Degradation of 2,4-dichlorophenoxyacetic acid by mixed cultures of bacteria

Summary We explored the feasibility of using mixed cultures for herbicide degradation, with the ultimate aim of application for effluent treatment. The present study reports on mixed cultures which were developed to grow aerobically with 2,4-dichlorophenoxyacetic acid (2,4-D) as the sole carbon substrate. Degradation of 2,4-D was verified by HPLC and UV-spectroscopic analysis of the residual 2,4-D concentration in the test cultures. Cultures that were initially developed with 2,4-D also grew readily with glucose, but the degradation of 2,4-D was effectively prevented under mixed substrate conditions. Mamor intermediates or metabolites resulting from 2,4-D degradation were not detected with the HPLC methodology except 2,4-dichlorophenol which appeared to accumulate transiently in the growth medium.     

Physiological and technological considerations for optimising mass algal cultures

The successful coupling between physiology andtechnology is central to the success of algalbiotechnology. Imperative is a proper understandingof the variables and their impacts on biomass and/orbiocompound production. The crux lies inphotosynthesis and the capturing of light energy atthe optimal rate for eventual maximal photochemistry(biosynthesis). It is in the hands of algalbiotechnologists to understand the dynamics andregulatory mechanisms of especially PSII (photosystemII) activity in order to advance this technologyfurther. Biophysical and technological optimisationand design aimed at maximising photon flux capture aresome of the avenues that needs be pursued. This needsto be augmented by molecular, biochemical andphysiological inputs. Unfortunately detailedsystematic analyses of the variables, theirinteraction and possible synergism have rarely beendone. The debate regarding the merits andproductivity in closed, either plate or tubular,vertical or horizontal, and open pond reactors need tobe resolved. Exciting developments regarding onlinemeasurements and feedback control for optimalproductivities are part of the solutions andapproaches that need to be followed. Multistagesystems that not only utilise autotrophic growth andstress components, but also combinedautotrophic/heterotrophic systems could providesolutions to specific production requirements. Theseand other important issues are addressed in theoverview. The challenges facing algalbiotechnologists and future research needs are also discussed.     

Significance of algal extracellular products to bacteria in lakes and in cultures

In simulated diurnal experiments withChlorella pyrenoidosa andPseudomonas fluorescens, bacterial growth was virtually confined to the daylight period and occurred at the expense of glycolate, the predominant extracellular product of the alga. Both glycolate levels and¹⁴C-DOC excretion rates were much lower in mixed algal-bacterial than in axenicChlorella cultures.This close coupling of bacterial growth to algal photosynthesis and extracellular release was also observed in Jack's Lake, but not in Lake Erie. Experimental enrichment with lake water particulates >30m suppressed the daytime growth of bacteria in Jack's Lake, but increased it dramatically in Lake Erie. Daylight doubling times for bacteria in lakewater ranged from 2 to 19 days. In mixed culture withChlorella, Pseudomonas had a doubling time of about 2 hours in the light.     

Degradation of trans-1,2-dichloroethene by mixed and pure cultures of methanotrophic bacteria

Summary Out of seven chlorinated aliphatic hydrocarbons tested, only trans-1,2-dichloroethene was relatively non-toxic for a mixed methanotrophic culture. The compound was degraded at a rate of 0.4 mol/mg protein·h^-1 and liberation of inorganic chloride was observed. Trans-2,3-dichlorooxirane was formed as an intermediate which was converted further only by chemical transformation with a half life of 31 h. From the consortium, a pure culture was isolated and found to be capable of degradation of trans-1,2-dichloroethene when grown in the presence of methane or methanol. The ability of cometabolic degradation of this compound was not specific for this isolate, since Methylomonas methanica NCIB11130 and Methylosinus trichosporium OB3b also showed degradation of trans-1,2-dichloroethene when grown with methane as sole carbon source.Abbreviations t12DCE trans-1,2-dichloroethene - t23DCO trans-2,3-dichlorooxirane - c23DCO cis-2,3-dichlorooxirane - ¹H-NMR proton nuclear magnetic resonance     

Turbulence in mass algal cultures and the role of light/dark fluctuations

In mass algal cultures, some form of agitation is usually provided; among other effects, this moves the organisms though an optically dense profile and provides mixing. During this transport, medium frequency fluctuations in the light energy supply are perceived by the algae, which are of the order of 1 Hz and less. It has been suggested that turbulence with the resultant light/dark cycles of medium frequency enhances productivity. However, turbulence has two major influences in a well mixed system: it facilitates fluctuating light regimes and increases the transfer rates between the growth medium and the cultured organism. An estimation of productivity as oxygen liberation was measured under laminar and turbulent flow rates, and varying light/dark ratios. Increased turbulence, which increased exchange rates of nutrients and metabolites between the cells and their growth medium, together with increased light/dark frequencies, increased productivity and photosynthetic efficiency.     

