Antibiotic activity of new cyanobacterial isolates from Australia and Asia against green algae and cyanobacteria

One hundred and ninety-eight cyanobacterial strains, newly isolated mainly from samples collected from diverse habitats in Australia, Indonesia, Nepal, Thailand and Vietnam, were screened from their antibiotic activity against green algal species of the genera Coelastrum, Scenedesmus and Monoraphidium. We report the discovery of ten strains of Fischerella, seven of Nostoc and three of Calothrix that produce antialgal compounds with a broad activity spectrum. Some of these bioactive cyanobacteria inhibited all three algae, whereas others inhibited only two, and some only one. In addition, the 20 active strains were tested against other selected cyanobacteria, including Anabaena doliolum which grows well both photoautotrophically in light and heterotrophically in darkness, and three toxic species, Microcytis aeruginosa, Anabaena circinalis and Nodularia spumigena, which are problems in Australia and other parts of the world. At least one Fischerella strain had bioactivity directed against photosynthetic electron transport of algal chloroplasts, whereas others had no effect on photosynthesis. In most cases the growth inhibitory effects were also tested in the presence of a proteinase. The results are discussed in the light of the possible nature of the chemical inhibition and also in relationship to competition and allelopathy in algal populations. This revised version was published online in June 2006 with corrections to the Cover Date.     

Allelopathic activity of Elodea canadensis and Elodea nuttallii against epiphytes and phytoplankton

Elodea nuttallii and Elodea canadensis have both been introduced from North America to Europe. They are now common in many water bodies where they often form dominating stands. It was suggested that negative relationships between Elodea and phytoplankton or epiphytic covers exist, probably due to the release of growth inhibiting allelochemicals. This would be an effective strategy to avoid light limitation caused by algae and cyanobacteria. We investigated the allelopathic potential of both E. nuttallii and E. canadensis against different photoautotrophs, focussing on epiphytic algae and cyanobacteria isolated from different submersed macrophytes and culture strains. Methanolic extracts of both species inhibited the growth of most of these organisms. Only a culture strain of Scenedesmus brevispina was stimulated. Further separation of extracts yielded several active fractions, indicating that hydrophilic and slightly lipophilic compounds were responsible for growth reduction. At least some of the activity seems to be related to phenolic substances, but flavonoids in these species are inactive. Since growth declined also in a moderately lipophilic fraction of culture filtrate of E. nuttallii, we assume that active compounds were exuded in the water. Allelopathy might thus be relevant in situ and suppress cyanobacteria and algae. We furthermore found differences in the susceptibility of target organisms, which could (1) at least partly be a result of adaptation to the respective host plants and (2) indicate that allelopathic interference might reduce the abundance of some species, especially cyanobacteria, in epiphytic biofilms.     

Antibiotic activity of epiphytic bacteria isolated from intertidal seaweeds

A survey of antibiotic-producing bacteria from the microbial flora attached to seaweeds and the study of their antibiotic capacities were carried out. From 5 species of green and brown marine algae, 224 bacterial strains were isolated and tested for antibiotic production. A total of 38 strains displayed antibiotic activity, withEnteromorpha intestinalis being the source of the highest number of producer strains. All epiphytic bacteria with antibiotic activity were assigned to thePseudomonas-Alteromonas group. Antagonism assays among the isolates demonstrated that each producer strain inhibits the growth of the other producers, as well as of some nonproducer strains also isolated from seaweeds. Likewise, an autoinhibitory effect was observed in all antibiotic-producing strains. Antibacterial spectra of all the strains include activity againstStaphylococcus, Alcaligenes, Pseudomonas, Vibrio, Pasteurella, andAchromobacter. A preliminary characterization of the antibiotic substances produced by these epiphytic bacteria demonstrated that they are low molecular weight compounds, thermolabile, and anionic and are not affected by proteolytic enzymes. The role that these inhibitory substances can play in the natural environment is discussed.     

