Marine Heterotrophic Bacteria Research Articles

Spontaneous mutations of a model heterotrophic marine bacterium.

Heterotrophic marine bacterioplankton populations display substantive genomic diversity that is commonly explained to be the result of selective forces imposed by resource limitation or interactions with phage and predators. Here we use a mutation-accumulation experiment followed by whole-genome sequencing of mutation lines to determine an unbiased rate and molecular spectrum of spontaneous mutations for a model heterotrophic marine bacterium in the globally important Roseobacter clade, Ruegeria pomeroyi DSS-3. We find evidence for mutational bias towards deletions over insertions, and this process alone could account for a sizable portion of genome size diversity among roseobacters and also implies that lateral gene transfer and/or selection must also play a role in maintaining roseobacters with large genome sizes. We also find evidence for a mutational bias in favor of changes from A/T to G/C nucleobases, which explains widespread occurrences of G/C-enriched Roseobacter genomes. Using the calculated mutation rate of 1.39 × 10-10 per base per generation, we implement a 'mutation-rate clock' approach to date the evolution of roseobacters by assuming a constant mutation rate along their evolutionary history. This approach gives an estimated date of Roseobacter genome expansion in good agreement with an earlier fossil-based estimate of ~250 million years ago and is consistent with a hypothesis of a correlated evolutionary history between roseobacters and marine eukaryotic phytoplankton groups.

Ingestion rate and grazing impact by the mixotrophic ciliate Mesodinium rubrum on natural populations of marine heterotrophic bacteria in the coastal waters of Korea

Ingestion rate and grazing impact by the mixotrophic ciliate Mesodinium rubrum on natural populations of marine heterotrophic bacteria in the coastal waters of Korea

Dimethylsulfoniopropionate biosynthesis in marine bacteria and identification of the key gene in this process.

Dimethylsulfoniopropionate (DMSP) is one of the Earth's most abundant organosulfur molecules, a signalling molecule1, a key nutrient for marine microorganisms2,3 and the major precursor for gaseous dimethyl sulfide (DMS). DMS, another infochemical in signalling pathways4, is important in global sulfur cycling2 and affects the Earth's albedo, and potentially climate, via sulfate aerosol and cloud condensation nuclei production5,6. It was thought that only eukaryotes produce significant amounts of DMSP7-9, but here we demonstrate that many marine heterotrophic bacteria also produce DMSP, probably using the same methionine (Met) transamination pathway as macroalgae and phytoplankton10. We identify the first DMSP synthesis gene in any organism, dsyB, which encodes the key methyltransferase enzyme of this pathway and is a reliable reporter for bacterial DMSP synthesis in marine Alphaproteobacteria. DMSP production and dsyB transcription are upregulated by increased salinity, nitrogen limitation and lower temperatures in our model DMSP-producing bacterium Labrenzia aggregata LZB033. With significant numbers of dsyB homologues in marine metagenomes, we propose that bacteria probably make a significant contribution to oceanic DMSP production. Furthermore, because DMSP production is not solely associated with obligate phototrophs, the process need not be confined to the photic zones of marine environments and, as such, may have been underestimated.

Synthesis of arborane triterpenols by a bacterial oxidosqualene cyclase

Cyclic triterpenoids are a broad class of polycyclic lipids produced by bacteria and eukaryotes. They are biologically relevant for their roles in cellular physiology, including membrane structure and function, and biochemically relevant for their exquisite enzymatic cyclization mechanism. Cyclic triterpenoids are also geobiologically significant as they are readily preserved in sediments and are used as biomarkers for ancient life throughout Earth's history. Isoarborinol is one such triterpenoid whose only known biological sources are certain angiosperms and whose diagenetic derivatives (arboranes) are often used as indicators of terrestrial input into aquatic environments. However, the occurrence of arborane biomarkers in Permian and Triassic sediments, which predates the accepted origin of angiosperms, suggests that microbial sources of these lipids may also exist. In this study, we identify two isoarborinol-like lipids, eudoraenol and adriaticol, produced by the aerobic marine heterotrophic bacterium Eudoraea adriatica Phylogenetic analysis demonstrates that the E. adriatica eudoraenol synthase is an oxidosqualene cyclase homologous to bacterial lanosterol synthases and distinct from plant triterpenoid synthases. Using an Escherichia coli heterologous sterol expression system, we demonstrate that substitution of four amino acid residues in a bacterial lanosterol synthase enabled synthesis of pentacyclic arborinols in addition to tetracyclic sterols. This variant provides valuable mechanistic insight into triterpenoid synthesis and reveals diagnostic amino acid residues to differentiate between sterol and arborinol synthases in genomic and metagenomic datasets. Our data suggest that there may be additional bacterial arborinol producers in marine and freshwater environments that could expand our understanding of these geologically informative lipids.

