Rungroch Sungthong

Is it possible to increase bioavailability but not environmental risk of PAHs in bioremediation

The current poor predictability of end points associated with the bioremediation of polycyclic aromatic hydrocarbons (PAHs) is a large limitation when evaluating its viability for treating contaminated soils and sediments. However, we have seen a wide range of innovations in recent years, such as an the improved use of surfactants, the chemotactic mobilization of bacterial inoculants, the selective biostimulation at pollutant interfaces, rhizoremediation and electrobioremediation, which increase the bioavailability of PAHs but do not necessarily increase the risk to the environment. The integration of these strategies into practical remediation protocols would be beneficial to the bioremediation industry, as well as improve the quality of the environment.

Bioavailability of pollutants and chemotaxis

The exposure of bacteria to pollutants induces frequently chemoattraction or chemorepellent reactions. Recent research suggests that the capacity to degrade a toxic compound has co-evolved in some bacteria with the capacity to chemotactically react to it. There is an increasing amount of data which show that chemoattraction to biodegradable pollutants increases their bioavailability which translates into an enhancement of the biodegradation rate. Pollutant chemoreceptors so far identified are encoded on degradation or resistance plasmids. Genetic engineering of bacteria, such as the transfer of chemoreceptor genes, offers thus the possibility to optimize biodegradation processes.

Nonomuraea monospora sp. nov., an actinomycete isolated from cave soil in Thailand, and emended description of the genus Nonomuraea

A novel actinomycete, designated strain PT708(T), was isolated from cave soil collected in Pha Tup Cave Forest Park, Nan province, Thailand. It produced compounds with antimicrobial and anticancer activities. Its chemotaxonomic properties were consistent with those of members of the genus Nonomuraea. The major menaquinone was MK-9(H(4)), with minor amounts of MK-9(H(6)), MK-9(H(2)), MK-10(H(2)) and MK-8(H(4)). The polar lipid profile contained phosphatidylmonomethylethanolamine, diphosphatidylglycerol, hydroxy-phosphatidylmonomethylethanolamine, hydroxy-phosphatidylethanolamine, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylinositol mannoside and phosphatidylinositol. The major fatty acids were iso-C(16:0), 10-methyl C(17:0), C(16:0) and C(17:1)ω6c. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain PT708(T) belonged to the genus Nonomuraea and was most closely related to Nonomuraea rhizophila YIM 67092(T) (98.50% sequence similarity) and Nonomuraea rosea GW 12687(T) (98.30%). The genomic DNA G+C content of strain PT708(T) was 73.3 mol%. Unlike the recognized members of the genus Nonomuraea, the novel strain formed single spores at the tips of aerial hyphae. Based on the phenotypic, phylogenetic and genotypic evidence, strain PT708(T) represents a novel species of the genus Nonomuraea, for which the name Nonomuraea monospora sp. nov. is proposed. The type strain is PT708(T) ( = TISTR 1910(T) = JCM 16114(T)).

Emerging investigators series: microbial communities in full-scale drinking water distribution systems – a meta-analysis

In this study, we co-analyze all available 16S rRNA gene sequencing studies from bulk drinking water samples in full-scale drinking water distribution systems. Consistent with expectations, we find that Proteobacteria, particularly Alpha- and Betaproteobacteria, dominate drinking water bacterial communities irrespective of origin of study and presence/absence of or disinfectant residual type. Microbial communities in disinfectant residual free systems are more diverse than in those that maintain a disinfectant residual. Further, we find positive associations between mean relative abundance and occurrence of bacteria within a disinfectant category group. The relative abundance and occurrence of key bacterial genera (e.g. Legionella, Mycobacterium, Pseudomonas) is influenced by the presence/absence of a disinfectant residual and the type of disinfectant residual used. Similarly, we find widespread distribution of bacterial genera that are of interest from both an ecological and process perspectives (e.g. nitrification, predation). By estimating the contribution of potential contaminating genera to published drinking water datasets, we recommend that routine sequencing of negative controls be included in drinking water studies. Finally, we test the utility of predicting the metabolic potential of drinking water communities using 16S rRNA gene data and recommend against this practice. Though data heterogeneity across available datasets is a major confounding factor in our meta-analysis, we recommend that efforts to standardize sample processing protocols to address it may not be optimal for the drinking water microbial ecology field at this juncture. Rather, we recommend standardizing data and meta-data reporting, starting with making all sequencing data publicly available, and sample sharing as means of supporting future efforts for comparative analyses across drinking water systems/studies.