链霉菌6803菌株对植物的化感作用

链霉菌属是绝大多数已知抗生素和一些重要活性物质的产生菌,它对高等植物是否具有化感作用尚缺乏研究. 从土壤中分离获得7个放线菌菌株,研究其对植物幼苗生长的抑制作用.结果表明： 链霉菌6803菌株在固体和液体发酵培养时均强烈抑制油菜根和稗草根的生长, 其液体发酵液的5倍稀释液对油菜和稗草苗生长的抑制分别达到60.7%和61.3%. 常规形态与生理生化试验表明,该菌株属于链霉菌属金色类群; 16S rRNA基因序列分析表明,该菌株为沙场链霉菌,基因序列相似性达到99.28%. 此菌株经过80～100 s紫外线照射筛选出的正突变菌株UV8024和UV100-2的10倍稀释发酵液对油菜幼苗生长的抑制作用比原始菌株分别提高了37.5%和38.1%, 经过1%硫酸二乙酯诱变50 min筛选出的正突变菌株D507的10倍稀释发酵液对油菜幼苗生长的抑制作用比原始菌株提高了29.8%. 链霉菌6803菌株对高等植物具有化感作用, 并可通过诱变育种提高其化感潜力.     

Characterization of true-branching cyanobacteria from geothermal sites and hot springs of Costa Rica

Costa Rica is at the centre of the Mesoamerican biodiversity hotspot. Little is known about cyanobacteria from this region so far. Here, four isolates of the order Stigonematales (section V) were characterized in a polyphasic approach. All strains were isolated from geothermal sites and hot springs of Costa Rica. However, one of them, identified as Westiellopsis sp. Ar73, did not grow at more than 40°C. Based on its identical 16S rRNA to several previously isolated Westiellopsis sp. and Fischerella muscicola strains, a ubiquitous distribution throughout tropical and subtropical regions can be implied. In contrast, the isolates MV9, MV11 and RV14 grew well up to 50–55°C. Based on morphologic, ultrastructural, molecular and physiologic data, MV9, MV11 and RV14 were identified to belong to the genus Fischerella . Two distinct intergenic transcribed spacer (ITS) types, with or without tRNA genes, were detected for all Stigonematales analysed here, indicating ITS polymorphism as a characteristic feature of heterocystous cyanobacteria. In phylogenetic trees, these Fischerella spp. formed a new and distinct clade within the wider lineage of thermophilic Fischerella ( Mastigocladus cf. laminosus ), which might represent a geographic lineage. Thus, geographic isolation may be an underestimated aspect of microbial evolution. The strains presented here are suitable as new models to study this group of cyanobacteria.     

Effect of Bacteria Associated with the Green Alga Ulva reticulata on Marine Micro- and Macrofouling

The green alga Ulva reticulata (Forsskal) is often free from biofouling in Hong Kong waters. An early study indicated that bioactive substances from this alga inhibit settlement of the polychaete Hydroides elegans (Haswell). It is also predicted that epibiotic bacteria protect this alga from micro- and macrofouling. In this study, bacterial strains from the surface of U. reticulata were isolated and their inhibitive activities on micro- and macrofouling assayed. The strains were identified by 16S rRNA analysis as belonging to the genera Alteromonas , Pseudoalteromonas and Vibrio . There was no significant effect of these strains or their extracts (aqueous and ethanol) on the growth of five Vibrio strains isolated from natural biofilm. Two bacterial strains ( Alteromonas sp. and Vibrio sp. 3) were non-toxic to the benthic diatom Nitzschia paleacea (Grunow) while the other five strains caused a low level of mortality. No one bacterial strain was toxic to the larvae of H. elegans . Aqueous extract of one of the isolated bacterial species, i.e. Vibrio sp. 2, significantly ( p <0.00001) inhibited the settlement and metamorphosis of H. elegans larvae. The putative antifouling compounds have a molecular weight of >100 kD. On the other hand, biofilm of Pseudoalteromonas sp. 2 and aqueous extract of Vibrio sp. 2 suppressed the settlement of larvae induced by 3-isobutyl-1-methylxanthine (IBMX). Other epibiotic bacteria and their extracts had neither inhibitive nor inductive effects on larval settlement of H. elegans . The results indicate that the antifouling mechanism of U. reticulata may be dependent not only on materials from the macroalga itself but also on the epibiotic bacteria on the algal surface.     