The role of nickel in urea assimilation by algae

Nickel is required for urease synthesis by Phaeodactylum tricornutum and Tetraselmis subcordiformis and for growth on urea by Phaeodactylum. There is no requirement for nickel for urea amidolyase synthesis by Chlorella fusca var. vacuolata. Neither copper nor palladium can substitute for nickel but cobalt partially restored urease activity in Phaeodactylum. The addition of nickel to nickel-deficient cultures of Phaeodactylum or Tetraselmis resulted in a rapid increase of urease activity to 7–30 times the normal level; this increase was not inhibited by cycloheximide. It is concluded that nickel-deficient cells over-produce a non-functional urease protein and that either nickel or the functional urease enzyme participates in the regulation of the production of urease protein.Abbreviation UALase ATP; urea amidolyase     

Tubular photobioreactor design for algal cultures.

Principles of fluid mechanics, gas-liquid mass transfer, and irradiance controlled algal growth are integrated into a method for designing tubular photobioreactors in which the culture is circulated by an airlift pump. A 0.2 m(3) photobioreactor designed using the proposed approach was proved in continuous outdoor culture of the microalga Phaeodactylum tricornutum. The culture performance was assessed under various conditions of irradiance, dilution rates and liquid velocities through the tubular solar collector. A biomass productivity of 1.90 g l(-1) d(-1) (or 32 g m(-2) d(-1)) could be obtained at a dilution rate of 0.04 h(-1). Photoinhibition was observed during hours of peak irradiance; the photosynthetic activity of the cells recovered a few hours later. Linear liquid velocities of 0.50 and 0.35 m s(-1) in the solar collector gave similar biomass productivities, but the culture collapsed at lower velocities. The effect of dissolved oxygen concentration on productivity was quantified in indoor conditions; dissolved oxygen levels higher or lower than air saturation values reduced productivity. Under outdoor conditions, for given levels of oxygen supersaturation, the productivity decline was greater outdoors than indoors, suggesting that under intense outdoor illumination photooxidation contributed to loss of productivity in comparison with productivity loss due to oxygen inhibition alone. Dissolved oxygen values at the outlet of solar collector tube were up to 400% of air saturation.     

Phosphate uptake and utilization by bacteria and algae

Bacterial uptake of inorganic phosphate (closely investigated in Escherichia coli) is maintained by two different uptake systems. One (Pst system) is P_i-repressible and used in situations of phosphorus deficiency. The other system (Pit system) is constitutive. The Pit system also takes part in the phosphate exchange process where orthophosphate is continuously exchanged between the cell and the surrounding medium.Algal uptake mechanisms are less known. The uptake capacity increases during starvation but no clearly defined transport systems have been described. Uptake capacity seems to be regulated by internal phosphorus pools, e.g., polyphosphates. In mixed algal and bacterial populations, bacteria generally seem to be more efficient in utilizing low phosphate concentrations. The second half of this paper discusses how bacteria and algae can share limiting amounts of phosphate provided that the bacteria have pronouncedly higher affinity for phosphate. Part of the solution to this problem may be that bacteria are energy-limited rather than phosphate-limited and dependent on algal organic exudates for their energy supply.The possible phosphate exchange mechanism so convincingly demonstrated in Escherichia coli is here suggested to play a key role for the flux of phosphorus between bacteria and algae. Such a mechanism can also be used to explain the rapid phosphate exchange between the particulate and the dissolved phase which always occurs in short-term ³²P-uptake experiments in lake waters.     

Degradation of alkanes by bacteria

Pollution of soil and water environments by crude oil has been, and is still today, an important problem. Crude oil is a complex mixture of thousands of compounds. Among them, alkanes constitute the major fraction. Alkanes are saturated hydrocarbons of different sizes and structures. Although they are chemically very inert, most of them can be efficiently degraded by several microorganisms. This review summarizes current knowledge on how microorganisms degrade alkanes, focusing on the biochemical pathways used and on how the expression of pathway genes is regulated and integrated within cell physiology.     

Degradation of polychlorinated biphenyls by mixed microbial cultures.

Three different enriched mixed cultures capable of degrading polychlorinated biphenylas were isolated from two soil samples and a river sediment, respectively. The predominant organisms found in all three mixed cultures were Alcaligenes odorans, Alcaligenes dentrificans, and an unidentified bacterium. The polychlorinated biphenyl isomers that were more water soluble and had lower chlorination were not only degraded at a faster rate than those that were less water soluble and had higher chlorination, but were also more completely utilized by these mixed cultures. This resulted in the presence in the environment of polychlorinated biphenyl residues consisting mainly of higher-chlorinated isomers. A form of cometabolism of polychlorinated biphenyls was also found with these cultures in the presence of acetate as the cosubstrate.     

Degradation of polychlorinated biphenyls by mixed microbial cultures.

Three different enriched mixed cultures capable of degrading polychlorinated biphenylas were isolated from two soil samples and a river sediment, respectively. The predominant organisms found in all three mixed cultures were Alcaligenes odorans, Alcaligenes dentrificans, and an unidentified bacterium. The polychlorinated biphenyl isomers that were more water soluble and had lower chlorination were not only degraded at a faster rate than those that were less water soluble and had higher chlorination, but were also more completely utilized by these mixed cultures. This resulted in the presence in the environment of polychlorinated biphenyl residues consisting mainly of higher-chlorinated isomers. A form of cometabolism of polychlorinated biphenyls was also found with these cultures in the presence of acetate as the cosubstrate.     

