Sweet Moulds

For reasons that shouldn't be too hard to work out, much of microbial diversity has only been identified within the last few decades. In 1985, researchers identified a distinctive new species of mycelium-forming bacterium from soil in China that they dubbed Glycomyces harbinensis. This was the first known species of the actinobacterial family Glycomycetaceae which have since been isolated from a wide range of soil microbiomes.

Agar culture of Stackebrandtia nassauensis (scanning electron micrograph), from Goodfellow et al. (2012).

Glycomycetes form pale (white to tan-coloured) branching mycelium a bit less than half a micron in diameter. Under certain conditions, they will form aerial mycelia comprising long chains of spores but these seem to only ever be sparse. The name of the family (which could be translated as 'sweet moulds') refers to the presence of the amino-acid glycine as a significant component of the cell wall. Other diagnostic components of the cell include the sugar ribose and the phospholipid phosphatidylglycerol (Goodfellow et al. 2012).

Since the original description of Glycomyces, half a dozen genera and numerous species have been recognised among the Glycomycetaceae. Some, such as Haloglycomyces and Natronoglycomyces, were described from high salinity soils (Sorokin et al. 2021). Other glycomycetes, such as Glycomyces sambucus, are endophytic, living inside the roots of plants. Doubtless (as always) many more remain to be discovered.

I haven't found any references to direct usage of glycomycetes by humans as yet. It has been suggested that endophytic bacteria may play a role in their hosts' uptake of nutrients from the soil. And I wonder if those species found in salty soils may have a contribution to make to the rehabilitation of such environments. In parts of the world such as here in southern Western Australia, where rising soil salinity is a concerning issue, any help would be more than welcome!

REFERENCES

Goodfellow, M., P. Kämpfer, H.-J. Busse, M. E. Trujillo, K. Suzuki, W. Ludwig & W. B. Whitman (eds) 2012. Bergey's Manual of Systematic Bacteriology 2^nd ed. vol. 5. The Actinobacteria, Part A and B. Springer.

Sorokin, D. Y., T. V. Khijniak, A. P. Zakharycheva, A. G. Elcheninov, R. L. Hahnke, O. V. Boueva, E. V. Ariskina, B. Bunk, I. V. Kublanov & L. I. Evtushenko. 2021. Natronoglycomyces albus gen. nov., sp. nov., a haloalkaliphilic actinobacterium from a soda solonchak soil. International Journal of Systematic and Evolutionary Microbiology 71: 004804.

Nocardia pseudovaccinii

As noted on this site before, the Actinobacteria are one of the most significant groups of bacteria in the terrestrial environment. Among the more diverse genera of Actinobacteria is Nocardia, members of which produce fine, branching mycelia that often fragment into individual rod-shaped or coccoid segments, each of which is capable of developing into a new mycelium (Goodfellow et al. 2012). As is the way of things, Nocardia species are usually soil dwellers but are more commonly studied as facultative pathogens. Nevertheless, recent years have seen the recognition of an increasing number of species isolated from soil samples with one such species being Nocardia pseudovaccinii.

Nocardia pseudovaccinii was described as a new species by Kim et al. (2002). In culture, N. pseudovaccinii grows a beige-red substrate mycelium supported a scarce, white aerial mycelium. Kim et al. (2002) identified the species as able to utilise a wide range of organic substrates such as ribose and glucosaminic acid though it could not break down others such as sucrose or citrate. Molecular analyses of Nocardia in Kim et al. (2002) and Goodfellow et al. (2012) do not really indicate a clear association of N. pseudovaccinii with any other species. Bacterial systematists apparently still maintain that neighbour-joining analyses are something more than a complete waste of time. I do not support this view.

The strains assigned to N. pseudovaccinii by Kim et al. (2002) had previously been identified as another species, N. vaccinii, hence the new species' name ('vaccinii', in case you were wondering, has no direct connection to vaccines but refers to Vaccinium, the plant genus including blueberries and from which N. vaccinii was first isolated). Nocardia vaccinii has been known to act as a facultative plant pathogen but I am not aware of this role being identified for N. pseudovaccinii. The original isolates were cultured from soil (though Kim et al. say nothing about what kind of soil or even where it was sampled). Nocardia pseudovaccinii has also been found forming part of the microbiome of wireworms of the genus Agriotes, beetle larvae that feed on plant roots. It may form a symbiotic association with these grubs that provides the latter with antibiotic protection from the pathogenic fungus Metarhizium brunneum (Kabaluk et al. 2017). A good thing for the wireworms but perhaps not so good for agriculturists who would like to keep them under control.

Goodfellow, M., P. Kämpfer, H.-J. Busse, M. E. Trujillo, K. Suzuki, W. Ludwig & W. B. Whitman (eds) 2012. Bergey's Manual of Systematic Bacteriology 2^nd ed. vol. 5. The Actinobacteria, Part A and B. Springer.

Kabaluk, T., E. Li-Leger & S. Nam. 2017. Metarhizium brunneum—an enzootic wireworm disease and evidence for its suppression by bacterial symbionts. Journal of Invertebrate Pathology 150: 82–87.

Kim, K. K., A. Roth, S. Andrees, S. T. Lee & R. M. Kroppenstedt. 2002. Nocardia pseudovaccinii sp. nov. International Journal of Systematic and Evolutionary Microbiology 52: 1825–1829.