Antibiotic effects of three strains of chrysophytes (Ochromonas, Poterioochromonas) on freshwater bacterial isolates

We investigated the antibiotic effects of extracts of freeze-dried biomass and culture supernatants from the mixotrophic chrysophyte species Ochromonas danica, Poterioochromonas sp. strain DS, and Poterioochromonas malhamensis on bacterial strains isolated from lake water. Methanolic biomass extracts inhibited the growth of all tested strains, albeit to a different extent, whereas aqueous biomass extracts only affected bacteria of the genus Flectobacillus . The antibiotic action of supernatants from flagellate cultures could be mostly attributed to lipophilic substances, but the growth of bacteria affiliated with Flectobacillus and Sphingobium was also affected by hydrophilic compounds. A comparison of biomass extracts from light- and dark-adapted cultures of Poterioochromonas sp. strain DS showed that the growth-inhibiting factor was unrelated to chlorophyll derivatives. Supernatants from a dark-adapted, phagotrophically grown flagellate culture had stronger antibiotic effects and affected more bacterial strains than the supernatant from a light-adapted culture. Significant growth reduction of a Flectobacillus isolate was already induced by extremely low concentrations of lipophilic extracts from these supernatants. Our results show that metabolites of the studied flagellates − either released actively or during cell lysis − may selectively affect the growth of some aquatic bacteria even in very small doses and thus potentially affect microbial community composition. Moreover, the antibiotic potential of mixotrophic chrysophytes may change with their nutritional mode.     

广西柳树桑寄生内生真菌的分离鉴定与抗肿瘤活性菌株筛选

该研究从广西钦州市采集健康的柳树桑寄生的根、茎和叶中分离并纯化内生真菌,对真菌进行形态学鉴定,提取内生真菌的DNA,采用真菌ITS序列对内生真菌进行分子鉴定。利用A549和H460细胞作为抗肿瘤活性指示细胞,采用MTT法测定真菌乙酸乙酯提取物的抗肿瘤活性。经过初步分离分析,从柳树桑寄生中纯化出27株内生真菌,经鉴定它们分别属于7个目9个属15个种。拟盘多毛孢属和间座壳属为优势属,其中拟盘多毛孢属全部定植于寄生根;其次为新壳梭孢属、拟茎点霉属和球座菌属,各分离到3株;其他包括青霉属、镰刀菌属、炭疽菌属和派伦霉属,各分离到1株。抗肿瘤活性研究表明,有一株与Pestalotiopsis protearum的ITS序列相似性达100%的拟盘多毛孢属菌株Gen24表现有抑制肿瘤细胞A549和H460生长的特性,在真菌乙酸乙酯浸提物浓度为800μg·mL~(-1)时,对A549细胞的抑制率达到了56.92%,对H460细胞的抑制率达到了70.11%。该研究结果表明广西柳树桑寄生内生真菌较丰富,在寄主中的分布表现了一定的组织特异性,而且还存在一些具有抗肿瘤活性的菌株及其活性物质可供进一步深入研究。     

Uptake of Pb2+ by a cyanobacterium belonging to the genus Synechocystis, isolated from East Kolkata Wetlands

