Insights into the bacterial community composition of farmed Caulerpa lentillifera: A comparison between contrasting health states

Abstract

The bacterial communities of Caulerpa lentillifera were studied during an outbreak of an unknown disease in a sea grape farm from Vietnam. Clear differences between healthy and diseased cases were observed at the order, genus, and Operational Taxonomic Unit (OTU) level. A richer diversity was detected in the diseased thalli of C. lentillifera, as well as the dominance of the orders Flavobacteriales (phylum Bacteroidetes) and Phycisphaerales (Planctomycetes). Aquibacter, Winogradskyella, and other OTUs of the family Flavobacteriaceae were hypothesized as detrimental bacteria, this family comprises some well-known seaweed pathogens. Phycisphaera together with other Planctomycetes and Woeseia were probably saprophytes of C. lentillifera. The Rhodobacteraceae and Rhodovulum dominated the bacterial community composition of healthy C. lentillifera. The likely beneficial role of Bradyrhizobium, Paracoccus, and Brevundimonas strains on nutrient cycling and phytohormone production was discussed. The bleaching of diseased C. lentillifera might not only be associated with pathogens but also with an oxidative response. This study offers pioneering insights on the co-occurrence of C. lentillifera-attached bacteria, potential detrimental or beneficial microbes, and a baseline for understanding the C. lentillifera holobiont. Further applied and basic research is urgently needed on C. lentillifera microbiome, shotgun metagenomic, metatranscriptomic, and metabolomic studies as well as bioactivity assays are recommended.

Keywords: 16S rRNA gene; Vietnam; aquaculture; green caviar; sea grape; seaweed.

Figure 1

Diseased Caulerpa lentillifera from the Vietnamese aquaculture. (A) White biofilm on the external circumference of the ramuli. (B) Bleaching of the ramuli. (C) Bleaching, shrinking, and loss of ramuli

Figure 2

Mean relative sequence abundance (±standard deviation) of the main bacterial orders and genera in healthy and diseased individuals of the sea grape Caulerpa lentillifera. *Significant differences at p < 0.05 according to the Mann–Whitney test. Caption superscript and color show correspondence between order and genus (e.g., ^Rho = Rhodobacterales). Aphaproteobact., Alphaproteobacteria; Cand. Kaiserbact., Candidatus Kaiserbacteria; Clostr., Clostridium; Flavobact., Flavobacteriaceae; mar. gr., marine group; Methyloligel., Methyloligellaceae; uncl., unclassified

Figure 3

Nonmetric multidimensional scaling ordination of healthy and diseased individuals of the sea grape Caulerpa lentillifera at Operational Taxonomic Unit level

Figure 4

Heatmap of the main Operational Taxonomic Units on healthy (H) and diseased (D) individuals of the sea grape Caulerpa lentillifera. (*) Unclassified (**) sensu stricto 7. The number after each genus refers to the sequence number or minimum entropy decomposition node

Figure 5

Diversity comparisons between healthy and diseased states of Caulerpa lentillifera according to the Chao1, Inverse Simpson (InvS), and Shannon indexes. *Significant differences at p < 0.05 according to the Mann–Whitney test