Tolerance of plastic-encapsulated Pseudomonas putida KT2440 to chemical stress

Comparative Study of Bacillus-Based Plant Biofertilizers: A Proposed Index

The market for bacteria as agricultural biofertilizers is growing rapidly, offering plant-growth stimulants; biofungicides; and, more recently, protectors against extreme environmental factors, such as drought. This abundance makes it challenging for the end user to decide on the product to use. In this work, we describe the isolation of a strain of Bacillus velezensis (belonging to the operational group Bacillus amyloliquefaciens) for use as a plant-growth-promoting rhizobacterium, a biofungicide, and a protector against drought. To compare its effectiveness with other commercial strains of the same operational group, Bacillus amyloliquefaciens, we analyzed its ability to promote the growth of pepper plants and protect them against drought, as well as its fungicidal activity through antibiosis and antagonism tests, its ability to solubilize potassium and phosphates, and its ability to produce siderophores. Finally, we used a probit function, a type of regression analysis used to model the outcomes of analyses, to quantify the biostimulatory effectiveness of the different plant-growth-promoting rhizobacteria, developing what we have called the Agricultural Protection Against Stress Index, which allowed us to numerically compare the four commercial strains of the operational group Bacillus amyloliquefaciens, based on a Delphi method-a type of regression analysis that can be used to model a cumulative normal distribution-and integrate the results from our panel of tests into a single value.

Plant Beneficial Deep-Sea Actinobacterium, Dermacoccus abyssi MT1.1T Promote Growth of Tomato (Solanum lycopersicum) under Salinity Stress

Simple Summary

Salt stress is an important environmental problem that negatively affects agricultural and food production in the world. Currently, the use of plant beneficial bacteria for plant growth promotion is attractive due to the demand for eco-friendly and sustainable agriculture. In this study, salt tolerant deep-sea actinobacterium, Dermacoccus abyssi MT1.1^T was investigated plant growth promotion and salt stress mitigation in tomato seedlings. In addition, D. abyssi MT1.1^T whole genome was analyzed for plant growth promoting traits and genes related to salt stress alleviation in plants. We also evaluated the biosafety of this strain on human health and organisms in the environment. Our results highlight that the inoculation of D. abyssi MT1.1^T could reduce the negative effects of salt stress in tomato seedlings by growth improvement, total soluble sugars accumulation and hydrogen peroxide reduction. Moreover, this strain could survive and colonize tomato roots. Biosafety testing and genome analysis of D. abyssi MT1.1^T showed no pathogenicity risk. In conclusion, we provide supporting evidence on the potential of D. abyssi MT1.1^T as a safe strain for use in plant growth promotion under salt stress.

Abstract

Salt stress is a serious agricultural problem threatens plant growth and development resulted in productivity loss and global food security concerns. Salt tolerant plant growth promoting actinobacteria, especially deep-sea actinobacteria are an alternative strategy to mitigate deleterious effects of salt stress. In this study, we aimed to investigate the potential of deep-sea Dermacoccus abyssi MT1.1^T to mitigate salt stress in tomato seedlings and identified genes related to plant growth promotion and salt stress mitigation. D. abyssi MT1.1^T exhibited plant growth promoting traits namely indole-3-acetic acid (IAA) and siderophore production and phosphate solubilization under 0, 150, 300, and 450 mM NaCl in vitro. Inoculation of D. abyssi MT1.1^T improved tomato seedlings growth in terms of shoot length and dry weight compared with non-inoculated seedlings under 150 mM NaCl. In addition, increased total soluble sugar and total chlorophyll content and decreased hydrogen peroxide content were observed in tomato inoculated with D. abyssi MT1.1^T. These results suggested that this strain mitigated salt stress in tomatoes via osmoregulation by accumulation of soluble sugars and H₂O₂ scavenging activity. Genome analysis data supported plant growth promoting and salt stress mitigation potential of D. abyssi MT1.1^T. Survival and colonization of D. abyssi MT1.1^T were observed in roots of inoculated tomato seedlings. Biosafety testing on D. abyssi MT1.1^T and in silico analysis of its whole genome sequence revealed no evidence of its pathogenicity. Our results demonstrate the potential of deep-sea D. abyssi MT1.1^T to mitigate salt stress in tomato seedlings and as a candidate of eco-friendly bio-inoculants for sustainable agriculture.