East Kolkata Wetlands is a conserved wetland utilizing sewage and garbage, generated by Kolkata Municipal Corporation area for cultivation purpose. Cyanobacteria are the photosynthetic prokaryotes having bioremedial capacity. We have isolated a cyanobacterium from the sewage recycling fish-pond of East Kolkata Wetlands. Partial sequence of 16S rDNA gene of the isolated strain showed 100% similarity with that of genus Synechocystis. Isolated strain and Synechocystis sp. PCC6803 survived up to 300 mug ml(-1) Pb(2+ )and growth was completely inhibited at 400 mug ml(-1) Pb(2+). All experiments were carried out with 100 mug ml(-1) Pb(2+) in which growth was the maximum. 91.67% of the total Pb(2+) got adsorbed to the outer surface of the cell and 1% of the total Pb(2+) entered the cell of the isolated strain as estimated by atomic absorption spectrometry, but in Synechocystis sp. PCC6803 72.72% adsorbed and 0.96% penetrated. Intracellular and periplasmic depositions of Pb(2+) were observed in both the strain. A filamentous structure developed outside the cell wall of the isolated cyanobacterium, but very little change was observed in Synechocystis sp. PCC6803. ZiaR-SmtB like regulator gene was expressed in both the strains after Pb(2+) induction. The cDNA sequence of ZiaR of the isolated cyanobacterium shows 100% homology with that of Synechocystis sp. PCC6803. Upon Pb(2+) induction, expression of SOD gene increased. cDNA sequence of the SOD gene from the isolated strain showed 98% homology with that of Synechocystis sp. PCC6803. Enzymatic activity of catalase and SOD was also increased. No DNA damage was monitored upon induction with Pb(2+).     

Microbial utilization of the industrial wastewater pollutants 2-ethylhexylthioglycolic acid and <Emphasis Type="Italic">iso</Emphasis>-octylthioglycolic acid by aerobic Gram-negative bacteria

Industrial wastewater from the production of sulfur containing esters and the resulting products of this synthesis, 2-ethylhexylthioglycolic acid (EHTG) and iso-octylthioglycolic acid (IOTG), were deployed in this study to enrich novel bacterial strains, since no wastewater and EHTG or IOTG degrading microorganisms were hitherto described or available. In addition, nothing is known about the biodegradation of these thiochemicals. The effect of this specific wastewater on the growth behaviour of microorganisms was investigated using three well-known Gram-negative bacteria (Escherichia coli, Pseudomonas putida, and Ralstonia eutropha). Concentrations of 5% (v/v) wastewater in complex media completely inhibited growth of these three bacterial strains. Six bacterial strains were successfully isolated, characterized and identified by sequencing their 16S rRNA genes. Two isolates referred to as Achromobacter sp. strain MT-E3 and Pseudomonas sp. strain MT-I1 used EHTG or IOTG, respectively, as well as the wastewater as sole source of carbon and energy for weak growth. More notably, both isolates removed these sulfur containing esters in remarkable amounts from the cultures supernatant. One further isolate was referred to as Klebsiella sp. strain 58 and exhibited an unusual high tolerance against the wastewater’s toxicity without utilizing the contaminative compounds. If cultivated with gluconic acid as additional carbon source, the strain grew even in presence of more than 40% (v/v) wastewater. Three other isolates belonging to the genera Bordetella and Pseudomonas tolerated these organic sulfur compounds but showed no degradation abilities.     

Antibacterial, antifungal and cytotoxic activity of terrestrial cyanobacterial strains from Serbia

Cyanobacteria are known to be a rich source of biologically active compounds some of which can have pharmaceutical importance. In this work we present the screening results of cyanobacterial strains for their antibacterial, antifungal, and cytotoxic activity. Cyanobacterial strains were isolated from various soil types in province of Vojvodina and Central Serbia, Republic of Serbia. The screening included 9 strains of Anabaena and 9 strains of Nostoc. Both, extracellular products (from the culture liquid) and cellular crude lipophilic extracts were tested against 13 bacterial strains and 8 fungal strains. Cytotoxic activity was tested against three human cell lines. Methanol extracts were prepared according to ?stensvik. Antibacterial and antifungal activities were determined measuring inhibition zone, 48 h after inoculation. The cytotoxic activity was determined by sulforhodamine B (SRB) colorimetric assay. Of all cyanobacterial strains tested, 52% showed some antifungal and 41% antibacterial activity. Two out of six tested strains possessed cytotoxic activity. The cytotoxic activity of Anabaena strain S12 was found both in culture liquid and crude cell extract. It occurred specifically between the 21st and 42nd day of cultivation against HeLa and MCF7 cells, but had no activity against cell line derived from a healthy tissue. A high percentage of the active strains among the tested strains justify the effort of screening cyanobacteria that are isolated from terrestrial environments. The most promising strains for the fur- ther study are Anabaena strain S12 which showed strong cytotoxic and antibacterial activity and Ana- baena strain S20 which produces a potent antifungal compound. The future work, besides further screening and chemical identification of the active compounds, should also include the development of culture techniques that would lead to more efficient production of biologically active compounds.     

