Biologically Active Compounds Of Semi-Metals

Out of the blue: Hyperaccumulation of molybdenum in the Indo-Pacific sponge Theonella conica

Molybdenum is an essential micronutrient, but because of its toxicity at high concentrations, its accumulation in living organisms has not been widely demonstrated. In this study, we report that the marine sponge Theonella conica accumulates exceptionally high levels of molybdenum (46,793 micrograms per gram of dry weight) in a wide geographic distribution from the northern Red Sea to the reefs of Zanzibar, Indian Ocean. The element is found in various sponge body fractions and correlates to selenium. We further investigated the microbial composition of the sponge and compared it to its more studied congener, Theonella swinhoei. Our analysis illuminates the symbiotic bacterium Entotheonella sp. and its role in molybdenum accumulation. Through microscopic and analytical methods, we provide evidence of intracellular spheres within Entotheonella sp. that exhibit high molybdenum content, further unraveling the intricate mechanisms behind molybdenum accumulation in this sponge species and its significance in the broader context of molybdenum biogeochemical cycling.

Structures of the DarR transcription regulator reveal unique modes of second messenger and DNA binding

The mycobacterial repressor, DarR, a TetR family regulator (TFR), was the first transcription regulator shown to bind c-di-AMP. However, the molecular basis for this interaction and the mechanism involved in DNA binding by DarR remain unknown. Here we describe DarR-c-di-AMP and DarR-DNA structures and complementary biochemical assays. The DarR-c-di-AMP structure reveals a unique effector binding site for a TFR, located between DarR dimer subunits. Strikingly, we show this motif also binds cAMP. The location of the adenine nucleotide binding site between subunits suggests this interaction may facilitate dimerization and hence DNA binding. Indeed, biochemical assays show cAMP enhances DarR DNA binding. Finally, DarR-DNA structures reveal a distinct TFR DNA-binding mechanism involving two interacting dimers on the DNA. Thus, the combined data unveil a newly described second messenger binding motif and DNA binding mode for this important family of regulators.

Physiological responses, tolerance, and remediation strategies in plants exposed to metalloids

Metalloids are a subset of particular concern to risk assessors and toxicologists because of their well-documented potential hazards to plant system. Most of the metalloids are major environmental contaminants which affect crop productivity when present in high concentrations in soil. Metalloids are coupled with carrier proteins of the plasma membrane and translocated to various organs causing changes in key metabolic processes, damages cell biomolecules, and finally inhibit its growth. Phytoremediation-based approaches help in understanding the molecular and biochemical mechanisms for prerequisite recombinant genetic approaches. Recent advancements in proteomics and plant genomics help in understanding the role of transcription factors, metabolites, and genes in plant system which confers metal tolerance. The present review summarizes our current status of knowledge in this direction related to various physiological responses, detoxification mechanisms, and remediation strategies of metalloids in crop plants in relation to plant-metalloid tolerance. Further, the role of various transcription factors and miRNAs in conferring metal tolerance is also briefed. Hence, the present review mainly focused on the alterations in the physiological activities of plants due to metalloid toxicity and the various mechanisms which get activated inside the plants to mitigate their toxic effects.

Exploration of silicon functions to integrate with biotic stress tolerance and crop improvement

In the era of climate change, due to increased incidences of a wide range of various environmental stresses, especially biotic and abiotic stresses around the globe, the performance of plants can be affected by these stresses. After oxygen, silicon (Si) is the second most abundant element in the earth's crust. It is not considered as an important element, but can be thought of as a multi-beneficial quasi-essential element for plants. This review on silicon presents an overview of the versatile role of this element in a variety of plants. Plants absorb silicon through roots from the rhizospheric soil in the form of silicic or monosilicic acid. Silicon plays a key metabolic function in living organisms due to its relative abundance in the atmosphere. Plants with higher content of silicon in shoot or root are very few prone to attack by pests, and exhibit increased stress resistance. However, the more remarkable impact of silicon is the decrease in the number of seed intensities/soil-borne and foliar diseases of major plant varieties that are infected by biotrophic, hemi-biotrophic and necrotrophic pathogens. The amelioration in disease symptoms are due to the effect of silicon on a some factors involved in providing host resistance namely, duration of incubation, size, shape and number of lesions. The formation of a mechanical barrier beneath the cuticle and in the cell walls by the polymerization of silicon was first proposed as to how this element decreases plant disease severity. The current understanding of how this element enhances resistance in plants subjected to biotic stress, the exact functions and mechanisms by which it modulates plant biology by potentiating the host defence mechanism needs to be studied using genomics, metabolomics and proteomics. The role of silicon in helping the plants in adaption to biotic stress has been discussed which will help to plan in a systematic way the development of more sustainable agriculture for food security and safety in the future.