Copper removal by algae Gelidium, agar extraction algal waste and granulated algal waste: kinetics and equilibrium

Biosorption of copper ions by an industrial algal waste, from agar extraction industry has been studied in a batch system. This biosorbent was compared with the algae Gelidium itself, which is the raw material for agar extraction, and the industrial waste immobilized with polyacrylonitrile (composite material). The effects of contact time, pH, ionic strength (IS) and temperature on the biosorption process have been studied. Equilibrium data follow both Langmuir and Langmuir-Freundlich models. The parameters of Langmuir equilibrium model were: q(max)=33.0mgg(-1), K(L)=0.015mgl(-1); q(max)=16.7mgg(-1), K(L)=0.028mgl(-1) and q(max)=10.3mgg(-1), K(L)=0.160mgl(-1) respectively for Gelidium, algal waste and composite material at pH=5.3, T=20 degrees C and IS=0.001M. Increasing the pH, the number of deprotonated active sites increases and so the uptake capacity of copper ions. In the case of high ionic strengths, the contribution of the electrostatic component to the overall binding decreases, and so the uptake capacity. The temperature has little influence on the uptake capacity principally for low equilibrium copper concentrations. Changes in standard enthalpy, Gibbs energy and entropy during biosorption were determined. Kinetic data at different solution pH (3, 4 and 5.3) were fitted to pseudo-first-order and pseudo-second-order models. The adsorptive behaviour of biosorbent particles was modelled using a batch reactor mass transfer kinetic model, which successfully predicts Cu(II) concentration profiles.     

Degradation of polysaccharides and lignin by ruminal bacteria and fungi.

Bermudagrass (Cynodon dactylon) leaf blades and whole cordgrass (Spartina alterniflora) fiber were evaluated for degradation of cell walls by microbial groups in ruminal fluid. The groups were selected by the addition of antibiotics to the inoculum as follows: (i) whole ruminal fluid (WRF), no antibiotics; (ii) cycloheximide (C) to inhibit fungi, thus showing potential bacterial activity; (iii) streptomycin and penicillin (S,P) to inhibit fiber-degrading bacteria, showing potential fungal activity; (iv) streptomycin, penicillin, and chloramphenicol (S,P,CAM) to inhibit all bacteria including methanogens; (v) streptomycin, penicillin, and cycloheximide (S,P,C) to inhibit all microbial activity as a control; and (vi) autoclaved ruminal fluid (ARF) to inhibit all biological activity as a second control. Scanning electron microscopy of tissue degradation indicated that tissues not giving a positive histological reaction for lignin were more readily degraded. Cordgrass was more highly lignified, with more tissues resisting degradation than in bermudagrass. Patterns of degradation due to treatment resulted in three distinct groups of data based on the extent of fiber or component losses: WRF and C greater than S,P and S,P,CAM greater than S,P,C and ARF. Therefore, bacterial activity was responsible for most of the fiber loss. Fiber degradation by anaerobic fungi was significantly less (P = 0.05). Cupric oxide oxidation of undigested and digested bermudagrass fiber indicated that phenolic constituents differed in their order of resistance to removal or solubilization. Vanillyl and syringyl components of lignin were the most resistant to decomposition, whereas ferulic acid was readily solubilized from fiber in the absence of microbial activity.(ABSTRACT TRUNCATED AT 250 WORDS)     

Present and future needs for algae and algal products

A review of the present needs, mainly for production of phycocolloids and food condiments, is given. Supply and demand vary from balanced, in some, to disproportionate in other fields. World-wide shortage of agarophytes contrasts with huge, unexploited beds of brown seaweeds.In future, partly conflicting trends will decide the needs for algae and algal products. Growth in the human population, pollution, overexploitation of land and lack of freshwater will encourage use of seaweeds. Modern biotechnology will favour this development, but will also be a serious threat to industrial exploitation of seaweeds. Future uses of marine algae will be decisively influenced by the effort put into and the results coming out of seaweed research.     

Degradation and fermentation of cellulose by the rumen anaerobic fungi in axenic cultures or in association with cellulolytic bacteria

Three rumen anaerobic fungi—Neocallinastix frontalis MCH3,Piromyces (Piromonas) communis FL, andCaecomyces (Sphaeromonas) communis FG10—were cultured on cellulose filter paper alone or in association with one of two rumen cellulolytic bacteria,Ruminococcus flavefaciens 007 andFibrobacter succinogenes S85. Cocultures ofN. frontalis orP. communis andR. flavefaciens were markedly less effective than the fungal monocultures in degrading cellulose but more effective than the bacterial monocultures.R. flavefaciens had an antagonistic effect against both of the fungal species. In contrast, no interaction was observed between the two fungal species andF. succinogenes. Cellulose was more effectively degraded by the cocultureC. communis-R. flavefaciens than by the corresponding fungal and bacterial monocultures. The effectiveness of degradation of the cocultureC. communis-F. succinogenes was comparable to that of the bacterial strains but greater than that of the fungi; no interaction was observed between these two microorganisms.