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This week, a heat-tolerant Metarhizium strain was scaled up in solid-state fermentation, and Timac Agro opened a new biotechnology unit at its plant in Spain to produce its INVOC range, built on compounds made by microorganisms. A newly described Streptomyces showed promise against a major tobacco disease, and a field study tested biochar and zeolite as carriers for Bacillus strains.

Let's dive in!

Heat accumulation is a major barrier to scaling solid-state fermentation. Researchers at the Universitat Autònoma de Barcelona have scaled conidia production of Metarhizium robertsii from 0.5 to 100 L in packed-bed bioreactors, using a thermotolerant strain to cope with the heat build-up.

The team cultivated strain EAMa 01/158-Su on brewers' spent grain mixed with wood chips, at 0.5, 22 and 100 L. The larger reactors used a higher proportion of wood chips to maintain space for airflow.

At 100 L the bed reached 55 °C and stayed above 50 °C for more than a day across most of its height, with no active cooling. Production reached 6.0 × 10⁹ conidia per gram of spent grain, compared with 7.2 × 10⁹ at 0.5 L, a difference the authors found not statistically significant. At the time of maximum conidia concentration, germination exceeded 95% at every scale.

Scaling still came with trade-offs. Conidia concentration per gram of dry mixture fell with each increase in volume, and the hottest upper half of the 100 L bed produced less than the lower half.

The pilot reactor operated at a superficial air velocity of 6.6 cm/min. The authors note that typical values in comparable packed-bed studies are 5 to nearly 100 times higher, and suggest the lower airflow could reduce aeration costs, although they did not assess the economics.

Virulence and storage stability of the pilot-scale conidia were not assessed. The authors present the work as the first pilot-scale report of its kind, and heat tolerance could give producers more room to manage the main limitation when scaling up.

Timac Agro, part of Groupe Roullier, inaugurated two industrial units at its plant in Lodosa, Navarre, on 29 September. One of them is a biotechnology unit able to produce more than 2,600 tonnes a year of INVOC, a range of products the company launched this year to help crops cope with stress.

According to the company, the unit cultivates its own selected microorganisms in bioreactors and fermenters designed to optimise their activity and the quality of the final product. INVOC is built on microbial volatile compounds, which the company says act as signals that adjust plant physiology under stress. The range has three products, aimed at salinity, degraded soils and water scarcity, and is applied through fertigation. Timac Agro reports that 15 years of research, 11 partner research centres, more than 100 trials and four patents stand behind it.

The second unit uses thermal and enzymatic hydrolysis to turn poultry feathers from nearby companies into 6,000 tonnes a year of liquid nitrogen fertiliser for organic farming.

The Lodosa opening adds Timac Agro to the fertiliser companies now running their own microbial fermentation to make biostimulants.

Researchers at Henan University of Science and Technology isolated a Streptomyces from the rhizosphere of healthy tobacco plants in Henan and described it as a new species, Streptomyces songxianensis, with SX92T as the type strain.

A field trial at Yiyang tested the strain against black shank, the disease caused by Phytophthora nicotianae. The researchers applied SX92T first at transplanting and then again a week later, and it cut black shank incidence from 49% to 29% in one plot and from 43% to 29% in the other.

Some plots received only the nutrient medium used to grow the strain, without the bacteria, to rule out that the medium itself protected the plants. Black shank appeared in 44% and 47% of those plants, close to the plots that received only water, supporting the conclusion that the effect was associated with the SX92T treatment rather than the growth medium.

The genome carries 26 gene clusters for secondary metabolites, including siderophore biosynthesis, and soil analyses detected changes in the microbial community around the roots and in soil enzyme activity. The authors have not yet shown whether these soil changes, or the compounds predicted from the genome, are what protect the plants.

A stable formulation and broader field testing remain the next steps. SX92T gives tobacco growers a new biological candidate against black shank, a disease that can cut yields by 30 to 50%.

Researchers in Greece and Serbia tested whether solid carriers change what plant growth-promoting bacteria do in the field. They immobilised six Bacillus strains, all isolated from maize rhizosphere, on hardwood biochar and on zeolite granules. The trial, carried out in an industrial tomato field at Oropos near Athens, compared these carriers with the same strains applied in water.

Three Bacillus subtilis strains, 548, Z3 and 557, gave the best results. Fruit yield rose by up to 23.8% over the uninoculated control, from 2,844 g to 3,522 g per plant, and plant dry weight by up to 32.9%. Carrier type made no significant difference to yield.

The carriers did matter for other traits. Plants in the biochar treatments had the highest photosynthetic rate 83 days after transplanting. B. subtilis 557 on zeolite produced fruit with up to 42% higher antioxidant capacity and up to 48% more phenolic compounds. Soluble solids, carotenoids and colour did not change.

The trial covered a single season and one tomato hybrid. The authors conclude that optimising the pairing between strain and carrier is key to improving both yield and quality in industrial tomato.