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Lemnaceae plants, commonly referred to as duckweeds, are small planktonic terrestrial freshwater plants that live in symbiosis with various microbial communities. These plants are model platforms for the study of host-microbe interactions (Yamakawa et al. 2018). Azotobacter vinelandii are typical free-living nitrogen fixing soil bacteria that indirectly benefit plants by providing nitrogen compounds. In this study, Lemna minor RDSC 5512 and A. vinelandii ATCC 12837 = NBRC 13581 were co-cultured under gnotobiotic conditions. The growth of L. minor colonized by A. vinelandii accelerated in both nitrogen-containing and nitrogen-free water conditions. Moreover, L. minor elevated the nitrogen fixing activity of A. vinelandii. Lastly, the cell number of A. vinelandii on L. minor increased continuously over 30 d. These observations indicated that L. minor provides a favorable environment for A. vinelandii colonization, allowing them to mutually benefit and flourish through syntrophism.

Duckweeds (Lemnaceae) are representative producers in fresh aquatic ecosystems and also yield sustainable biomass for animal feeds, human foods, and biofuels, and contribute toward effective wastewater treatment; thus, enhancing duckweed productivity is a critical challenge. Plant-growth-promoting bacteria (PGPB) can improve the productivity of terrestrial plants; however, duckweed–PGPB interactions remain unclear and no previous study has investigated the molecular mechanisms underlying duckweed–PGPB interaction. Herein, a PGPB, Ensifer sp. strain SP4, was newly isolated from giant duckweed (Spirodela polyrhiza), and the interactions between S. polyrhiza and SP4 were investigated through physiological, biochemical, and metabolomic analyses. In S. polyrhiza and SP4 coculture, SP4 increased the nitrogen (N), chlorophyll, and ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) contents and the photosynthesis rate of S. polyrhiza by 2.5-, 2.5-, 2.7-, and 2.4-fold, respectively. Elevated photosynthesis increased the relative growth rate and biomass productivity of S. polyrhiza by 1.5- and 2.7-fold, respectively. Strain SP4 significantly altered the metabolomic profile of S. polyrhiza, especially its amino acid profile. N stable isotope analysis revealed that organic N compounds were transferred from SP4 to S. polyrhiza. These N compounds, particularly glutamic acid, possibly triggered the increase in photosynthetic and growth activities. Accordingly, we propose a new model for the molecular mechanism underlying S. polyrhiza growth promotion by its associated bacteria Ensifer sp. SP4, which occurs through enhanced N compound metabolism and photosynthesis. Our findings show that Ensifer sp. SP4 is a promising PGPB for increasing biomass yield, wastewater purification activity, and CO2 capture of S. polyrhiza. [Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Salinity (NaCl) stress treatment is a strategy to induce lipid accumulation in microalgae. This study aimed to investigate the effect of a combination of two salts (NaCl/CaCl2) on lipid productivity of Chlamydomonas reinhardtii. C. reinhardtii was cultured in a two-stage culture comprising 9-day active growth in C medium followed by 3-day salt stress in C medium with various concentrations of NaCl (50‒200 mM)/CaCl2 (100 mM). In salt stress stage, NaCl (200 mM), CaCl2 (100 mM), and the NaCl/CaCl2 mixture inhibited growth but increased the lipid content in C. reinhardtii in comparison with NaCl (0, 50, and 100 mM) conditions. Combinatorial treatment with 100 mM NaCl/100 mM CaCl2 resulted in the highest lipid content (73.4%) and lipid productivity (10.9 mg/L/days), being 3.5- and 2.1-fold, respectively, in salt-free control conditions, and 1.8- and 1.5-folds, respectively, with 200 mM NaCl. Furthermore, 100 mM NaCl/100 mM CaCl2 treatment markedly upregulated glycerol-3-phosphate dehydrogenase (GPDH), lysophosphatidic acid acyltransferase (LPAAT), and diacylglycerol acyltransferase (DAGAT), which are involved in lipid accumulation in C. reinhardtii. The upregulation of these genes with 100 mM NaCl/100 mM CaCl2 resulted in the highest lipid content in C. reinhardtii. Therefore, stress treatment using two salts, 100 mM NaCl/100 mM CaCl2, is a potentially promising strategy to enhance lipid productivity in microalgae.