Synergistic effects in mixed Escherichia coli biofilms: conjugative plasmid transfer drives biofilm expansion

Bacterial biofilms, often composed of multiple species and genetically distinct strains, develop under complex influences of cell-cell interactions. Although detailed knowledge about the mechanisms underlying formation of single-species laboratory biofilms has emerged, little is known about the pathways governing development of more complex heterogeneous communities. In this study, we established a laboratory model where biofilm-stimulating effects due to interactions between genetically diverse strains of Escherichia coli were monitored. Synergistic induction of biofilm formation resulting from the cocultivation of 403 undomesticated E. coli strains with a characterized E. coli K-12 strain was detected at a significant frequency. The survey suggests that different mechanisms underlie the observed stimulation, yet synergistic development of biofilm within the subset of E. coli isolates (n = 56) exhibiting the strongest effects was most often linked to conjugative transmission of natural plasmids carried by the E. coli isolates (70%). Thus, the capacity of an isolate to promote the biofilm through cocultivation was (i) transferable to the K-12 strain, (ii) was linked with the acquisition of conjugation genes present initially in the isolate, and (iii) was inhibited through the presence in the cocultured K-12 strain of a related conjugative plasmid, presumably due to surface exclusion functions. Synergistic effects of cocultivation of pairs of natural isolates were also observed, demonstrating that biofilm promotion in this system is not dependent on the laboratory strain and that the described model system could provide relevant insights on mechanisms of biofilm development in natural E. coli populations.     

两株溶藻细菌的分离及初步研究

选择藻华现象严重的巢湖作为采样点,取3个不同位置的水样通过0.22μm的纤维滤膜过滤,培养后加入适应期的藻液中,取黄化藻液作为分离菌种的材料,初筛菌株经反复试验获得有较强抑藻能力的菌株,经生理生化鉴定及16S rDNA分子鉴定其种属。初筛得到45个菌株,有两个菌株WD1和WD2表现出溶藻作用。两株细菌的菌液经离心、高温灭菌、细胞破碎等处理对供试藻鱼腥藻也均有不同程度的抑制作用。分离得到两株溶藻细菌,WD1为约氏不动杆菌,WD2为门多萨假单胞菌。     

Microbial Community Changes Elicited by Exposure to Cyanobacterial Allelochemicals

An increasing body of evidence points out that allelopathy may be an important process shaping microbial communities in aquatic ecosystems. Cyanobacteria have well-documented allelopathic properties, mainly derived from the evaluation of the activity of allelopathic extracts or pure compounds towards monocultures of selected target microorganisms. Consequently, little is known regarding the community dynamics of microorganisms associated with allelopathic interactions. In this laboratory-based study, a Microcystis spp.-dominated microbial community from a freshwater lake was exposed, for 15 days, to exudates from the cyanobacterium Oscillatoria sp. strain LEGE 05292 in laboratory conditions. This cyanobacterium is known to produce the allelochemicals portoamides, which were among the exuded compounds. The community composition was followed (by means of polymerase chain reaction followed by denaturing gradient gel electrophoresis and microscopic analyses) and compared to that of a non-exposed situation. Following exposure, clear differences in the community structure were observed, in particular for cyanobacteria and unicellular eukaryotic taxa. Interestingly, distinct Microcystis genotypes present in the community were differentially impacted by the exposure, highlighting the fine-scale dynamics elicited by the exudates. These results support a role for cyanobacterial allelochemicals in the structuring of aquatic microbial communities.     

