scholarly journals Relationship between Abundance and Specific Activity of Bacterioplankton in Open Ocean Surface Waters

2012 ◽  
Vol 79 (1) ◽  
pp. 177-184 ◽  
Author(s):  
Dana E. Hunt ◽  
Yajuan Lin ◽  
Matthew J. Church ◽  
David M. Karl ◽  
Susannah G. Tringe ◽  
...  
Keyword(s):  
Microbial Communities ◽  
Specific Activity ◽  
Marine Ecosystem ◽  
Open Ocean ◽  
Rrna Genes ◽  
Cdna Libraries ◽  
Content Type ◽  
The Pacific ◽  
Specific Activities ◽  
Marine Microbial Communities

ABSTRACTMarine microbial communities are complex and dynamic, and their ecology impacts biogeochemical cycles in pelagic ecosystems. Yet, little is known about the relative activities of different microbial populations within genetically diverse communities. We used rRNA as a proxy for activity to quantify the relative specific activities (rRNA/ribosomal DNA [rDNA or rRNA genes]) of the eubacterial populations and to identify locations or clades for which there are uncouplings between specific activity and abundance. After analyzing 1.6 million sequences from 16S rDNA and rRNA (cDNA) libraries from two euphotic depths from a representative site in the Pacific Ocean, we show that although there is an overall positive relationship between the abundances (rDNAs) and activities (rRNAs) among populations of the bacterial community, for some populations these measures are uncoupled. Different ecological strategies are exemplified by the two numerically dominant clades at this site: the cyanobacteriumProchlorococcusis abundant but disproportionately more active, while the heterotrophic SAR11 is abundant but less active. Other rare populations, such asAlteromonas, have high specific activities in spite of their low abundances, suggesting intense population regulation. More detailed analyses using a complementary quantitative PCR (qPCR)-based approach of measuring relative specific activity forProchlorococcuspopulations in the Pacific and Atlantic Oceans also show that specific activity, but not abundance, reflects the key drivers of light and nutrients in this system; our results also suggest substantial top-down regulation (e.g., grazing, viruses, or organismal interactions) or transport (e.g., mixing, immigration, or emigration) of these populations. Thus, we show here that abundance and specific activity can be uncoupled in open ocean systems and that describing both is critical to characterizing microbial communities and predicting marine ecosystem functioning and responses to change.

scholarly journals Novel Microbial Assemblages Dominate Weathered Sulfide-Bearing Rock from Copper-Nickel Deposits in the Duluth Complex, Minnesota, USA

2017 ◽  
Vol 83 (16) ◽  
Author(s):  
Daniel S. Jones ◽  
Kim A. Lapakko ◽  
Zachary J. Wenz ◽  
Michael C. Olson ◽  
Elizabeth W. Roepke ◽  
...  
Keyword(s):  
Microbial Communities ◽  
Microbial Ecology ◽  
Mine Waste ◽  
Experimental Treatment ◽  
Sulfide Mineral ◽  
16S Rrna Genes ◽  
Rrna Genes ◽  
Content Type ◽  
Duluth Complex ◽  
Copper Nickel

