柳珊瑚共附生放线菌Streptomyces sp. SCSGAA0009中生物碱类化合物及其抗菌和抗附着活性

【目的】从南海柳珊瑚共附生放线菌的次生代谢产物中寻找具有抗菌和抗附着活性的先导化合物。【方法】应用化学与生物活性相结合的筛选方法,从柳珊瑚共附生微生物中筛选获得代谢产物丰富且具有生物活性的目标菌株并通过大发酵提取浸膏,利用硅胶柱色谱、凝胶柱色谱和高效液相色谱等方法对发酵产物进行分离、纯化,运用波谱解析鉴定化合物的结构。【结果】从采自海南三亚的柳珊瑚(Muricella flexuosa)样品中分离到一株放线菌SCSGAA0009,鉴定为链霉属Streptomycessp.,从其改良ISP2发酵液中分离到新化合物N-(2-(1H-indol-3-yl)ethyl)propionamide(1)和已知化合物phenazine-1-carboxylic acid(2),其中化合物2对大肠杆菌和海洋细菌假单胞菌(Pseudoaltermonas piscida)具有较好抗菌活性,且有强抗草苔虫(Bugulaneritina)幼虫附着活性。【结论】首次从柳珊瑚共附生放线菌的次生代谢产物中获得新的生物碱化合物1,首次报道化合物2的抗海洋细菌活性和抗附着活性;从南海柳珊瑚共附生微生物的次生代谢产物中可以得到新化合物和活性化合物,这一来源的微生物资源值得深入研究。     

北欧海海水可培养细菌多样性

【目的】为了解北欧海表层海水可培养细菌多样性与所在水文环境的关系。【方法】利用2216E、R2A和海水培养基对该海域暖流区、寒流区、海盆区及交汇区等多个区域不同站位的表层海水样品中的可培养细菌进行分离培养,通过16S r RNA基因测序对分离的菌株进行分类鉴定,并构建系统发育树进行系统发育分析。【结果】从北欧海表层海水中共分离到407株细菌,通过RFLP分析选取其中154株进行测序,结果表明此154株细菌分属于3个门,18个属,27个种。3个门包括变形菌门、厚壁菌门和放线菌门,优势属为假交替单胞菌属、嗜冷杆菌属等,优势种为食琼脂假交替单胞菌、海雪嗜冷杆菌等,并分离到闪烁交替单胞菌等多株嗜冷菌。比较不同区域的微生物多样性可以看出,γ-变形菌纲的细菌在各个区域均占较高比例。交汇区的细菌多样性最高,分离到了10个不同属的细菌,而海盆区细菌多样性最低,只分离到了4种。除了海盆区外,其他3个区域的样品中都分离到了特有的类群。【结论】从以上结果可以看出,北欧海域有较为丰富的微生物资源,且交汇区微生物多样性较其他区域高。     

涠洲岛2种造礁珊瑚共附生可培养潜在耐热细菌多样性

【背景】珊瑚适应环境的能力与机体内共附生细菌有关,然而,这些细菌在珊瑚宿主适应环境变化过程中所起的作用尚不清楚。对珊瑚共附生细菌进行纯培养,探究其生物功能和生态作用,是解析珊瑚宿主环境适应机理的重要途径。【目的】研究热耐受性不同的2种造礁珊瑚共附生可培养潜在耐热细菌多样性和功能,为理解珊瑚适应环境的能力提供新的认识。【方法】从涠洲岛选取2种热耐受性差异显著的霜鹿角珊瑚(Acropora pruinosa)和丛生盔形珊瑚(Galaxea fascicularis)为研究对象,采用2216E、海水R₂A和海水GYP这3种琼脂培养基,于32℃(珊瑚热耐受阈值)培养条件下对珊瑚共附生潜在耐热细菌进行分离培养,对分离菌株进行16S rRNA基因测序和序列相似性分析。选取代表菌株进行热耐受性检验,并利用平板对峙法进行抗菌活性检测。【结果】2种造礁珊瑚共附生可培养潜在耐热细菌的多样性存在显著差异。从热敏型的霜鹿角珊瑚中获得44株细菌,隶属于4个门22个属,其中弧菌属(Vibrio)、假交替单胞菌属(Pseudoalteromonas)和Tenacibaculum为优势属;从热耐...     