Habitat and taxon as driving forces of carbohydrate catabolism in marine heterotrophic bacteria: example of the model algae-associated bacterium Zobellia galactanivorans DsijT.

The marine flavobacterium Zobellia galactanivorans DsijT was isolated from a red alga and by now constitutes a model for studying algal polysaccharide bioconversions. We present an in-depth analysis of its complete genome and link it to physiological traits. Z. galactanivorans exhibited the highest gene numbers for glycoside hydrolases, polysaccharide lyases and carbohydrate esterases and the second highest sulfatase gene number in a comparison to 125 other marine heterotrophic bacteria (MHB) genomes. Its genome contains 50 polysaccharide utilization loci, 22 of which contain sulfatase genes. Catabolic profiling confirmed a pronounced capacity for using algal polysaccharides and degradation of most polysaccharides could be linked to dedicated genes. Physiological and biochemical tests revealed that Z. galactanivorans stores and recycles glycogen, despite loss of several classic glycogen-related genes. Similar gene losses were observed in most Flavobacteriia, suggesting presence of an atypical glycogen metabolism in this class. Z. galactanivorans features numerous adaptive traits for algae-associated life, such as consumption of seaweed exudates, iodine metabolism and methylotrophy, indicating that this bacterium is well equipped to form profitable, stable interactions with macroalgae. Finally, using statistical and clustering analyses of the MHB genomes we show that their carbohydrate catabolism correlates with both taxonomy and habitat.

A Decadal (2002–2014) Analysis for Dynamics of Heterotrophic Bacteria in an Antarctic Coastal Ecosystem: Variability and Physical and Biogeochemical Forcings

We investigated the dynamics of heterotrophic bacteria in the coastal western Antarctic Peninsula (WAP), using decadal (2002-2014) time series of two bacterial variables, bacterial production (BP) via 3H-leucine incorporation rates and bacterial biomass (BB) via bacterial abundance, collected at Palmer Antarctica Long Term Ecological Research (LTER) Station B (64.8°S, 64.1°W) over a full austral growing season (October-March). Strong seasonal and interannual variability in the degree of bacterial coupling with phytoplankton processes were observed with varying lags. On average, BP was only 4% of primary production (PP), consistent with low BP:PP ratios observed in polar waters. BP was more strongly correlated with chlorophyll (Chl), than with PP, implying that bacteria feed on DOC produced from a variety of trophic levels (e.g. zooplankton sloppy feeding and excretion) as well as directly on phytoplankton-derived DOC. The degree of bottom-up control on bacterial abundance was moderate and relatively consistent across entire growing seasons, suggesting that bacteria in the coastal WAP are under consistent DOC limitation. Temperature also influenced BP rates, though its effect was weaker than DOC. We established generalized linear models (GLMs) for monthly composites of BP and BB via stepwise regression to explore a set of physical and biogeochemical predictors. Physically, high BP and large BB were shaped by a stratified water-column, similar to forcing mechanisms favoring phytoplankton blooms, but high sea surface temperature (SST) also significantly promoted bacterial processes. High BP and large BB were influenced by high PP and bulk DOC concentrations. Based on these findings, we suggest an increasingly important role of marine heterotrophic bacteria in the coastal WAP food-web as climate change introduces a more favorable environmental setting for promoting BP, with increased DOC from retreating glaciers, a more stabilized upper water-column from ice-melt, and a baseline shift of water temperature due to more frequent delivery of warming Upper Circumpolar Deep Water (UCDW) onto the WAP shelf.

