Alexander A. Kamnev

Chemical and Biological Parameters as Tools to Evaluate and Improve Heavy Metal Phytoremediation

In this review, chemical and biological parameters are discussed thatstrongly influence the speciation of heavy metals, their availability tobiological systems and, consequently, the possibilities to usebioremediation as a cleanup tool for heavy metal polluted sites. In orderto assess heavy metal availability, a need exists for rapid, cost-effectivesystems that reliably predict this parameter and, based on this, thefeasibility of using biological remediation techniques for site managementand restoration. Special attention is paid to phytoremediation as anemerging technology for stabilization and remediation of heavy metalpollution. In order to improve phytoremediation of heavy metal pollutedsites, several important points relevant to the process have to beelucidated. These include the speciation and bioavailability of the heavymetals in the soil determined by many chemical and biological parameters,the role of plant-associated soil microorganisms and fungi inphytoremediation, and the plants. Several options are described how plant-associated soil microorganisms canbe used to improve heavy metal phytoremediation.

Tricalcium phosphate is inappropriate as a universal selection factor for isolating and testing phosphate-solubilizing bacteria that enhance plant growth: a proposal for an alternative procedure

Literature analysis and chemical considerations of biological phosphate solubilization have shown that the commonly used selection factor for this trait, tricalcium phosphate (TCP), is relatively weak and unreliable as a universal selection factor for isolating and testing phosphate-solubilizing bacteria (PSB) for enhancing plant growth. Most publications describing isolation of PSB employed TCP. The use of TCP usually yields many (up to several thousands per study) isolates “supposedly” PSB. When these isolates are further tested for direct contribution of phosphorus to the plants, only a very few are true PSB. Other compounds are also tested, but on a very small scale. These phosphates (P), mainly Fe-P, Al-P, and several Ca-P, are even less soluble than TCP in water. Because soils greatly vary by pH and several chemical considerations, it appears that there is no metal-P compound that can serve as the universal selection factor for PSB. A practical approach is to use a combination of two or three metal-P compounds together or in tandem, according to the end use of these bacteria—Ca-P compounds (including rock phosphates) for alkaline soils, Fe-P and Al-P compounds for acidic soils, and phytates for soils rich in organic P. Isolates with abundant production of acids will be isolated. This approach will reduce the number of potential PSB from numerous isolates to just a few. Once a potential isolate is identified, it must be further tested for direct contribution to P plant nutrition and not necessarily to general growth promotion, as commonly done because promotion of growth, even by PSB, can be the outcome of other mechanisms. Isolates that do not comply with this general sequence of testing should not be declared as PSB.

Comparative spectroscopic characterization of different pectins and their sources

The results of atomic absorption spectrometry (AAS) analyses and Fourier transform infrared (FTIR) spectroscopic studies of several pectins obtained from pumpkin and sugar beet, as well as of their vegetable sources, are compared and discussed. Special emphasis is put on the state of carboxylic groups of the polymer backbone and the mineral composition of both the sources and the resulting pectins, including the content of alkaline (Na, K) and alkaline-earth metals (Mg, Ca), as well as traces of heavy metals (V, Fe, Cu, Pb). The pectins were obtained from dried pumpkin pulp by extraction with dilute hydrochloric acid or using a biotechnological process involving the multi-enzyme cell-free culture supernatant from the bacterium Xanthomonas campestris; commercial sugar beet pectin extracted by the standard method of acid treatment was obtained from a sugar beet processing plant in Krasnodar (Russia). For comparison, a sample of commercial acid-extracted citrus pectin (Copenhagen, Denmark) was also studied. The results obtained show that potassium seems to occur as a relatively free constituent, whereas a more specific interaction between sodium ions and pectic substances may be assumed depending on the origin of the pectin and obviously on its properties. Much higher amounts of Mg and, especially, Ca found in pumpkin biopectin as compared to all of the three pumpkin, sugar beet and citrus acid-extracted products correlate with a relatively well exhibited capability of pectins to bind these two cations, which is noticeably suppressed in acidic media. The increased content of Ca (and, probably, Mg) may in principle contribute to poorer gelling properties of pumpkin pectin and, in general, of biopectins as compared to the corresponding acid extracts. The results on the mineral fraction of the samples are compared considering the FTIR spectroscopic data for the pectins studied as well as for their sources featuring, in particular, the state of carboxylic groups responsible for metal binding. It has also been found that lead and copper essentially accumulate in pectins upon extraction, whereas iron does not, being relatively more weakly bound by pectic substances (which may, however, depend on its oxidation state) than other heavy metals; the accumulation process is slightly (for Fe and Pb) or not at all (for Cu) suppressed during acid extraction. Comparing the content of vanadium in the pectins and their sources, it may be concluded that this element occurring in plant tissue obviously in different chemical forms may be partly transferred to pectin during its extraction in a proportion similar to that in which it is bound to pectic substances in the plant cell wall, thus indicating its strong binding not affected by acid treatment.