ABSTRACT The Duluth Complex in northeastern Minnesota hosts economically significant deposits of copper, nickel, and platinum group elements (PGEs). The primary sulfide mineralogy of these deposits includes the minerals pyrrhotite, chalcopyrite, pentlandite, and cubanite, and weathering experiments show that most sulfide-bearing rock from the Duluth Complex generates moderately acidic leachate (pH 4 to 6). Microorganisms are important catalysts for metal sulfide oxidation and could influence the quality of water from mines in the Duluth Complex. Nevertheless, compared with that of extremely acidic environments, much less is known about the microbial ecology of moderately acidic sulfide-bearing mine waste, and so existing information may have little relevance to those microorganisms catalyzing oxidation reactions in the Duluth Complex. Here, we characterized the microbial communities in decade-long weathering experiments (kinetic tests) conducted on crushed rock and tailings from the Duluth Complex. Analyses of 16S rRNA genes and transcripts showed that differences among microbial communities correspond to pH, rock type, and experimental treatment. Moreover, microbial communities from the weathered Duluth Complex rock were dominated by taxa that are not typically associated with acidic mine waste. The most abundant operational taxonomic units (OTUs) were from the genera Meiothermus and Sulfuriferula, as well as from diverse clades of uncultivated Chloroflexi, Acidobacteria, and Betaproteobacteria. Specific taxa, including putative sulfur-oxidizing Sulfuriferula spp., appeared to be primarily associated with Duluth Complex rock, but not pyrite-bearing rocks subjected to the same experimental treatment. We discuss the implications of these results for the microbial ecology of moderately acidic mine waste with low sulfide content, as well as for kinetic testing of mine waste. IMPORTANCE Economic sulfide mineral deposits in the Duluth Complex may represent the largest undeveloped source of copper and nickel on Earth. Microorganisms are important catalysts for sulfide mineral oxidation, and research on extreme acidophiles has improved our ability to manage and remediate mine wastes. We found that the microbial assemblages associated with weathered rock from the Duluth Complex are dominated by organisms not widely associated with mine waste or mining-impacted environments, and we describe geochemical and experimental influences on community composition. This report will be a useful foundation for understanding the microbial biogeochemistry of moderately acidic mine waste from these and similar deposits.

scholarly journals Defining the Core Citrus Leaf- and Root-Associated Microbiota: Factors Associated with Community Structure and Implications for Managing Huanglongbing (Citrus Greening) Disease

2017 ◽  
Vol 83 (11) ◽  
Author(s):  
Ryan A. Blaustein ◽  
Graciela L. Lorca ◽  
Julie L. Meyer ◽  
Claudio F. Gonzalez ◽  
Max Teplitski
Keyword(s):  
Community Structure ◽  
Microbial Community ◽  
Microbial Communities ◽  
Illumina Sequencing ◽  
Symptom Severity ◽  
16S Rrna Genes ◽  
Rrna Genes ◽  
Content Type ◽  
The Core ◽  
Symptom Progression

ABSTRACTStable associations between plants and microbes are critical to promoting host health and productivity. The objective of this work was to test the hypothesis that restructuring of the core microbiota may be associated with the progression of huanglongbing (HLB), the devastating citrus disease caused byLiberibacter asiaticus,Liberibacter americanus, andLiberibacter africanus. The microbial communities of leaves (n= 94) and roots (n= 79) from citrus trees that varied by HLB symptom severity, cultivar, location, and season/time were characterized with Illumina sequencing of 16S rRNA genes. The taxonomically rich communities contained abundant core members (i.e., detected in at least 95% of the respective leaf or root samples), some overrepresented site-specific members, and a diverse community of low-abundance variable taxa. The composition and diversity of the leaf and root microbiota were strongly associated with HLB symptom severity and location; there was also an association with host cultivar. The relative abundance ofLiberibacterspp. among leaf microbiota positively correlated with HLB symptom severity and negatively correlated with alpha diversity, suggesting that community diversity decreases as symptoms progress. Network analysis of the microbial community time series identified a mutually exclusive relationship betweenLiberibacterspp. and members of theBurkholderiaceae,Micromonosporaceae, andXanthomonadaceae. This work confirmed several previously described plant disease-associated bacteria, as well as identified new potential implications for biological control. Our findings advance the understanding of (i) plant microbiota selection across multiple variables and (ii) changes in (core) community structure that may be a precondition to disease establishment and/or may be associated with symptom progression.IMPORTANCEThis study provides a comprehensive overview of the core microbial community within the microbiomes of plant hosts that vary in extent of disease symptom progression. With 16S Illumina sequencing analyses, we not only confirmed previously described bacterial associations with plant health (e.g., potentially beneficial bacteria) but also identified new associations and potential interactions between certain bacteria and an economically important phytopathogen. The importance of core taxa within broader plant-associated microbial communities is discussed.

scholarly journals Expression of overdominance for specific activity at the phosphoglucomutase-2 locus in the Pacific oyster, Crassostrea gigas.