西沙石珊瑚共附生放线菌的分离培养及抗菌活性评价

【背景】珊瑚礁生态系统是海洋中一类极其重要的生态系统,健康珊瑚礁中丰富的共附生放线菌群体是珊瑚抵御各种致病菌的重要防线,因此,这类放线菌是寻找抗菌活性分子的重要资源,其药用潜力巨大。【目的】从西沙石珊瑚样品中分离共附生放线菌,并从中筛选具有良好抗菌活性的菌株。【方法】通过稀释涂布法分离珊瑚共附生放线菌,并根据16S rRNA基因序列构建系统发育树进行菌种鉴定;通过平板对峙法对放线菌进行抗菌活性筛选并确定目标菌株;将目标菌株涂布于不同氯化钠浓度的ISP2固体培养基上培养,测试其盐度耐受能力;通过平板对峙法对该菌株发酵产物的热稳定性和光稳定性进行测试;采用NanoPore和Illumina方法完成目标活性放线菌全基因组测序,并通过antiSMASH在线分析预测其次级代谢产物生物合成基因簇及其结构类型。【结果】从6份西沙石珊瑚样品中分离得到104株可培养放线菌,根据菌落形态和分离来源去重后对其中27株放线菌进行16S rRNA基因序列测序,通过序列比对和系统发育树分析将菌株初步鉴定为盐孢菌属(Salinispora)(25株)、链霉菌属(Streptomyces)(1株)和戈登菌属(Gord...     

海假交替单胞菌fliC-02330基因缺失影响生物被膜形成及厚壳贻贝幼虫附着变态

【背景】假交替单胞菌属是一种广泛分布于海洋环境的革兰氏阴性细菌,存在于海底沉积物中,能分泌大量的胞外产物形成海洋微生物被膜,从而诱导海洋无脊椎动物的附着。【目的】探究海假交替单胞菌鞭毛蛋白fliC基因对生物被膜形成及厚壳贻贝诱导活性的影响。【方法】通过基因敲除构建海假交替单胞菌fliC-02330基因缺失突变菌,研究突变菌和野生菌菌落形态、生物被膜形成能力、胞外物质以及对厚壳贻贝幼虫附着变态的诱导能力等的差异性。【结果】与野生菌相比,突变菌菌落表型出现褶皱,运动能力下降,形成被膜膜厚增加,以及对幼虫附着变态诱导活性下降。共聚焦扫描发现,fliC-02330基因缺失突变菌胞外多糖含量下降,而蛋白含量上升。【结论】海假交替单胞菌鞭毛蛋白fliC-02330基因缺失促进生物被膜形成,但抑制厚壳贻贝幼虫附着变态。本研究为探究细菌鞭毛蛋白基因与厚壳贻贝幼虫的作用机制,以及后续进一步探索微生物参与海洋无脊椎动物附着变态提供一定的理论依据。     

永兴岛白穗软珊瑚共附生放线菌筛选及部分活性次级代谢产物的鉴定

【目的】从白穗软珊瑚中分离和鉴定共附生放线菌,运用PCR技术对所分离的放线菌进行I型聚酮合酶(PKS)筛选,研究其次级代谢产物。【方法】使用11种培养基对白穗软珊瑚共附生放线菌进行分离、鉴定,构建16S rRNA基因系统发育进化树,以基于I型PKS的KS基因设计的简并引物对所分离放线菌进行基因筛选,对阳性菌株用3种培养基发酵检测,对目标菌株进行放大规模发酵分离鉴定次级代谢产物。【结果】从白穗软珊瑚中分离到20株共附生放线菌,包括链霉菌属10株、迪茨氏菌属2株和盐水孢菌属8株,筛选获得18株I型PKS阳性菌株,并从菌株Salinospora arenicola SH04中分离到化合物rifamycin S和rifamycin W。【结论】首次从珊瑚共附生环境中分离得到海洋专属性稀有放线菌盐水孢菌属,并以I型PKS基因筛选为指导,分离鉴定了聚酮类化合物rifamycins,为研究软珊瑚共附生可培养放线菌的多样性和基于基因筛选指导分离次级代谢产物提供了可靠依据。     