Regulation of PSII function in Cyanothece sp. ATCC 51142 during a light–dark cycle

Photosynthesis Research - Cyanobacteria, as well as green algae and higher plants, have highly conserved photosynthetic machinery. Cyanothece sp. ATCC 51142 is a unicellular, aerobic, diazotrophic...     

Isolation and characterization of endophytic streptomycete antagonists of Fusarium wilt pathogen from surface-sterilized banana roots

A total of 131 endophytic actinomycete strains were successfully isolated from surface-sterilized banana roots. These isolates belonged to Streptomyces (n=99), Streptoverticillium (n=28), and Streptosporangium (n=2) spp. The remaining 2 isolates were not identified. About 18.3% of the isolates inhibited the growth of pathogenic Fusarium oxysporum f. sp. cubense on banana tissue extract medium. The most frequently isolated Streptomyces sp. strain S96 was similar to Streptomyces griseorubiginosus. About 37.5% of the S. griseorubiginosus strains were antagonistic to F. oxysporum f. sp. cubense. The antagonism of strain S96 was lost when FeCl(3) was introduced into the inhibition zone. In vivo biocontrol assays showed that the disease severity index (DSI) was significantly (P=0.05) reduced and mean fresh weight increased (P=0.001) in plantlets treated with strain S96 compared to those grown in the absence of the biocontrol strain. These findings indicate the potential of developing siderophore-producing Streptomyces endophytes for the biological control of fusarium wilt disease of banana.     

Characterization of S-triazine herbicide metabolism by a Nocardioides sp. isolated from agricultural soils

Atrazine, a herbicide widely used in corn production, is a frequently detected groundwater contaminant. Nine gram-positive bacterial strains able to use this herbicide as a sole source of nitrogen were isolated from four farms in central Canada. The strains were divided into two groups based on repetitive extragenic palindromic (rep)-PCR genomic fingerprinting with ERIC and BOXA1R primers. Based on 16S ribosomal DNA sequence analysis, both groups were identified as Nocardioides sp. strains. None of the isolates mineralized [ring-U-(14)C]atrazine. There was no hybridization to genomic DNA from these strains using atzABC cloned from Pseudomonas sp. strain ADP or trzA cloned from Rhodococcus corallinus. S-Triazine degradation was studied in detail in Nocardioides sp. strain C190. Oxygen was not required for atrazine degradation by whole cells or cell extracts. Based on high-pressure liquid chromatography and mass spectrometric analyses of products formed from atrazine in incubations of whole cells with H(2)(18)O, sequential hydrolytic reactions converted atrazine to hydroxyatrazine and then to the end product N-ethylammelide. Isopropylamine, the putative product of the second hydrolytic reaction, supported growth as the sole carbon and nitrogen source. The triazine hydrolase from strain C190 was isolated and purified and found to have a K(m) for atrazine of 25 microM and a V(max) of 31 micromol/min/mg of protein. The subunit molecular mass of the protein was 52 kDa. Atrazine hydrolysis was not inhibited by 500 microM EDTA but was inhibited by 100 microM Mg, Cu, Co, or Zn. Whole cells and purified triazine hydrolase converted a range of chlorine or methylthio-substituted herbicides to the corresponding hydroxy derivatives. In summary, an atrazine-metabolizing Nocardioides sp. widely distributed in agricultural soils degrades a range of s-triazine herbicides by means of a novel s-triazine hydrolase.     