Impacts of Agriculture on the Environment and Soil Microbial Biodiversity

Agriculture represents an important mechanism in terms of reducing plant, animal, and microbial biodiversity and altering the environment. The pressure to cope with the increasing food demands of the human population has intensified the environmental impact, and alternative ways to produce food are required in order to minimize the decrease in biodiversity. Conventional agricultural practices, such as floods and irrigation systems; the removal of undesired vegetation by fires, tilling, and plowing; the use of herbicides, fertilizers, and pesticides; and the intensification of these practices over the last 50 years, have led to one of the most important environmental threats—a major loss of biodiversity. In this study, we review the impact that agriculture and its intensification have had on the environment and biodiversity since its invention. Moreover, we demonstrate how these impacts could be reduced through the use of microorganisms as biostimulants.

Deep-Sea Actinobacteria Mitigate Salinity Stress in Tomato Seedlings and Their Biosafety Testing

Soil salinity is an enormous problem affecting global agricultural productivity. Deep-sea actinobacteria are interesting due to their salt tolerance mechanisms. In the present study, we aim to determine the ability of deep-sea Dermacoccus (D. barathri MT2.1^T and D. profundi MT2.2^T) to promote tomato seedlings under 150 mM NaCl compared with the terrestrial strain D. nishinomiyaensis DSM20448^T. All strains exhibit in vitro plant growth-promoting traits of indole-3-acetic acid production, phosphate solubilization, and siderophore production. Tomato seedlings inoculated with D. barathri MT2.1^T showed higher growth parameters (shoot and root length, dry weight, and chlorophyll content) than non-inoculated tomato and the terrestrial strain under 150 mM NaCl. In addition, hydrogen peroxide (H₂O₂) in leaves of tomatoes inoculated with deep-sea Dermacoccus was lower than the control seedlings. This observation suggested that deep-sea Dermacoccus mitigated salt stress by reducing oxidative stress caused by hydrogen peroxide. D. barathri MT2.1^T showed no harmful effects on Caenorhabditis elegans, Daphnia magna, Eisenia foetida, and Escherichia coli MC4100 in biosafety tests. This evidence suggests that D. barathri MT2.1^T would be safe for use in the environment. Our results highlight the potential of deep-sea Dermacoccus as a plant growth promoter for tomatoes under salinity stress.

Programmable design of seed coating function induces water-stress tolerance in semi-arid regions

In semi-arid regions, water stress during seed germination and early seedling growth is the highest cause of crop loss. In nature, some seeds (for example, chia and basil) produce a mucilage-based hydrogel that creates a germination-promoting microenvironment by retaining water, regulating nutrient entry and facilitating interactions with beneficial microorganisms. Inspired by this strategy, a two-layered biopolymer-based seed coating has been developed to increase germination and water-stress tolerance in semi-arid, sandy soils. Seeds are coated with a silk/trehalose inner layer containing rhizobacteria and a pectin/carboxymethylcellulose outer layer that reswells upon sowing and acts as a water jacket. Using Phaseolus vulgaris (common bean) cultured under water-stress conditions in an experimental farm in Ben Guerir, Morocco, the proposed seed coating effectively delivered rhizobacteria to form root nodules, resulted in plants with better health and mitigated water stress in drought-prone marginal lands. A programmable seed coating technology has the potential to increase seed germination and water-stress tolerance in semi-arid, sandy soils.

Compatible solutes adaptive alterations in Arthrobacter simplex during exposure to ethanol, and the effect of trehalose on the stress resistance and biotransformation performance

Ethanol-tolerant Arthrobacter simplex is desirable since ethanol facilitates hydrophobic substrates dissolution on an industrial scale. Herein, alterations in compatible solutes were investigated under ethanol stress. The results showed that the amount of trehalose and glycerol increased while that of glutamate and proline decreased. The trehalose protectant role was verified and its concentration was positively related to the degree of cell tolerance. otsA, otsB and treS, three trehalose biosynthesis genes in A. simplex, also enhanced Escherichia coli stress tolerance, but the increased tolerance was dependent on the type and level of the stress. A. simplex strains accumulating trehalose showed a higher productivity in systems containing more ethanol and substrate because of better viability. The underlying mechanisms of trehalose were involved in better cell integrity, higher membrane stability, stronger reactive oxygen species scavenging capacity and higher energy level. Therefore, trehalose was a general protectant and the upregulation of its biosynthesis by genetic modification enhanced cell stress tolerance, consequently promoted productivity.