珊瑚礁生态系统中珊瑚藻的生态作用研究进展

珊瑚藻是海洋红藻中的大型钙化藻类,全球分布623种,中国现有记录共77种。随着生态科学研究的广泛展开,人们越来越认识到,珊瑚藻在海洋生态系统中,尤其在维持珊瑚礁生态系统的生物多样性及生态功能中发挥着重要作用。目前,科研人员对有关珊瑚藻的初级生产力、钙化作用以及在诱导底栖无脊椎动物幼虫的附着与变态等方面已有多方面的研究和探索。然而,有关珊瑚藻生态功能的深层次机理问题有待进一步深入研究。文章着重围绕目前珊瑚藻研究中的一些热点问题,从近年来珊瑚藻在珊瑚礁生态系统中的生态功能方面的研究概况进行综述,以期加深人们对珊瑚藻的认识,并促进对珊瑚藻生态功能的进一步深入研究。     

南海硇洲岛潮汐带栉江珧可培养细菌的系统发育多样性

【目的】研究南海硇洲岛潮汐带栉江珧(Atrina pectinata)样品相关可培养细菌的多样性。【方法】采用纯培养法和基于16S r RNA基因序列的系统发育分析,法对样品中可培养细菌(含放线菌)的类群多样性、物种多样性和遗传多样性进行研究。【结果】用补充0–25%(质量体积比)Na Cl的MA、MH和NA培养基从栉江珧样品中分离到125株细菌。在形态观察和部分生理生化实验结果的基础上去冗余,选取90个代表性菌株进行基于16S r RNA基因序列的系统发育多样性分析。结果表明,这90个分离菌株分属于3个大的系统发育类群(Gamma-proteobacteria、Firmicutes、Actinobacteria)、6个科、10个属,可分为33个物种。优势类群为厚壁菌门(Firmicutes)(56株,62.2%)和γ-变形杆菌亚门(Gamma-proteobacteria)(31株,34.5%)。大多数菌株与其系统发育关系最密切的已知物种的典型菌株之间存在一定的遗传差异(16S r RNA基因序列相似性为95.7%–99.9%),其中有5株可能代表新的分类单元(Potential new taxa)。分析表明,菌株JSM 112024可能代表了盐单胞菌科(Halomonadaceae)的一个属一级新分类单元;菌株JSM 112019、JSM 114045、JSM 114058和JSM 114083可能分别代表盐弧菌属(Salinivibrio)、芽孢杆菌属(Bacillus)、盐单胞菌属(Halomonas)和枝芽孢菌属(Virgibacillus)的新物种。【结论】湛江硇洲岛潮汐带栉江珧中存在较为丰富的可培养细菌物种多样性和系统发育多样性,并潜藏着较多的新微生物类群(物种)。     

南海珊瑚来源真菌Aspergillus sp.SCSIO 40435的分离鉴定及其次级代谢产物研究

【目的】南海珊瑚共附生真菌Aspergillus sp. SCSIO 40435次级代谢产物分离鉴定及抑菌活性筛选。【方法】利用稀释涂布平板法分离珊瑚共附生真菌。采用单菌多代谢产物方法(one strain many compounds,OSMAC)对分离菌株进行化学多样性筛选,并采用滤纸片扩散法对真菌发酵产物进行抑菌活性分析。通过ITS测序鉴定活性菌株SCSIO 40435的分类地位,运用多种色谱手段从其粗提物中分离纯化单体化合物,并利用各种波谱手段(HRESIMS、1D和2D NMR、单晶X-ray衍射法等)确定化合物的结构。最后,采用微量肉汤稀释法对单体化合物的抑菌活性进行评估。【结果】从南海珊瑚样品中分离得到19株共附生真菌,结合化学多样性和抑菌活性分析,筛选出1株产物丰富且具有多种抑菌活性的菌株SCSIO40435。利用ITS测序分析将其鉴定为曲霉属真菌(Aspergillus sp.),进一步从其发酵产物中分离鉴定了4个对三联苯类化合物：dicandidusin A(1)、candidusin A(2)、terphenyllin(3)和4″-deoxyterphenylli...     