Aureobasidium pullulans YTP6-14 was demonstrated to be an excellent multiple biosurfactant producer utilizing cheap carbon sources available in Thailand, including glycerol and cassava flour hydrolysate. A. pullulans YTP6-14 maximally produced 1.81 g/l biosurfactant in an aqueous layer (BS-AQ) in a medium containing glycerol, and 7.37 or 6.37 g/l biosurfactant in a heavy oil layer (BS-HO) in cassava flour hydrolysate or a glucose containing medium, respectively. Each BS-AQ and BS-HO had critical micelle concentration values of 41.32 mg/l and 13.51 mg/l, and both biosurfactants formed a stable food oil emulsion and reduced the amount of biofilms formed by Streptococcus sobrinus and Streptococcus mutans. BS-AQ and BS-HO were mainly composed of liamocins or exophilins and massoia lactone, respectively.

We report a complete genome sequence of a novel bacterial isolate, strain TBR-22, belonging to the class

Here, we report a draft genome sequence of a bacterial strain, F-183, isolated from a duckweed frond. Strain F-183 belongs to the family Bryobacteraceae of the phylum Acidobacteria , and its genomic information would contribute to understanding the ecophysiology of this abundant but rarely characterized phylum.

Duckweeds (Lemnaceae) are representative producers in fresh aquatic ecosystems and also yield sustainable biomass for animal feeds, human foods, and biofuels, and contribute toward effective wastewater treatment; thus, enhancing duckweed productivity is a critical challenge. Plant-growth-promoting bacteria (PGPB) can improve the productivity of terrestrial plants; however, duckweed-PGPB interactions remain unclear and no previous study has investigated the molecular mechanisms underlying duckweed-PGPB interaction. Herein, a PGPB

BackgroundEuglena gracilis, a unicellular flagellated microalga, is regarded as one of the most promising species as microalgal feedstock for biofuels. Its lipids (mainly wax esters) are suitable for biodiesel and jet fuel. Culture ofE. gracilisusing wastewater effluent will improve the economics ofE. gracilisbiofuel production. Enhancement of the productivity ofE. gracilisbiomass is critical to creating a highly efficient biofuels production system. Certain bacteria have been found to promote microalgal growth by creating a favorable microenvironment. These bacteria have been characterized as microalgae growth-promoting bacteria (MGPB). Co-culture of microalgae with MGPB might offer an effective strategy to enhance microalgal biomass production in wastewater effluent culture systems. However, no MGPB has been identified to enhance the growth ofE. gracilis. The objectives of this study were, therefore, to isolate and characterize the MGPB effective forE. gracilisand to demonstrate that the isolated MGPB indeed enhances the production of biomass and lipids byE. gracilisin wastewater effluent culture system.ResultsA bacterium,Emticiciasp. EG3, which is capable of promoting the growth of microalgaE. gracilis, was isolated from anE. gracilis-municipal wastewater effluent culture. Biomass production rate ofE. graciliswas enhanced 3.5-fold and 3.1-fold by EG3 in the co-culture system using a medium of heat-sterilized and non-sterilized wastewater effluent, respectively, compared to growth in the same effluent culture but without EG3. Two-step culture system was examined as follows:E. graciliswas cultured with or without EG3 in wastewater effluent in the first step and was further grown in wastewater effluent in the second step. Production yields of biomass and lipids byE. graciliswere enhanced 3.2-fold and 2.9-fold, respectively, in the second step of the system in whichE. graciliswas co-cultured with EG3 in the first step.ConclusionEmticiciasp. EG3 is the first MGPB forE. gracilis. Growth-promoting bacteria such as EG3 will be promising agents for enhancingE. gracilisbiomass/biofuel productivities.

Despite the considerable role of aquatic plant-associated bacteria in host plant growth and nutrient cycling in aquatic environments, the mode of their plant colonization has hardly been understood. This study examined the colonization and competition dynamics of a plant growth-promoting bacterium (PGPB) and two plant growth-inhibiting bacteria (PGIB) in the aquatic plant Lemna minor (common duckweed). When inoculated separately to L. minor, each bacterial strain quickly colonized at approximately 106 cells per milligram (plant fresh weight) and kept similar populations throughout the 7-day cultivation time. The results of two-membered co-inoculation assays revealed that the PGPB strain Aquitalea magnusonii H3 consistently competitively excluded the PGIB strain Acinetobacter ursingii M3, and strain H3 co-existed at almost 1:1 proportion with another PGIB strain, Asticcacaulis excentricus M6, regardless of the inoculation ratios (99:1-1:99) and inoculation order. We also found that A. magnusonii H3 exerted its growth-promoting effect over the negative effects of the two PGIB strains even when only a small amount was inoculated, probably due to its excellent competitive colonization ability. These experimental results demonstrate that there is a constant ecological equilibrium state involved in the bacterial colonization of aquatic plants.

