Light and electron microscope assessment of the lytic activity of Bacillus on Microcystis aeruginosa

During the screening of lytic bacteria, plaques were obtained on Microcystis lawns. In the plaques, at least five distinct morphotypes of bacteria were found. The plumb rod-shaped bacilli were the most abundant and were found aggregated around unhealthy Microcystis cells and were the probable cause of deflation and lysis. These bacteria may have utilized the cyanobacteria cell contents as their nutrient source. In contrast to the control areas, the cyanobacteria cells were healthy and did not show any visible distortion of cell structure. The presence and possible role of the free-bacteria, that is, bacteria that were not attached or associated with the cyanobacteria in the plaque is not clear. Maybe their function is to scavenge the skeletal remains of Microcystis cells. Bacillus mycoides B16 were found to have a lytic effect on Microcystis cells. Scanning electron micrographs (SEM) images of B. mycoides B16 did not reveal any unique attachments that may have allowed them to adhere to Microcystis cells. The Microcystis cells were exposed to copper, B. mycoides B16 and Triton X-100, in order to ascertain the level of cell membrane damage. The membrane cell damage was most severe with copper stripping the entire Microcystis cell membrane leaving a honeycomb skeletal structure and B. mycoides B16, leaving perforations on the cell membrane. The electron microscopy observations appeared to reveal at least two mechanisms of Microcystis lysis (contact and parasitism). The light and electron microscope (LEM) observations did not reveal any endoparasitism of B. mycoides B16 or Bdellovibrio-like behaviour.The authors wish to acknowledge the NRF and University of Pretoria (UP) for the financial support for the study.http://www.academicjournals.org/AJ

Mechanism of Microcystis aeruginosa death upon exposure to Bacillus mycoides

Electron microscopy observations revealed at least two mechanisms of Microcystis aeruginosa cell death upon exposure to Bacillus mycoides, i.e. cell membrane lysis and shadowing of algal cells leading to photoinhibition. There were ultra-structural changes that occurred in bacteria treated M. aeruginosa cells. SEM images showed swollen M. aeruginosa cells due to cell membrane damage and increased osmotic pressure. The production of intracellular stress related structures by M. aeruginosa indicated cell stress as a result of bacteria causing shadowing and photo-inhibition affecting the photosynthetic system. There is evidence, which showed that B. mycoides B16 might be an ectoparasite during the lysis of Microcystis cells and exhibit multicellular forms that are Bdellovibrio-like bacteria during the last stages lysis of Microcystis cells in order to survive an adverse external environment that was nutrient limited. The mechanism of cyanobacterial lysis may involve changes in ultrastructure of M. aeruginosa, possibly affecting energy sources and the photosynthetic system after exposure to bacteria. This may lead to the death of the cyanobacteria after exhaustion of energy sources and loss of nutrients to the predator bacteria, B. mycoides B16. A better understanding of the interactions between B. mycoides 16 and M. aeruginosa is important for the development of a biological control agent and ultimately the management of harmful algal blooms dominated by M. aeruginosa.NRF and University of Pretoria (UP)http://www.elsevier.com/locate/pcenf201

The effect of ultrasound at 256 KHz on Microcystis aeruginosa, with and without gas vacuoles

The effect of ultrasound on the growth of M. aeruginosa confirmed to contain gas vacuoles and on a laboratory culture with no gas vacuoles was investigated. Both cultures were treated continuously for 9 d with an ultrasonic flow device. To evaluate the influence of ultrasound during the treatment, the chlorophyll-a concentration was measured daily. Furthermore, changes in culture characteristics, e.g., flotation and gas vesicle formation, were determined. The results showed that, in contrast to the control, both ultrasonic-treated cultures had a lower chlorophyll-a concentration and cell aggregates were disrupted. Transmission electron microscopy confirmed a collapse of gas vacuoles in the environmental culture, while the laboratory culture, which did not contain gas vacuoles, showed many membrane-damaged cells. It was concluded that ultrasonic treatment of M. aeruginosa caused the disruption of gas vacuoles and destruction of cell membranes.http://www.wrc.org.zaam201

Relationship between plant growth and organic acid exudates from ectomycorrhizal and non-ectomycorrhizal Pinus patula