硇洲岛潮汐带牡蛎相关可培养细菌多样性

[目的]了解南海硇洲岛潮汐带香港巨牡蛎(Crassostrea hongkongensis)相关可培养细菌的多样性.[方法]应用纯培养法分离样品中的细菌(含放线菌),采用基于16S rRNA基因序列的系统发育分析方法研究这些分离菌株的生物多样性.[结果]用补充0-25％(W/V) NaC1的MA、MH和NA培养基从样品中分离到102株细菌,在形态观察和部分生理生化实验结果的基础上去冗余,选取74个代表性菌株进行基于16S rRNA基因序列的系统发育分析.结果表明,这些菌株归为38个物种,属于4个大的系统发育类群(Gamma-Proteobacteria,Alpha-Proteobacteria,Bacteroidetes,Firmicutes)的16个科、18个属.大多数菌株属于Gamma-Proteobacteria亚门(45株,60.8％),其余依次是Firmicutes门(12株,16.2％)、Bacteroidetes门(11株,14.9％)和Alpha-Proteobacteria亚门(6株,8.1％).大多数菌株与其系统发育关系最密切的有效发表种典型菌株之间(16S rRNA基因序列相似性为94.3％-99.8％)存在一定的遗传差异,其中JSM 111069可能代表Carnobacteriaceae科的潜在新属;菌株JSM 111039和JSM 111085可能分别代表Bacillus属的两个新物种,菌株JSM 111020、JSM 111072和JSM 111090可能分别代表Pseudoalteromonas、Proteus和Idiomarina属的新物种.[结论]南海硇洲岛潮汐带牡蛎中存在较为丰富的原核生物多样性,并潜藏着一定数量的微生物新类群(物种).     

Induction of larval metamorphosis of the coral Acropora millepora by tetrabromopyrrole isolated from a Pseudoalteromonas bacterium

The induction of larval attachment and metamorphosis of benthic marine invertebrates is widely considered to rely on habitat specific cues. While microbial biofilms on marine hard substrates have received considerable attention as specific signals for a wide and phylogenetically diverse array of marine invertebrates, the presumed chemical settlement signals produced by the bacteria have to date not been characterized. Here we isolated and fully characterized the first chemical signal from bacteria that induced larval metamorphosis of acroporid coral larvae (Acropora millepora). The metamorphic cue was identified as tetrabromopyrrole (TBP) in four bacterial Pseudoalteromonas strains among a culture library of 225 isolates obtained from the crustose coralline algae Neogoniolithon fosliei and Hydrolithon onkodes. Coral planulae transformed into fully developed polyps within 6 h, but only a small proportion of these polyps attached to the substratum. The biofilm cell density of the four bacterial strains had no influence on the ratio of attached vs. non-attached polyps. Larval bioassays with ethanolic extracts of the bacterial isolates, as well as synthetic TBP resulted in consistent responses of coral planulae to various doses of TBP. The lowest bacterial density of one of the Pseudoalteromonas strains which induced metamorphosis was 7,000 cells mm(-2) in laboratory assays, which is on the order of 0.1-1% of the total numbers of bacteria typically found on such surfaces. These results, in which an actual cue from bacteria has been characterized for the first time, contribute significantly towards understanding the complex process of acroporid coral larval settlement mediated through epibiotic microbial biofilms on crustose coralline algae.     

Can benthic algae mediate larval behavior and settlement of the coral Acropora muricata?

The resilience of coral reefs relies significantly on the ability of corals to recover successfully in algal-dominated environments. Larval settlement is a critical but highly vulnerable stage in the early life history of corals. In this study, we analyzed how the presence of two upright fleshy algae, Sargassum mcclurei (SM) and Padina australis (PA), and one crustose coralline algae, Mesophyllum simulans (MS), affects the settlement of Acropora muricata larvae. Coral larvae were exposed to seawater flowing over these algae at two concentrations. Larval settlement and mortality were assessed daily through four variables related to their behavior: swimming, substratum testing, metamorphosis, and stresses. Temperature, dissolved oxygen, pH, algal growth, and photosynthetic efficiency were monitored throughout the experiment. Results showed that A. muricata larvae can settle successfully in the absence of external stimuli (63 ± 6 % of the larvae settled in control treatments). While algae such as MS may stimulate substrate testing and settlement of larvae in the first day after competency, they ultimately had a lower settlement rate than controls. Fleshy algae such as PA, and in a lesser measure SM, induced more metamorphosis than controls and seemed to eventually stimulate settlement. A diverse combination of signals and/or modifications of microenvironments by algae and their associated microbial communities may explain the pattern observed in coral settlement. Overall, this study contributes significantly to the knowledge of the interaction between coral and algae, which is critical for the resilience of the reefs.     