Genetics ◽  
1991 ◽  
Vol 128 (1) ◽  
pp. 133-141 ◽  
Author(s):  
G H Pogson
Keyword(s):  
Crassostrea Gigas ◽  
Pacific Oyster ◽  
Specific Activity ◽  
Enzyme Polymorphism ◽  
Direct Role ◽  
Activity Data ◽  
Frequency Distributions ◽  
Genetic Components ◽  
The Pacific ◽  
Specific Activities

Abstract Environmental and genetic components of specific activity variation at the phosphoglucomutase-2 locus in the Pacific oyster, Crassostrea gigas, were examined to assess the direct role played by this polymorphism in a heterozygosity/growth relationship. Both environmental variables studied, season and intertidal position, exerted highly significant effects on phosphoglucomutase specific activity but no interactions occurred between these factors and Pgm-2 genotype. Highly significant differences were also detected between Pgm-2 genotypes. The three most common heterozygotes (Pgm-2(92/100), Pgm-2(96/100) and Pgm-2(100/104) consistently expressed greater specific activities than the Pgm-2(92/92), Pgm-2(96/96), Pgm-2(100/100) and Pgm-2(104/104) homozygotes. Overall, the specific activities of heterozygotes for the Pgm-2(100) allele exceeded heterozygotes by 24% and 20% in the mantle and adductor muscle tissues, respectively. Heterozygotes formed between the three less frequent Pgm-2(92), Pgm-2(96) and Pgm-2(104) alleles differed sharply from those possessing the Pgm-2(100) allele in being indistinguishable from homozygotes. The possibility of these patterns arising from the undetected presence of an inactive Pgm-2 allele was examined and found to be inconsistent with all of its predicted effects on the specific activity data. Genuine overdominance was shown to be capable of explaining the specific activities of ten structural locus genotypes, allelic frequency distributions in natural populations, and the maintenance of the enzyme polymorphism in a balanced state. The results provide evidence favoring the overdominance explanation for one locus involved in a heterozygosity/growth relationship and suggest that the reported effects of this locus on adult body weight may have been caused by the greater flux capacities of heterozygotes for the Pgm-2(100) allele.

scholarly journals Revisiting the Dilution Procedure Used To Manipulate Microbial Biodiversity in Terrestrial Systems

2015 ◽  
Vol 81 (13) ◽  
pp. 4246-4252 ◽  
Author(s):  
Yan Yan ◽  
Eiko E. Kuramae ◽  
Peter G. L. Klinkhamer ◽  
Johannes A. van Veen
Keyword(s):  
Microbial Community ◽  
Microbial Communities ◽  
Terrestrial Ecosystems ◽  
Diversity Indices ◽  
Soil Samples ◽  
16S Rrna Genes ◽  
Rrna Genes ◽  
Dilution Method ◽  
Soil Suspension ◽  
Content Type

ABSTRACTIt is hard to assess experimentally the importance of microbial diversity in soil for the functioning of terrestrial ecosystems. An approach that is often used to make such assessment is the so-called dilution method. This method is based on the assumption that the biodiversity of the microbial community is reduced after dilution of a soil suspension and that the reduced diversity persists after incubation of more or less diluted inocula in soil. However, little is known about how the communities develop in soil after inoculation. In this study, serial dilutions of a soil suspension were made and reinoculated into the original soil previously sterilized by gamma irradiation. We determined the structure of the microbial communities in the suspensions and in the inoculated soils using 454-pyrosequencing of 16S rRNA genes. Upon dilution, several diversity indices showed that, indeed, the diversity of the bacterial communities in the suspensions decreased dramatically, withProteobacteriaas the dominant phylum of bacteria detected in all dilutions. The structure of the microbial community was changed considerably in soil, withProteobacteria,Bacteroidetes, andVerrucomicrobiaas the dominant groups in most diluted samples, indicating the importance of soil-related mechanisms operating in the assembly of the communities. We found unique operational taxonomic units (OTUs) even in the highest dilution in both the suspensions and the incubated soil samples. We conclude that the dilution approach reduces the diversity of microbial communities in soil samples but that it does not allow accurate predictions of the community assemblage during incubation of (diluted) suspensions in soil.

