Seasonal Shifts in Pathogenic Microbes Mapped in the South China Sea

Marine waters teem with microorganisms, and among them are species with the potential to cause disease in humans, fish, and other aquatic life. A new study from Guangdong Ocean University and Kyonggi University has taken a detailed look at which of these putative pathogens live in the shelf-margin sea of the northwestern South China Sea, and how their communities change with the seasons. The work, published in Frontiers in Microbiology in the aquatic microbiology section, combined high-throughput sequencing of 16S rRNA and ITS genes with two specialized tools: multiple bacterial pathogen detection, known as MBPD, and the FUNGuild database for assigning ecological roles to fungi.

The researchers set out to describe the composition, diversity, complexity, and stability of putative pathogenic microbial communities in this understudied region, and to identify which environmental factors are most closely associated with them. The results reveal a clear cast of dominant players. Among putative pathogenic bacteria, Escherichia coli was the most abundant, accounting for 31.77 percent of the community, followed by Pseudomonas fluorescens at 16.25 percent and Sphingomonas paucimobilis at 6.90 percent.

On the fungal side, the community was dominated almost equally by two species: Pseudozyma sp. at 48.36 percent and Malassezia globosa at 48.34 percent. These figures describe the relative abundance of organisms classified as putative pathogens by the detection methods used, meaning they are identified as potential pathogens based on sequence data rather than confirmed disease cases in the study area. Seasonality emerged as a defining feature of these communities, but in opposite directions for bacteria and fungi.

The putative pathogenic bacterial community showed higher alpha diversity, a measure of species richness and evenness within samples, in winter. The putative pathogenic fungal community, by contrast, displayed greater alpha diversity in summer. This divergence suggests that bacterial and fungal pathogens respond differently to the seasonal cycle of the shelf-margin sea, a finding with potential relevance for aquaculture planning and ecological monitoring in the region.

Beta diversity analysis, which examines differences in community composition between samples, confirmed significant seasonal dynamics in both groups. For bacteria, the seasonal effect explained an R2 of 0.12 with a p-value of 0.001, while for fungi the corresponding figures were R2 of 0.08 and p of 0.007. In practical terms, knowing the season of a sample provides statistically significant, though partial, information about which putative pathogens are likely to be present.

The modest R2 values also indicate that factors beyond season alone shape these communities. To uncover those other factors, the team turned to Spearman's correlation analysis, which linked community structure to a suite of environmental variables. Temperature, pH, dissolved oxygen, chlorophyll a, and nutrients all played significant roles in influencing the structure of putative pathogenic microbial communities.

The correlations establish associations between environmental conditions and pathogen community composition, though they do not by themselves prove causal mechanisms. The study went further by applying partial least squares path modeling, or PLS-PM, a statistical framework that tests hypothesized relationships among multiple variables simultaneously. For the putative pathogenic bacterial community, alpha diversity was positively associated with both community complexity, measured through co-occurrence network properties, and community stability.

The path coefficients corresponded to an R2 of 0.10 for complexity with a p-value below 0.01, and an R2 of 0.45 for stability with a p-value below 0.001. The latter is a notably strong relationship, indicating that bacterial alpha diversity accounted for a substantial share of the variation in community stability in this system. For fungi, the pattern was different but complementary.

Both alpha diversity and beta diversity showed positive correlations with the stability of the putative pathogenic fungal community, with R2 values of 0.10 and 0.21 and p-values below 0.05 and 0.001 respectively. Taken together, the modeling results suggest that diversity is a key ingredient in maintaining stable pathogen communities in the shelf-margin sea, whether measured within samples for bacteria or across samples for fungi. Co-occurrence networks, one of the study's stated keywords, provide the lens through which complexity was assessed, mapping which taxa tend to appear together more often than chance would predict.

Why does this matter? Marine pathogenic microorganisms are described by the authors as crucial to ecological health and fishery aquaculture. The authors frame their contribution as revealing seasonal patterns of putative pathogenic microorganisms in the shelf-margin sea of the northwestern South China Sea and enhancing understanding of the mechanisms that maintain these communities.

As with any sequencing-based survey, the findings describe putative pathogens identified from genetic signatures, and the correlations reported are associations within a single regional study rather than demonstrations of causation. The final formatted version of the article is scheduled for publication soon, with the work accepted in October 2026 and available under a Creative Commons Attribution license. For researchers monitoring coastal disease ecology, the study provides both a seasonal roadmap and a statistical template for connecting microbial diversity to the stability of the communities they inhabit.

Subject of Research: Seasonal community structure and environmental drivers of putative pathogenic bacteria and fungi in the northwestern South China Sea shelf margin

Article Title: Seasonal community structure and environmental associations of putative pathogenic microorganisms in the Shelf-Margin Sea of the Northwestern South China Sea

Article References: Deng, X., Chen, Q., Ferdoush, J., Huang, C., Tang, Y., Zhang, G., Zhu, Y., Jiang, G., Dong, K., Li, N., & Huang, L. (2026). Seasonal community structure and environmental associations of putative pathogenic microorganisms in the Shelf-Margin Sea of the Northwestern South China Sea. Frontiers in Microbiology, 17, Article 1980205. https://doi.org/10.3389/fmicb.2026.1980205

Image Credits: AI Generated

DOI: 10.3389/fmicb.2026.1980205

Keywords: South China Sea, pathogenic microorganisms, 16S rRNA sequencing, ITS sequencing, MBPD, FUNGuild, alpha diversity, beta diversity, PLS-PM, co-occurrence network, community stability, aquatic microbiology