Propionicimonas ferrireducens sp. nov., isolated from dissimilatory iron(III)-reducing microbial enrichment obtained from paddy soil

Functional genome-centric view of the CO-driven anaerobic microbiome

CO is a promising substrate for producing biochemicals and biofuels through mixed microbial cultures, where carboxydotrophs play a crucial role. The previous investigations of mixed microbial cultures focused primarily on overall community structures, but under-characterized taxa and intricate microbial interactions have not yet been precisely explicated. Here, we undertook DNA-SIP based metagenomics to profile the anaerobic CO-driven microbiomes under 95 and 35% CO atmospheres. The time-series analysis of the isotope-labeled amplicon sequencing revealed the essential roles of Firmicutes and Proteobacteria under high and low CO pressure, respectively, and Methanobacterium was the predominant archaeal genus. The functional enrichment analysis based on the isotope-labeled metagenomes suggested that the microbial cultures under high CO pressure had greater potential in expressing carboxylate metabolism and citrate cycle pathway. The genome-centric metagenomics reconstructed 24 discovered and 24 under-characterized metagenome-assembled genomes (MAGs), covering more than 94% of the metagenomic reads. The metabolic reconstruction of the MAGs described their potential functions in the CO-driven microbiomes. Some under-characterized taxa might be versatile in multiple processes; for example, under-characterized Rhodoplanes sp. and Desulfitobacterium_A sp. could encode the complete enzymes in CO oxidation and carboxylate production, improving functional redundancy. Finally, we proposed the putative microbial interactions in the conversion of CO to carboxylates and methane.

Phylogenetic diversity contributes more to sediment magnetism than abundance during incubation of iron-reducing sediment from a non-active volcanic lake in Northeast China

AIM

This study aimed to analyse bacterial community and biomineralization products from Wudalianchi non-active volcanic field and the relationship between magnetization and bacterial community.

METHODS AND RESULTS

Eighteen sediment samples obtained from Wenbo Lake, high-throughput sequencing and quantitative PCR (qPCR) were separately employed to investigate the bacterial community composition dynamics and abundance variation of the sediment sample with the highest iron-reducing capacity during incubation. The mineralization products were characterized by transmission electron microscopy, scanning electron microscopy, X-ray diffraction (XRD), Raman spectroscopy, vibrating sample magnetometer (VSM) and variable-temperature magnetism analyses. The results showed that the highest iron reduction rate was 98·06%. Seven phyla were identified as dominant bacterial phyla during the incubation process. Iron-reducing bacteria (FeRB) including Geobacter, Desulfosporosinus and Clostridium were involved in the iron mineralization process. The 16S rDNA copy numbers of sediment decreased quickly and then stayed steady during the incubation. Bacteria with rod-shaped and spheroid species were involved in extracellular iron reduction to produce magnetic particles with massive aggregation and columnar structures on the mineral surface morphologies. The materials produced by the microbial community over the incubation period were sequentially identified as siderite, magnetite and maghemite. The magnetism of the mineral samples gradually increased from 0·31748 to 33·58423 emu g^-1 with increased incubation time. The final products showed relatively stable magnetism under 0-400 K. Meanwhile, the saturation magnetization (M_S ) of the mineralized substance was tightly associated with bacterial diversity (P < 0·05).

CONCLUSIONS

Bacterial community varied during incubation of iron-reducing sediment of volcanic lake. Various iron mineral crystals were in turn formed extracellularly by FeRB. The magnetism of mineralized products was tightly associated with bacterial community.

SIGNIFICANCE AND IMPACT OF THE STUDY

These results not only help us to better understand the iron mineralization of FeRB in the volcanic lake sediments but also provide basic information for the future application of FeRB in environmental bioremediation.

Cactus-induced keratoconjunctivitis in Texas: A case series of three dogs and one cat

OBJECTIVE

To describe the historical, clinical, and diagnostic features of small animal patients affected by cactus-induced keratoconjunctivitis and their response to therapy.

ANIMALS STUDIED

Three dogs and one cat.

PROCEDURES

Ophthalmic examination directed subsequent selected diagnostic tests in each case including light microscopy of extracted foreign bodies, in vivo confocal microscopy (IVCM), corneal histopathology, and corneal bacterial culture. Treatments consisted of foreign body surgical extraction with concurrent medical therapy (three cases), or medical therapy alone (one case).

RESULTS

Clinical histories obtained supported acute cactus injury in all cases. Ophthalmic abnormalities were unilateral in each case and included ulcerative keratoconjunctivitis associated with linear, microscopic conjunctival and/or corneal penetrating cactus spines, known as glochids. Light microscopy and IVCM showed glochids to be heavily barbed, consistent with the spine morphology Prickly Pear (Opuntia) cactus species. Bacterial culture yielded Proprionicimonas sp. in one case with keratomalacia. Surgical extraction of spines was challenging, and residual conjunctival and/or corneal glochids were present in all cases. Patient discomfort resolved at a median of 21 days (range 10-51 days). Vision-threatening complications were not observed in any case at the time of last follow-up examination. Epithelial downgrowth, demonstrated by IVCM and histopathology, was present in one case at 108-day follow-up.

CONCLUSIONS

Cactus-induced keratoconjunctivitis should be considered as a differential in regions in which Opuntia cacti are prevalent, and microscopic ocular foreign bodies are observed. Although glochids are difficult to extract, positive clinical outcomes can occur in small animal patients despite the presence of residual organic corneal foreign material.