Experimental evidence that clay inhibits bacterial decomposers: Implications for preservation of organic fossils

Abstract Exceptionally preserved organic fossils are commonly associated with clay-rich horizons or directly with clay minerals. It has been posited that interactions between clay minerals and organic tissues inhibit enzymatic reactions or protect carcasses in such a way that decay is impeded. However, interactions between clay minerals and the biological agents of decay, especially bacteria, may be at least as important to preservation potential. Here we show that clays of particle size <2 μm in suspensions exceeding 10 mg/ml in concentration inhibit the growth of Pseudoalteromonas luteoviolacea, a marine heterotrophic bacterium involved in the decay of marine animals. Such clay-microbe interactions can contribute to exceptional preservation, and specific examples may play a role in shaping the distribution of Konservat-Lagerstätten through time.

Metagenomics unveils the attributes of the alginolytic guilds of sediments from four distant cold coastal environments.

Alginates are abundant polysaccharides in brown algae that constitute an important energy source for marine heterotrophic bacteria. Despite the key role of alginate degradation processes in the marine carbon cycle, little information is available on the bacterial populations involved in these processes. The aim of this work was to gain a better understanding of alginate utilization capabilities in cold coastal environments. Sediment metagenomes from four high-latitude regions of both Hemispheres were interrogated for alginate lyase gene homologue sequences and their genomic context. Sediments contained highly abundant and diverse bacterial assemblages with alginolytic potential, including members of Bacteroidetes and Proteobacteria, as well as several poorly characterized taxa. The microbial communities in Arctic and Antarctic sediments exhibited the most similar alginolytic profiles, whereas brackish sediments showed distinct structures with a higher proportion of novel genes. Examination of the gene neighbourhood of the alginate lyase homologues revealed distinct patterns depending on the potential lineage of the scaffolds, with evidence of evolutionary relationships among alginolytic gene clusters from Bacteroidetes and Proteobacteria. This information is relevant for understanding carbon fluxes in cold coastal environments and provides valuable information for the development of biotechnological applications from brown algae biomass.

A mechanism for bacterial transformation of dimethylsulfide to dimethylsulfoxide: a missing link in the marine organic sulfur cycle.

The volatile organosulfur compound, dimethylsulfide (DMS), plays an important role in climate regulation and global sulfur biogeochemical cycles. Microbial oxidation of DMS to dimethylsulfoxide (DMSO) represents a major sink of DMS in surface seawater, yet the underlying molecular mechanisms and key microbial taxa involved are not known. Here, we reveal that Ruegeria pomeroyi, a model marine heterotrophic bacterium, can oxidize DMS to DMSO using trimethylamine monooxygenase (Tmm). Purified Tmm oxidizes DMS to DMSO at a 1:1 ratio. Mutagenesis of the tmm gene in R. pomeroyi completely abolished DMS oxidation and subsequent DMSO formation. Expression of Tmm and DMS oxidation in R. pomeroyi is methylamine-dependent and regulated at the post-transcriptional level. Considering that Tmm is present in approximately 20% of bacterial cells inhabiting marine surface waters, particularly the marine Roseobacter clade and the SAR11 clade, our observations contribute to a mechanistic understanding of biological DMSO production in surface seawater.

Colwellia psychrerythraea Strains from Distant Deep Sea Basins Show Adaptation to Local Conditions