Effect of Bacteria Associated with the Green Alga Ulva reticulata on Marine Micro- and Macrofouling

The green alga Ulva reticulata (Forsskal) is often free from biofouling in Hong Kong waters. An early study indicated that bioactive substances from this alga inhibit settlement of the polychaete Hydroides elegans (Haswell). It is also predicted that epibiotic bacteria protect this alga from micro- and macrofouling. In this study, bacterial strains from the surface of U. reticulata were isolated and their inhibitive activities on micro- and macrofouling assayed. The strains were identified by 16S rRNA analysis as belonging to the genera Alteromonas , Pseudoalteromonas and Vibrio . There was no significant effect of these strains or their extracts (aqueous and ethanol) on the growth of five Vibrio strains isolated from natural biofilm. Two bacterial strains ( Alteromonas sp. and Vibrio sp. 3) were non-toxic to the benthic diatom Nitzschia paleacea (Grunow) while the other five strains caused a low level of mortality. No one bacterial strain was toxic to the larvae of H. elegans . Aqueous extract of one of the isolated bacterial species, i.e. Vibrio sp. 2, significantly ( p <0.00001) inhibited the settlement and metamorphosis of H. elegans larvae. The putative antifouling compounds have a molecular weight of >100 kD. On the other hand, biofilm of Pseudoalteromonas sp. 2 and aqueous extract of Vibrio sp. 2 suppressed the settlement of larvae induced by 3-isobutyl-1-methylxanthine (IBMX). Other epibiotic bacteria and their extracts had neither inhibitive nor inductive effects on larval settlement of H. elegans . The results indicate that the antifouling mechanism of U. reticulata may be dependent not only on materials from the macroalga itself but also on the epibiotic bacteria on the algal surface.     

第六次北极科学考察海洋沉积物可培养细菌的多样性分析

【目的】研究北极海洋沉积物可培养细菌的菌种资源多样性。【方法】采用海水Zobell2216E培养基和涂布平板法对第六次北极科学考察获得的海洋沉积物开展细菌分离培养,通过16S rRNA基因系统发育分析了解可培养细菌的多样性。【结果】根据菌落形态特征,从40个站位的北极海洋沉积物样品中共分离并获得16S rRNA基因有效序列的细菌达445株;基于16S rRNA基因的相似性分析与系统发育研究结果表明,分离获得的细菌分属于细菌域的4个门、6个纲、13个目、28个科、49个属、91个种,其中γ-Proteobacteria占大多数;有12株与模式菌株的16S rRNA基因序列相似性小于97%,可能代表了6个潜在的细菌新物种;此次获得的细菌种类组成与以往第五次北极科考获得的相比,在属水平上差异较大。【结论】北极海洋沉积物中存在着丰富的微生物菌种资源,具有很多新型微生物仍未被发现,是亟待开发的微生物资源宝库。     

Coral mucus-associated bacteria: a possible first line of defense

Interactions among microorganisms found in coral mucus can be either symbiotic or competitive. It has been hypothesized that microbial communities found on the surface of coral play a role in coral holobiont defense, possibly through production of antimicrobial substances. Selected microorganisms isolated from the mucus layer of a number of coral species were grown using agar-plating techniques. Screening for antimicrobial substances was performed using overlay and drop techniques, employing several indicator microorganisms. Between 25% and 70% of cultivable mucus-associated bacteria from scleractinian corals demonstrated bioactivity. Higher percentages of activity were evident in mucus-associated cultivable bacteria from massive and solitary corals, as compared with bacteria from branching or soft corals. Isolates related to the genera Vibrio and Pseudoalteromonas demonstrated high activity against both Gram-positive and Gram-negative bacteria. Gram-positive bacteria ( Bacillus, Planomicrobium ) demonstrated lower levels of activity, primarily against other Gram-positive bacteria. In some cases, inhibitory effects were confined to the cell fraction, suggesting the involvement of a cell-bound molecule, sensitive to temperature and most likely proteinaceous in nature. These results demonstrate the existence of microorganisms with antimicrobial activity on the coral surface, possibly acting as a first line of defense to protect the coral host against pathogens.     

