Early stage biofilm formation on bio-based microplastics in a freshwater reservoir

Bio-based plastics (BP) produced from renewable biomass resources, such as high-density polyethylene (HDPE), polylactic acid (PLA) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), is currently increasing in terms of both products and applications. However, their biodegradability and environmental fate are not yet fully understood, especially in freshwaters. Here, we present the results of an in-situ study in a freshwater reservoir, where we submerged HDPE, PLA and PHBV microscale BP (mBP) in dialysis bags to enable exchange of small organic and inorganic molecules, including nutrients, with the surrounding water. After one and two months, the bacterial biofilm that formed on each mBP was characterised by 16S rRNA amplicon sequencing. After two-months, Oxalobacteraceae, Pedosphaeraceae, Flavobacteriaceae (Flavobacterium) and Chitinophagaceae (Ferruginibacter) had increased by up to four times. Both these and other common members (≥1 % relative total biomass) of the microbial community were similarly abundant on all mBP. Low-abundance (0.3-1 %) bacterial taxa, however, were significantly more diverse and differed on each mBP. Notably, some low-abundance families and genera increased on specific materials, e.g. Sphingomonadaceae on HDPE, Sphingobacteriaceae on PHBV, Gemmatimonas and Crenothrix on PLA. Overall, abundant bacteria were regarded as a pioneering community, while low-abundance bacteria were more diverse and preferred mBP types in the early stages of biofilm formation on mBP. It could be influenced by the environmental conditions, where nutrient levels and low temperatures might shape the low-abundance of attached bacterial communities than the plastic material itself.

Research on removal of fluoroquinolones in rural domestic wastewater by vertical flow constructed wetlands under different hydraulic loads

Antibiotics had attracted more and more attention in recent years due to their harmfulness. Fluoroquinolones (FQs), one class of antibiotics widely used in human and veterinary medicine, were found in various water bodies in China. Therefore, in order to found an efficient method for removing FQs in rural domestic wastewater and optimize the process parameters, ceramsite and soil were applied in vertical flow constructed wetlands (VFCWs) to study the effects of different hydraulic loads and different substrates on the removal of FQs and conventional pollutants. The results showed the VFCW-D filled with 45 cm soil layer and 15 cm ceramasite layer had the highest removal efficiency of conventional pollutants and FQs under low hydraulic load. Nevertheless, the removal efficiency of conventional pollutants was significantly declined for the VFCWs which contained soil substrates under high hydraulic load due to the soil pores were clogged by the accumulation of organic matter. Finally, VFCW-A filled with 60 cm ceramasite layer revealed good ability to remove conventional pollutants and FQs under high hydraulic load. Deinococcus played a vital role here due to its excellent removal effect on conventional pollutants. The microbial composition in the substrate changed greatly after adding antibiotics under high hydraulic load. Devosia, Pseudorhodoferax, Cellvibrio, Bosea, Caulobacter, Acinetobacter, Zoogloea, Arcobacter, Dechloromonas, Flavobacterium, Nakamurella, Chloroplast, Clostridium_sensu_stricto_1, Pelosinus, UTCFX1 and Hypnocyclicus became the new dominated genera and were essential to remove pollutants. In summary, VFCW was an effective system to remove fluoroquinolones in rural domestic wastewater.

Photodegradation, bacterial metabolism, and photosynthesis drive the dissolved organic matter cycle in the Heilongjiang River

Dissolved organic matter (DOM) plays a vital role in the biogeochemistry of aquatic ecosystems. However, the mechanisms of DOM cycling in the water column during different seasons have not been fully elucidated to date. The differences in DOM degradation in summer, autumn, and winter water columns were evaluated in this study. The results showed that bacteria played an essential role in the degradation of DOM in the summer water column. Photochemical degradation was the primary degradation pathway of DOM in the autumn and winter water columns. Notably, while DOM is degraded, photosynthetic bacteria produce organic matter through photosynthesis to replenish the water column. EEM-PARAFAC analysis indicated more tryptophan component C1 in summer, but the contents of humic substance component C2 and terrestrial substance C3 were higher in autumn and winter. In summer, more tryptophan-like components were consumed by bacteria, and Cyanobacteria produced more organic matter through photosynthesis to replenish the water column. Moreover, a similar bacterial community structure and a more active tryptophan biosynthesis pathway were found in autumn and winter. Random forest models identified representative bacteria involved in the DOM transformation process in different seasons. The above findings may be helpful to explore the degradation characteristics of DOM in different seasons and predict the fate of DOM in the water column in the future.

