The Light in the Water

In 1989, one day before his son Cameron was born, Mark Woodward reported for his first day at Microbics in Carlsbad, California. The Model 500 production run was still in its earliest serial numbers, somewhere around fifty. He had taken an electronics job and would remain with the product line for the rest of his working life.

The method uses a living organism to show whether a water sample is toxic.

The Microtox method uses a naturally luminous marine bacterium now classified as Aliivibrio fischeri, though standards and older manuals still commonly call it Vibrio fischeri. Under healthy conditions, the bacteria emit light as part of their metabolism. Expose them to a toxic sample and their metabolism is inhibited; their light output changes. The instrument measures that change across controls and sample dilutions and turns it into a quantitative indication of acute toxicity.

A Microtox test generally does not identify the chemical in a sample. It shows whether the sample is interfering with living metabolism. If the screen is positive, the operator knows to investigate further, contain the sample, or run chemical analysis.

Because the bacteria respond to many kinds of toxic stress, the method has been used with wastewater, surface water, groundwater, leachates, sediment extracts, industrial process water, and individual substances diluted in water. It does not replace analytical chemistry. It shows the combined effect of a sample on a living organism.

“It’s a canary in a coal mine. It just makes sense.”

The documented history begins earlier than Mark’s own time in the industry. Contemporary reporting traced the technology to chemical-warfare detection work performed for the U.S. Air Force at North American Rockwell in the early 1960s. Researchers later carried the work into Beckman Instruments.

By 1979, Beckman had introduced the Microtox Model 2055, a large, metal-bodied predecessor to the Model 500. Beckman’s corporate history records that the Microtox product line and its microbial sensor technology were sold to Microbics in Carlsbad in 1985. Foundational technical papers from that period carry the names Anthony A. Bulich, Malbone W. Greene, and Don L. Isenberg. Their work helped convert a biological observation into a fast, temperature-controlled and repeatable toxicity assay.

The Model 500 entered production in 1989, the same year Mark arrived.

Mark had already spent years in electronics, building and troubleshooting control systems before computers absorbed many of those functions. His Microbics hiring test was written by outside electronics consultant Joel Fenton. He then received a draft schematic and was asked to find its mistakes. He found four.

He was hired.

At first, the job was practical: assemble instruments, test boards, trace faults, improve circuits, and get machines out the door. The instrument converted light from living bacteria into an electrical signal, processed it through analog and digital circuitry, and reported a result an operator could act on.

The Carlsbad shop on Rutherford Road had sunlight, low windows that could be opened for a breeze, and, during migration season, monarch butterflies passing through in such numbers that they became part of the landscape. The people mattered as much as the equipment: scientists, engineers, software people, salespeople, production workers, and people whose roles crossed several disciplines.

Among them, Malbone W. Greene became Mark’s most important engineering mentor. Public records place Greene in Beckman’s Microtox technical lineage and on later patents involving photometers, temperature control, and toxicity-test methods. In the shop, he was a man who moved easily among circuitry, mathematics, poetry, and jazz, and who treated a younger technician as someone capable of learning more.

Don L. Isenberg led Microbics and appears in the early scientific literature. He was the biological mind of the company, the person who understood how to culture, preserve, and tune the organisms so they could function as a sensitive reagent.

The Model 500’s thirty-well incubator block and read well are maintained at 15°C for acute testing; a separate reagent well holds the reconstituted bacteria at 5.5°C. Cooling devices, optics, a shutter mechanism, a photomultiplier tube, and separate analog and digital electronics control and measure the test.

The same failures appeared repeatedly. Temperature problems often lead back to a Peltier device. A motor warning may begin with glass or residue in the read well, a dirty optical sensor, or a failing component in the drive circuit. Two aging EPROMs can cause a shutter to cycle without reason or a display to return nonsense instead of a result.

Years of returned instruments revealed failure patterns that the service manual did not cover.

Some returned units arrived from harsh industrial environments with green corrosion covering metal and plastic alike. One contained a rat’s nest. More than one contained a dead lizard, though Mark still cannot explain how the animals entered. Other machines arrived with hand-sewn covers, handwritten instructions, or names given to them by operators who had used the same analyzer for years.