Microbial Production of Ethanol From Sludge Derived From an Urban Wastewater Treatment Plant

A collection of lipase-producing microorganisms was isolated from sludge derived from an urban wastewater treatment plant. The microorganisms with the highest levels of lipase activity were selected in order to use triglycerides present in the sludge effectively and were then transformed with pdc:adhB genes for the production of ethanol. The transgenic strains showed high growth rates in diluted sludge and produced lipase protein in order to utilize fat present in the sludge, which provides an abundant source of carbon. Using sludge derived from treated wastewater as nutrient source, ethanol was produced by certain transgenic species belonging to the genera Proteus. Different forms of sludge were tested for maximal ethanol production, with dehydrated sludge being found to produce the best performance.

The significance of proline and glutamate on butanol chaotropic stress in Bacillus subtilis 168

BACKGROUND

Butanol is an intensively used industrial solvent and an attractive alternative biofuel, but the bioproduction suffers from its high toxicity. Among the native butanol producers and heterologous butanol-producing hosts, Bacillus subtilis 168 exhibited relatively higher butanol tolerance. Nevertheless, organic solvent tolerance mechanisms in Bacilli and Gram-positive bacteria have relatively less information. Thus, this study aimed to elucidate butanol stress responses that may involve in unique tolerance of B. subtilis 168 to butanol and other alcohol biocommodities.

RESULTS

Using comparative proteomics approach and molecular analysis of butanol-challenged B. subtilis 168, 108 butanol-responsive proteins were revealed, and classified into seven groups according to their biological functions. While parts of them may be similar to the proteins reportedly involved in solvent stress response in other Gram-positive bacteria, significant role of proline in the proline-glutamate-arginine metabolism was substantiated. Detection of intracellular proline and glutamate accumulation, as well as glutamate transient conversion during butanol exposure confirmed their necessity, especially proline, for cellular butanol tolerance. Disruption of the particular genes in proline biosynthesis pathways clarified the essential role of the anabolic ProB-ProA-ProI system over the osmoadaptive ProH-ProA-ProJ system for cellular protection in response to butanol exposure. Molecular modifications to increase gene dosage for proline biosynthesis as well as for glutamate acquisition enhanced butanol tolerance of B. subtilis 168 up to 1.8% (vol/vol) under the conditions tested.

CONCLUSION

This work revealed the important role of proline as an effective compatible solute that is required to protect cells against butanol chaotropic effect and to maintain cellular functions in B. subtilis 168 during butanol exposure. Nevertheless, the accumulation of intracellular proline against butanol stress required a metabolic conversion of glutamate through the specific biosynthetic ProB-ProA-ProI route. Thus, exogenous addition of glutamate, but not proline, enhanced butanol tolerance. These findings serve as a practical knowledge to enhance B. subtilis 168 butanol tolerance, and demonstrate means to engineer the bacterial host to promote higher butanol/alcohol tolerance of B. subtilis 168 for the production of butanol and other alcohol biocommodities.

