Metagenomic analysis reveals wide distribution of phototrophic bacteria in hydrothermal vents on the ultraslow-spreading Southwest Indian Ridge

Deep-sea hydrothermal vents are known as chemosynthetic ecosystems. However, high temperature vents emit light that hypothetically can drive photosynthesis in this habitat. Metagenomic studies have sporadically reported the occurrence of phototrophic populations such as cyanobacteria in hydrothermal vents. To determine how geographically and taxonomically widespread phototrophs are in deep-sea hydrothermal vents, we collected samples from three niches in a hydrothermal vent on the Southwest Indian Ridge and carried out an integrated metagenomic analysis. We determined the typical community structures of microorganisms found in active venting fields and identified populations of known potential chlorophototrophs and retinalophototrophs. Complete chlorophyll biosynthetic pathways were identified in all samples. By contrast, proteorhodopsins were only found in active beehive smoker diffusers. Taxonomic groups possessing potential phototrophy dependent on semiconductors present in hydrothermal vents were also found in these samples. This systematic comparative metagenomic study reveals the widespread distribution of phototrophic bacteria in hydrothermal vent fields. Our results support the hypothesis that the ocean is a seed bank of diverse microorganisms. Geothermal vent light may provide energy and confer a competitive advantage on phototrophs to proliferate in hydrothermal vent ecosystems.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42995-021-00121-y.

Aqueous oxygen: a highly O2-supersaturated infusate for regional correction of hypoxemia and production of hyperoxemia

BACKGROUND

High levels of hyperoxemia may have utility in the treatment of regional tissue ischemia, but current methods for its implementation are impractical. A catheter-based method for infusion of O2, dissolved in a crystalloid solution at extremely high concentrations, ie, 1 to 3 mL O2/g (aqueous oxygen [AO]), into blood without bubble nucleation was recently developed for the potential hyperoxemic treatment of regional tissue ischemia.

METHODS AND RESULTS

To test the hypotheses that hypoxemia is correctable and that hyperoxemia can be produced locally by AO infusion, normal saline equilibrated with O2 at 3 MPa (30 bar; 1 mL O2/g) was delivered into arterial blood in two different animal models. In 15 New Zealand White rabbits with systemic hypoxemia, AO was infused into the midabdominal aorta at 1 g/min. Mean distal arterial PO2 increased to 236+/-113 and 593+/-114 mm Hg on 1-hour periods of air and O2 breathing, respectively, from a baseline of 70+/-10 mm Hg (P<.01). In contrast, infusion of ordinary normal saline in a control group (n=7) had no effect on arterial PO2. No differences between groups (P>.05) in temporal changes in blood counts and chemistries were identified. In 10 dogs, low coronary blood flow in the circumflex artery was delivered with a roller pump through the central channel of an occluding balloon catheter. Hypoxemic, normoxemic, and AO-induced hyperoxemic blood perfusates (mean PO2, 52+/-4, 111+/-22, and 504+/-72 mm Hg, respectively) were infused for 3-minute periods in a randomized sequence. Short-axis two-dimensional echocardiography demonstrated a significant decrease (P<.05) in left ventricular ejection fraction compared with baseline physiological values with low-flow hypoxemic and normoxemic perfusion but not with low-flow hyperoxemic perfusion.

CONCLUSIONS

Intra-arterial AO infusion was effective in these models for regional correction of hypoxemia and production of hyperoxemia.

Laser balloon angioplasty combined with local intracoronary heparin therapy: immediate and short-term follow-up results

Laser balloon angioplasty (LBA) has been shown to acutely increase angiographic luminal dimensions after conventional balloon angioplasty (PTCA) without a favorable impact on chronic restenosis. Experimentally, laser and thermal energy enhance binding of heparin to the injured arterial wall and to the thrombus. In view of the anticoagulant, antiproliferative, and antifibrotic activities of the drug, a pilot study was performed to evaluate the potential safety and efficacy of LBA combined with local heparin therapy. Ten patients scheduled for elective PTCA were entered in the study. In each patient, a single lesion was treated with a laser balloon and coated with a heparin film (3000 I.U. at a concentration > 100,000 I.U./gm) immediately after optimal PTCA. The mean minimum luminal diameter and mean percent stenosis of the 10 treated lesions after PTCA were 1.62 +/- 0.39 mm and 37% +/- 9%, respectively. After LBA and local heparin therapy, the mean minimal lumen diameter increased to 2.01 +/- 0.34 mm (p < 0.01) and the mean percent stenosis decreased to 20% +/- 10% (p < 0.01). Systemic heparin was discontinued immediately after the procedure in all patients. Acute or inhospital complications, either major or minor, occurred in none (0%) of the 10 patients (95% confidence interval 0% to 31%); all were discharged home on the day after the procedure. All patients remained well and free of cardiac symptoms for at least 2 months after the procedure. However, restenosis developed in six (60%) of the 10 patients (95% confidence interval 26% to 88%) 2 to 6 months after the procedure. The results suggest that LBA and local heparin therapy, with discontinuation of systemic heparin immediately after angioplasty, is a safe treatment modality that yields favorable acute angiographic results.