Many Model 500s have remained serviceable for decades. Their operators know the procedures, trust the results, and prefer to maintain a familiar instrument rather than replace it without a technical reason.

He compares the Model 500 to vinyl records.

“People cherish them. If it isn’t broken, why replace it?”

Mark also assembled, tested, repaired, or helped develop other instruments across the Microtox and related product lines.

His proudest engineering memory is the original Deltatox, a portable photon-counting instrument developed from earlier work for Nalco. He worked closely with Malbone Greene on a system that moved a neutral-density filter into and out of the light path and measured an exceptionally wide range of light levels.

Deltatox II later became the basis of the Microtox FX. Modern Water’s own launch record describes the FX as an updated version of the instrument formerly sold as Deltatox II. The LX brought the familiar laboratory method into a newer integrated platform. The RPA I and RPA II belonged to a related but technically different family: they are photometers used with analyte-specific RaPID Assay immunoassay kits, reading absorbance rather than bacterial bioluminescence.

General toxicity screening, ATP measurement, and analyte-specific photometric immunoassays answer different questions. The fact that the instruments all measure light does not make them interchangeable.

The Microtox product line changed ownership several times.

1. 1979Beckman’s Model 2055 debuted.
2. 1985Beckman sold the Microtox product line and microbial sensor technology to Microbics in Carlsbad.
3. 1989The Model 500 entered production.
4. 1996Microbics changed its name to AZUR Environmental.
5. 2001Strategic Diagnostics acquired AZUR.
6. 2011Modern Water acquired the SDIX Water Quality business, including Microtox.
7. 2024Microsaic Systems acquired specified Modern Water assets, including Microtox reagent manufacturing and rights associated with the FX, LX, and continuous-monitoring equipment.
8. 2025Microsaic Systems was renamed Metir plc; Modern Water now operates as its environmental division.

Mark continued building and servicing the instruments through each change in ownership. That experience later formed the basis of Rematek’s manufacturing and service work.

When Strategic Diagnostics decided it no longer wanted to operate an instrument-production department, Mark and his colleague Renie saw an opening. They already knew the parts, vendors, tooling, assembly sequence, quality checks, and repair history. Their proposal was direct: let them form a company and continue building the instruments as an outside supplier.

They named it Rematek: “RE” from Renie, “MA” from Mark, and “TEK” in the style of the period.

Renie handled purchasing, inventory, scheduling, and the paper systems that kept production coherent. Mark concentrated on assembly, testing, electronics, and service. He arrived at Microbics when Model 500 serial numbers were in the fifties and had a hand in the product line through serial number 3,208. In the later production years, he assembled and tested the machines himself.

Rematek’s experience comes from inside the product line. Mark helped improve the instruments, built and tested them, trained other service technicians, and continued with the products as their corporate owners changed.

Today, Mark Woodward owns and operates Rematek from Fallbrook, California. The company services Microtox, Deltatox, LX, FX, and RPA instruments and supplies Modern Water products as an authorized representative. It is a small shop with direct knowledge of how these instruments were built and how they fail in service.

Mark describes repair work as meditative.

“You look at the symptom, think of the possibilities, and eliminate them one after another until you find it. There’s ritual and meditation in it.”

In practice, that means observing the fault, listing the likely causes, and choosing the next test that will rule one out. The process repeats until the evidence points to the failed part.

The approach works on a pre-digital control cage with hundreds of hand-wired connections and on a Model 500 whose shutter has begun cycling for no clear reason. After decades with the instruments, Mark usually knows which causes to check first.

The work still brings together the same elements: bacterial light, optical measurement, electronics, machined parts, and systematic troubleshooting. Instruments built decades ago continue to return for service and can still be repaired.

Mark has spent most of his working life building and repairing instruments that measure changes in bacterial light.

This oral history was edited from a recorded conversation between Mark Woodward and Cameron Woodward and checked against archival, scientific, and company sources.