Rhizosphere Microbiome Cooperations: Strategies for Sustainable Crop Production.

Interactions between microorganisms and host plants determine the growth and development as well as the health of the host plant. Various microbial groups inhabit the rhizosphere, each with its peculiar function. The survival of each microbial group depends to a large extent on its ability to colonize the plant root and outcompete the native organisms. The role of the rhizospheric microbiome in enhancing plant growth has not been fully maximized. An understanding of the complexities of microbial interactions and factors affecting their assembly in the community is necessary to benefit maximally from the cooperations of various microbial communities for sustainable crop production. In this review, we outline the various organisms associated with the plant rhizosphere with emphasis on their interactions and mechanisms used in plant growth promotion.

Genomic insights into plant growth promoting rhizobia capable of enhancing soybean germination under drought stress.

BACKGROUND: The role of soil microorganisms in plant growth, nutrient utilization, drought tolerance as well as biocontrol activity cannot be over-emphasized, especially in this era when food crisis is a global challenge. This research was therefore designed to gain genomic insights into plant growth promoting (PGP) Rhizobium species capable of enhancing soybean (Glycine max L.) seeds germination under drought condition. RESULTS: Rhizobium sp. strain R1, Rhizobium tropici strain R2, Rhizobium cellulosilyticum strain R3, Rhizobium taibaishanense strain R4 and Ensifer meliloti strain R5 were found to possess the entire PGP traits tested. Specifically, these rhizobial strains were able to solubilize phosphate, produce exopolysaccharide (EPS), 1-aminocyclopropane-1-carboxylate (ACC), siderophore and indole-acetic-acid (IAA). These strains also survived and grew at a temperature of 45 °C and in an acidic condition with a pH 4. Consequently, all the Rhizobium strains enhanced the germination of soybean seeds (PAN 1532 R) under drought condition imposed by 4% poly-ethylene glycol (PEG); nevertheless, Rhizobium sp. strain R1 and R. cellulosilyticum strain R3 inoculations were able to improve seeds germination more than R2, R4 and R5 strains. Thus, genomic insights into Rhizobium sp. strain R1 and R. cellulosilyticum strain R3 revealed the presence of some genes with their respective proteins involved in symbiotic establishment, nitrogen fixation, drought tolerance and plant growth promotion. In particular, exoX, htrA, Nif, nodA, eptA, IAA and siderophore-producing genes were found in the two rhizobial strains. CONCLUSIONS: Therefore, the availability of the whole genome sequences of R1 and R3 strains may further be exploited to comprehend the interaction of drought tolerant rhizobia with soybean and other legumes and the PGP ability of these rhizobial strains can also be harnessed for biotechnological application in the field especially in semiarid and arid regions of the globe.

Fungal bio-sorption potential of chromium in Norkrans liquid medium by shake flask technique.

In this study, the myco-reduction potential of fungi isolated from soil was ascertained by Norkrans shake flask experiment contaminated with chromium(VI). Fungal tolerance assay and induced tolerance training of the fungi were also carried out. Aspergillus niger, Penicillium, and Saccharomyces strains were isolated from the soil samples using culture based technique. Norkrans samples were collected and analyzed for Cr(VI) concentration using diphenylcarbazide spectrophotometric method. Penicillium strain was observed to be most effect at Cr(VI) concentrations of 16.1 and 8.1 mg L-1 since it was able to reduce Cr(VI) more than Saccharomyces strain and A. niger on day 20. Bio-sorption kinetics for this study was better described by pseudo second order model while Langmuir isotherm model fitted better to the equilibrium data. There was virtually steady increase in fungal growth for all the treatments through-out the experimental period. Significant negative correlation (p < 0.05) was observed between fungal growth and Cr(VI) reduction rate. The results from the induced tolerance training showed that Penicillium had the highest tolerance index (TI) values at 18, 20, and 25 mg L-1 concentrations of Cr(VI) compared to A. niger and Saccharomyces strain. These results demonstrated that these fungi have the potential to bio-absorb Cr(VI) and if properly harnessed, could be used in place of conventional remediation technology to clean-up the Cr(VI) contaminant in the field.

Biofertilizers and sustainable agriculture: exploring arbuscular mycorrhizal fungi.