Phylogenetic analysis of antimicrobial lactic acid bacteria from farmed seabass Dicentrarchus labrax

The use of lactic acid bacteria (LAB) in the prevention or reduction of fish diseases is receiving increasing attention. In the present study, 47 LAB strains were isolated from farmed seabass ( Dicentrarchus labrax ) and were phenotypically and phylogenetically analysed by 16S rDNA and randomly amplified polymorphic DNA - polymerase chain reaction (RAPD-PCR). Their antimicrobial effect was tested in vitro against a wide variety of pathogenic and spoilage bacteria. Most of the strains isolated were enterococci belonging to the following species: Enterococcus faecium (59%), Enterococcus faecalis (21%), Enterococcus sanguinicola (4 strains), Enterococcus mundtii (1 strain), Enterococcus pseudoavium (1 strain), and Lactococcus lactis (1 strain). An Aerococcus viridans strain was also isolated. The survey of their antimicrobial susceptibility showed that all isolates were sensitive to vancomycin and exhibited resistance to between 4 and 10 other antibiotics relevant for therapy in human and animal medicine. Different patterns of resistance were noted for skin and intestines isolates. More than 69% (32 strains) of the isolates inhibited the growth of the majority of pathogenic and spoilage bacteria tested, including Listeria monocytogenes, Staphylococcus aureus, Aeromonas hydrophila, Aeromonas salmonicida, Vibrio anguillarum, and Carnobacterium sp. To our knowledge, this is the first report of bioactive enterococcal species isolated from seabass that could potentially inhibit the undesirable bacteria found in food systems.     

Evidence for a new pathway in the bacterial degradation of 4-fluorobenzoate

Six bacterial strains able to use 4-fluorobenzoic acid as their sole source of carbon and energy were isolated by selective enrichment from various water and soil samples from the Stuttgart area. According to their responses in biochemical and morphological tests, the organisms were assigned to the genera Alcaligenes, Pseudomonas, and Aureobacterium. To elucidate the degradation pathway of 4-fluorobenzoate, metabolic intermediates were identified. Five gram-negative isolates degraded this substrate via 4-fluorocatechol, as described in previous studies. In growth experiments, these strains excreted 50 to 90% of the fluoride from fluorobenzoate. Alcaligenes sp. strains RHO21 and RHO22 used all three isomers of monofluorobenzoate. Alcaligenes sp. strain RHO22 also grew on 4-chlorobenzoate. Aureobacterium sp. strain RHO25 transiently excreted 4-hydroxybenzoate into the culture medium during growth on 4-fluorobenzoate, and stoichiometric amounts of fluoride were released. In cell extracts from this strain, the enzymes for the conversion of 4-fluorobenzoate, 4-hydroxybenzoate, and 3,4-dihydroxybenzoate could be detected. All these enzymes were inducible by 4-fluorobenzoate. These data suggest a new pathway for the degradation of 4-fluorobenzoate by Aureobacterium sp. strain RHO25 via 4-hydroxybenzoate and 3,4-dihydroxybenzoate.     

Evidence for a new pathway in the bacterial degradation of 4-fluorobenzoate.

Six bacterial strains able to use 4-fluorobenzoic acid as their sole source of carbon and energy were isolated by selective enrichment from various water and soil samples from the Stuttgart area. According to their responses in biochemical and morphological tests, the organisms were assigned to the genera Alcaligenes, Pseudomonas, and Aureobacterium. To elucidate the degradation pathway of 4-fluorobenzoate, metabolic intermediates were identified. Five gram-negative isolates degraded this substrate via 4-fluorocatechol, as described in previous studies. In growth experiments, these strains excreted 50 to 90% of the fluoride from fluorobenzoate. Alcaligenes sp. strains RHO21 and RHO22 used all three isomers of monofluorobenzoate. Alcaligenes sp. strain RHO22 also grew on 4-chlorobenzoate. Aureobacterium sp. strain RHO25 transiently excreted 4-hydroxybenzoate into the culture medium during growth on 4-fluorobenzoate, and stoichiometric amounts of fluoride were released. In cell extracts from this strain, the enzymes for the conversion of 4-fluorobenzoate, 4-hydroxybenzoate, and 3,4-dihydroxybenzoate could be detected. All these enzymes were inducible by 4-fluorobenzoate. These data suggest a new pathway for the degradation of 4-fluorobenzoate by Aureobacterium sp. strain RHO25 via 4-hydroxybenzoate and 3,4-dihydroxybenzoate.