A headful of germs - Metagenomic analysis of the scalp microbiota in young and elderly women

The human scalp carries a moderately diverse microbiota [1]. Ageing changes skin and scalp physiology which might impact the resident microbiota [2,3] and call for adapted care strategies. Our previous, PCR-based research suggested that age might increase scalp species richness [1]. This prompted us to investigate age-related changes in the scalp microbiota in more detail with a PCR-independent, metagenomic approach to also address the functional potential of the scalp microbes.
We collected a total of 46 scalp swab samples from healthy, preconditioned women aged 21-36 years ("young") and 64-87 years ("old"), respectively. After DNA isolation and Illumina MiSeq-based shotgun sequencing, the samples underwent bioinformatic analyses. Taxonomic profiling of quality-filtered sequences (average sequencing depth: 131150 reads/sample) against the RefSeq database, limited to microbial sequences, revealed that bacterial (36 %) and eukaryotic (34 %) sequences were relatively most abundant. Viral and archaeal sequences accounted for less than 1 % of all sequences. Consistent with other studies, the most common bacterial genera were Cutibacterium and Staphylococcus, while the primary fungal genus was Malassezia [1,3]. 30 % of the sequences could not be taxonomically annotated using this database. To gain insight into potential functional properties, sequences were summarised using GO terms, based on their SwissProt match.
However, neither taxonomic nor functional analyses revealed significant differences between younger and older subjects, even after increasing the average sequencing depth for selected samples to 285543 reads. So far, our data do not indicate a significant effect of age on the structure and function of the scalp microbiota. However, future studies might include a greater sequencing depth to better account for rare sequence types and more function-oriented approaches, such as metatranscriptomics. In addition, male test persons might be included and the pre-conditioning treatment adapted.

[1] Jacksch et al. (2023) Int J Cosmet Sci, 10.1111/ics.12895; [2] Shibagaki et al. (2017) Sci Rep 7(1):10567; [3] Saxena et al. (2018) Front Cell Infect Microbiol 8:346