six-membered rings, including
thiazoles and azaindoles. —JSY
Angew. Chem. Int. Ed. 10.1002/
anie.201915425 (2020).
PHYSIOLOGY
Humans on a chip
Organ chips are devices in which
epithelial and/or stromal cells are
grown in a chamber filled with
medium connected by a porous
matrix-like membrane to another
chamber lined with endothelial
cells and containing a blood
substitute. Depending on the cell
types used and the contents of
the blood substitute and medium,
these chips can model organ-
specific environments. Novak et
al. devised an automated system
to connect up to 10 different
organ chips with a common blood
substitute to model physiological
systems. In a series of reports,
they show that this system could
be used to predict drug dynamics
and drug toxicity. These devices
have numerous potential applica-
tions, including modeling complex
environments and disease devel-
opment. —GKA
Nat. Biomed. Eng. 10.1038/s41551-
019-0497-x, s41551-019-0498-9,
s41551-019-0495-z (2020).SCIENTIFIC WORKFORCE
It takes a village
STEM Ph.D. students often select
a lab based on the reputation of
the principle investigator (PI),
who mentors students as they
develop research skills. Feldon et
al. sought to empirically deter-
mine how PI mentorship affectsstudents’ skill development in a
long-term study involving 336
Ph.D. students in the biologi-
cal sciences. Specifically, skills
including establishing testable
hypotheses, experimental design,
and data analysis were measured
using writing samples and addi-
tional qualitative data that were
collected. Results showed that
the mentoring activities of PIs do
not significantly predict students’
skill development trajectories. In
fact, Ph.D. students were more
than four times as likely to have
positive skill development when
engaging with postdocs, sup-
porting the idea that “cascading
mentorship” is an effective and
critical element of Ph.D. training.
—MMc
Proc. Natl. Acad. Sci. U.S.A. 116 , 20910
(2019).1088 6 MARCH 2020 • VOL 367 ISSUE 6482 sciencemag.org SCIENCE
RESEARCH | IN OTHER JOURNALS
MICROBIAL GENOMICS
Closing the loop on
sequencing
Sequencing of microorganisms
in the context of metagenomes,
such as human microbiomes,
can be difficult. It is not only
the diversity of species but also
the occurrence of repeated
sequences, such as trans-
posable elements, that are
challenging. Furthermore, long-
read sequencing often requires
large amounts of DNA, which
can be difficult to obtain from
a microbiome. To assemble
full bacterial genomes for
analysis of the role of repeats
in bacterial genomes, Moss et
al. used nanopore sequencing,
assembly, and error correc-
tion to extract closed bacterial
genomes from microbiomes.
From this, they were able to
resolve difficult-to-assemble
bacterial genomes. —LMZ
Nat. Biotechnol. 10.1038/
s41587-020-0422-6 (2020).IMMUNOLOGY
Wisdom of the crowd
Quorum sensing is used by
bacteria to sense local cell
density in order to regu-
late and coordinate a wide
array of functions, including
biofilm formation. Muldoon
et al. report that a somewhat
analogous process may play a
role in macrophage responses.
Macrophages exposed to
bacterial lipopolysaccharide—
a potent immune stimulant—
showed a bimodal activation
profile that could be tuned by
adjusting cell density before
stimulation. The authors then
used dynamical modeling and
single-cell tracking to propose
a mechanism they termed
quorum licensing. In bacterial
quorum sensing, all players are
uniformly activated. By con-
trast, quorum licensing entails
the transformation of “digital”
single-cell decisions into “ana-
log” population-wide outputs.
This phenomenon may help
macrophages limit inflamma-
tory responses to local sites of
injury and infection. —STS
Nat. Commun. 11 , 878 (2020).PLANT DISEASESniffing out disease
D
ogs have extraordinary noses and can detect odors at sensitivities well beyond human
technologies. Gottwald et al. tested the talents of dogs for sniffing out the pandemic and eco-
nomically severe bacterial disease of citrus trees called huanglongbing. The dogs were first
trained by positive reinforcement on potted citrus plants. Gradually, the tests were scaled up
to grids of 10 trees by 10 trees and finally to orchard conditions. The dogs detected 30-day-
old infections compared with genetic testing that only started to identify infections 3 months after
insect-vectored transmission. If two dogs were used, detection accuracies of 100% were achieved,
not only in commercial orchards but also among a range of plants in residential areas known to be
foci of infection. By modeling the data, the authors estimated that dogs could save up to 92% of
the trees in an orchard by early detection followed by removal of individual infected trees. —CA
Proc. Natl. Acad. Sci. U.S.A. 117 , 3492 (2020).PHOTO: MARYBETH OKERSON/ALAMY STOCK PHOTODogs have an
amazing sense of
smell, which can
be put to use in the
early detection of
tree diseases.Published by AAAS