Removal of Acetone Vapor from Air Using a Biotrickling Filter Packed with Polymeric Bioballs

Acetone released into the atmosphere can adversely affect human health and the environment. The aim of this work was to evaluate the performance of a laboratory-scale biotrickling filter (BTF) with bioball packing material to remove acetone vapor from contaminated air. The acetone removal efficiency was investigated in two different scenarios: with and without the inoculation of microorganisms. Three strains of bacteria, Pseudomonas putida, Rhodococcus aerolatus, and Aquaspirillum annulus, were used in the BTF. In both cases, the filter units were simultaneously operated for 100 days under three different inlet acetone concentrations (0.18 ± 0.01 g/m3, 0.25 ± 0.01 g/m3, and 0.40 ± 0.02 g/m3) and two different gas flow rates (2.54 and 5.09 m3/h). The results showed that acetone removal was greater in the filter with the inoculated bacteria. In the filter operated without inoculum, the acetone removal efficiency gradually decreased with filtration time from 90.1% to 6.1%. While employing three types of bacteria in the BTF, the efficiency of acetone removal remained relatively stable and varied between 70.2% and 97.6%. The study also revealed that bioballs can be successfully used as a packing material in air biofiltration systems designed for acetone removal from the air.

Performance of polychaete assisted sand filters under contrasting nutrient loads in an integrated multi-trophic aquaculture (IMTA) system

Polychaete assisted sand filters (PASFs) allow to combine a highly efficient retention of particulate organic matter (POM) present in aquaculture effluent water and turn otherwise wasted nutrients into valuable worm biomass, following an integrated multi-trophic aquaculture (IMTA) approach. This study evaluated the bioremediation and biomass production performances of three sets of PASFs stocked with ragworms (Hediste diversicolor) placed in three different locations of an open marine land-based IMTA system. The higher organic matter (OM) recorded in the substrate of the systems which received higher POM content (Raw and Df PASFs – filtered raw and screened by drum filter effluent, respectively) likely prompted a superior reproductive success of stocked polychaetes (final densities 2–7 times higher than initial stock; ≈1000–3000 ind. m⁻²). Bioremediation efficiencies of ≈70% of supplied POM (≈1.5–1.8 mg L⁻¹) were reported in these systems. The PASFs with lower content of OM in the substrate (Df + Alg PASFs – filtered effluent previously screened by drum filter and macroalgae biofilter) differed significantly from the other two, with stocked polychaetes displaying a poorer reproductive success. The PASFs were naturally colonized with marine invertebrates, with the polychaetes Diopatra neapolitana, Terebella lapidaria and Sabella cf. pavonina being some of the species identified with potential for IMTA.

Biological filters regulate water quality, modulate health status, immune indices and gut microbiota of freshwater crayfish, marron (Cherax cainii, Austin, 2002)

Water quality has significant impacts on the health and immune responses of aquaculture species. This study aimed to analyse and compare the effects of two biological filters namely, gravel and, Bio-Ball with a recently developed filter called Water-cleanser on regulation of water quality parameters, health and immune response of marron reared in plastic tanks for 60 days. Results showed that addition of Bio-Ball significantly (P < 0.05) reduced the concentration of ammonia, nitrate and phosphate while Water-cleanser showed the ability to reduce ammonia and nitrate from water in aquaculture tanks. Although the biological filters had no significant effect on marron growth but inclusion of Bio-Ball and Water-cleanser positively influenced the biochemical composition of tail muscle and some haemolymph parameters of marron. The next generation sequence data demonstrated higher bacterial diversity in the hindgut of marron with Water-cleanser, followed by Bio-Ball and gravel, respectively. In addition, the predicted metabolic pathways revealed a significantly higher bacterial activity and gene function correlated to metabolism and biosynthesis of protein, energy and secondary metabolites in Bio-Ball and Water-cleanser. Bio-Ball and Water-cleanser were also associated with up-regulation of innate immune responsive genes of marron gut. Overall, Bio-Ball and Water-cleanser proved to have higher water remediation and immune response modulation capabilities, and therefore could be used as preferred filters for growth of beneficial bacteria in crayfish culture.