scholarly journals Comparative Survey of Rumen Microbial Communities and Metabolites across One Caprine and Three Bovine Groups, Using Bar-Coded Pyrosequencing and1H Nuclear Magnetic Resonance Spectroscopy

2012 ◽  
Vol 78 (17) ◽  
pp. 5983-5993 ◽  
Author(s):  
Hyo Jung Lee ◽  
Ji Young Jung ◽  
Young Kyoon Oh ◽  
Sang-Suk Lee ◽  
Eugene L. Madsen ◽  
...  
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
16S Rrna ◽  
Microbial Communities ◽  
16S Rrna Genes ◽  
Rrna Genes ◽  
Content Type ◽  
Dietary Shift ◽  
Metabolite Profiles ◽  
Nuclear Magnetic

ABSTRACTPyrosequencing of 16S rRNA genes (targetingBacteriaandArchaea) and1H nuclear magnetic resonance were applied to investigate the rumen microbiota and metabolites of Hanwoo steers in the growth stage (HGS), Hanwoo steers in the late fattening stage (HFS), Holstein-Friesian dairy cattle (HDC), and Korean native goats (KNG) in the late fattening stage. This was a two-part investigation. We began by comparing metabolites and microbiota of Hanwoo steers at two stages of husbandry. Statistical comparisons of metabolites and microbial communities showed no significant differences between HFS and HGS (differing by a dietary shift at 24 months and age [67 months versus 12 months]). We then augmented the study by extending the investigation to HDC and KNG. Overall, pyrosequencing of 16S rRNA genes showed that the rumens had highly diverse microbial communities containing many previously undescribed microorganisms. Bioinformatic analysis revealed that the bacterial sequences were predominantly affiliated with four phyla—Bacteroidetes,Firmicutes,Fibrobacteres, andProteobacteria—in all ruminants. However, interestingly, the bacterial reads belonging toFibrobactereswere present at a very low abundance (<0.1%) in KNG. Archaeal community analysis showed that almost all of these reads fell into a clade related to, but distinct from, known cultivated methanogens. Statistical analyses showed that the microbial communities and metabolites of KNG were clearly distinct from those of other ruminants. In addition, bacterial communities and metabolite profiles of HGS and HDC, fed similar diets, were distinctive. Our data indicate that bovine host breeds override diet as the key factor that determines bacterial community and metabolite profiles in the rumen.

scholarly journals Distinct Microbial Communities within the Endosphere and Rhizosphere of Populus deltoides Roots across Contrasting Soil Types

2011 ◽  
Vol 77 (17) ◽  
pp. 5934-5944 ◽  
Author(s):  
Neil R. Gottel ◽  
Hector F. Castro ◽  
Marilyn Kerley ◽  
Zamin Yang ◽  
Dale A. Pelletier ◽  
...  
Keyword(s):  
Microbial Communities ◽  
Populus Deltoides ◽  
Operational Taxonomic Unit ◽  
Rrna Genes ◽  
28S Rrna ◽  
Principal Coordinates Analysis ◽  
Content Type ◽  
Abundance Patterns ◽  
Community Profiling ◽  
Principal Coordinates

