The Scientist - USA (2020-01 & 2020-02)

THE PAPER

M. Jahn et al., “A phage protein aids bacterial

symbionts in eukaryote immune evasion,”

Cell Host Microbe, 26:542–50, 2019.

While studying sponges and their

endosymbiotic microbes for his PhD,

Martin Jahn found himself pondering

where viruses fit into the mix. “We didn’t

know anything about the viruses associated

with sponges,” says Jahn, now wrapping up

his doctorate at the GEOMAR Helmholtz

Centre for Ocean Research Kiel in Germany.

To investigate, Jahn and his colleagues

sampled four sponge species off the coast

of northern Spain and analyzed both the

sponges and samples of the surrounding

seawater for the presence of viruses. Not

only did the researchers find viruses living

in sponges that weren’t in the seawater,

they discovered substantial diversity in

the viromes of different species, and even

among conspecifics.

Digging further into the genomic data,

the team noticed one group of previously

unidentified bacteriophages that were

particularly abundant in sponge viromes.

To Jahn’s surprise, these phages contained

genetic sequences for so-called ankyrin

repeats, protein motifs usually studied in

bacteria that help pathogenic or commensal

microbes infect and manipulate eukaryotic

hosts. He wondered if the viruses, which the

team dubbed ankyphages, might facilitate

interactions between sponges and their

resident bacteria.

Both sponge cells and their endo-

symbiotic bacteria are difficult to cul-

ture, so to test Jahn’s idea, the team set up

an experiment with mouse cell lines and E.

coli. The researchers first cultured E. coli

with ankyrin protein synthesized from the

viral sequences. Then they added the bacte-

ria, which displayed the protein on their cell

surfaces, to murine immune cells.

Sure enough, the E. coli that had been

cultured with ankyrin protein were better

at surviving exposure to mouse immune

cells: they escaped being engulfed by

macrophages more often than control

bacteria did. E. coli engineered to produce

and secrete the phage proteins themselves

also survived macrophage exposure. The

team ran further experiments to confirm

that the protein wasn’t toxic to either the

bacterial or murine cells, and concluded that

phage-derived ankyrin was indeed helping

to suppress macrophage responses toward

the bacteria.

“I was quite impressed by these...

proteins being associated with sponge-

specific phage communities,” says Breck

Duerkop, a microbiologist at the University

of Colorado School of Medicine who

wasn’t involved in the work. That phages

might moderate host immunity is a “really

interesting idea,” he adds, although the

team’s experiments don’t quite establish that

such three-way interactions are playing an

important role in sponges.

Scanning genome databases for other

phyla, Jahn and his colleagues found evidence

that ankyphages are also present in the

microbiomes of other eukaryotic organisms,

including humans. The findings hint at the

importance of bacteriophages in eukaryotic

function, says Jahn. Far from being incidental

stowaways in eukaryotic organisms, phages

“are central elements,” he says. “It opens a lot

of perspective for further research.”

—Catherine Offord © KELLY FINAN

44 THE SCIENTIST | the-scientist.com

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BETTER TOGETHER: Researchers have discovered a diverse set of bacteriophages in tissue samples

from marine sponges, which are known to host abundant endosymbiotic bacteria A. In vitro experiments

revealed that a protein made by a subset of the sponge-borne viruses, known as ankyphages, appears to

help suppress immune responses in murine macrophages when taken up and displayed, or expressed and

secreted, by E. coli B —bacteria with the protein, ankyrin, were less likely to be consumed by the immune

cells than were controls. The results suggest that ankyphages could facilitate the cohabitation of commensal

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