The genus Nonomuraea: A review of a rare actinomycete taxon for novel metabolites.

The genus Nonomuraea is a rare actinomycete taxon with a long taxonomic history, while its generic description was recently emended. The genus is less known among the rare actinomycete genera as its taxonomic position was revised several times. It can be found in diverse ecological niches, while most of its member species were isolated from soil samples. However, new trends to discover the genus in other habitats are increasing. Generic abundance of the genus was found to be dependent on geographical changes. Novel sources together with selective and invented isolation techniques might increase a chance to explore the genus and its novel candidates. Interestingly, some of its members have been revealed as a valuable source of novel metabolites for medical and industrial purposes. Broad‐range of potent bioactive compounds including antimicrobial, anticancer, and antipsychotic substances, broad‐spectrum antibiotics and biocatalysts can be synthesized by the genus. In order to investigate biosynthetic pathways of the bioactive compounds and self‐resistant mechanisms to these compounds, the links from genes to metabolites have yet been needed for further discovery and biotechnological development of the genus Nonomuraea.

Comparative study of endophytic and endophytic diazotrophic bacterial communities across rice landraces grown in the highlands of northern Thailand

AbstractCommunities of bacterial endophytes within the rice landraces cultivated in the highlands of northern Thailand were studied using fingerprinting data of 16S rRNA and nifH genes profiling by polymerase chain reaction–denaturing gradient gel electrophoresis. The bacterial communities’ richness, diversity index, evenness, and stability were varied depending on the plant tissues, stages of growth, and rice cultivars. These indices for the endophytic diazotrophic bacteria within the landrace rice Bue Wah Bo were significantly the lowest. The endophytic bacteria revealed greater diversity by cluster analysis with seven clusters compared to the endophytic diazotrophic bacteria (three clusters). Principal component analysis suggested that the endophytic bacteria showed that the community structures across the rice landraces had a higher stability than those of the endophytic diazotrophic bacteria. Uncultured bacteria were found dominantly in both bacterial communities, while higher generic varieties were observed in the endophytic diazotrophic bacterial community. These differences in bacterial communities might be influenced either by genetic variation in the rice landraces or the rice cultivation system, where the nitrogen input affects the endophytic diazotrophic bacterial community.

Untapped Endophytic Colonization and Plant Growth-Promoting Potential of the Genus Novosphingobium to Optimize Rice Cultivation

With the aim of searching for potent diazotrophic bacteria that are free of public health concerns and optimize rice cultivation, the endophytic colonization and plant growth-promoting activities of some endophytic diazotrophic bacteria isolated from rice were evaluated. Among these bacteria, the emerging diazotrophic strains of the genus Novosphingobium effectively associated with rice plant interiors and consequently promoted the growth of rice, even with the lack of a nitrogen source. These results suggest that diazotrophic Novosphingobium is an alternative microbial resource for further development as a safe biological enhancer in the optimization of organic rice cultivation.

Development of eukaryotic zoospores within polycyclic aromatic hydrocarbon (PAH)-polluted environments: A set of behaviors that are relevant for bioremediation