Heat shock protein 90 (Hsp90) is essential for eukaryotic cells, whereas bacterial homologs play a role under stresses and in pathogenesis. Identifying species-specific Hsp90 inhibitors is challenging because Hsp90 is evolutionarily conserved. We found that a cyclic lipopeptide surfactin inhibits the ATPase activity of Hsp90 from the cyanobacterium Synechococcus elongatus (S.elongatus) PCC 7942 but does not inhibit Escherichia coli (E.coli), yeast and human Hsp90s. Molecular docking simulations indicated that surfactin could bind to the N-terminal dimerization interface of the cyanobacterial Hsp90 in the ATP- and ADP-bound states, which provided molecular insights into the species-selective inhibition. The data suggest that surfactin inhibits a rate-limiting conformational change of S.elongatus Hsp90 in the ATP hydrolysis. Surfactin also inhibited the interaction of the cyanobacterial Hsp90 with a model substrate, and suppressed S.elongatus growth under heat stress, but not that of E.coli. Surfactin did not show significant cellular toxicity towards mammalian cells. These results indicate that surfactin inhibits the cellular function of Hsp90 specifically in the cyanobacterium. The present study shows that a cyclic peptide has a great specificity to interact with a specific homolog of a highly conserved protein family.

Aureobasidium pullulans YTP6-14 was demonstrated to be an excellent multiple biosurfactant producer utilizing cheap carbon sources available in Thailand, including glycerol and cassava flour hydrolysate. A. pullulans YTP6-14 maximally produced 1.81 g/l biosurfactant in an aqueous layer (BS-AQ) in a medium containing glycerol, and 7.37 or 6.37 g/l biosurfactant in a heavy oil layer (BS-HO) in cassava flour hydrolysate or a glucose containing medium, respectively. Each BS-AQ and BS-HO had critical micelle concentration values of 41.32 mg/l and 13.51 mg/l, and both biosurfactants formed a stable food oil emulsion and reduced the amount of biofilms formed by Streptococcus sobrinus and Streptococcus mutans. BS-AQ and BS-HO were mainly composed of liamocins or exophilins and massoia lactone, respectively.

The advantages of aquatic biomass production using wastewater as a cost-free fertilizer have recently been highlighted. Here, we report a successful study in which duckweed, Lemna gibba, biomass production in a food factory effluent containing low nitrogen and high salts was enhanced by employing customized plant growth-promoting bacteria (PGPB). Two common PGPB strains previously obtained from natural pond water, Acinetobacter calcoaceticus P23 and Pseudomonas fulva Ps6, hardly promoted the growth of duckweed; on the contrary, they inhibited its growth in treated factory wastewater, far different water conditions. Then, we asked if some indigenous wastewater bacteria could promote the growth of duckweed. We found that Chryseobacterium strains, a group of bacteria with limited nitrogen metabolism, were dominantly selected as effective PGPB. Moreover, we demonstrated that nitrogen limitation is the crucial environmental factor that induces the plant growth-inhibiting behavior of A. calcoaceticus P23 through competition for mineral nutrients with the host duckweed. This study uncovered points to be considered in PGPB technology to achieve efficient production of duckweed biomass in a factory effluent with unbalanced content of mineral nutrients.

Chemical investigation of the organic extract from Moorea bouillonii, collected in Sabah, Malaysia, led to the isolation of three new chlorinated fatty acid amides, columbamides F (1), G (2), and H (3). The planar structures of 1-3 were established by a combination of mass spectrometric and NMR spectroscopic analyses. The absolute configuration of 1 was determined by Marfey's analysis of its hydrolysate and chiral-phase HPLC analysis after conversion and esterification with Ohrui's acid, (1S,2S)-2-(anthracene-2,3-dicarboximido)cyclohexanecarboxylic acid. Compound 1 showed biosurfactant activity by an oil displacement assay. Related known fatty acid amides columbamide D and serinolamide C exhibited biosurfactant activity with critical micelle concentrations of about 0.34 and 0.78 mM, respectively.