Worldwide agricultural food production has to double in 2050 so as to feed the global increasing population while reducing dependency on conventional chemical fertilizers plus pesticides. To accomplish this objective, there is the need to explore the several mutualistic interactions between plant roots and rhizosphere microbiome. Biofertilization is the process of boosting the abundance of microorganisms such as arbuscular mycorrhizal fungi (AMF) in the natural plant rhizosphere which depicts a beneficial alternative to chemical fertilization practices. Mineral nutrients uptake by AMF are plausible by means of transporters coded for by different genes and example include phosphate transporter. These fungi can be produced industrially using plant host and these, including the possibility of AMF contamination by other microorganism, are factors militating against large scale production of AMF. AMF isolates can be inoculated in the greenhouse or field, and it has been shown that AMF survival and colonization level were enhanced in soybeans grown on land that was previously cultivated with the same plant. Next generation sequencing (NGS) is now used to gain insight into how AMF interact with indigenous AMF and screen for beneficial microbial candidates. Besides application as biofertilizers, novel findings on AMF that could contribute to maintenance of agricultural development include AMF roles in controlling soil erosion, enhancing phytoremediation, and elimination of other organisms that may be harmful to crops through common mycelia network. The combination of these potentials when fully harnessed under agricultural scenario will help to sustain agriculture and boost food security globally.

Toxicological profile of chlorophenols and their derivatives in the environment: the public health perspective.

Chlorophenol compounds and their derivatives are ubiquitous contaminants in the environment. These compounds are used as intermediates in manufacturing agricultural chemicals, pharmaceuticals, biocides, and dyes. Chlorophenols gets into the environment from a variety of sources such as industrial waste, pesticides, and insecticides, or by degradation of complex chlorinated hydrocarbons. Thermal and chemical degradation of chlorophenols leads to the formation of harmful substances which constitute public health problems. These compounds may cause histopathological alterations, genotoxicity, mutagenicity, and carcinogenicity amongst other abnormalities in humans and animals. Furthermore, the recalcitrant nature of chlorophenolic compounds to degradation constitutes an environmental nuisance, and a good understanding of the fate and transport of these compounds and their derivatives is needed for a clearer view of the associated risks and mechanisms of pathogenicity to humans and animals. This review looks at chlorophenols and their derivatives, explores current research on their effects on public health, and proffers measures for mitigation.

Effects of rhizobia and arbuscular mycorrhizal fungi on yield, size distribution and fatty acid of soybean seeds grown under drought stress.

Soybean (Glycine max L.) is among the most economically important legumes that provide more than 1/4 of food (for man) and animal feed. However, its yield is comparatively low, most especially under drought stress. The aim of this study therefore was to assess the ability of Rhizobium spp. and mycorrhizal fungi to enhance the yield, seed size and fatty acid content of soybean grown under semi-arid environment. Rhizobium sp. strain R1 was found to possess nitrogen-fixing gene coniferyl aldehyde dehydrogenase function while Rhizobium cellulosilyticum strain R3 was found to have nitrogen-fixing genes cysteine desulfurase SufS and cysteine desulfurase IscS activity. Soybean (Glycine max L) seeds inoculated with Rhizobium spp. and mycorrhizal fungi were cultivated in soil exposed to drought stress. Rhizobium spp. inoculation and mycorrhization alleviate drought stress and increase yield, size and fat content of soybean seeds. This increase in the aboveground parameters was accompanied with an increase in belowground mycorrhizal spore number, percentage root mycorrhization and aboveground shoot relative water content (RWC) in the dually inoculated (R1 + R3MY) soybean plants. In particular, the dually inoculated (R1 + R3MY) soybean plants revealed 34.3 g fresh weight, 15.1 g dry weight and soybean plants singly inoculated with Rhizobium sp. strain R1 (R1) produced more large seeds with 12.03 g dry weight. The non-inoculated (control) seeds contained a higher percentage of moisture content compared to the microbially amended seeds while seeds co-inoculated with Rhizobium cellulosilyticum strain R3 and mycorrhizal consortium revealed the highest percent (8.4 %) of fat. Several fatty acids that are of significant health benefits to humans were observed in the soybean seeds. In order to gain insights into the bacterial communities of rhizospheric soil collected at different stages of soybean growth, class-based Heat-map analysis was performed on the Miseq sequenced data. The core bacteria that were found in the rhizospheric soil were Verrumicrobia, Proteobacteria, Gemmatimonadetes, Firmicutes, Cyanobacteria, Chloroflexi, Bacteroidetes, Actinobacteria, Acidobacteria, Planctomycetes, Deinococcus thermus and Nitrospira suggesting that the rhizobia and fungi used in this study can also improve soil microbial diversity.

Below-ground-above-ground Plant-microbial Interactions: Focusing on Soybean, Rhizobacteria and Mycorrhizal Fungi.

