene (PE) was studied in Tethys and Road Bays (Ross Sea, Antarctica) in order to evaluate the metabolic profiles of the plastisphere community in comparison with those of the surrounding waters. PVC and PE panels, mounted on stainless steel structures, were deployed in the austral summer 2017 at 5 and 20 m and recovered one year later at four different stations (Amorphous Glacier-AG was potentially impacted by the ice-melting process, and its control site was within Tethys Bay-TB; Road Bay-RB, close to the wastewater plant of the Italian research station Mario Zucchelli and its control site Punta Stocchino-PTS). Additional panels were settled in Road Bay at 5 m and recovered after three months to follow time variability in the microbial colonization process. At the same times and depths as plastic substrates, water samples were also collected. Carbon substrates’ utilization rates were determined on scraped microbial biofilm and water samples, with a fluorimetric assay based on 96-well Biolog Ecoplates. Complex carbon sources, carbohydrate and amines were the organic substrates that mostly fuelled the community metabolism in the RB area, while in the TB area, in addition to carbohydrates, phosphate carbon compounds and amino acids were also actively utilized. Within Road Bay, small differences in the physiological profiles were found, with higher metabolic rates in the biofilm community after 3 months’ deployment (late austral summer period) compared to 12 months, suggesting that autumn to spring period conditions negatively affected foulers’ metabolism. Moreover, different metabolic profiles between the plastisphere and the pelagic microbial community were observed; this last utilized a higher number of carbon sources, while plastic substrates were colonized by a more specialized community. Higher carbon substrate utilization rates were recorded at RB and AG stations, receiving organic supply from anthropic activity or ice melting sources, respectively, compared to their control sites. These results highlighted the functional plasticity of the microbial community, with the adaptive ability to utilize a diversified range of organic substrates.

PH-Responsive Biomaterials for the Treatment of Dental Caries-A Focussed and Critical Review.

Dental caries is a common and costly multifactorial biofilm disease caused by cariogenic bacteria that ferment carbohydrates to lactic acid, demineralizing the inorganic component of teeth. Therefore, low pH (pH 4.5) is a characteristic signal of the localised carious environment, compared to a healthy oral pH range (6.8 to 7.4). The development of pH-responsive delivery systems that release antibacterial agents in response to low pH has gained attention as a targeted therapy for dental caries. Release is triggered by high levels of acidogenic species and their reduction may select for the establishment of health-associated biofilm communities. Moreover, drug efficacy can be amplified by the modification of the delivery system to target adhesion to the plaque biofilm to extend the retention time of antimicrobial agents in the oral cavity. In this review, recent developments of different pH-responsive nanocarriers and their biofilm targeting mechanisms are discussed. This review critically discusses the current state of the art and innovations in the development and use of smart delivery materials for dental caries treatment. The authors' views for the future of the field are also presented.

Thiobacillus as a key player for biofilm formation in oligotrophic groundwaters of the Fennoscandian Shield

Biofilm formation is a common adaptation for microbes in energy-limited conditions such as those prevalent in the vast deep terrestrial biosphere. However, due to the low biomass and the inaccessible nature of subsurface groundwaters, the microbial populations and genes involved in its formation are understudied. Here, a flow-cell system was designed to investigate biofilm formation under in situ conditions in two groundwaters of contrasting age and geochemistry at the Äspö Hard Rock Laboratory, Sweden. Metatranscriptomes showed Thiobacillus, Sideroxydans, and Desulforegula to be abundant and together accounted for 31% of the transcripts in the biofilm communities. Differential expression analysis highlighted Thiobacillus to have a principal role in biofilm formation in these oligotrophic groundwaters by being involved in relevant processes such as the formation of extracellular matrix, quorum sensing, and cell motility. The findings revealed an active biofilm community with sulfur cycling as a prominent mode of energy conservation in the deep biosphere.

Joint toxicity mechanisms of perfluorooctanoic acid and sulfadiazine on submerged macrophytes and periphytic biofilms

Hazardous chemicals, such as perfluoroalkyl substances (PFASs) and antibiotics, coexist in aquatic environments and pose a severe threat to aquatic organisms. However, research into the toxicity of these pollutants on submerged macrophytes and their periphyton is still limited. To assess their combined toxicity, Vallisneria natans (V. natans) was exposed to perfluorooctanoic acid (PFOA) and sulfadiazine (SD) at environmental concentrations. Photosynthetic parameters such as chlorophyll a, chlorophyll b, total chlorophyll, and carotenoids were lower in the SD exposure group, indicating that SD had a significant effect on the photosynthesis of aquatic plants. Single and combined exposures effectively induced antioxidant responses, with increases in superoxide dismutase, peroxidase activities, and ribulose-1,5-bisphosphate carboxylase concentrations, as well as malondialdehyde content. Accordingly, antagonistic toxicity was assessed between PFOA and SD. Furthermore, metabolomics revealed that V. natans improved stress tolerance through changes in enoic acid, palmitic acid, and palmitoleoyloxymyristic acid related to the fatty acid metabolism pathway responding to the coexisting pollutants. Additionally, PFOA and SD in combination induced more effects on the microbial community of biofilm. The alternation of α- and β-D-glucopyranose polysaccharides and the increased content of autoinducer peptides and N-acylated homoserine lactones indicated that PFOA and SD changed the structure and function of biofilm. These investigations provide a broader perspective and comprehensive analysis of the responses of aquatic plants and periphyton biofilms to PFAS and antibiotics in the environment.