Many studies have shown that microbes, which share nearly identical 16S rRNA genes, can have highly divergent genomes. Microbes from distinct parts of the ocean also exhibit biogeographic patterning. Here we seek to better understand how certain microbes from the same species have adapted for growth under local conditions. The phenotypic and genomic heterogeneity of three strains of Colwellia psychrerythraea was investigated in order to understand adaptions to local environments. Colwellia are psychrophilic heterotrophic marine bacteria ubiquitous in cold marine ecosystems. We have recently isolated two Colwellia strains: ND2E from the Eastern Mediterranean and GAB14E from the Great Australian Bight. The 16S rRNA sequence of these two strains were greater than 98.2% identical to the well-characterized C. psychrerythraea 34H, which was isolated from arctic sediments. Salt tolerance, and carbon source utilization profiles for these strains were determined using Biolog Phenotype Microarrays’. These strains exhibited distinct salt tolerance, which was not associated with the salinity of sites of isolation. The carbon source utilization profiles were distinct with less than half of the tested carbon sources being metabolized by all three strains. Whole genome sequencing revealed that the genomes of these three strains were quite diverse with some genomes having up to 1600 strain-specific genes. Many genes involved in degrading strain-specific carbon sources were identified. There appears to be a link between carbon source utilization and location of isolation with distinctions observed between the Colwellia isolate recovered from sediment compared to water column isolates.

Desempenho de alevinos de Centropomus parallelus alimentados com dietas suplementadas com citrato e acetato

This study aimed to evaluate the addition of sodium acetate and sodium citrate in the diets of fingerling fat snook (Centropomusparallelus), through growth performance and modification of the intestinal microbiota. In the experiment, 3,000 fat snook fingerlings were used, with an initial average weight of 0.57 ± 0.10 g. The fish were stocked into 12 tanks (50 L) at a density of 5 fingerlings L-1 per tank distributed in three treatments with four replicates. The treatments were as follows: control group (without supplementation), one group supplemented with sodium acetate, and another group supplemented with sodium citrate. The diets supplemented with organic salts were sprayed with cod liver oil previously homogenized with 3% sodium acetate or sodium citrate. The fish supplemented with sodium acetate showed higher final weight, length, and yield, compared with the control group fish. The intestine of fingerling fat snook showed lower counts of total heterotrophic marine bacteria in the fish supplemented with acetate and citrate in relation to fish of the control group. Lower counts of sucrose non-fermenting vibrios were also observed in fish supplemented with acetate. Through this study, it was possible to evaluate for the first time the dietary inclusion of organic salts in the diets of marine fish in Brazil, with the dietary inclusion of 3% sodium acetate showing benefits for performance of fingerling fat snook.

Experimental Identification of Small Non-Coding RNAs in the Model Marine Bacterium Ruegeria pomeroyi DSS-3.

In oligotrophic ocean waters where bacteria are often subjected to chronic nutrient limitation, community transcriptome sequencing has pointed to the presence of highly abundant small RNAs (sRNAs). The role of sRNAs in regulating response to nutrient stress was investigated in a model heterotrophic marine bacterium Ruegeria pomeroyi grown in continuous culture under carbon (C) and nitrogen (N) limitation. RNAseq analysis identified 99 putative sRNAs. Sixty-nine were cis-encoded and located antisense to a presumed target gene. Thirty were trans-encoded and initial target prediction was performed computationally. The most prevalent functional roles of genes anti-sense to the cis-sRNAs were transport, cell-cell interactions, signal transduction, and transcriptional regulation. Most sRNAs were transcribed equally under both C and N limitation, and may be involved in a general stress response. However, 14 were regulated differentially between the C and N treatments and may respond to specific nutrient limitations. A network analysis of the predicted target genes of the R. pomeroyi cis-sRNAs indicated that they average fewer connections than typical protein-encoding genes, and appear to be more important in peripheral or niche-defining functions encoded in the pan genome.

Beneficial effects of carpet shell clam (Ruditapes decussatus) depuration during short periods of conditioning in shellfish hatchery: Role of the temperature and phytoplankton on reduction and diversity of vibrios

