Hwangdonia lutea sp. nov., isolated from the Haima cold seep, South China Sea.

A Gram-stain-negative, orange-yellow, rod-shaped bacterium, designated strain SCSIO 19198T, was isolated from sediment of the Haima cold seep in the South China Sea, PR China. The strain was aerobic and non-motile. Growth of strain SCSIO 19198T occurred at pH 7-9 (optimum, pH 7), 15-37 °C (optimum, 25-32 °C) and with 3-8 % (w/v) NaCl (optimum, 3-6 % NaCl). Phylogenetic analyses based on 16S rRNA sequences revealed that strain SCSIO 19198T belonged to the genus Hwangdonia, having the highest similarity to Hwangdonia seohaensis HD-3T (98.35 %), followed by Algibacter aquimarinus KYW589T (95.17 %) and Gelatiniphilus marinus GYP-24T (94.89 %). The DNA G+C content was 35.92 mol%. The average nucleotide identity value between the genome of strain SCSIO 19198T and that of H. seohaensis HD-3T was 88.49 %. The digital DNA-DNA hybridization value between strain SCSIO 19198T and H. seohaensis HD-3T was 36 %. The major fatty acids (>10 %) of strain SCSIO 19198T were iso-C15 : 0, iso-C15 : 1 G, summed feature 3 (C16 : 1 ω6c/C16 : 1 ω7c) and anteiso-C15 : 0. MK-6 was the only detected respiratory quinone. The polar lipids of strain SCSIO 19198T included phosphatidylethanolamine, two aminolipids, glycolipid and two unidentified lipids. The phenotypic, phylogenetic, chemotaxonomic and genomic data clearly suggest that strain SCSIO 19198T represents a novel species of the genus Hwangdonia, for which the name Hwangdonia lutea sp. nov. is proposed. The type strain is SCSIO 19198T (=MCCC 1K08674T=KCTC 102078T).

Ammonia removal mitigates white plague type II in the coral Pocillopora damicornis.

White Plague Type II (WPL II) is a disease increasingly affecting scleractinian coral species and progresses rapidly. However, the etiological pathogen and remedy remain elusive. In this study, transmission experiments demonstrated that Aureimonas altamirensis and Aurantimonas coralicida, representing the WPL II pathogens, could infect Pocillopora damicorni. The infection produced selected pathological symptoms, including bleaching, tissue loss, and decolorization. Furthermore, ammonia degradation significantly reduced the severity of infection by these pathogens, indicating that ammonia may be a virulence factor for WPL II. Coral microbiome analysis suggested that ammonia degradation mediates the anti-white plague effect by maintaining the density of Symbiodiniaceae and stabilizing the core and symbiotic bacteria. Aureimonas altamirensis and Aurantimonas coralicida have been shown to cause diseases of P. damicornis, with ammonia acting as a virulence factor, and ammoniac degradation may be a promising and innovative approach to mitigate coral mortality suffering from increasing diseases.

Significant Shifts in Microbial Communities Associated with Scleractinian Corals in Response to Algae Overgrowth.

Microbes play a key role in reef dynamics, mediating the competition between scleractinian corals and benthic algae; however, major shifts in bacterial communities among coral species in response to increases in the abundance of algae are not well understood. We investigated the taxonomic composition of coral-associated microbial communities under algae-overgrowth conditions using 16S rRNA gene sequencing. The results showed that non-algal (i.e., healthy) tissue (HH) had lower bacterial abundance and diversity than tissue collected from the coral-algae interface boundary (HA) and areas of algae growth (AA). Specifically, the HA and AA samples had higher relative abundances of Saprospiraceae, Rhodobacteraceae, and Alteromonadaceae. Compared with Platygyra sp. and Montipora sp., the physiological response of Pocillopora sp. was more intense under algae-induced stress based on microbial gene function prediction. Our results indicate that algal pressure can significantly alter the microbial community structure and function of coral ecosystems. Our data thus provide new insight into the relationship between corals and their microbiome under environmental stress.

A Novel Neutral and Mesophilic ß-Glucosidase from Coral Microorganisms for Efficient Preparation of Gentiooligosaccharides.

ß-glucosidases can produce gentiooligosaccharides that are lucrative and promising for the prebiotic and alternative food industries. However, the commercial production of gentiooligosaccharides using ß-glucosidase is challenging, as this process is limited by the need for high thermal energy and increasing demand for the enzyme. Here, a putative ß-glucosidase gene, selected from the coral microbial metagenome, was expressed in Escherichia coli. Reverse hydrolysis of glucose by Blg163 at pH 7.0 and 40 °C achieved a gentiooligosaccharide yield of 43.02 ± 3.20 g·L-1 at a conversion rate of 5.38 ± 0.40%. Transglycosylation of mixed substrates, glucose and cellobiose, by Blg163 consumed 21.6 U/0.5 g glucose/g cellobiose, achieving a gentiooligosaccharide yield of 70.34 ± 2.20 g·L-1 at a conversion rate of 15.63%, which is close to the highest yield reported in previous findings. Blg163-mediated synthesis of gentiooligosaccharides is the mildest reaction and the lowest ß-glucosidase consumption reported to date.

Diversity of cultivable protease-producing bacteria and their extracellular proteases associated to scleractinian corals.

Protease-producing bacteria play a vital role in degrading organic nitrogen in marine environments. However, the diversity of the bacteria and extracellular proteases has seldom been addressed, especially in communities of coral reefs. In this study, 136 extracellular protease-producing bacterial strains were isolated from seven genera of scleractinian corals from Luhuitou fringing reef, and their protease types were characterized. The massive coral had more cultivable protease-producing bacteria than branching or foliose corals. The abundance of cultivable protease-producing bacteria reached 106 CFU g-1 of coral. Phylogenetic analysis of 16S rRNA gene sequences revealed that the isolates were assigned to 24 genera, from which 20 corresponded to the phyla Firmicutes and Proteobacteria. Bacillus and Fictibacillus were retrieved from all coral samples. Moreover, Vibrio and Pseudovibrio were most prevalent in massive or foliose coral Platygyra and Montipora. In contrast, 11 genera were each identified in only one isolate. Nearly all the extracellular proteases from the bacteria were serine proteases or metalloproteases; 45.83% of isolates also released cysteine or aspartic proteases. These proteases had different hydrolytic ability against different substrates. This study represents a novel insight on the diversity of cultivable protease-producing bacteria and their extracellular proteases in scleractinian corals.