Hey readers,

First, an apology for missing last week's edition while I was traveling. Thank you for your patience and for sticking around.

In this edition, Belgian Bradyrhizobium strains improved nodulation and yield in early-maturing soybean, and Embrapa reported low-cost media and three years of shelf life for a Bacillus velezensis strain. A Pseudomonas chlororaphis strain from the poplar rhizosphere also protected cut twigs against canker.

On the industry side, Switch Bioworks moved toward field trials in Brazil for its engineered nitrogen fixers.

Let’s dive in!

Researchers at Flanders' agricultural research institute (ILVO) and Ghent University compared four Bradyrhizobium strains isolated in Belgium with strains used in two commercial inoculants. The trials used early-maturing soybean in a growth chamber and in five field trials across Flanders over 2022 and 2023.

All four Belgian strains formed active nodules in the growth chamber, and plants inoculated with them had higher leaf chlorophyll than plants inoculated with one of the commercial strains.

The 2022 season was one of the driest since 1991. One commercial strain yielded about the same as uninoculated plots that year, while two Belgian strains raised yield at one site and lifted grain protein to 38.5% and 37.7%, against 33.2% without inoculation. Yields rose in the wetter 2023 season, when two Belgian strains matched the commercial ones for grain yield and inoculated plots averaged 37.3% protein against 29.2% for uninoculated plots.

The team switched from a liquid seed coating in 2022 to a vermiculite-based one in 2023, after the liquid coating failed to form nodules in several plots that year. The difference between years therefore reflects both weather and method.

Commercial inoculants used in Europe were mostly developed for soybean regions elsewhere, and this work shows that locally isolated strains can perform alongside them, a step toward inoculants matched to Northwestern Europe.

Switch Bioworks announced on 30 September that Brazil's National Technical Biosafety Commission (CTNBio) approved its dossiers. The approval moves the company toward field testing its engineered nitrogen-fixing microbes in Brazil.

The microbes carry genetic switches that let them establish on plant roots before activating nitrogen production. The company says this addresses the energy trade-off that has limited biological nitrogen fixation, and reports that its switchable microbes fixed about five times as much nitrogen on plants as always-on controls in laboratory studies.

Switch says its product, an intergeneric genetically engineered microbe designed to live and function in the field, represents a new category of biological fertilizer in Brazil, based on publicly available information. Switch already runs USDA- and EPA-authorized corn trials across six Midwest states, and the company is testing candidates with smallholder farmers in Kenya.

Founder and CEO Tim Schnabel said Brazil gives the company a new regulatory pathway and a way to show how its microbes perform consistently across distinct agricultural environments.

The Guangdong Academy of Forestry screened 74 bacteria isolated from the rhizosphere soil of healthy poplar trees in Beijing against Cytospora chrysosperma, the fungus behind poplar canker. XZL-8 showed the strongest antifungal activity and was identified as Pseudomonas chlororaphis subsp. aureofaciens (CGMCC no. 12555).

Its genome carries 22 predicted secondary metabolite gene clusters, including those associated with hydrogen cyanide and pyrrolnitrin production. The fermentation broth completely stopped fungal growth on plates, the cell-free filtrate reached about 94% inhibition, and the volatiles released by the strain reached about 82%.

Poplar twigs cut from the tree, wounded, treated with the broth and then inoculated with the fungus showed no obvious lesions at any check over 28 days, a biocontrol efficacy of 90.3%.

The authors see XZL-8 as a promising candidate for microbial products against woody stem canker, with formulation and field trials as the next steps.

Researchers at Embrapa Environment and the Federal University of Lavras optimized the fermentation of Bacillus velezensis AP-3, a strain originally isolated from rice with activity against soybean rust, coffee leaf rust and nematodes. Temperature was the physical factor with the strongest effect, with endospore counts rising from 4.17 × 10⁷ CFU/mL at 22 °C to 7.30 × 10⁸ at 34 °C.

Molasses with cottonseed flour gave the numerically highest yield, 2.32 × 10⁹ CFU/mL in 72 hours, more than three times the 6.75 × 10⁸ of the chemically defined medium used as a reference.

The team made wettable powders in a separate experiment, using broth from a chemically defined medium with corn or potato starch and soybean lecithin. Both kept viable endospores for three years at room temperature, although counts in the corn-starch powder fell from 5.54 × 10⁸ to 2.37 × 10⁸ CFU per gram, and storage at 40 °C caused a much faster decline. All fermentations ran in 250 mL flasks.

The authors see these results, together with earlier work on AP-3, as support for stable and economically viable endospore products, and name pilot- and industrial-scale fermentation as the next step.