INTRODUCTION: Organisms seldom exist in isolation and are usually involved in interactions with several hosts and these interactions in conjunction with the physicochemical parameters of the soil affect plant growth and development. Researches into below and aboveground microbial community are unveiling a myriad of intriguing interactions within the rhizosphere, and many of the interactions are facilitated by exudates that are secreted by plants roots. These interactions can be harnessed for beneficial use in agriculture to enhance crop productivity especially in semi-arid and arid environments. THE RHIZOSPHERE: The rhizosphere is the region of soil close to plants roots that contain large number of diverse organisms. Examples of microbial candidates that are found in the rhizosphere include the Arbuscular Mycorrhizal Fungi (AMF) and rhizobacteria. These rhizosphere microorganisms use plant root secretions such as mucilage and flavonoids which are able to influence their diversity and function and also enhance their potential to colonize plants root. NATURAL INTERACTIONS BETWEEN MICROORGANISMS AND PLANT: In the natural environments, plants live in interactions with different microorganisms, which thrive belowground in the rhizosphere and aboveground in the phyllosphere. Some of the plant-microbial interactions (which can be in the form of antagonism, amensalism, parasitism and symbiosis) protect the host plants against detrimental microbial and non-microbial invaders and provide nutrients for plants while others negatively affect plants. These interactions can influence below-ground-above-ground plants' biomass development thereby playing significant role in sustaining plants. Therefore, understanding microbial interactions within the rhizosphere and phyllosphere is urgent towards farming practices that are less dependent on conventional chemical fertilizers, which have known negative impacts on the environments. BELOW GROUND RHIZOBACTERIA INTERACTIONS ALLEVIATE DROUGHT STRESS: Drought stress is one of the major factors militating against agricultural productivity globally and is likely to further increase. Belowground rhizobacteria interactions could play important role in alleviating drought stress in plants. These beneficial rhizobacterial colonize the rhizosphere of plants and impart drought tolerance by up regulation or down regulation of drought responsive genes such as ascorbate peroxidase, S-adenosyl-methionine synthetase, and heat shock protein. INSIGHTS INTO BELOW AND ABOVE THE GROUND MICROBIAL INTERACTIONS VIA OMIC STUDIES: Investigating complex microbial community in the environment is a big challenge. Therefore, omic studies of microorganisms that inhabit the rhizosphere are important since this is where most plant-microbial interactions occur. One of the aims of this review is not to give detailed account of all the present omic techniques, but instead to highlight the current omic techniques that can possibly lead to detection of novel genes and their respective proteins within the rhizosphere which may be of significance in enhancing crop plants (such as soybean) productivity especially in semi-arid and arid environments. FUTURE PROSPECTS AND CONCLUSIONS: Plant-microbial interactions are not totally understood, and there is, therefore, the need for further studies on these interactions in order to get more insights that may be useful in sustainable agricultural development. With the emergence of omic techniques, it is now possible to effectively monitor transformations in rhizosphere microbial community together with their effects on plant development. This may pave way for scientists to discover new microbial species that will interact effectively with plants. Such microbial species can be used as biofertilizers and/or bio-pesticides to increase crop yield and enhance global food security.

In vitro assessment of antioxidant, phytochemical and nutritional properties of extracts from the leaves of Ocimum gratissimum (Linn).

The antioxidant, phytochemical and nutritional properties of acetone, methanol and aqueous extracts of the leaves of Ocimum gratissimum (Linn) were investigated to evaluate the therapeutic and nutritional potential of the leaves of this plant. The antioxidant of the plant extracts were assessed against 1,1-Diphenyl-2-picrylhydrazyl (DPPH) and 2,2-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) and ferric reducing agent. Total phenolics, flavonoids, flavonols and proanthocyanidins were determined to assess their corresponding effect on the antioxidant activity of this plant. The extracts exhibited DPPH and ABTS(·+) radical scavenging activities, which was comparable to butylated hydroxytoluene (BHT). The phytochemical screening revealed the presence of alkaloids, tannins, saponin, steroids, cardiacglycoside, flavonoid, terpenoids and phenol. The proximate analysis confirms that the leaves contain appreciable amount of ash, crude protein, lipids, fibre and carbohydrates. The macro and micro elements and constituents revealed that the leaves contain significant amount of sodium, potassium, calcium, magnesium, iron, zinc, phosphorus, copper, nitrogen, and manganese. This study shows that the leaf can be used as a therapeutic agent and justifies its application in folkloric medicine.