Junde Dong

Bacteria play a significant role in triggering coral larval metamorphosis and settlement in many coral species. However, the underlying molecular mechanisms behind coral larval metamorphosis and settlement triggered by bacteria remain enigmatic. Thus, we perform a bacteria-induced metamorphosis and settlement experiment using larvae of Pocillopora damicornis along with high-throughput sequencing, proteomic, and metabolomic analyses. Our results demonstrate that the Metabacillus indicus strain cB07 significantly alters the composition of the microbial community in cultured seawater and coral larvae. Genera associated with promoting coral larval metamorphosis and settlement, including Leisingera and Thalassobius, along with the anti - fouling genus Winogradskyella, undergo notable changes in the coral larvae and culture water. Differentially expressed proteins (DEPs) and metabolites (DEMs) in the cB07 - induced coral larvae are significantly enriched in the immune system, signal transduction, and energy metabolism. According to a protein and metabolite change model, strain cB07 induces coral larval settlement and metamorphosis through retinoic aldehyde pathway, the tricarboxylic acid cycle, and GABA synthesis. Our findings together help to elucidate how associated bacteria interact with coral holobionts and how M. indicus cB07 triggers coral larval metamorphosis and settlement, providing insight into the role bacteria play in marine invertebrates.

Spotted knifejaw (Oplegnathus punctatus) is an economically important marine cultured species exhibiting a unique complex sex chromosome system (X₁X₁X₂X₂ in females and X₁X₂Y in males), with males possessing one fewer chromosome (2n = 47) than females (2n = 48) and an abnormally large Y chromosome. Additionally, males demonstrate significant growth advantages over females. Rapid and accurate sex identification is essential for effective culture management, selective breeding, and population control. In this study, we identified a homologous region of the tmem88 gene containing large DNA insertion markers on the X and Y chromosomes through whole-genome sequencing of O. punctatus. The X₁ chromosome harbors a 278 bp DNA fragment, whereas the Y chromosome contains a 1472 bp fragment, resulting in a 1194 bp size difference indicative of structural variation in the non-coding region of the tmem88 gene. We developed a rapid detection method based on this variation, utilizing a pair of primers that amplify two distinct bands (278 bp and 1472 bp) in male (X₁X₂Y) individuals and a single 278 bp band in female (X₁X₁X₂X₂) individuals when analyzed by agarose gel electrophoresis. This method enables efficient and accurate sex differentiation in O. punctatus, significantly reducing the time required for identification and enhancing detection efficiency. This study provides a valuable tool for the rapid identification of sex in O. punctatus, facilitating improved breeding strategies and supporting the large-scale production of high-quality fry.

In the background of global warming, coral bleaching induced by elevated seawater temperature is the primary cause of coral reef degradation. Coral microbiome engineering using the beneficial microorganisms for corals (BMCs) has become a hot spot in the field of coral reef conservation and restoration. Investigating the potential of alleviating thermal stress by quorum quenching (QQ) bacteria may provide more tools for coral microbial engineering remediation. In this study, QQ bacteria strain Pseudoalteromonas piscicida SCSIO 43740 was screened among 75 coral-derived bacterial strains, and its quorum sensing inhibitor (QSI) compound was isolated and identified as 2,4-di-tert-butylphenol (2,4-DTBP). Then, the thermal stress alleviating potential of QQ bacteria on coral Pocillopora damicornis was tested by a 30-day controlled experiment with three different treatments: control group (Con: 29 °C), high temperature group (HT: 31 °C), and the group of high temperature with QQ bacteria inoculation (HTQQ: 31 °C + QQ bacteria). The results showed that QQ bacteria SCSIO 43740 inoculation can significantly mitigate the loss of symbiotic algae and impairment of photosynthesis efficiency of coral P. damicornis under thermal stress. Significant difference in superoxide dismutase (SOD) and catalase (CAT) enzyme activities between HT and HTQQ was not observed. In addition, QQ bacteria inoculation suppressed the coral microbial community beta-dispersion and improved the stability of microbial co-occurrence network under thermal stress. It was suggested that QQ bacteria inoculation can alleviate coral thermal stress via reshaping microbial interaction and maintain community stability of coral microbiome. This study provided new evidence for the probiotic function of QQ bacteria in corals, which shedding light on the development of new microbiological tools for coral reef conservation.

