Science - USA (2021-12-24)

SCIENCE science.org 24 DECEMBER 2021 • VOL 374 ISSUE 6575 1573

CREDIT: MAX HERMAN/ALAMY STOCK PHOTO

the drug reached concentra-

tions expected to inhibit the virus

based on in vitro studies. It also

inhibited other coronaviruses,

including severe acute respira-

tory syndrome coronavirus 1 and

Middle East respiratory syndrome

coronavirus, and could be in

the armory against future viral

threats. —VV

Science, abl4784, this issue p. 1586

ELECTROCHEMISTRY

Boosting ammonia with

a little oxygen

Ammonia synthesis from nitrogen

for fertilizer production is highly

energy intensive. Chemists are

therefore exploring electrochemi-

cal approaches that could draw

power from renewable sources

while generating less waste.

One promising cycle involves

the reduction of lithium ions at

an electrode, with the resultant

metal in turn reducing nitrogen

and regenerating the ions. Li et al.

report the counterintuitive result

that small quantities of oxygen

could enhance the efficiency of

this process, which they attribute

to diffusional effects that limit

excessive lithium reduction. —JSY

Science, abl4300, this issue p. 1593

IMMUNOTHERAPY

Another benefit of

dietary fiber

The gut microbiome can

modulate the immune system

and influence the therapeutic

response of cancer patients,

yet the mechanisms underly-

ing the effects of microbiota are

presently unclear. Spencer et al.

add to our understanding of how

dietary habits affect microbiota

and clinical outcomes to immu-

notherapy. In an observational

study, the researchers found that

melanoma patients reporting

high fiber (prebiotic) consump-

tion had a better response to

checkpoint inhibitor immuno-

therapy compared with those

patients reporting a low-fiber

diet. The most marked benefit

was observed for those patients

reporting a combination of high

fiber consumption and no use

HIV

TR cells are state

of the ART

Recent advances in antiretro-

viral therapy (ART) and testing

have restored the life expectan-

cies of people infected with HIV.

However, HIV-positive individu-

als still show a higher risk for

malignancies of the skin and

mucosa associated with human

papilloma virus (HPV). Saluzzo

et al. report that HIV-positive

individuals who begin ART late

show good recovery of circulat-

ing CD4 T cells but exhibit an

irreversible depletion of CXCR3+

tissue-resident memory T (TR)

cells in the skin. Their skin is

instead repopulated by T helper

2–like cells, which appear to

foster a permissive immune

environment. By contrast,

of over-the-counter probiotic

supplements. These findings

provide early insights as to how

diet-related factors may influence

the immune response. —PNK

Science, aaz7015, this issue p. 1632

CARBON NANOTUBES

Straining to make

a transistor

The use of carbon nanotubes

(CNTs) as short-channel-length

transistors will require control of

their chirality, which determines

whether they are semiconduct-

ing or metallic and if they form

strong, low-resistance contacts.

Tang et al. fabricated CNT

intramolecular transistors by

progressive heating and strain-

ing of individual CNTs within a

transmission electron micro-

scope. Changes to chirality along

sections of the nanotube created

metallic-to-semiconducting

transitions. A semiconducting

nanotube channel was covalently

bonded to the metallic nanotube

source and drain regions. The

resulting CNT intramolecular

transistors had channel lengths

as short as 2.8 nanometers.

—PDS

Science, abi8884, this issue p. 1616

ANTIBIOTICS

Metabolite mitigates

resistance

Antibiotic resistance is a per-

vasive and increasing problem.

Zhao et al. show that glutamine

promotes increase the influx and

efficacy of a variety of antibiot-

ics against multiple species of

pathogenic Gram-negative bac-

teria. Mechanistically, glutamine

promoted changes in nucleotide

metabolism that led to the up-

regulation of a two-component

regulatory system, resulting in

increased, nonspecific membrane

permeability in bacteria having

varied resistance mechanisms.

Glutamine supplementation was

also effective in mouse models

of systemic or biofilm infection,

suggesting a potential strategy

to enhance antibiotic efficacy.

—CAC

Sci. Transl. Med. 13 , eabj0716 (2021).

Algal blooms occur in modern-day Lake Amatitlán as result of human

activities, as they did in prehistoric times.

PALEOLIMNOLOGY

Pollution in prehistory

H

armful algal blooms in oceans and lakes are a frequent

consequence of anthropogenic pollution. For instance,

sewage discharge or nutrient runoff from farms can

lead to anoxic conditions toxic to eukaryotic life.

Waters et al. show that this is not just a phenomenon

of the industrial age. Sediment cores from Lake Amatitlán,

Guatemala, indicate the presence of cyanobacteria charac-

teristic of harmful blooms during the pre-Columbian Mayan

occupation of the watershed, with algal spikes coinciding

with periods of maximum human population. At their peak,

chemical signatures of the algal blooms in Mayan times

show concentrations and toxicity similar to present-day

blooms in the same lake. —AMS

Proc. Natl. Acad. Sci. U.S.A. 118 , e2109919118 (2021).

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Edited by Caroline Ash

and Jesse Smith