Rembrandt’s The Night Watch Yields at Least 20 Microbial Types

Cultures grown from samples taken from Rembrandt’s The Night Watch have yielded at least 20 microbial types, according to Deutschlandfunk, while ARTIS-Micropia has publicly named three bacteria from the first results. The discovery matters to conservation because it records living material on a surface now undergoing treatment—but it does not reveal when the microbes arrived or whether they belong to the painting’s 400-year history.

 
 

At Least 20 Types, but Only Three Are Named

The count of at least 20 microbial types comes from a Deutschlandfunk item dated November 11 and broadcast on November 12, one day after the installation opened to the public. ARTIS-Micropia’s own November 10 announcement describes the first cultures and the continuing study, but it does not give a total or publish a complete species list.

Deutschlandfunk’s German word Sorten is a broad description of types or kinds. Neither its short report nor the official release establishes that all 20 are distinct species. The official results released by ARTIS name Staphylococcus epidermidis, Micrococcus luteus and Microbacterium saccharophilum. They also refer more generally to bacteria associated with soil and the area around plant roots.

Evidence	Reported result	What it does not prove
Named species	S. epidermidis, M. luteus, M. saccharophilum	A complete list of 20
Broader groups	Skin-, soil- and root-associated bacteria	How they reached the painting
Study design	About 60 locations over six months	A completed surface map
Current risk	No harm reported from identified cultures	That every future sample is harmless

A 2013 taxonomic paper first described Microbacterium saccharophilum from a type strain isolated in soil at a Japanese sucrose refinery. Identifying the same species on The Night Watch does not show that the painting’s strain traveled from Japan. The refinery is part of the species’ scientific description, not a provenance record for the newly cultured organism.

The sampling program is still in progress. ARTIS says laboratory technicians and Rijksmuseum conservators are sampling about 60 locations over six months, including areas with and without varnish. The microbes are cultured into visible colonies at Micropia and identified by an external laboratory. The installation is expected to be fully formed sometime in February 2027 and will remain on view through the end of May.

 

A Culture Is a Selective Window

A colony that grows demonstrates that viable organisms were recovered under the laboratory conditions used. It does not constitute a complete census of the painting’s microbiome: organisms that do not grow in the selected media and conditions will remain outside that cultured result. A peer-reviewed review of microbes in cultural-heritage environments accordingly describes conservation assessment as a combination of cultivation, molecular methods and physical or chemical examination of the object. The reported minimum of 20 should therefore be read as a result from the cultures to date, not as the final number of microorganisms on the canvas.

 

Rembrandt’s The Night Watch inside the glass chamber created for Operation Night Watch in 2019. Photograph by Tastenlöwe, via Wikimedia Commons, licensed under Creative Commons Attribution-Share Alike 4.0 International. Cropped.

 
 

A Conservation Finding, Not a Rembrandt Fingerprint

The samples establish microbial presence at the time they were collected. They do not date that presence. In reporting based on Agence France-Presse, ARTIS microbiologist Eline van Bloois explained that a single microbe cannot disclose whether it has occupied the painting for 400 years or one day. No published result ties any organism to Rembrandt, his workshop or the painting’s original installation in Amsterdam’s Kloveniersdoelen.

Labels such as “skin bacterium” and “soil bacterium” describe familiar ecological associations. They are hypotheses about possible sources, not proof of a route. Skin-associated organisms could reflect handling at many moments in the painting’s long history, while dust and the museum environment offer other pathways. The project’s own public questions—skin, airborne dust or another source—remain questions.

Van Bloois also told AFP that the microorganisms identified so far are not harmful to the painting. That is reassuring but narrower than saying the work has no biological risk. It applies to the current identified cultures, while sampling and identification continue. Nor does the absence of reported harmful organisms make the surface sterile: the cultures themselves demonstrate the opposite.

For conservators, presence and consequence are separate findings. A microbe becomes significant to treatment when evidence connects it to material change, active growth or a condition that could threaten paint, varnish or canvas. The November release reports identities and broad associations; it does not report biodeterioration caused by them.

The Night Watch undergoing restoration in 2024. Photograph by Vbena, via Wikimedia Commons, licensed under CC BY 4.0.

 
 

Why the Sampling Belongs to Operation Night Watch

The microbial survey is nested within a much larger examination of the painting. The Rijksmuseum launched Operation Night Watch in 2019, and its current conservation record says restorers are removing old varnish layers inside the museum’s glass chamber. That treatment makes the distinction between varnished and unvarnished sampling zones especially relevant: the surface is neither uniform nor untouched.

ARTIS announced on September 10 that samples would come from areas both with and without varnish. AFP later reported that M. saccharophilum was recovered from an area where varnish had been removed. Hyperallergic reports that the installation marks sampling sites by number and date, although no released analysis compares microbial abundance across varnished and unvarnished areas.

The original project announcement also asked whether the painted girl and dog might carry different microbial populations. Those were research prompts, not findings. No released result yet supports a comparison between the figures or shows that one part of the composition hosts more microbes than another.

The September 10 announcement established the collaboration, sampling plan and November exhibition. The November 10 release supplied the first named organisms, and visitors could see the cultures from November 11. The identities should not be backdated to the earlier project announcement, when ARTIS said identification was still to come.

The Night Watch (1642) by Rembrandt van Rijn, Rijksmuseum, via Wikimedia Commons. Public domain.

 
 

What Is Established, and What Remains Unknown

• Deutschlandfunk reports at least 20 cultured microbial types, while ARTIS has officially named three species and several broader ecological categories.
• The Japanese connection belongs to the history of the M. saccharophilum type strain; it does not trace the Night Watch organism’s geographic origin.
• The identified cultures are not currently reported as harmful, but the continuing survey is not proof that every organism on the painting is harmless.
• The microbes’ arrival dates, routes, distribution across the image and long-term conservation significance remain unresolved.