Aseptic Lemna minor was soaked for 4 h in pond water where wild L. minor was naturally flourishing. Seven of the eight surface-colonizing bacterial strains were found capable of promoting the growth of L. minor. This high appearance of plant growth-promoting bacteria (PGPB) suggests that association of environmental bacteria is generally beneficial rather than harmful for host plants. One of the PGPB, Pseudomonas sp. Ps6, enhanced the growth of L. minor by 2–2.5-fold in 10 days. This activity was higher than that previously reported for Acinetobacter calcoaceticus P23, which enhanced growth of L. minor by 1.5–2-fold. Ps6 mostly adhered to and colonized the root rather than the frond, a leaf-like structure of duckweed where P23 preferentially adheres. It was expected that these two strains can share niches, coexist, and enhance the growth of duckweed additively upon co-inoculation. However, contrary to expectation, the growth of L. minor was enhanced by only 2.3-fold by co-inoculation of these two bacteria. P23 lowered the initial adhesion of Ps6 cells by 98.2% on the fronds and by 79.5% on the roots. However, initial adhesion of P23 cells to the roots increased dramatically, by 47.2-fold, following co-inoculation with Ps6. However, the number of P23 cells decreased dramatically to 0.7% on the root and to 3.6% on the frond after 10 days, whereas Ps6 cells increased by 12.5-fold on the frond and kept 69% on the root, thereby eventually restoring the population on the plant surfaces. Because duckweed is the fastest growing vascular plant and it is easy to grow an aseptic and axenic plant, the duckweed/bacteria co-culture system will be a model platform for studying multiple interactions among host plants and the associated bacteria.

Plant growth-promoting bacteria (PGPB) have recently been demonstrated as a promising agent to improve wastewater treatment and biomass production efficiency of duckweed hydrocultures. With a view to their reliable use in aqueous environments, this study analysed the plant colonization dynamics of PGPB and the ecological consequences for the entire duckweed-associated bacterial community. A PGPB strain, Aquitalea magnusonii H3, was inoculated to duckweed at different cell densities or timings in the presence of three environmental bacterial communities. The results showed that strain H3 improved duckweed growth by 11.7–32.1% in five out of nine experiments. Quantitative-PCR and amplicon sequencing analyses showed that strain H3 successfully colonized duckweed after 1 and 3 d of inoculation in all cultivation tests. However, it significantly decreased in number after 7 d, and similar bacterial communities were observed on duckweed regardless of H3 inoculation. Predicted metagenome analysis suggested that genes related to bacterial chemotactic motility and surface attachment systems are consistently enriched through community assembly on duckweed. Taken together, strain H3 dominantly colonized duckweed for a short period and improved duckweed growth. However, the inoculation of the PGPB did not have a lasting impact due to the strong resilience of the natural duckweed microbiome.

Salinity (NaCl) stress treatment is a strategy to induce lipid accumulation in microalgae. This study aimed to investigate the effect of a combination of two salts (NaCl/CaCl

Plant growth-promoting bacteria (PGPB) are considered a promising tool to improve biomass production and water remediation by the aquatic plant, duckweed; however, no effective methodology is available to utilize PGPB in large hydroponic systems. In this study, we proposed a two-step cultivation process, which comprised of a “colonization step” and a “mass cultivation step,” and examined its efficacy in both bucket-scale and flask-scale cultivation experiments. We showed that in the outdoor bucket-scale experiments using three kinds of environmental water, plants cultured through the two-step cultivation method with the PGPB strain, Acinetobacter calcoaceticus P23, yielded 1.9 to 2.3 times more biomass than the control (without PGPB inoculation). The greater nitrogen and phosphorus removals compared to control were also attained, indicating that this strategy is useful for accelerating nutrient removal by duckweed. Flask-scale experiments using non-sterile pond water revealed that inoculation of strain P23 altered duckweed surface microbial community structures, and the beneficial effects of the inoculated strain P23 could last for 5–10 d. The loss of the duckweed growth-promoting effect was noticeable when the colonization of strain P23 decreased in the plant. These observations suggest that the stable colonization of the plant with PGPB is the key for maintaining the accelerated duckweed growth and nutrient removal in this cultivation method. Overall, our results suggest the possibility of an improved duckweed production using a two-step cultivation process with PGPB.

