Neocallimastix constans G3 is an anaerobic fungus (class Neocallimastigomycetes) isolated from the fecal pellets of a San Clemente Island goat at the Santa Barbara Zoo. This fungus was initially obtained as part of a microbial community containing fungi, methanogens, and potentially antibiotic resistant bacteria. This community was treated with penicillin and streptomycin and enriched on an alfalfa substrate (Peng et al., 2021), though it was later grown on reed canary grass. N. constans G3 was isolated using the roll tube technique, which entails inoculating an anaerobic agar tube, selecting a colony after growth, inoculating liquid media with that colony, and repeating this process multiple times to ensure a pure strain has been selected (Haitjema et al., 2014). Prior to its isolation, N. constans G3 was cultivated in vitro with other rumen microorganisms for over three years. Hence, this fungus has the potential to grow well with other gut microbes and might be an ideal candidate to use in forming lignocellulose-degrading synthetic consortia.
Anaerobic fungi are present in the guts of large herbivores, and despite being few in number compared to the rest of the microbial community, they contribute heavily to the breakdown of lignocellulosic materials that ultimately yields energy and nutrients for the animal (Theodorou et al., 1996). Anaerobic fungi produce numerous carbohydrate-active enzymes (Solomon et al., 2016), and certain anaerobic fungi physically break apart lignocellulose by means of their pervasive rhizoids (Haitjema et al., 2014). N. constans G3 has this type of rhizoidal system. There are a limited number of anaerobic fungal isolates, and as such, these microbes have not been sufficiently characterized. A comprehensive understanding of anaerobic fungal metabolism, including their ability to produce hydrogen, is particularly lacking. This genome and transcriptome will provide insight into the unique metabolic potential this strain may possess, and it will also aid in unmasking several genes of unknown function across the anaerobic fungi. In their natural environment, gut microbes rely on fungal fermentation products as an input to make short- and medium-chain fatty acids, among other end products. With a better understanding of gut fungal metabolism, it becomes possible to enhance the flow of chemical products in herbivores. Moreover, with genetic engineering and synthetic biology, fungal products can be upgraded to more valuable products by members of a synthetic microbial community.
References:
Haitjema, C. H., Solomon, K. V., Henske, J. K., Theodorou, M. K., and O’Malley, M. A. (2014). Anaerobic gut fungi: Advances in isolation, culture, and cellulolytic enzyme discovery for biofuel production. Biotechnol. Bioeng. 111, 1471–1482. doi:10.1002/bit.25264.
Peng, X., Wilken, S. E., Lankiewicz, T. S., Gilmore, S. P., Brown, J. L., Henske, J. K., et al. (2021). Genomic and functional analyses of fungal and bacterial consortia that enable lignocellulose breakdown in goat gut microbiomes. Nat. Microbiol. 6, 499–511. doi:10.1038/s41564-020-00861-0.
Solomon, K. V., Haitjema, C. H., Henske, J. K., Gilmore, S. P., Borges-Rivera, D., Lipzen, A., et al. (2016). Early-branching gut fungi possess a large, comprehensive array of biomass-degrading enzymes. Science 351, 1192–1195. doi:10.1126/science.aad1431.
Theodorou, M. K., Mennim, G., Davies, D. R., Zhu, W.-Y., Trinci, A. P. J., and Brookman, J. L. (1996). Anaerobic fungi in the digestive tract of mammalian herbivores and their potential for exploitation. Proc. Nutr. Soc. 55, 913–926. doi:10.1079/PNS19960088.