Interactive Role of Silicon and Plant-Rhizobacteria Mitigating Abiotic Stresses: A New Approach for Sustainable Agriculture and Climate Change

Abiotic stresses are the major constraints in agricultural crop production across the globe. The use of some plant-microbe interactions are established as an environment friendly way of enhancing crop productivity, and improving plant development and tolerance to abiotic stresses by direct or indirect mechanisms. Silicon (Si) can also stimulate plant growth and mitigate environmental stresses, and it is not detrimental to plants and is devoid of environmental contamination even if applied in excess quantity. In the present review, we elaborate the interactive application of Si and plant growth promoting rhizobacteria (PGPRs) as an ecologically sound practice to increase the plant growth rate in unfavorable situations, in the presence of abiotic stresses. Experiments investigating the combined use of Si and PGPRs on plants to cope with abiotic stresses can be helpful in the future for agricultural sustainability.

Use of heavy metals resistant bacteria-a strategy for arsenic bioremediation

A large number of industries release their untreated wastes in the environment causing an increase in the concentration of toxic pollutants including heavy metal ions in ground and drinking water which is above the WHO limit. The presence of toxic pollutants in the industrial wastes pollutes our environment. Arsenic (As) is a ubiquitous toxic metalloid. Its amount varies in different parts on the earth, and its concentration is increasing in our environment day by day both by natural and anthropogenic activities. It is found in two forms; one is arsenate (As⁵⁺) and other is arsenite (As³⁺) and the latter is more toxic due to high mobility across the cell membrane. The long-term use of arsenic-containing water causes arsenicosis. High arsenic consumption, revealed by skin harms, color change, and spots on hands and feet, may cause skin cancer and affect lungs and kidneys. Hypertension, a state of high blood pressure, and lack of insulin which causes diabetes and many other disorders which relate to reproduction are the consequences of arsenic contamination. Several methods have been employed to decontaminate arsenic pollution, but the bioremediation by using biomass of bacteria, algae, fungi, and yeasts is the most compromising approach and has gained much attention from researchers in the last few decades. The microbial detoxification of arsenic can be achieved by reduction, oxidation, and methylation. High bioremediation potential and feasibility of the process make bacteria an impending foundation for green chemistry to exterminate arsenic in the environment.

The Fructoborates: Part of a Family of Naturally Occurring Sugar-Borate Complexes-Biochemistry, Physiology, and Impact on Human Health: a Review

Sugar-borates (SBs) are mono- or di-sugar-borate esters (SBEs) comprised of one or two monosaccharide molecules linked to a boron (B) atom. SBEs occur naturally in commonly consumed herbs, vegetables, fruits, seeds, and nuts and, other than greatly varying levels of B found in local drinking water, are the primary natural dietary sources of B-containing molecules in humans. To date, the most studied SBE is calcium fructoborate (CaFB). CaFB represents an important example of how organic B-containing molecules are significantly distinct from their inorganic counterparts. During these past two decades, CaFB has been researched for its physical and biochemical characteristics, safety, and clinical outcomes. Results of these researches are presented and discussed herein. CaFB has been characterized using Fourier-transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), high-performance thin-layer chromatography (HPTLC), nuclear magnetic resonance (NMR), liquid chromatography-multistage accurate mass spectrometry (LC-MSn), X-ray diffraction (XRD), Raman spectroscopy, and inductively coupled plasma (ICP) in non-biological and biological specimens. Potential health benefits of CaFB have been clinically investigated in pilot and efficacy studies demonstrating (i) significant reductions in knee discomfort and improved flexibility within 7, 14, and 90 days and (ii) significant effect on blood levels of inflammatory, cardiovascular, and other biomarkers. These studies support the use of CaFB as a dietary supplement for the management of joint discomfort. CaFB is presented here in order to illustrate how physiological benefits are imparted by distinct organic boron-containing molecules rather than solely by the element B itself. Considering recent National Health and Nutrition Examination Survey (NHANES) data reporting increases in age-related joint pain and an increasing elderly demographic, SBEs offer potential for safe, natural, and effective management of joint discomfort and improved mobility in human and animal health applications. Several of these studies may also open new opportunities for use of SBEs for health benefits beyond joint health.