Plant–mycorrhizal interaction is an important association in the ecosystem with significant impacts on the physical, biological and chemical properties of the soil. In the present study, potential relationships that exist between organic acid production by ectomycorrhizal pine seedlings and plant parameters in the absence of any significant environmental stress were investigated. The aim of the study was to investigate the contribution of organic acid production to plant growth. Four different ectomycorrhizal fungi were used in a mycorrhizal synthesis experiment to colonise roots of Pinus patula. Ectomycorrhizal and nonectomycorrhizal plants were used in a pot trial experiment that lasted for 24 weeks. After harvesting, plant materials as well as soil samples underwent different analyses, which included the determination of pH, organic acids, plant biomass, and foliar and root phosphorus and potassium. The results indicated a significant interaction (P < 0.0001) between fungal type and organic acid production. This reflects the influence of fungal type on organic acid production. However, it was observed that organic acids secreted into the soil do not have a direct link to the quantity of nutrients detected in either the root or shoot, but seemed to positively influence plant growth as reflected in the result from root and shoot biomass.http://www.tandfonline.com/loi/tjps202016-06-04hb201

The viability assessment of Microcystis aeruginosa cells after co-culturing with Bacillus mycoides B16 using flow cytometry

Microcystis aeruginosa is the dominate cyanobacteria in freshwater bodies causing proliferation of toxic harmful algal blooms (HABs), worldwide. Thus a biological control method based on predatory bacteria is an alternative environmental solution to the control of these HABs, A Flow cytometric technique was used to assess the viability of Microcystis spp. cells after deliberate co-culturing with a predatory bacterium, Bacillus mycoides B16. Under static conditions, B. mycoides had a lytic effect on Microcystis cells that resulted in a significant (p = 0.0000) population decline of 97% in six days. In contrast under turbulent conditions, B. mycoides had a lytic effect on Microcystis spp. cells resulting in a significant (df = 5; t = 7.21; p = 0.0003) population decrease of 85% in the same time period. The Levene test also showed a significant (p = 0.0003) decrease in Microcystis cell numbers, which also coincided with a significant (t = 11.31; p = 0.0001) increase in B. mycoides cell numbers. This suggested that B. mycoides, a heterotroph, was utilizing the Microcystis as a source of nutrition. The effect of agitation may have contributed to the delay in cell lysis as it disturbed the physical contact between the predator and prey. The control samples showed a significant (df = 5; t = +6.86; p = 0.0010) increase in Microcystis spp. cell numbers. B. mycoides was able to lyse Microcystis spp. cells under these conditions and may thus be considered as a potential biological control agent for the management of Microcystis spp. harmful algal blooms.National Research Foundation (NRF) and University of Pretoria (UP)http://www.elsevier.com/locate/pcehb201

Microorganisms : life forms with macro impact

Text only of inaugural address by Prof. Eugene Cloete, Department Of Microbiology and Plant Pathology.http://explore.up.ac.za/record=b143583

Resistance mechanisms of bacteria to antimicrobial compounds

A range of antimicrobial compounds (bactericides) commonly termed biocides, microbicides, sanitizers, antiseptics and disinfectants are available, all of which are claimed by their producers to kill bacteria. Resistance has been defined as the temporary or permanent ability of an organism and its progeny to remain viable and/or multiply under conditions that would destroy or inhibit other members of the strain. Bacteria may be defined as resistant when they are not susceptible to a concentration of antibacterial agent used in practice. Traditionally, resistance refers to instances where the basis of increased tolerance is a genetic change, and where the biochemical basis is known. Antimicrobial substances target a range of cellular loci, from the cytoplasmic membrane to respiratory functions, enzymes and the genetic material. However, different bacteria react differently to bactericides, either due to inherent differences such as unique cell envelope composition and non-susceptible proteins, or to the development of resistance, either by adaptation or by genetic exchange. At low concentrations bactericides often act bacteriostatically, and are only bacteriocidal at higher concentrations. For bactericides to be effective, they must attain a sufficiently high concentration at the target site in order to exert their antibacterial action. In order to reach their target site(s), they must traverse the outer membrane of the gram negative bacteria. Bacteria with effective penetration barriers to biocides generally display a higher inherent resistance than those bacteria which are readily penetrated. The rate of penetration is linked to concentration, so that a sufficiently high bactericide concentration will kill bacteria with enhanced penetration barriers. It has been indicated that susceptible bacterial isolates acquire increased tolerance to bactericides following serial transfer in sub-inhibitory concentrations. Whereas the basis of bacterial resistance to antibiotics is well know, that of resistance to antiseptics, disinfectants and food preservatives is less well understood. Three mechanisms of resistance that have been reported include: •limited diffusion of antimicrobial agents through the biofilm matrix, •interaction of the antimicrobial agents with the biofilm matrix (cells and polymer), •enzyme mediated resistance, •level of metabolic activity within the biofilm, •genetic adaptation •efflux pumps and •outer membrane structure