Duckweeds are small, fast growing, and starch- and protein-rich aquatic plants expected to be a next generation energy crop and an excellent biomaterial for phytoremediation. Despite such an importance, very little is known about duckweed–microbe interactions that would be a key biological factor for efficient industrial utilization of duckweeds. Here we first report the duckweed growth promoting ability of bacterial strains belonging to the phylum Acidobacteria, the members of which are known to inhabit soils and terrestrial plants, but their ecological roles and plant–microbe interactions remain largely unclear. Two novel Acidobacteria strains, F-183 and TBR-22, were successfully isolated from wild duckweeds and phylogenetically affiliated with subdivision 3 and 6 of the phylum, respectively, based on 16S rRNA gene sequence analysis. In the co-culture experiments with aseptic host plants, the F-183 and TBR-22 strains visibly enhanced growth (frond number) of six duckweed species (subfamily Lemnoideae) up to 1.8–5.1 times and 1.6–3.9 times, respectively, compared with uninoculated controls. Intriguingly, both strains also increased the chlorophyll content of the duckweed (Lemna aequinoctialis) up to 2.4–2.5 times. Under SEM observation, the F-183 and TBR-22 strains were epiphytic and attached to the surface of duckweed. Taken together, our findings suggest that indigenous plant associated Acidobacteria contribute to a healthy growth of their host aquatic plants.

A mass spectrometry (MS)-guided isolation has led to the purification of a new cyanobactin, wewakazole B (1), along with the known compound curacin D from a Red Sea Moorea producens. The planar structure of 1 was elucidated using a combination of NMR and MS techniques. After ozonolysis and acid hydrolysis, the absolute configurations of the amino acid components of 1 were determined by chiral-phase LC-MS and HPLC analyses. Notably, compound 1 exhibited cytotoxic activity toward human MCF7 breast cancer cells (IC50 = 0.58 μM) and human H460 lung cancer cells (IC50 = 1.0 μM) and was also found to be inactive in a siderophore assay.

Gibberellic acid (GA(3)), indole-3-acetic acid (IAA), salicylic acid (SA), abscidic acid (ABA), jasmonic acid (JA) 1-amino cyclopropane-1-carboxylic acid (ACC) and aminoethoxyvinylglycine (AVG) are popular growth regulators of plants. However, the effects of their exogenous addition on the biomass production of aquatic plants, including Lemnoideae plants, "duckweeds," are largely unknown. In this study, the growth of Lemna minor was tested for 10 d in Hoagland medium containing each compound at different concentrations of 0-50 mu M. GA(3), IAA, and SA were found to have no apparent positive effect on the growth at all concentrations tested. Conversely, ACC and JA moderately and AVG and ABA severely inhibited the growth of L. minor. Among the tested compounds, ascorbic acid had an apparent growth-promoting effect.

Background Microalgae are a promising biomass feedstock for biofuels production. The use of wastewater effluent as a nutrient medium would improve the economics of microalgal biofuels production. Bacterial communities in aquatic environments may either stimulate or inhibit microalgal growth. Microalgal productivity could be enhanced if the positive effects of indigenous bacteria could be exploited. However, much is unknown about the effects of indigenous bacteria on microalgal growth and the characteristics of bacterial communities associated with microalgae in microalgae–effluent culture. To assess the effects of the indigenous bacteria in wastewater effluent on microalgal growth, three microalgae, Chlamydomonas reinhardtii, Chlorella vulgaris, and Euglena gracilis, were cultured in two municipal wastewater effluents and one swine wastewater effluent with and without indigenous bacteria for 7 days. Results All microalgae grew better in all effluents with indigenous bacteria than without bacteria. Biomass production of C. reinhardtii, C. vulgaris, and E. gracilis increased > 1.5, 1.8–2.8, and > 2.1-fold, respectively, compared to the axenic cultures of each microalga. The in situ indigenous bacterial communities in the effluents therefore promoted the growth of the three microalgae during 7-day cultures. Furthermore, the total numbers of bacterial 16S rRNA genes in the 7-day microalgae–effluent cultures were 109‒793 times the initial numbers. These results suggest that the three microalgae produced and supplied organic carbon that supported bacterial growth in the effluent. At the phylum and class levels, Proteobacteria (Alphaproteobacteria and Betaproteobacteria) and Bacteroidetes (Sphingobacteriia and Saprospirae) were selectively enriched in all microalgae–effluent cultures. The enriched core bacterial families and genera were functions of the microalgal species and effluents. These results suggest that certain members of the bacterial community promote the growth of their “host” microalgal species. Conclusion To enhance their own growth, microalgae may be able to selectively stimulate specific bacterial groups from among the in situ indigenous bacterial community found in wastewater effluent (i.e., microalgae growth-promoting bacteria: MGPB). The MGPB from effluent cultures could be used as “probiotics” to enhance microalgal growth in effluent culture. Wastewater effluent may therefore be a valuable resource, not only of nutrients, but also of MGPB to enable more efficient microalgal biomass production. Electronic supplementary material The online version of this article (10.1186/s13068-018-1174-0) contains supplementary material, which is available to authorized users.