Broodstock conditioning in hatcheries is the step previous to spawning and its optimization may be a key to the success of larval cultures. Cleaning and brushing of the broodstock and the utilization of antibiotics to reduce their vibrios load are used regularly as routine prophylactic measures prior to spawning induction. The development of protocols to reduce these bacteria using cheap and harmless techniques is of utmost importance for commercial bivalve production in hatcheries. With this aim, we have evaluated initially different conditionings (A–D) during short periods (a total of four weeks): first two weeks under gradient temperature (increasing +0.3°Cday−1 from 14.5°C to 20°C), without (A) or with phytoplankton (B), and constant temperature (20°C) without (C) or with phytoplankton (D). Afterwards, all conditionings were kept at 20°C and fed for two more weeks. Furthermore, broodstock optimal feeding time was re-evaluated during a second trial series. In all conditionings, bacterial loads were determined in terms of marine heterotrophic bacteria (MHB) and presumptive vibrios (PV). Broodstock under the optimal short period of conditioning (conditioning C) obtained the best gonadal development and a significant reduction in PV load at a lower expense. A total of 61 PV were isolated from all conditionings and identified by sequencing the 16S rRNA gene. Splendidus clade was dominant in the samples coming from natural beds. Diversity of vibrios changed throughout the conditionings in the hatchery favoured by exogenous factors whose effect was mainly observed at the end of the trials: Splendidus clade was also dominant in the broodstock conditioned at gradient temperature and Mediterranei and Harveyi clades were prevalent at constant temperature. Moreover, the percentage of transformation to D-larvae was estimated and the vertical transmission of vibrios from broodstock to eggs and D-larvae was suggested. Implementation of conditioning C reduces considerably the Vibrio load of clams without using antibiotics, and thus it represents a novel, cheap, environmental friendly and harmless methodology that can be easily transferred to commercial hatchery. Statement of relevanceRoutine prophylactic measures for bivalve broodstock arriving hatchery facilities include its cleaning/brushing and the frequent use of antibiotics to reduce its bacterial load, particularly Vibrio, as step previous to spawning induction. The depuration protocol proposed reduces significantly Vibrio load without using antibiotics and represents a novel, cheap, environmental friendly and harmless methodology that can be easily transferred to commercial hatcheries.

Why Close a Bacterial Genome? The Plasmid of Alteromonas Macleodii HOT1A3 is a Vector for Inter-Specific Transfer of a Flexible Genomic Island.

Genome sequencing is rapidly becoming a staple technique in environmental and clinical microbiology, yet computational challenges still remain, leading to many draft genomes which are typically fragmented into many contigs. We sequenced and completely assembled the genome of a marine heterotrophic bacterium, Alteromonas macleodii HOT1A3, and compared its full genome to several draft genomes obtained using different reference-based and de novo methods. In general, the de novo assemblies clearly outperformed the reference-based or hybrid ones, covering >99% of the genes and representing essentially all of the gene functions. However, only the fully closed genome (∼4.5 Mbp) allowed us to identify the presence of a large, 148 kbp plasmid, pAM1A3. While HOT1A3 belongs to A. macleodii, typically found in surface waters (“surface ecotype”), this plasmid consists of an almost complete flexible genomic island (fGI), containing many genes involved in metal resistance previously identified in the genomes of Alteromonas mediterranea (“deep ecotype”). Indeed, similar to A. mediterranea, A. macleodii HOT1A3 grows at concentrations of zinc, mercury, and copper that are inhibitory for other A. macleodii strains. The presence of a plasmid encoding almost an entire fGI suggests that wholesale genomic exchange between heterotrophic marine bacteria belonging to related but ecologically different populations is not uncommon.

Performance of Centropomus parallelus fingerlings fed a diet supplemented with citrate and acetate

This study aimed to evaluate the addition of sodium acetate and sodium citrate in the diets of fingerling fat snook (Centropomus parallelus), through growth performance and modification of the intestinal microbiota. In the experiment, 3,000 fat snook fingerlings were used, with an initial average weight of 0.57 ± 0.10 g. The fish were stocked into 12 tanks (50 L) at a density of 5 fingerlings L-1 per tank distributed in three treatments with four replicates. The treatments were as follows: control group (without supplementation), one group supplemented with sodium acetate, and another group supplemented with sodium citrate. The diets supplemented with organic salts were sprayed with cod liver oil previously homogenized with 3% sodium acetate or sodium citrate. The fish supplemented with sodium acetate showed higher final weight, length, and yield, compared with the control group fish. The intestine of fingerling fat snook showed lower counts of total heterotrophic marine bacteria in the fish supplemented with acetate and citrate in relation to fish of the control group. Lower counts of sucrose non-fermenting vibrios were also observed in fish supplemented with acetate. Through this study, it was possible to evaluate for the first time the dietary inclusion of organic salts in the diets of marine fish in Brazil, with the dietary inclusion of 3% sodium acetate showing benefits for performance of fingerling fat snook.