ABSTRACTThe root-rhizosphere interface ofPopulusis the nexus of a variety of associations between bacteria, fungi, and the host plant and an ideal model for studying interactions between plants and microorganisms. However, such studies have generally been confined to greenhouse and plantation systems. Here we analyze microbial communities from the root endophytic and rhizospheric habitats ofPopulus deltoidesin mature natural trees from both upland and bottomland sites in central Tennessee. Community profiling utilized 454 pyrosequencing with separate primers targeting the V4 region for bacterial 16S rRNA and the D1/D2 region for fungal 28S rRNA genes. Rhizosphere bacteria were dominated byAcidobacteria(31%) andAlphaproteobacteria(30%), whereas most endophytes were from theGammaproteobacteria(54%) as well asAlphaproteobacteria(23%). A singlePseudomonas-like operational taxonomic unit (OTU) accounted for 34% of endophytic bacterial sequences. Endophytic bacterial richness was also highly variable and 10-fold lower than in rhizosphere samples originating from the same roots. Fungal rhizosphere and endophyte samples had approximately equal amounts of thePezizomycotina(40%), while theAgaricomycotinawere more abundant in the rhizosphere (34%) than endosphere (17%). Both fungal and bacterial rhizosphere samples were highly clustered compared to the more variable endophyte samples in a UniFrac principal coordinates analysis, regardless of upland or bottomland site origin. Hierarchical clustering of OTU relative abundance patterns also showed that the most abundant bacterial and fungal OTUs tended to be dominant in either the endophyte or rhizosphere samples but not both. Together, these findings demonstrate that root endophytic communities are distinct assemblages rather than opportunistic subsets of the rhizosphere.

scholarly journals Differences in Temperature and Water Chemistry Shape Distinct Diversity Patterns in Thermophilic Microbial Communities

2017 ◽  
Vol 83 (21) ◽  
Author(s):  
Cecilia M. Chiriac ◽  
Edina Szekeres ◽  
Knut Rudi ◽  
Andreea Baricz ◽  
Adriana Hegedus ◽  
...  
Keyword(s):  
Water Chemistry ◽  
Microbial Communities ◽  
Community Composition ◽  
Microbial Mats ◽  
Hot Spring ◽  
Environmental Data ◽  
16S Rrna Genes ◽  
Rrna Genes ◽  
Thermal Gradients ◽  
Content Type

ABSTRACT This report describes the biodiversity and ecology of microbial mats developed in thermal gradients (20 to 65°C) in the surroundings of three drillings (Chiraleu [CH], Ciocaia [CI], and Mihai Bravu [MB]) tapping a hyperthermal aquifer in Romania. Using a metabarcoding approach, 16S rRNA genes were sequenced from both DNA and RNA transcripts (cDNA) and compared. The relationships between the microbial diversity and the physicochemical factors were explored. Additionally, the cDNA data were used for in silico functionality predictions, bringing new insights into the functional potential and dynamics of these communities. The results showed that each hot spring determined the formation of distinct microbial communities. In the CH mats (40 to 53°C), the abundance of Cyanobacteria decreased with temperature, opposite to those of Chloroflexi and Proteobacteria. Ectothiorhodospira, Oscillatoria, and methanogenic archaea dominated the CI communities (20 to 65°C), while the MB microbial mats (53 to 65°C) were mainly composed of Chloroflexi, Hydrogenophilus, Thermi, and Aquificae. Alpha-diversity was negatively correlated with the increase in water temperature, while beta-diversity was shaped in each hot spring by the unique combination of physicochemical parameters, regardless of the type of nucleic acid analyzed (DNA versus cDNA). The rank correlation analysis revealed a unique model that associated environmental data with community composition, consisting in the combined effect of Na+, K+, HCO3 −, and PO4 3− concentrations, together with temperature and electrical conductivity. These factors seem to determine the grouping of samples according to location, rather than with the similarities in thermal regimes, showing that other parameters beside temperature are significant drivers of biodiversity. IMPORTANCE Hot spring microbial mats represent a remarkable manifestation of life on Earth and have been intensively studied for decades. Moreover, as hot spring areas are isolated and have a limited exchange of organisms, nutrients, and energy with the surrounding environments, hot spring microbial communities can be used in model studies to elucidate the colonizing potential within extreme settings. Thus, they are of great importance in evolutionary biology, microbial ecology, and exobiology. In spite of all the efforts that have been made, the current understanding of the influence of temperature and water chemistry on the microbial community composition, diversity, and abundance in microbial mats is limited. In this study, the composition and diversity of microbial communities developed in thermal gradients in the vicinity of three hot springs from Romania were investigated, each having particular physicochemical characteristics. Our results expose new factors that could determine the formation of these ecosystems, expanding the current knowledge in this regard.