In this study, we assessed the development (formation, taxis and settlement) of eukaryotic zoospores under different regimes of exposure to polycyclic aromatic hydrocarbons (PAHs), which imitated environmental scenarios of pollution and bioremediation. With this aim, we used an oomycete, Pythium aphanidermatum, as a source of zoospores and two PAH-degrading bacteria (Mycobacterium gilvum VM552 and Pseudomonas putida G7). The oomycete and both bacteria were not antagonistic, and zoospore formation was diminished only in the presence of the highest bacterial cell density (10(8)-10(10) colony-forming units mL(-1)). A negative influence of PAHs on zoospore formation and taxis was observed when PAHs were exposed in combination with organic solutions and polar solvents. Co-exposure of PAHs with non-polar solvents [hexadecane (HD) and 2,2,4,4,6,8,8-heptamethylnonane (HMN)] did not affect zoospore settlement at the interfaces of the organic solvents and water. However, zoospores settled and created mycelial networks only at HD-water interfaces. Both bacteria diminished the toxic influence of PAHs on zoospore formation and taxis, and they did not interrupt zoospore settlement. The results suggest that zoospore development could be applicable for toxicity assessment of PAHs and enhancement of their bioavailability. Microbial interactions during both swimming modes and community formation at pollutant interfaces were revealed as major factors that have potential relevance to bioremediation.

Termite nests as an abundant source of cultivable actinobacteria for biotechnological purposes

A total of 118 actinobacterial isolates were collected from the three types of termite nests (mound, carton, and subterranean nests) to evaluate their potential as a source of bioactive actinobacteria with antimicrobial activity. The highest number (67 isolates) and generic abundance (7 known genera) of actinobacterial isolates were obtained from carton nests. Streptomyces was the dominant genus in each type of termite nest. In the non-Streptomyces group, Nocardia was the dominant genus detected in mound and carton nests, while Pseudonocardia was the dominant genus in subterranean nests. A discovery trend of novel species (<99% similarity in the 16S rRNA gene sequence) was also observed in the termite nests examined. Each type of termite nest housed >20% of bioactive actinobacteria that could inhibit the growth of at least one test organism, while 12 isolates, belonging to the genera Streptomyces, Amycolatopsis, Pseudonocardia, Micromonospora and Nocardia, exhibited distinct antimicrobial activities. Streptomyces sp. CMU-NKS-3 was the most distinct bioactive isolate. It was closely related to S. padanus MITKK-103T, which was confirmed by 99% similarities in their 16S rRNA gene sequences. The highest level of extracellular antimicrobial substances was produced by the isolate CMU-NKS-3, which was grown in potato dextrose broth and exhibited a wide range (6.10×10−4–1.25 mg mL−1) of minimum inhibitory concentrations against diverse pathogens. We concluded that termite nests are an abundant source of bioactive strains of cultivable actinobacteria for future biotechnological needs.

Mobilization of Pollutant-Degrading Bacteria by Eukaryotic Zoospores

The controlled mobilization of pollutant-degrading bacteria has been identified as a promising strategy for improving bioremediation performance. We tested the hypothesis whether the mobilization of bacterial degraders may be achieved by the action of eukaryotic zoospores. We evaluated zoospores that are produced by the soil oomycete Pythium aphanidermatum as a biological vector, and, respectively, the polycyclic aromatic hydrocarbon (PAH)-degrading bacteria Mycobacterium gilvum VM552 and Pseudomonas putida G7, acting as representative nonflagellated and flagellated species. The mobilization assay was performed with a chemical-in-capillary method, in which zoospores mobilized bacterial cells only when they were exposed to a zoospore homing inducer (5% (v/v) ethanol), which caused the tactic response and settlement of zoospores. The mobilization was strongly linked to a lack of bacterial motility, because the nonflagellated cells from strain M. gilvum VM552 and slightly motile, stationary-phase cells from P. putida G7 were mobilized effectively, but the actively motile, exponentially grown cells of P. putida G7 were not mobilized. The computer-assisted analysis of cell motility in mixed suspensions showed that the swimming rate was enhanced by zoospores in stationary, but not in exponentially grown, cells of P. putida G7. It is hypothesized that the directional swimming of zoospores caused bacterial mobilization through the thrust force of their flagellar propulsion. Our results suggest that, by mobilizing pollutant-degrading bacteria, zoospores can act as ecological amplifiers for fungal and oomycete mycelial networks in soils, extending their potential in bioremediation scenarios.