Glacial recession in Andean North-Patagonia (Argentina): microbial communities in benthic biofilms of glacier-fed streams

Glacial recession in Andean North-Patagonia (Argentina): microbial communities in benthic biofilms of glacier-fed streams

Intra-annual patterns in biofilm communities and cellulose decomposition in a headwater stream network with spatially variable groundwater inputs

Intra-annual patterns in biofilm communities and cellulose decomposition in a headwater stream network with spatially variable groundwater inputs

A Meta-Analysis of Bacterial Communities in Food Processing Facilities: Driving Forces for Assembly of Core and Accessory Microbiomes across Different Food Commodities.

Microbial spoilage is a major cause of food waste. Microbial spoilage is dependent on the contamination of food from the raw materials or from microbial communities residing in food processing facilities, often as bacterial biofilms. However, limited research has been conducted on the persistence of non-pathogenic spoilage communities in food processing facilities, or whether the bacterial communities differ among food commodities and vary with nutrient availability. To address these gaps, this review re-analyzed data from 39 studies from various food facilities processing cheese (n = 8), fresh meat (n = 16), seafood (n = 7), fresh produce (n = 5) and ready-to-eat products (RTE; n = 3). A core surface-associated microbiome was identified across all food commodities, including Pseudomonas, Acinetobacter, Staphylococcus, Psychrobacter, Stenotrophomonas, Serratia and Microbacterium. Commodity-specific communities were additionally present in all food commodities except RTE foods. The nutrient level on food environment surfaces overall tended to impact the composition of the bacterial community, especially when comparing high-nutrient food contact surfaces to floors with an unknown nutrient level. In addition, the compositions of bacterial communities in biofilms residing in high-nutrient surfaces were significantly different from those of low-nutrient surfaces. Collectively, these findings contribute to a better understanding of the microbial ecology of food processing environments, the development of targeted antimicrobial interventions and ultimately the reduction of food waste and food insecurity and the promotion of food sustainability.

Spatial stratification of cathodic biofilm on nitrogen removal in the microbial fuel cell under different carbon/nitrogen ratios

The aim of this study was to investigate nitrogen removal in the microbial fuel cell (MFC) related to spatial stratification of bacterial community in cathodic biofilm under different carbon/nitrogen ratios. Single-chamber air-cathode MFC was tested under different ratio of COD/N (i.e., 40, 16, and 10), respectively. With the freezing microtome method, matured cathodic biofilms after 13 operation cycles were sliced into 5 layers (layer 1 close to anolyte and layer 5 close to cathode) with a thickness of 20–30 μm each layer. Results showed that high removals of ammonia and total nitrogen were achieved with stratification of bacterial communities in the cathodic biofilms of MFC. The relative abundance of SM1A02 was in a range of 14.7 % – 26.5 % in all the layers under COD/N of 40, but only 0.5 % in layers of 1 and 2 under COD/N of 10. Paracoccus had the relative abundance higher than 30 % and lower than 1.5 % in all the layers under COD/N of 10 and 40, respectively. The functional genes including AMO, nxrA, nxrB, narG, nirS and norC were upregulated under low COD/N ratio, indicating that the nitrification and denitrification were enhanced in the cathodic biofilms. The freezing microtome combined with high throughput sequencing of biofilms provided a useful way to characterize the spatial stratification of bacterial community in the nitrogen removal.

Microbial community structure and settlement induction capacity of marine biofilms developed under varied reef conditions

Coral larval settlement relies on biogenic cues such as those elicited by microbial biofilm communities, a crucial element of coral recruitment. Eutrophication can modify these biofilm-associated communities, but studies on how this affects coral larval settlement are limited. In this study, we developed biofilm communities on glass slides at four sites with increasing distance from a mariculture zone. Biofilms farthest from the mariculture area were more effective at inducing the settlement of Acropora tenuis larvae. These biofilms were characterized by a greater proportion of crustose coralline algae (CCA) and gammaproteobacterial taxa compared to biofilms from sites closer to the mariculture zone, which had a greater proportion of cyanobacteria and no CCA. These findings suggest that nutrient enrichment due to mariculture activities alters the composition of biofilm-associated microbiome at nearby reef sites and indirectly causes poor coral larval settlement.