Diversity, abundance, and distribution of anammox bacteria in shipping channel sediment of Hong Kong by analysis of DNA and RNA

N2O emission in temperate seagrass meadows: Fluxes, pathway and molecular mechanism

Seagrass meadows act as filters for nitrogen in coastal areas, but whether they are a source or sink for N2O has been still controversy. Additionally, the production pathways of N2O as well as the microbial driving mechanism in seagrass meadows are seldom reported. In this study, the air-sea fluxes, sediment release potential, and production pathway of N2O in a temperate Zostera marina and Z. japonica mixed meadow were investigated by using gas chromatography and 15N isotopic tracing methods. The qPCR and metagenome sequencing were used to compare the difference in functional gene abundance and expression between seagrass vegetated and non-grass sediments. The results showed that the N2O air-sea fluxes in the meadow ranged from -1.97 to -1.77 nmol m⁻2 h⁻1, which was slightly lower in the seagrass region than in the adjacent bare region. Seagrass sediment N2O release potential dramatically increased after warming and nitrogen enrichment treatments. Heterotrophic nitrification was firstly investigated in seagrass meadows, and the process (26.80%-62.41%) and denitrification (37.55%-72.83%) contributed significantly to N2O production in the meadow, affected deeply by sediment organic content, while the contribution of autotrophic nitrification can be neglected. Compared with the bare sediments, the ammonia monooxygenase genes amoA, amoB and amoC, and nitrite oxidoreductase genes nxrA and nxrB, as well as nitrite reductase gene nirS and nitric oxide reductase gene norB were down-regulated, while the nitrous oxide reductase gene nosZ was up-regulated in the seagrass sediments, explaining less N2O emission in seagrass regions from the perspective of molecular. The nosZII-bearing bacteria like Bacteroidia, Polyangia, Anaerolineae, and Verrucomicrobiae could play important roles in N2O reduction in the seagrass meadow. The result is of great significance for highlighting the ability of seagrass meadows to mitigate climate changes.

In vitro and in vivo detection of microbial gene expression in bioactivated scaffolds seeded with cyanobacteria

Dermal replacement materials bioactivated with cyanobacteria have shown promising potential for wound regeneration. To date, extraction of cyanobacteria RNA from seeded scaffolds has not been described. Aim of this study was to develop a method to isolate total RNA from bioactivated scaffolds and to propose a new approach in determining living bacteria based on real-time PCR. Transgenic synechococcus sp. PCC 7002 (tSyn7002) were seeded in liquid cultures or in scaffolds for dermal regeneration in vitro and in vivo for 7 days. RNA was extracted with a 260/280 ratio of ≥ 2. The small subunit of the 30S ribosome in prokaryotes (16S) and RNAse P protein (rnpA) were validated as reference transcripts for PCR analysis. Gene expression patterns differed in vitro and in vivo. Expression of 16S was significantly upregulated in scaffolds in vitro, as compared to liquid cultures, while rnpA expression was comparable. In vivo, both 16S and rnpA showed reduced expression compared to in vitro (16S: in vivo Ct value 13.21±0.32, in vitro 12.44±0.42; rnpA in vivo Ct value 19.87±0.41, in vitro 17.75±1.41). Overall, the results demonstrate rnpA and 16S expression after 7 days of implantation in vitro and in vivo, proving presence of living bacteria embedded in scaffolds using qPCR.