Evidence for quorum sensing and differential metabolite production by a marine bacterium in response to DMSP.

Microbes, the foundation of the marine foodweb, do not function in isolation, but rather rely on molecular level interactions among species to thrive. Although certain types of interactions between autotrophic and heterotrophic microorganisms have been well documented, the role of specific organic molecules in regulating inter-species relationships and supporting growth are only beginning to be understood. Here, we examine one such interaction by characterizing the metabolic response of a heterotrophic marine bacterium, Ruegeria pomeroyi DSS-3, to growth on dimethylsulfoniopropionate (DMSP), an abundant organosulfur metabolite produced by phytoplankton. When cultivated on DMSP, R. pomeroyi synthesized a quorum-sensing molecule, N-(3-oxotetradecanoyl)-l-homoserine lactone, at significantly higher levels than during growth on propionate. Concomitant with the production of a quorum-sensing molecule, we observed differential production of intra- and extracellular metabolites including glutamine, vitamin B2 and biosynthetic intermediates of cyclic amino acids. Our metabolomics data indicate that R. pomeroyi changes regulation of its biochemical pathways in a manner that is adaptive for a cooperative lifestyle in the presence of DMSP, in anticipation of phytoplankton-derived nutrients and higher microbial density. This behavior is likely to occur on sinking marine particles, indicating that this response may impact the fate of organic matter.

Bacterial pollution, activity and heterotrophic diversity of the northern part of the Aegean Sea, Turkey.

Isolation and characterization studies of marine heterotrophic bacteria are important to describe and understand eco-metobolism of the marine environments. In this study, diversity and community structures of the culturable heterotrophic bacteria, metabollicaly active bacteria and bacterial pollution in the coastal and offshore areas of Gökçeada Island, in the Northern Aegean Sea, Turkey were investigated from March 2012 to November 2013. The primary hydrographic parameters were recorded in situ. The frequency of the metabolically active bacteria was determined by using a modified staining technique. The indicator bacteria were determined by using membrane filtration technique; 126 bacteria isolates, 24 of them first records for this region, were identified using an automated micro-identification system, VITEK2 Compact30. The results showed that detected bacterial community profiles were significantly different when compared with previous studies conducted in polluted marine areas of Turkey. High frequency of faecal bacteria detected at station 2 indicated that increasing human activities and terrestrial pollution sources are shaping factors for possible risks, regarding recreational uses of this region, in the summer seasons.