Larval settlement of the common Australian sea urchin Heliocidaris erythrogramma in response to bacteria from the surface of coralline algae

Bacterial biofilms are increasingly seen as important for the successful settlement of marine invertebrate larvae. Here we tested the effects of biofilms on settlement of the sea urchin Heliocidaris erythrogramma. Larvae settled on many surfaces including various algal species, rocks, sand and shells. Settlement was reduced by autoclaving rocks and algae, and by treatment of algae with antibiotics. These results, and molecular and culture-based analyses, suggested that the bacterial community on plants was important for settlement. To test this, approximately 250 strains of bacteria were isolated from coralline algae, and larvae were exposed to single-strain biofilms. Many induced rates of settlement comparable to coralline algae. The genus Pseudoalteromonas dominated these highly inductive strains, with representatives from Vibrio, Shewanella, Photobacterium and Pseudomonas also responsible for a high settlement response. The settlement response to different bacteria was species specific, as low inducers were also dominated by species in the genera Pseudoalteromonas and Vibrio. We also, for the first time, assessed settlement of larvae in response to characterised, monospecific biofilms in the field. Larvae metamorphosed in higher numbers on an inducing biofilm, Pseudoalteromonas luteoviolacea, than on either a low-inducing biofilm, Pseudoalteromonas rubra, or an unfilmed control. We conclude that the bacterial community on the surface of coralline algae is important as a settlement cue for H. erythrogramma larvae. This study is also an example of the emerging integration of molecular microbiology and more traditional marine eukaryote ecology.     

Culture and identification of Desulfovibrio spp. from corals infected by black band disease on Dominican and Florida Keys reefs

Black band disease (BBD) of corals is characterized as a pathogenic microbial consortium composed of a wide variety of microorganisms. Together, many of these microorganisms contribute to an active sulfur cycle that produces anoxia and high levels of sulfide adjacent to the coral surface, conditions that are lethal to coral tissue. Sulfate-reducing bacteria, as sulfide producers, are an important component of the sulfur cycle and the black band community. Previous molecular survey studies have shown multiple Desulfovibrio species present in BBD but with limited consistency between bacterial species and infections. In this study we compared 16S rRNA gene sequences of sulfate-reducing bacteria selectively cultured from 6 BBD bands on 4 coral species, Diploria clivosa, D. strigosa, D. labyrinthiformes, and Siderastrea siderea, in the Florida Keys and Dominica. The 16S rRNA gene sequences were obtained through direct sequencing of PCR products or by cloning. A BLAST search revealed that 8 out of 10 cultures sequenced were highly homologous to Desulfovibrio sp. strain TBP-1, a strain originally isolated from marine sediment. Although the remaining 2 sequences were less homologous to Desulfovibrio sp. strain TBP-1, they did not match any other sulfate-reducing (or other) species in GenBank.     

Ocean acidification reduces induction of coral settlement by crustose coralline algae

Crustose coralline algae (CCA) are a critical component of coral reefs as they accrete carbonate for reef structure and act as settlement substrata for many invertebrates including corals. CCA host a diversity of microorganisms that can also play a role in coral settlement and metamorphosis processes. Although the sensitivity of CCA to ocean acidification (OA) is well established, the response of their associated microbial communities to reduced pH and increased CO₂ was previously not known. Here we investigate the sensitivity of CCA‐associated microbial biofilms to OA and determine whether or not OA adversely affects the ability of CCA to induce coral larval metamorphosis. We experimentally exposed the CCA Hydrolithon onkodes to four pH/pCO₂ conditions consistent with current IPCC predictions for the next few centuries (pH: 8.1, 7.9, 7.7, 7.5, pCO₂: 464, 822, 1187, 1638 μatm). Settlement and metamorphosis of coral larvae was reduced on CCA pre‐exposed to pH 7.7 (pCO₂ = 1187 μatm) and below over a 6‐week period. Additional experiments demonstrated that low pH treatments did not directly affect the ability of larvae to settle, but instead most likely altered the biochemistry of the CCA or its microbial associates. Detailed microbial community analysis of the CCA revealed diverse bacterial assemblages that altered significantly between pH 8.1 (pCO₂ = 464 μatm) and pH 7.9 (pCO₂ = 822 μatm) with this trend continuing at lower pH/higher pCO₂ treatments. The shift in microbial community composition primarily comprised changes in the abundance of the dominant microbes between the different pH treatments and the appearance of new (but rare) microbes at pH 7.5. Microbial shifts and the concomitant reduced ability of CCA to induce coral settlement under OA conditions projected to occur by 2100 is a significant concern for the development, maintenance and recovery of reefs globally.