Chlamydomonas reinhardtii and Microbacterium forte sp. nov., a mutualistic association that favors sustainable hydrogen production

A naturally occurring multispecies bacterial community composed of Bacillus cereus and two novel bacteria (Microbacterium forte sp. nov. and Stenotrophomonas goyi sp. nov.) has been identified from a contaminated culture of the microalga Chlamydomonas reinhardtii. When incubated in mannitol- and yeast extract-containing medium, this bacterial community can promote and sustain algal hydrogen production up to 313 mL H2·L-1 for 17 days and 163.5 mL H2·L-1 for 25 days in high-cell (76.7 μg·mL-1 of initial chlorophyll) and low-cell density (10 μg·mL-1 of initial chlorophyll) algal cultures, respectively. In low-cell density algal cultures, hydrogen production was compatible with algal growth (reaching up to 60 μg·mL-1 of chlorophyll). Among the bacterial community, M. forte sp. nov. was the sole responsible for the improvement in hydrogen production. However, algal growth was not observed in the Chlamydomonas-M. forte sp. nov. consortium during hydrogen-producing conditions (hypoxia), suggesting that the presence of B. cereus and S. goyi sp. nov. could be crucial to support the algal growth during hypoxia. Still, under non‑hydrogen producing conditions (aerobiosis) the Chlamydomonas-M. forte sp. nov. consortium allowed algal growth (up to 40 μg·mL-1 of chlorophyll) and long-term algal viability (>45 days). The genome sequence and growth tests of M. forte sp. nov. have revealed that this bacterium is auxotroph for biotin and thiamine and unable to use sulfate as sulfur source; it requires S-reduced forms such as cysteine and methionine. Cocultures of Chlamydomonas reinhardtii and M. forte sp. nov. established a mutualistic association: the alga complemented the nutrient deficiencies of the bacterium, while the bacterium released ammonium (0.19 mM·day-1) and acetic acid (0.15 mM·day-1) for the alga. This work offers a promising avenue for photohydrogen production concomitant with algal biomass generation using nutrients not suitable for mixotrophic algal growth.

Oxygen affinity and light intensity induced robust phosphorus removal and fragile ammonia removal in a non-aerated bacteria-algae system

Non-aerated bacteria-algae system gaining O2 through photosynthesis presents an alternative for costly mechanical aeration. This study investigated oxygen supply and performance of nutrients removal at low and high light intensity (LL and HL). The results showed that P removal was high and robust (LL 97 ± 1.8 %, HL 95 % ± 2.9 %), while NH4+-N removal fluctuated dramatically (LL 66 ± 14.7 %, HL 84 ± 8.6 %). Oxygen generated at illumination of 200 μmol m-2 s-1, 6 h was sufficient to sustain aerobic phase for 2.25 g/L MLSS. However, O2 produced by algae was preferentially captured in the order of heterotrophic bacteria (HB), ammonia oxidizing bacteria (AOB), nitrite oxidizing bacteria (NOB). Oxygen affinity coupled with light intensity led to NOB suppression with stable nitrite accumulation ratio of 57 %. Free nitrous acid (FNA) and light stimulated the abundance of denitrifying polyphosphate accumulating organism (DPAO) of Flavobacterium, but with declined P-accumulating metabolism (PAM) of P release, P/C, K/P and Mg/P ratios. Flavobacterium and cyanobacteria Leptolyngbya, along with biologically induced CaP in extracellular polymeric substances was the key to robust P removal. AOB of Ellin6067 and DPAO of Flavobacteria offer a promising scenario for partial nitrification-denitrifying phosphorus removal.

Antibiotic resistance gene profile in aerobic granular reactor under antibiotic stress: Can eukaryotic microalgae act as inhibiting factor?

Antibiotic resistance gene (ARG) pollution is critical environmental problem, and horizontal gene transfer acts as a driving evolutionary force. In theory, due to the phylogenetic distance between eukaryotes and prokaryotes, eukaryotic microalgae can be a natural barrier that plays a negative role in ARG transfer among the symbiotic bacteria to decrease ARG abundance in sludge during wastewater treatment. However, this hypothesis is far from proven and needs to be tested experimentally, so this study investigated the influence of eukaryote microalgae (Scenedesmus) on the ARG profile of symbiotic bacteria based on aerobic granular reactor. The results indicated that Scenedesmus symbiosis could affect ARG diversity of bacteria, and the detected numbers of ARG in aerobic granular sludge (AG) group and algae-bacteria granular consortia (AAG) group were 45-53 and 44-47, respectively. In terms of relative abundance, after target microalgae symbiosis, the total abundance of ARGs significantly decreased from 1.17 × 10°, 2.69 × 10° and 1.36 × 10^-1 to 6.53 × 10^-1, 9.64 × 10^-1 and 1.04 × 10^-1 in the systems with the addition of streptomycin, azithromycin and vancomycin, respectively (P < 0.05), yet there was no significant difference between AG and AAG under the stress of ampicillin, sulfamethazine and tetracycline (P > 0.05). Redundancy analysis showed that the eukaryotic microalgae were significant factor explaining the change in ARG relative abundance (P < 0.05), which contributed 15.3% of ARG variation. Furthermore, the results show that, except for the tetracycline treatment system, the total relative abundances of MGEs in the AAG under the stress of the other five antibiotics were 3.54 × 10^-2-7.13 × 10^-1, which were all significantly lower than those in the AG (8.38 × 10^-2-1.59 × 10°). There was a more significant positive correlation relationship between ARGs and mobile genetic elements (MGEs) than that between ARGs and dominated bacteria.

Algae-mediated antibiotic wastewater treatment: A critical review

The existence of continually increasing concentrations of antibiotics in the environment is a serious potential hazard due to their toxicity and persistence. Unfortunately, conventional treatment techniques, such as those utilized in wastewater treatment plants, are not efficient for the treatment of wastewater containing antibiotic. Recently, algae-based technologies have been found to be a sustainable and promising technique for antibiotic removal. Therefore, this review aims to provide a critical summary of algae-based technologies and their important role in antibiotic wastewater treatment. Algal removal mechanisms including bioadsorption, bioaccumulation, and biodegradation are discussed in detail, with using algae-bacteria consortia for antibiotic treatment, integration of algae with other microorganisms (fungi and multiple algal species), hybrid algae-based treatment and constructed wetlands, and the factors affecting algal antibiotic degradation comprehensively described and assessed. In addition, the use of algae as a precursor for the production of biochar is highlighted, along with the modification of biochar with other materials to improve its antibiotic removal capacity and hybrid algae-based treatment with advanced oxidation processes. Furthermore, recent novel approaches for enhancing antibiotic removal, such as the use of genetic engineering to enhance the antibiotic degradation capacity of algae and the integration of algal antibiotic removal with bioelectrochemical systems are discussed. Finally, some based on the critical review, key future research perspectives are proposed. Overall, this review systematically presents the current progress in algae-mediated antibiotic removal technologies, providing some novel insights for improved alleviation of antibiotic pollution in aquatic environments.