Duckweed offers the promise of a co-benefit culture combining water purification with biomass production. Acinetobacter calcoaceticus P23 is a plant growth-promoting bacterium isolated from a duckweed, Lemna aequinoctialis. This study quantified its growth-promoting effect on three duckweeds (L. aoukikusa, L. minor, and Spirodela polyrhiza) in sterile Hoagland solution and evaluated its usefulness in duckweed culture under non-sterile conditions. P23 promoted growth of three duckweeds in sterile Hoagland solution at low to high nutrient concentrations (1.25–10 mg NO3-N/L and 0.25–2.0 mg PO4-P/L). It increased the biomass production of L. aequinoctialis 3.8–4.3-fold, of L. minor 2.3–3.3-fold, and of S. polyrhiza 1.4–1.5-fold after 7 days compared with noninoculated controls. P23 also increased the biomass production of L. minor 2.4-fold in pond water and 1.7-fold in secondary effluent of a sewage treatment plant under non-sterile conditions at laboratory-scale experiments. P23 rescued L. minor from growth inhibition caused by microorganisms indigenous to the pond water. The results demonstrate that the use of P23 in duckweed culture can improve the efficiency of duckweed biomass production, and a positive effect of P23 on duckweed-based wastewater treatment can be assumed.

To assess the potential of duckweeds as agents for nitrogen removal and biofuel feedstocks, Spirodela polyrhiza, Lemna minor, Lemna gibba, and Landoltia punctata were cultured in effluents of municipal wastewater, swine wastewater, or anaerobic digestion for 4 days. Total dissolved inorganic nitrogen (T-DIN) of 20–50 mg/L in effluents was effectively removed by inoculating with 0.3–1.0 g/L duckweeds. S. polyrhiza showed the highest nitrogen removal (2.0–10.8 mg T-DIN/L/day) and biomass production (52.6–70.3 mg d.w./L/day) rates in all the three effluents. Ethanol and methane were produced from duckweed biomass grown in each effluent. S. polyrhiza and L. punctata biomass showed higher ethanol (0.168–0.191, 0.166–0.172 and 0.174–0.191 g-ethanol/g-biomass, respectively) and methane (340–413 and 343–408 NL CH4/kg VS, respectively) production potentials than the others, which is related to their higher carbon and starch contents and calorific values.

Bacteria colonizing the plant rhizosphere are believed to positively or negatively affect the host plant productivity. This feature has inspired researchers to engineer such interactions to enhance crop production. However, it remains to be elucidated whether rhizobacteria influences plant oxidative stress vis-a-vis other environmental stressors, and whether such influence is associated with their growth promoting/inhibiting ability. In this study, two plant growth-promoting bacteria (PGPB) and two plant growth-inhibiting bacteria (PGIB) were separately inoculated into axenic duckweed (Lemna minor) culture under laboratory conditions for 4 and 8 days in order to investigate their effects on plant oxidative stress and antioxidant activities. As previously characterized, the inoculation of PGPB and PGIB strains accelerated and reduced the growth of L. minor, respectively. After 4 and 8 days of cultivation, compared to the PGPB strains, the PGIB strains induced larger amounts of O2•-, H2O2, and malondialdehyde (MDA) in duckweed, although all bacterial strains consistently increased O2•- content by two times more than that in the aseptic control plants. Activities of five antioxidant enzymes were also elevated by the inoculation of PGIB, confirming the severe oxidative stress condition in plants. These results suggest that the surface attached bacteria affect differently on host oxidative stress and its response, which degree correlates negatively to their effects on plant growth.