海水中天然细菌对不同生源要素有机物的矿化作用

PDF HTML阅读 XML下载 导出引用 引用提醒 海水中天然细菌对不同生源要素有机物的矿化作用 DOI: 10.5846/stxb201408291720 作者: 作者单位: 中国海洋大学化学化工学院,中国海洋大学海洋生命学院,美国加州大学圣芭芭拉分校海洋科学系,加州 圣芭芭拉 CA-,中国海洋大学化学化工学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家海洋局海洋生态环境科学与工程重点实验室开放基金(MESE-2014-03) Mineralization of different dissolved organic matter containing various biogenic elements by natural bacteria in seawater Author: Affiliation: College of Chemistry and Chemical Engineering,Ocean University of China,College of Marine Life Sciences,Ocean University of China,Marine Science Institute,University of California,Santa Barbara,California ,USA,College of Chemistry and Chemical Engineering,Ocean University of China Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:海洋异养细菌是微食物网中非常重要的一部分,它消耗海洋中的溶解有机物并进行细菌的二次生产。细菌对不同种类的溶解有机物分解速率不同,并且有机物的生物利用率影响细菌的生长。研究了含有不同生源要素的4种溶解有机物(DOM)在海洋异养细菌存在下的矿化作用及对细菌生长的影响。结果表明:添加不同生源要素的有机物,对海洋天然异养细菌的生长均有促进作用,其比生长速率(μ)的大小顺序为:N > C > P > S > 对照组,说明含氮有机物更有助于细菌的生长;细菌生长效率(BGE)的大小顺序为:对照组 > C > P > N > S,说明细菌的二次生产跟有机物的分解速率没有直接相关性;单个细菌对有机物的消耗速率I为:N > C >P > S > 对照组,说明细菌生长速率与有机物消耗速率直接相关;有机物的生物可利用性顺序为:N > C > P > S > 对照组,与有机物的消耗速率顺序一致。上述结果表明,具有相同结构但不同生源要素的有机物的矿化速率存在差异,含氮有机物最容易分解,其次是含碳有机物,然后是含磷有机物,含硫有机物分解最慢,说明细菌对含有不同生源要素有机物的分解利用存在差异。 Abstract:Heterotrophic bacteria in seawater play an important role in biogeochemical cycling of biogenic elements. The decomposition rate of different dissolved organic matter (DOM) is related to the amount of heterotrophic bacteria, and the biological utilization ratio of DOM influences the growth of bacteria. In this study, mineralization and the effect of four kinds of DOM with similar structure but different biogenic elements on bacterial growth were investigated. The results suggested that organic matter added to cultures promoted the growth of natural marine heterotrophic bacteria, and the order of specific growth rate (μ) was as follows: N > C > P > S > control. DOM with nitrogen and carbon was the most effective in accelerating the growth of bacteria. The order of bacterial growth efficiency was as follows: Control > C > P > N > S; these results indicated that bacterial secondary production has no direct correlation with the decomposition rate of organic matter. The consumption rate of organic matter per individual bacterium (I) was in the following order: N > C > P > S > control, which was the same for biological availability of different organic matter. These results suggested that the mineralization rate is different for various organic matters having similar structure but different biogenic elements. The organic matter with nitrogen was decomposed most easily, followed by carbonaceous organic matter and organic phosphorus, but organic sulfur remained somewhat refractory to decomposition. 参考文献 相似文献 引证文献

Nitrate assimilation by marine heterotrophic bacteria

Nitrate assimilation is a process where bacteria utilize nitrate as a nitrogen source and synthesize it into organic nitrogen. We found that nitrate-assimilating bacteria (NAB) are widely distributed in various marine environments, from surface to the deep ocean and sediment, which indicates that NAB are significant to the oceanic nitrogen cycle. Comparative genomic analysis revealed nitrate-assimilating genes (nasA) in these marine heterotrophic NAB showed different gene arrangements and diverse regulation systems. Summary on recent findings will contribute to understanding the process of nitrate assimilation in NAB and their ecological significance in the nitrogen cycle. A systematic analysis of a number of studies on bacterial nitrate assimilation in marine ecological systems was conducted to clarify directions for future research.

Lipid remodelling is a widespread strategy in marine heterotrophic bacteria upon phosphorus deficiency.

Upon phosphorus (P) deficiency, marine phytoplankton reduce their requirements for P by replacing membrane phospholipids with alternative non-phosphorus lipids. It was very recently demonstrated that a SAR11 isolate also shares this capability when phosphate starved in culture. Yet, the extent to which this process occurs in other marine heterotrophic bacteria and in the natural environment is unknown. Here, we demonstrate that the substitution of membrane phospholipids for a variety of non-phosphorus lipids is a conserved response to P deficiency among phylogenetically diverse marine heterotrophic bacteria, including members of the Alphaproteobacteria and Flavobacteria. By deletion mutagenesis and complementation in the model marine bacterium Phaeobacter sp. MED193 and heterologous expression in recombinant Escherichia coli, we confirm the roles of a phospholipase C (PlcP) and a glycosyltransferase in lipid remodelling. Analyses of the Global Ocean Sampling and Tara Oceans metagenome data sets demonstrate that PlcP is particularly abundant in areas characterized by low phosphate concentrations. Furthermore, we show that lipid remodelling occurs seasonally and responds to changing nutrient conditions in natural microbial communities from the Mediterranean Sea. Together, our results point to the key role of lipid substitution as an adaptive strategy enabling heterotrophic bacteria to thrive in the vast P-depleted areas of the ocean.