In the background of global warming, coral bleaching induced by elevated seawater temperature is the primary cause of coral reef degradation. Coral microbiome engineering using the beneficial microorganisms for corals (BMCs) has become a hot spot in the field of coral reef conservation and restoration. Investigating the potential of alleviating thermal stress by quorum quenching (QQ) bacteria may provide more tools for coral microbial engineering remediation. In this study, QQ bacteria strain Pseudoalteromonas piscicida SCSIO 43740 was screened among 75 coral-derived bacterial strains, and its quorum sensing inhibitor (QSI) compound was isolated and identified as 2,4-di-tert-butylphenol (2,4-DTBP). Then, the thermal stress alleviating potential of QQ bacteria on coral Pocillopora damicornis was tested by a 30-day controlled experiment with three different treatments: control group (Con: 29°C), high temperature group (HT: 31°C), and the group of high temperature with QQ bacteria inoculation (HTQQ: 31°C + QQ bacteria). The results showed that QQ bacteria SCSIO 43740 inoculation can significantly mitigate the loss of symbiotic algae and impairment of photosynthesis efficiency of coral P. damicornis under thermal stress. In addition, QQ bacteria inoculation suppressed the coral microbial community beta-dispersion and improved the stability of microbial co-occurrence network under thermal stress. It was suggested that QQ bacteria inoculation can alleviate coral thermal stress via reshaping microbial interaction and maintain community stability of coral microbiome. This study provided new evidence for the probiotic function of QQ bacteria in corals, which shedding light on the development of new microbiological tools for coral reef conservation.

Mangrove ecosystems play curial roles in providing many ecological services and alleviating global climate change. However, they are in decline globally, mainly threatened by human activities and global warming, and organic pollutants, especially PAHs, are among the crucial reasons. Microbial remediation is a cost-effective and environmentally friendly way of alleviating PAH contamination. Therefore, understanding the effects of environmental and nutritional parameters on the biodegradation of polycyclic aromatic hydrocarbons (PAHs) is significant for the bioremediation of PAH contamination. In the present study, five bacterial strains, designated as Bp1 (Genus Rhodococcus), Sp8 (Genus Nitratireductor), Sp13 (Genus Marinobacter), Sp23 (Genus Pseudonocardia), and Sp24 (Genus Mycolicibacterium), have been isolated from mangrove sediment and their ring hydroxylating dioxygenase (RHD) genes have been successfully amplified. Afterward, their degradation abilities were comprehensively evaluated under normal cultural (monoculture and co-culture) and different nutritional (tryptone, yeast extract, peptone, glucose, sucrose, and NPK fertilizer) and environmental (cetyl trimethyl ammonium bromide (CTAB), sodium dodecyl sulfate (SDS)) parameters, as well with different co-contaminants (phenanthrene and naphthalene) and heavy metals (Cd²⁺, Cu²⁺, Fe³⁺, Ni²⁺, Mg²⁺, Mn²⁺, and Co²⁺). The results showed that strain Sp24 had the highest pyrene degradation rate (85%) in the monoculture experiment after being cultured for 15 days. Adding nitrogen- and carbon-rich sources, including tryptone, peptone, and yeast extract, generally endorsed pyrene degradation. In contrast, the effects of carbon sources (glucose and sucrose) on pyrene degradation were distinct for different bacterial strains. Furthermore, the addition of NPK fertilizer, SDS, Tween-80, phenanthrene, and naphthalene enhanced the bacterial abilities of pyrene removal significantly (p < 0.05). Heavy metals significantly reduced all bacterial isolates’ degradation potentials (p < 0.05). The bacterial consortia containing high bio-surfactant-producing strains showed substantially higher pyrene degradation. Moreover, the consortia of three and five bacterial strains showed more degradation efficiency than those of two bacterial strains. These results provide helpful microbial resources for mangrove ecological remediation and insight into optimized culture strategies for the microbial degradation of PAHs.