Distribution of Radioactive and Stable Zinc in an Experimental Marine Ecosystem

1971 ◽  
Vol 28 (11) ◽  
pp. 1783-1788 ◽  
Author(s):  
Ford A. Cross ◽  
James N. Willis ◽  
John P. Baptist
Keyword(s):  
Sea Water ◽  
Specific Activity ◽  
Marine Ecosystem ◽  
Water Concentration ◽  
Benthic Algae ◽  
Particulate Material ◽  
The Mean ◽  
Concentration Factors ◽  
Specific Activities ◽  
Extractable Zn

The distribution of radioactive and stable Zn in an experimental marine ecosystem is described. We added 1 mCi of 65Zn to 2000 liters of sea water and a mixed community of planktonic and benthic algae in a fiberglass tank, after which the ecosystem was left undisturbed for 9 months. We then measured the 65Zn specific activities for (1) particulate Zn (0.45 μ filterable), (2) extractable Zn (from water passed through a 0.45-μ filter and then treated with dithizone), (3) total dissolved Zn (from samples passed through a 0.45-μ filter and treated with acid prior to extraction with dithizone), and (4) dialyzable Zn. Zinc-65 specific activities were not significantly different among the extractable, dialyzable, or acid-treated samples of the water. Further, absolute concentrations of 65Zn and total Zn were no higher in the acid-treated samples than in the extracted or dialyzed samples, which indicates that nearly all of the soluble Zn in the water was dithizone-extractable and dialyzable. Zinc-65 specific activities were significantly less, however, in the particulate material than in the water. This difference indicates that equilibrium of Zn between particulate material and water had not been reached after 9 months. Three months later (December 1969) 65Zn specific activities were determined again for particulate material and total dissolved Zn. The mean specific activity of 65Zn in the particulate samples showed a small but significant increase, but it was still less than in the water. Concentration factors in the particulate matter were 980 for 65Zn and 1400 for total Zn. Samples of benthic algae taken in March 1970 had a mean specific activity of 65Zn similar to the mean 65Zn specific activity of water samples taken 3 months earlier.

scholarly journals Abundance and Distribution of Dimethylsulfoniopropionate Degradation Genes and the Corresponding Bacterial Community Structure at Dimethyl Sulfide Hot Spots in the Tropical and Subtropical Pacific Ocean

2015 ◽  
Vol 81 (12) ◽  
pp. 4184-4194 ◽  
Author(s):  
Yingshun Cui ◽  
Shotaro Suzuki ◽  
Yuko Omori ◽  
Shu-Kuan Wong ◽  
Minoru Ijichi ◽  
...  
Keyword(s):  
Pacific Ocean ◽  
Marine Bacteria ◽  
Dimethyl Sulfide ◽  
16S Rrna Genes ◽  
Rrna Genes ◽  
Surface Seawater ◽  
Content Type ◽  
The Pacific ◽  
The Pacific Ocean ◽  
Abundance And Distribution