A proposal for isolating and testing phosphate-solubilizing bacteria that enhance plant growth

A proposal for isolating and testing phosphate-solubilizing bacteria that enhance plant growth

Fourier transform infrared spectroscopic study of intact cells of the nitrogen-fixing bacterium Azospirillum brasilense

Abstract The data of Fourier transform infrared (FTIR) spectroscopic measurements performed on intact cells of the soil nitrogen-fixing bacterium Azospirillum brasilense grown in a standard medium and under the conditions of an increased metal uptake are compared and discussed. The structural FTIR information obtained is considered together with atomic absorption spectrometry (AAS) data on the content of metal cations in the bacterial cells. Some methodological aspects concerning preparation of bacterial cell samples for FTIR measurements are also discussed.

Spectroimmunochemistry Using Colloidal Gold Bioconjugates

Using surface-enhanced infrared absorption (SEIRA) spectroscopy of dry films of colloidal gold (CG) bioconjugates with protein A, it is shown that certain characteristic bands of the protein (e.g., amide I, amide II and some other vibration modes) are essentially affected by the metal surface. Thus, the method may be used for controlling the quality of such bioconjugates. Moreover, it is demonstrated that the biospecific reaction of protein A attached to CG particles with human immunoglobulin G (IgG) results in further essential changes in SEIRA spectra, providing a means for an easy and rapid IR spectroscopic detection of biospecific immunochemical interactions (i.e., spectroimmunochemistry). The results obtained can form a basis for developing test systems for detecting various biospecific interactions.

Spectroscopic characterization of cell membranes and their constituents of the plant-associated soil bacterium Azospirillum brasilense

Abstract Structural and compositional features of bacterial membranes and some of their isolated constituents (cell surface lipopolysaccharide, phospholipids) of the plant-growth-promoting diazotrophic rhizobacterium Azospirillum brasilense (wild-type strain Sp245) were characterized using Fourier transform infrared (FTIR) spectroscopy and some other techniques. FTIR spectra of the cell membranes were shown to comprise the main vibration modes of the relevant lipopolysaccharide and protein components which are believed to be involved in associative plant–bacterium interactions, as well as of phospholipid constituents. The role and functions of metal cations in the structural organization and physicochemical properties of bacterial cell membranes are also discussed considering their accumulation in the membranes from the culture medium.

Spectroscopic investigation of indole-3-acetic acid interaction with iron(III)

Abstract FeIII was found to be gradually reduced by indole-3-acetic acid (IAA) in slightly acidic nitrate solution with further re-oxidation of the resulting FeII upon drying in air, which is reasoned to be of ecological significance considering IAA excretion by many soil micro-organisms. FeIII–IAA complex was isolated; its composition, some physicochemical properties and structural aspects were studied using Mossbauer, FTIR spectroscopic and other techniques. Possible influence of FeIII coordination on the redox properties of the ligand is also considered from the viewpoint of the nature of the bonding system which involves the conjugated π-electronic system of the pyrrole cycle along with the carboxylic O-donor atom.

SPECTROSCOPIC CHARACTERIZATION OF THE UPTAKE OF ESSENTIAL AND XENOBIOTIC METAL CATIONS IN CELLS OF THE SOIL BACTERIUM AZOSPIRILLUM BRASILENSE

The results of flame (FAAS) or graphite furnace atomic absorption spectrometric (GFAAS) analyses are presented and discussed on the accumulation of essential metals (Mg, Ca, Mn and Fe contained in the cultivation medium) and traces of each one of the conventionally xenobiotic elements from the group V, Co, Ni, Cu, Zn or Pb, added to the medium in concentrations (0.2 mM) which do not essentially suppress growth of the bacterial culture, in cells of the plant root‐associated nitrogen‐fixing bacterium Azospirillum brasilense. Along with the essential cations assimilated by the bacterium, Zn and Cu were found to effectively accumulate in the biomass from the environment. The uptake of Co and Ni was significantly less pronounced, whereas Pb and V appeared to be present in cells in much lower concentrations than in the cultivation medium evidently showing no tendency to be assimilated by azospirilla. The effect of the above xenobiotics on the uptake level of the four essential elements provided evidence that they may compete for the formation of biologically active complexes with substances of both intracellular and extracellular localization. The analytical data obtained are compared with Fourier transform infrared (FTIR) spectra of intact vacuum‐dried bacterial cells grown in a standard medium and under the conditions of an increased metal uptake.

Mössbauer and FTIR spectroscopic studies of iron anthranilates: coordination, structure and some ecological aspects of iron complexation

Abstract The data on the coordination and structure of iron(II) and iron(III) anthranilates in the solid state and in aqueous medium are presented and discussed, as studied using Mossbauer (for solid products and frozen solutions) and FTIR spectroscopy (for solid samples). Whereas, in slightly acidic nitrate solutions under aerobic conditions ferric ions can still be gradually reduced by anthranilic ( o -aminobenzoic) acid, which may have some ecological significance, in circumneutral media this process is retarded. Mossbauer parameters calculated for iron(II) and iron(III) anthranilates, as well as characteristic vibration modes of certain functional groups involved in coordination with iron cations are discussed. The FTIR data obtained for ferrous anthranilates, as compared to anthranilic acid, definitely exhibit the direct involvement of both the carboxylic and the amino groups of anthranilic acid in coordination with iron.