Biofouling and biocorrosion in industrial water systems

Corrosion associated with microorganisms has been recognized for over 50 years and yet the study of microbiologically influenced corrosion (MIC) is relatively new. MIC can occur in diverse environments and is not limited to aqueous corrosion under submerged conditions, but also takes place in humid atmospheres. Biofouling of industrial water systems is the phenomenon whereby surfaces in contact with water are colonized by microorganisms, which are ubiquitous in our environment. However, the economic implications of biofouling in industrial water systems are much greater than many people realize. In a survey conducted by the National Association of Corrosion Engineers of the United States ten years ago, it was found that many corrosion engineers did not accept the role of bacteria in corrosion, and many of them that did, could not recognize and mitigate the problem. Biofouling can be described in terms of its effects on processes and products such as material degradation (bio-corossion), product contamination, mechanical blockages, and impedance of heat transfer. Microorganisms distinguish themselves from other industrial water contaminants by their ability to utilize available nutrient sources, reproduce, and generate intra- and extracellular organic and inorganic substances in water. A sound understanding of the molecular and physiological activities of the microorganisms involved is necessary before strategies for the long term control of biofouling can be format. Traditional water treatment strategies however, have largely failed to address those factors that promote biofouling activities and lead to biocorrosion. Some of the major developments in recent years have been a redefinition of biofilm architecture and the realization that MIC of metals can be best understood as biomineralization

Removal of Aroclor 1254 by the white rot fungus Coriolus versicolor in the presence of different concentrations of Mn(IV)oxide

Lignin peroxidase (LiP) plays an active role in the biodegradation of lignin and phenolic structures resembling lignin. The role of other enzymes in the biodegradation of recalcitrant compounds, e.g. manganese(II)-peroxidase, is uncertain. Solid manganese(IV)oxide addition improved the production of manganese(II)-dependant peroxidase (MnP) and H202 and increased the rate of biodegradation of Aroclor 1254 in a nitrogen-limited medium by the white rot fungus Coriolus versicolor. MnP activity was detected 48 h after the addition of Mn02 to the cultures and was absent in cultures that did not receive Mn02. The rate of Aroclor 1254 removal by C. versicolor was influenced by the concentration of Mn02. 34.5 mM concentrations only increased the H202 production. Removal of Aroclor 1254 in the absence of Mn02 still took place which implied the presence of (LiP) or nonspecific absorption. The cultures containing 57.5 mM Mn02 removed ca. 84% of the initial 750 mg 1-1 Aroclor in 6 days of incubation. Cultures with no Mn02 and 34.5 mM removed 79 and 76%, respectively. Cultures with MnP or LiP as the dominant enzyme species removed penta- and hexachlorobiphenyls at a slower rate than tri- and tetrachlorobiphenyl

Acinetobacter cell biomass, growth stage and phosphorus uptake from activated sludge mixed liquor

Enhanced biological phosphorus removal activated sludge plants often do not remove phosphorus adequately in order to meet legal demands. Currently FeS04 is being added to almost all South African nutrient removal activated sludge systems discharging effluents to the sensitive catchments to prevent phosphorus from entering fresh water systems. In order to understand biological phosphorus removal mechanisms in order to optimise the process, the role of growth rate and phosphorus removal in Acinetobacter was investigated. Phosphorus was accumulated in the lag phase of the normal growth cycle. Little or no phosphorus was accumulated in the logarithmic growth phase, instead phosphorus was released at the beginning of logarithmic growth. Further phosphorus accumulation took place in the stationary phase, once active growth had ceased. Cells had a limit to the amount of phosphorus that could be accumulated per cell irrespective of substrate availability. It was therefore concluded, that the number of cells (biomass) in a system and their growth stage were crucial factors governing biological phosphorus removal. Maximum cell numbers should therefore be obtained and logarithmic growth should be prevented in the aerobic zone, in order to optimize biological phosphorus removal from activated sludge