ABSTRACTDimethylsulfoniopropionate (DMSP) is mainly produced by marine phytoplankton but is released into the microbial food web and degraded by marine bacteria to dimethyl sulfide (DMS) and other products. To reveal the abundance and distribution of bacterial DMSP degradation genes and the corresponding bacterial communities in relation to DMS and DMSP concentrations in seawater, we collected surface seawater samples from DMS hot spot sites during a cruise across the Pacific Ocean. We analyzed the genes encoding DMSP lyase (dddP) and DMSP demethylase (dmdA), which are responsible for the transformation of DMSP to DMS and DMSP assimilation, respectively. The averaged abundance (±standard deviation) of these DMSP degradation genes relative to that of the 16S rRNA genes was 33% ± 12%. The abundances of these genes showed large spatial variations.dddPgenes showed more variation in abundances thandmdAgenes. Multidimensional analysis based on the abundances of DMSP degradation genes and environmental factors revealed that the distribution pattern of these genes was influenced by chlorophyllaconcentrations and temperatures.dddPgenes,dmdAsubclade C/2 genes, anddmdAsubclade D genes exhibited significant correlations with the marineRoseobacterclade, SAR11 subgroup Ib, and SAR11 subgroup Ia, respectively. SAR11 subgroups Ia and Ib, which possesseddmdAgenes, were suggested to be the main potential DMSP consumers. TheRoseobacterclade members possessingdddPgenes in oligotrophic subtropical regions were possible DMS producers. These results suggest that DMSP degradation genes are abundant and widely distributed in the surface seawater and that the marine bacteria possessing these genes influence the degradation of DMSP and regulate the emissions of DMS in subtropical gyres of the Pacific Ocean.

scholarly journals Microbial Communities of Orange Tubercles in Accelerated Low-Water Corrosion

2020 ◽  
Vol 86 (13) ◽  
Author(s):  
Hoang C. Phan ◽  
Scott A. Wade ◽  
Linda L. Blackall
Keyword(s):  
Microbial Communities ◽  
Steel Sheet ◽  
Localized Corrosion ◽  
16S Rrna Genes ◽  
Rrna Genes ◽  
Accelerated Corrosion ◽  
Content Type ◽  
Sulfate Reducing ◽  
Different Types ◽  
Different Levels

ABSTRACT The rapid degradation of marine infrastructure at the low tide level due to accelerated low-water corrosion (ALWC) is a problem encountered worldwide. Despite this, there is limited understanding of the microbial communities involved in this process. We obtained samples of the orange-colored tubercles commonly associated with ALWC from two different types of steel sheet piling, located adjacent to each other but with different levels of localized corrosion, at a seaside harbor. The microbial communities from the outer and inner layers of the orange tubercles and from adjacent seawater were studied by pure culture isolation and metabarcoding of the 16S rRNA genes. A collection of 119 bacterial isolates was obtained from one orange tubercle sample, using a range of media in anaerobic and aerobic conditions. The metabarcoding results showed that sulfur and iron oxidizers were more abundant on the outer sections of the orange tubercles compared to the inner layers, where Deltaproteobacteria (which include many sulfate reducers) were more abundant. The microbial communities varied significantly between the inner and outer layers of the orange tubercles and also with the seawater but overall did not differ significantly between the two steel sheet types. Hence, we saw similar microbial communities in orange tubercles present, but different levels of localized corrosion, for two different types of colocated steel sheet piling. Metallurgical analysis found differences in composition, grain size, ferrite-pearlite ratio, and the extent of inclusions present between the two steel types investigated. IMPORTANCE The presence of orange tubercles on marine steel pilings is often used as an indication that accelerated low-water corrosion is taking place. We studied the microbial communities in attached orange tubercles on two closely located sheet pilings that were of different steel types. The attached orange tubercles were visually similar, but the extents of underlying corrosion on the different steel surfaces were substantially different. No clear difference was found between the microbial communities present on the two different types of sheet piling. However, there were clear differences in the microbial communities in the corrosion layers of tubercles, which were also different from the microbes present in adjacent seawater. The overall results suggest that the presence of orange tubercles, a single measurement of water quality, or the detection of certain general types of microbes (e.g., sulfate-reducing bacteria) should not be taken alone as definitive indications of accelerated corrosion.

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