Lactobacillus acidophilus and L. plantarum improve health status, modulate gut microbiota and innate immune response of marron (Cherax cainii)

This study aimed to investigate the combined effects of two most potent probiotic bacteria Lactobacillus acidophilus and Lactobacillus plantarum on overall health and immune status of freshwater crayfish, marron under laboratory conditions. A total of 36 marron were distributed into six different tanks and two different feeding groups, control and probiotic-fed group. After acclimation, control group was fed with basal diet while probiotic group was fed 109 CFU/mL per kg of bacterial supplemented feed for 60 days. The results showed no significant differences in weight gain, however, probiotic feed significantly enhanced some hemolymph parameters and biochemical composition of tail muscle. Histology data revealed better hepatopancreas health and higher microvilli counts in the marron gut fed probiotic diet. The probiotic bacteria triggered significant shift of microbial communities at different taxa level, mostly those reported as beneficial for crayfish. The probiotic diet also enriched the metabolic functions and genes associated with innate immune response of crayfish. Further correlation analysis revealed significant association of some taxa with increased activity for hemolymph and immune genes. Therefore, dietary Lactobacillus supplementation can modulate the overall health and immunity as well as gut microbial composition and interaction network between gut microbiota and immune system in crayfish.

Next-generation sequencing reveals significant variations in bacterial compositions across the gastrointestinal tracts of the Indian major carps, rohu (Labeo rohita), catla (Catla catla) and mrigal (Cirrhinus cirrhosis)

Bacterial communities strongly influence the digestion, health and immune status of fish. This study investigates the microbial distribution of the anterior, middle and distal gut sections of three economically important carp species in Bangladesh, rohu, catla and mrigal (commonly known as Indian major carps), using 16S rRNA-based Illumina sequencing technology. The alpha-diversity measurement with one-way ANOVA indicated high species richness, Shannon and Simpson indices in the middle and distal gut, while the anterior gut of IMCs had the lowest diversity. At the phylum level, there was high abundance of Proteobacteria in the GITs of rohu and mrigal, whereas Fusobacteria was dominant in the anterior and middle guts of catla. At the genus level, diverse microbial communities were identified across the three GIT sections, with six indicator genera found in rohu, catla and mrigal, as revealed by linear discriminant analysis (LDA) at a 0·05 level of significance. Of the 218 genera identified, only 33 were common across the anterior, middle and distal guts of all three species. Bacterial diversity was significantly higher (P < 0·05) in mrigal, followed by catla and rohu, respectively. Alongside the common bacteria Aeromonas, Enterobacter and Serratia, the overwhelming abundance of Cetobacterium, Shewanella and Plesiomonas warrants further investigation. SIGNIFICANCE AND IMPACT OF THE STUDY: This study investigates the microbial communities of the gastrointestinal tracts (GITs) of three Indian major carp (IMC) species-rohu, catla and mrigal, obtained from a polyculture pond under the same feeding regime. Diverse microbial communities were found, with significantly different relative abundances and diversities of phyla and genera. The results provide valuable information on GIT microbial communities that may be useful for nutrition and health management in IMCs.

Dietary supplementation of black soldier fly (Hermetica illucens) meal modulates gut microbiota, innate immune response and health status of marron (Cherax cainii, Austin 2002) fed poultry-by-product and fishmeal based diets

The present study aimed to evaluate the dietary supplementary effects of black soldier fly (Hermetia illucens) (BSF) meal on the bacterial communities in the distal gut, immune response and growth of freshwater crayfish, marron (Cherax cainii) fed poultry-by-product meal (PBM) as an alternative protein source to fish meal (FM). A total of 64 marron were randomly distributed into 16 different tanks with a density of four marron per tank. After acclimation, a 60-days feeding trial was conducted on marron fed isonitrogenouts and isocalorific diets containing protein source from FM, PBM, and a combination of FM + BSF and PBM + BSF. At the end of the trial, weight gain and growth of marron were found independent of any dietary treatment, however, the two diets supplemented with BSF significantly (P < 0.05) enhanced haemolymph osmolality, lysozyme activity, total haemocyte counts, and protein and energy contents in the tail muscle. In addition, the analysis of microbiota and its predicted metabolic pathways via 16s rRNA revealed a significantly (P < 0.05) higher bacterial activity and gene function correlated to biosynthesis of protein, energy and secondary metabolites in PBM + BSF than other dietary groups. Diets FM + BSF and PBM + BSF were seen to be associated with an up-regulation of cytokine genes in the intestinal tissue of marron. Overall, PBM + BSF diet proved to be a superior diet in terms of improved health status, gut microbiota and up-regulated expression of cytokine genes for marron culture.