An in-depth characterization of the entomopathogenic strain Bacillus pumilus 15.1 reveals that it produces inclusion bodies similar to the parasporal crystals of Bacillus thuringiensis

In the present work, the local isolate Bacillus pumilus 15.1 has been morphologically and biochemically characterized in order to gain a better understanding of this novel entomopathogenic strain active against Ceratitis capitata. This strain could represent an interesting biothechnological tool for the control of this pest. Here, we report on its nutrient preferences, extracellular enzyme production, motility mechanism, biofilm production, antibiotic suceptibility, natural resistance to chemical and physical insults, and morphology of the vegetative cells and spores. The pathogen was found to be β-hemolytic and susceptible to penicillin, ampicillin, chloramphenicol, gentamicin, kanamycin, rifampicin, tetracycline, and streptomycin. We also report a series of biocide, thermal, and UV treatments that reduce the viability of B. pumilus 15.1 by several orders of magnitude. Heat and chemical treatments kill at least 99.9 % of vegetative cells, but spores were much more resistant. Bleach was the only chemical that was able to completely eliminate B. pumilus 15.1 spores. Compared to the B. subtilis 168 spores, B. pumilus 15.1 spores were between 2.67 and 350 times more resistant to UV radiation while the vegetative cells of B. pumilus 15.1 were almost up to 3 orders of magnitude more resistant than the model strain. We performed electron microscopy for morphological characterization, and we observed geometric structures resembling the parasporal crystal inclusions synthesized by Bacillus thuringiensis. Some of the results obtained here such as the parasporal inclusion bodies produced by B. pumilus 15.1 could potentially represent virulence factors of this novel and potentially interesting strain.

Enhancement of solvent tolerance in Pseudomonas sp. BCNU 106 with trehalose

As the solvent hyper-resistant Pseudomonas sp. BCNU 106 experiences limited growth with solvents, a strategy is therefore needed to allow better growth to broaden its performance in biotechnological applications. Pseudomonas sp. BCNU 106 was cultivated in a medium supplemented with 0·05 mol l(-1) trehalose, and the cell survival was observed during subsequent growth with 1% (v/v) toluene. Exogenously added trehalose was transported into the cells and conferred protection against toluene stress. BCNU 106 grown in the presence of exogenous trehalose showed higher solvent tolerance, it can thus have more potential for biotransformation and biodegradation.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study shows that exogenously supplemented trehalose confers protection against toluene stress and enhances the bacterial cell growth in the presence of toluene. This is of importance to the mass cultivation of solvent-tolerant bacteria, where some of the growth-related limitations of solvent-tolerant bacteria can be overcome, and their performance in biotechnological applications for biotransformation and biodegradation broadened.

Genome Sequence of Microbacterium sp. Strain 3J1, a Highly Desiccation-Tolerant Bacterium That Promotes Plant Growth

The genome sequence for Microbacterium sp. strain 3J1, a desiccation-tolerant organism isolated from the Nerium oleander rhizosphere, is reported here. The genome is estimated to be approximately 3.5 Mb in size, with an average G+C content of 67.7% and a predicted number of protein-coding sequences of 3,310.

Genome Sequence of Arthrobacter koreensis 5J12A, a Plant Growth-Promoting and Desiccation-Tolerant Strain

Arthrobacter koreensis 5J12A is a desiccation-tolerant organism isolated from the Nerium oleander rhizosphere. Here, we report its genome sequence, which may shed light on its role in plant growth promotion. This is believed to be the first published genome of a desiccation-tolerant plant growth promoter from the genus Arthrobacter.

Genome Sequence of Rhodococcus sp. 4J2A2, a Desiccation-Tolerant Bacterium Involved in Biodegradation of Aromatic Hydrocarbons

The genome sequence for Rhodococcus sp. 4J2A2, a newly described desiccation-tolerant strain that removes aromatic hydrocarbons, is reported here. The genome is estimated to be around 7.5 Mb in size, with an average G+C content of 60.77% and a predicted number of protein-coding sequences of 6,354.

Genome Sequence of Leucobacter sp. 4J7B1, a Plant-Osmoprotectant Soil Microorganism

We report the first genome sequence for Leucobacter sp. 4J7B1, a newly described desiccation-tolerant strain. The complete genome sequence of Leucobacter sp. 4J7B1 has been sequenced and is estimated to be around 3.5 Mb in size, with an average GC content of 62.18%. We predict 2,953 protein-coding sequences.

Genome Sequence of Arthrobacter siccitolerans 4J27, a Xeroprotectant-Producing Desiccation-Tolerant Microorganism

We report the first genome sequence for Arthrobacter siccitolerans 4J27, a newly described desiccation-tolerant species. The complete genome of A. siccitolerans 4J27 has been sequenced and is estimated to be around 5.3 Mb in size, with an average GC content of 65.13%. We predict 4,480 protein-coding sequences (CDSs).