The Physiological Role of Boron on Health

Boron is an essential mineral that plays an important role in several biological processes. Boron is required for growth of plants, animals, and humans. There are increasing evidences of this nutrient showing a variety of pleiotropic effects, ranging from anti-inflammatory and antioxidant effects to the modulation of different body systems. In the past few years, the trials showed disease-related polymorphisms of boron in different species, which has drawn attention of scientists to the significance of boron to health. Low boron profile has been related with poor immune function, increased risk of mortality, osteoporosis, and cognitive deterioration. High boron status revealed injury to cell and toxicity in different animals and humans. Some studies have shown some benefits of higher boron status, but findings have been generally mixed, which perhaps accentuates the fact that dietary intake will benefit only if supplemental amount is appropriate. The health benefits of boron are numerous in animals and humans; for instance, it affects the growth at safe intake. Central nervous system shows improvement and immune organs exhibit enhanced immunity with boron supplementation. Hepatic metabolism also shows positive changes in response to dietary boron intake. Furthermore, animals and human fed diets supplemented with boron reveal improved bone density and other benefits including embryonic development, wound healing, and cancer therapy. It has also been reported that boron affects the metabolism of several enzymes and minerals. In the background of these health benefits, low or high boron status is giving cause for concern. Additionally, researches are needed to further elucidate the mechanisms of boron effects, and determine the requirements in different species.

Expanding beyond canonical metabolism: Interfacing alternative elements, synthetic biology, and metabolic engineering

Metabolic engineering offers an exquisite capacity to produce new molecules in a renewable manner. However, most industrial applications have focused on only a small subset of elements from the periodic table, centered around carbon biochemistry. This review aims to illustrate the expanse of chemical elements that can currently (and potentially) be integrated into useful products using cellular systems. Specifically, we describe recent advances in expanding the cellular scope to include the halogens, selenium and the metalloids, and a variety of metal incorporations. These examples range from small molecules, heteroatom-linked uncommon elements, and natural products to biomining and nanotechnology applications. Collectively, this review covers the promise of an expanded range of elemental incorporations and the future impacts it may have on biotechnology.

Physiological and genomic insights into the lifestyle of arsenite-oxidizing Herminiimonas arsenitoxidans

Arsenic, a representative toxic metalloid, is responsible for serious global health problems. Most organisms possess arsenic resistance strategies to mitigate this toxicity. Here, we reported a microorganism, strain AS8, from heavy metal/metalloid-contaminated soil that is able to oxidize arsenite, and investigated its physiological and genomic traits. Its cells were rod-shaped and Gram-negative, and formed small beige-pigmented colonies. 16S rRNA-based phylogenetic analysis indicated that the strain belongs to the genus Herminiimonas and is closely related to Herminiimonas glaciei UMB49^T (98.7% of 16S rRNA gene sequence similarity), Herminiimonas arsenicoxydans ULPAs1^T (98.4%), and Herminiimonas saxobsidens NS11^T (98.4%). Under chemolithoheterotrophic conditions, the strain utilized some organic acids and amino acids as carbon and/or nitrogen sources but not electron sources. Further, the strain grew as a sulfur oxidizer in a complex medium (trypticase soy agar). Unexpectedly, most carbohydrates failed to support its growth as sole carbon sources. Genome sequencing supported these observations, and very few ABC transporters capable of oligo/monosaccharide uptake were identified in the AS8 genome. The genome harbored genes required for the colonization, flagella biosynthesis, urea degradation, and heavy metal and antibiotic resistance. Based on these polyphasic and genomic analyses, we propose that the strain AS8 be named Herminiimonas arsenitoxidans.

Silicon as Versatile Player in Plant and Human Biology: Overlooked and Poorly Understood

Silicon (Si) serves as bioactive beneficial element. Si is highly abundant in soil, and occurs ubiquitously in all organisms including plants and humans. During the last three decades, nutritional significance of Si for plant and human health has received increasing attention. Plant Si plays a pivotal role in growth and development, and this beneficial effect depends usually on accumulation in plant tissues, which are then protected from various forms of biotic and abiotic stresses. Likewise, human exposure to Si imparts health benefits and essentially occurs through plant-derived food products. Si bioavailability in human diet, e.g., strengthens bones and improves immune response, as well as neuronal and connective tissue health. Despite this empiric knowledge, the essentiality of Si still remains enigmatic. Thus the link between Si availability for plant development and its profound implication for human welfare should receive attention. This review aims to provide a broad perspective on Si as important element for plant and human nutrition and to define research fields for interdisciplinary research.