Publications

4877

ABSTRACT Biogas reactors operating at elevated ammonia levels are commonly susceptible to process disturbances, further augmented at thermophilic temperatures. The major cause is assumed to be linked to inhibition followed by an imbalance between different functional microbial groups, centred around the last two steps of the anaerobic digestion, involving acetogens, syntrophic acetate oxidisers (SAOB) and methanogens. Acetogens are key contributors to reactor efficiency, acting as the crucial link between the hydrolysis and fermentation steps and the final methanogenesis step. Their major product is acetate, at high ammonia levels further converted by SAOB and hydrogenotrophic methanogens to biogas. Even though these functionally different processes are well recognised, less is known about the responsible organism at elevated temperature and ammonia conditions. The main aim of this study was to garner insights into the penultimate stages in three thermophilic reactors (52°C) operated under high ammonia levels (FAN 0.7–1.0 g/L; TAN 3.6–4.4 g/L). The primary objective was to identify potential acetogens and SAOBs. Metagenomic data from the three reactors were analysed for the reductive acetyl‐CoA pathway (Wood–Ljungdahl Pathway) and glycine synthase reductase pathway. The results revealed a lack of true acetogens but uncovered three potential SAOB candidates that harbour the WLP, ‘ Candidatus Thermodarwinisyntropha acetovorans’, ‘ Candidatus Thermosyntrophaceticus schinkii’, ‘ Candidatus Thermotepidanaerobacter aceticum’, and a potential lipid‐degrader ‘ Candidatus Thermosyntrophomonas ammoiaca’.

Abstract Legumes Lessertia diffusa and Calobota sericea, indigenous to South Africa, are commonly used as fodder crops with potential for sustainable livestock pasture production. Rhizobia were isolated from their root nodules grown in their respective soils from the Succulent Karoo biome (SKB) in South Africa, identified and characterized using a polyphasic approach. Sequence analysis of the 16S rRNA gene confirmed all isolates as Mesorhizobium members, which were categorized into two distinct lineages using five housekeeping protein-coding genes. Lineage I included 14 strains from both legumes, while Lineage II comprised a single isolate from C. sericea. Differences in phenotypic traits were observed between the lineages and corroborated by average nucleotide identity analyses. While all strains nodulated their original hosts, strains from C. sericea failed to effectively nodulate L. diffusa and vice versa. Phylogenetic analyses of nitrogen fixation (nifH) and nodulation (nodA, nodC) loci grouped all strains in a single clade, suggesting that unique symbiotic loci determine nodulation of these legumes. We designated Lineage I and II as Mesorhizobium salmacidum sp. nov. (Ld1326Ts; GCA_037179605.1Ts) and Mesorhizobium argentiipisi sp. nov. (Cs1330R2N1Ts; GCA_037179585.1Ts), using genome sequences as nomenclatural types according to the Nomenclatural Code for Prokaryotes using Sequence Data, thus avoiding complications with South Africa's biodiversity regulations. Identifying effective microsymbionts of L. diffusa and C. sericea is essential for conservation of Succulent Karoo Biome, where indigenous invasive species like Vachellia karroo and non-native Australian acacia species are present. Furthermore, targeted management practices using effective symbionts of the studied legumes can sustain the biome's socio-economic contribution through fodder provision.

AbstractBACKGROUNDThe brown marmorated stink bug Halyomorpha halys has become an invasive insect pest of many crops. A promising control strategy to manage the proliferation of H. halys is based on the suppression of its obligate and vertically transmitted uncultivated symbiotic bacterium Candidatus Pantoea carbekii through surface‐sterilization of H. halys eggs. Indeed, the application of antimicrobial formulations on the eggs of H. halys could cause mortality of endosymbiont and consequently of newly emerged nymphs.In this study, a microbial live/dead assay was applied directly on H. halys eggs to evaluate Ca. P. carbekii loss of viability after treatments with seven commercial formulations including fungicides (copper hydroxide, sulphur, sweet orange essential oil) and plant biostimulants (flavonoids and chestnut tannin extract) compared with two disinfectants for civil and industrial use (sodium hypochlorite/hydrated sodium/tetraborate decahydrate and peracetic acid/hydrogen peroxide). Impact of mode of application was also evaluated, as surface treatment of egg masses was performed through spraying and dipping in laboratory conditions. Antimicrobial activity data were finally complemented with observations of egg hatching and vitality of the nymphs.RESULTSThe optimization of live/dead staining is useful for evaluating Ca. P. carbekii mortality directly on eggs, providing a rapid and reliable culture‐independent approach. Sodium hypochlorite, copper, sulphur, tannins and sweet orange essential oil showed an antimicrobial effect against Ca. P. carbekii and a H. halys egg hatching reduction and nymph's vitality.CONCLUSIONSThe antimicrobial and insecticidal effects of these commercial products should be further studied to assess their in‐field efficiency as well as the impact of these substances on non‐target organisms. The approach followed in this study could be considered a robust pipeline of analyses to evaluate the effectiveness of antimicrobial eco‐friendly compounds in symbiotic control of H. halys. © 2024 Society of Chemical Industry.

ABSTRACT Various morphotypes of large filamentous bacteria were isolated through micromanipulation from sulphidic sediment mats in the Bay of Concepción, central Chile. This study employed DNA amplification, whole‐genome sequencing and bioinformatics analyses to unveil the taxonomic and genomic features of previously unidentified bacteria. The results revealed several novel genera, families and species, including three specimens belonging to Beggiatoales (Beggiatoaceae family), five to Desulfobacterales (Desulfobacteraceae family), two to the Chloroflexi phylum and one to the phylum Firmicutes. Metabolically, Beggiatoaceae bacteria exhibit a flexible and versatile genomic repertoire, enabling them to adapt to variable conditions at the sediment–water interface. All the bacteria demonstrated a mixotrophic mode, gaining energy from both inorganic and organic carbon sources. Except for the Firmicutes bacterium, all others displayed the ability to grow chemolithoautotrophically using H 2 and CO 2 . Remarkably, the reverse tricarboxylic acid (rTCA) and Calvin–Benson–Bassham (CBB) pathways coexisted in one Beggiatoaceae bacterium. Additionally, various defence systems, such as CRISPR‐Cas, along with evidence of viral interactions, have been identified. These defence mechanisms suggest that large filamentous bacteria inhabiting sulphidic sediments frequently encounter bacteriophages. Thus, robust defence mechanisms coupled with multicellularity may determine the survival or death of these large bacteria.