Xeroprotectants for the stabilization of biomaterials

With the advancement of science and technology, it is crucial to have effective preservation methods for the stable long-term storage of biological material (biomaterials). As an alternative to cryopreservation, various techniques have been developed, which are based on the survival mechanism of anhydrobiotic organisms. In this sense, it has been found that the synthesis of xeroprotectants can effectively stabilize biomaterials in a dry state. The most widely studied xeroprotectant is trehalose, which has excellent properties for the stabilization of certain proteins, bacteria, and biological membranes. There have also been attempts to apply trehalose to the stabilization of eukaryotic cells but without conclusive results. Consequently, a xeroprotectant or method that is useful for the stable drying of a particular biomaterial might not necessarily be suitable for another one. This article provides an overview of recent advances in the use of new techniques to stabilize biomaterials and compare xeroprotectants with other more standard methods.

Biotechnological uses of desiccation-tolerant microorganisms for the rhizoremediation of soils subjected to seasonal drought

Plant growth-promoting rhizobacteria (PGPR) increase the viability and health of host plants when they colonize roots and engage in associative symbiosis (Bashan et al. 2004). In return, PGPR viability is increased by host plant roots by the provision of nutrients and a more protective environment (Richardson et al. in Plant Soil 321:305-339, 2009). The PGPR have great potential in agriculture since the combination of certain microorganisms and plants can increase crop production and increase protection against frost, salinity, drought and other environmental stresses such as the presence of xenobiotic pollutants. But there is a great challenge in combining plants and microorganisms without compromising the viability of either microorganisms or seeds. In this paper, we review how anhydrobiotic engineering can be used for the formulation of biotechnological tools that guarantee the supply of both plants and microorganisms in the dry state. We also describe the application of this technology for the selection of desiccation-tolerant PGPR for polycyclic aromatic hydrocarbons bioremediation, in soils subjected to seasonal drought, by the rhizoremediation process.

Rapid method for isolation of desiccation-tolerant strains and xeroprotectants

A novel biotechnological process has been developed for the isolation of desiccation-tolerant microorganisms and their xeroprotectants, i.e., compatible solutes involved in long-term stability of biomolecules in the dry state. Following exposure of soil samples to chloroform, we isolated a collection of desiccation-tolerant microorganisms. This collection was screened for the production of xeroprotectants by a variation of the bacterial milking (osmotic downshock) procedure and by a novel air-drying/rehydration ("dry milking") incubation method. The resultant solutes were shown to protect both proteins and living cells against desiccation damage, thereby validating them as xeroprotectants. Nuclear magnetic resonance (NMR) analytical studies were performed to identify the xeroprotectants; synthetic mixtures of these compounds were shown to perform similarly to natural isolates in drying experiments with proteins and cells. This new approach has biotechnological and environmental implications for the identification of new xeroprotectants of commercial and therapeutic value.

Protection of live bacteria from bile acid toxicity using bile acid adsorbing resins

We previously demonstrated that a dry, room temperature stable formulation of a live bacterial vaccine was highly susceptible to bile, and suggested that this will lead to significant loss of viability of any live bacterial formulation released into the intestine using an enteric coating or capsule. We found that bile and acid tolerance is very rapidly recovered after rehydration with buffer or water, raising the possibility that rehydration in the absence of bile prior to release into the intestine might solve the problem of bile toxicity to dried cells. We describe here a novel formulation that combines extensively studied bile acid adsorbent resins with the dried bacteria, to temporarily adsorb bile acids and allow rehydration and recovery of bile resistance of bacteria in the intestine before release. Tablets containing the bile acid adsorbent cholestyramine release 250-fold more live bacteria when dissolved in a bile solution, compared to control tablets without cholestyramine or with a control resin that does not bind bile acids. We propose that a simple enteric coated oral dosage form containing bile acid adsorbent resins will allow improved live bacterial delivery to the intestine via the oral route, a major step towards room temperature stable, easily administered and distributed vaccine pills and other bacterial therapeutics.