Aims In order to add to the existing knowledge about structural diversity of biosurfactants, marine environment was chosen to discover a new type of biosurfactant-producing fungus. Methods and Results A number of fungi were collected from the Gulf of Thailand and examined for biosurfactant productivities. A dimorphic fungus, Aureobasidium pullulans YTP6-14, produced several different biosurfactants in both heavy oil and aqueous layers of the culture. Surface tension of the aqueous layer was decreased to 31·4 mN m−1 and oil displacement area reached 53 cm2/10 μl after 7 days of cultivation. Critical micelle concentration and minimum surface tension values of the crude biosurfactants prepared from the aqueous layer were 39 mg l−1 and 31·6 mN m−1 respectively. Surface tension values remained unchanged over a wide range of pH and NaCl concentrations, suggesting their nonionic feature. LC/MS and NMR analyses revealed that one of the main active compounds in the aqueous layer was 5-hydroxy-2-decenoic acid delta-lactone, known as massoia lactone. Massoia lactone indeed showed significant surface tension reduction capacity of 43·3 mN m−1 at 1 mg ml−1. Significance and Impact of the Study This is the first report for the production of a fragrant biosurfactant, massoia lactone by a fungus A. pullulans. Massoia lactone has been industrially prepared from aromatic bark of an endangered tree species, Cryptocarya massoy, growing in rainforests. This report expands the diversity of biosurfactants produced by A. pullulans and also points to its possibility in contributing to the green sustainable chemistry, and ultimately rainforest conservation.

An extremely thermophilic bacterium, Geobacillus thermoleovorans B23, is capable of degrading a broad range of alkanes (with carbon chain lengths ranging between C11 and C32) at 70 A degrees C. Whole-genome sequence analysis revealed that unlike most alkane-degrading bacteria, strain B23 does not possess an alkB-type alkane monooxygenase gene. Instead, it possesses a cluster of three ladA-type genes, ladA alpha(B23), ladA beta(B23), and ladB (B23), on its chromosome, whose protein products share significant amino acid sequence identities, 49.8, 34.4, and 22.7 %, respectively, with that of ladA alkane monooxygenase gene found on a plasmid of Geobacillus thermodetrificans NG 80-2. Each of the three genes, ladA alpha(B23), ladA beta(B23), and ladB (B23), was heterologously expressed individually in an alkB1 deletion mutant strain, Pseudomonas fluorescens KOB2 Delta 1. It was found that all three genes were functional in P. fluorescens KOB2 Delta 1, and partially restored alkane degradation activity. In this study, we suggest that G. thermoleovorans B23 utilizes multiple LadA-type alkane monooxygenases for the degradation of a broad range of alkanes.

This work is aimed to assess the aerobic biotransformation of a branched side chain alkylbenzene, iso-pentylbenzene, by Candida viswanathii TH1. The yeast Candida viswanathii TH1 isolated from oil-polluted sediments collected in coastal zones in Vietnam exhibited as a strain that could better transform branched aromatic hydrocarbons in biofilm (pellicle) than in planktonic form. During incubation of TH1 as biofilm with iso-pentylbenzene, the seven intermediates produced were benzoic acid, phenylacetic acid, 2-methyl-4-phenyl-butan-1-ol, 2-hydroxy-phenylacetic acid, 2-methyl-4-phenylbutyric acid, succinic acid and iso-valerophenone as revealed by gas chromatography/mass spectra and high-performance liquid chromatography analyses. The occurrence of these intermediates showed that iso-pentylbenzene could be oxidized not only via mono- but also by a sub-terminal oxidation pathway. This is the first study on iso-pentylbenzene transformation by a biofilm-forming Candida viswanathii strain. The catabolic versatility of the biofilm-forming strain TH1 and its use for mono and sub-terminal oxidation during the transformation of iso-pentylbenzene enhance our understanding of the degradation of branched side chain phenylalkanes and give new insight into the potential role of such species in the transformation of other recalcitrant aromatic compounds.