Screening for biologically active metabolites with endosymbiotic bacilli isolated from arthropods

GC Analysis, Anticancer, and Antibacterial Activities of Secondary Bioactive Compounds from Endosymbiotic Bacteria of Pomegranate Aphid and Its Predator and Protector

Bacterial secondary metabolites are a valuable source of various molecules that have antibacterial and anticancer activity. In this study, ten endosymbiotic bacteria of aphids, aphid predators and ants were isolated. Bacterial strains were identified according to the 16S rRNA gene. Ethyl acetate fractions of methanol extract (EA-ME) were prepared from each isolated bacterium and tested for their antibacterial activities using the disk diffusion method. The EA-ME of three bacterial species, Planococcus sp., Klebsiella aerogenes, Enterococcus avium, from the pomegranate aphids Aphis punicae, Chrysoperia carnea, and Tapinoma magnum, respectively, exhibited elevated antibacterial activity against one or several of the five pathogenic bacteria tested. The inhibition zones ranged from 10.00 ± 0.13 to 20.00 ± 1.11 mm, with minimum inhibitory concentration (MIC) values ranging from 0.156 mg/mL to 1.25 mg/mL. The most notable antibacterial activity was found in the EA-ME of K. aerogenes against Klebsiella pneumonia and Escherichia coli, with an MIC value of 0.156 mg/mL. The cytotoxic activity of EA-ME was dependent on the cell line tested. The most significant cytotoxicity effect was observed for extracts of K. aerogenes and E. avium, at 12.5 µg/mL, against the epithelial cells of lung carcinoma (A549), with a cell reduction of 79.4% and 67.2%, respectively. For the EA-ME of K. aerogenes and Pantoea agglomerans at 12.5 µg/mL, 69.4% and 67.8% cell reduction were observed against human colon cancer (Hct116), respectively. Gas chromatography-mass spectrometry (GC-MS) analysis of three EA-ME revealed the presence of several bioactive secondary metabolites that have been reported previously to possess antibacterial and anticancer properties. To the best of our knowledge, this is the first study to examine the biological activities of endosymbiotic bacteria in aphids, aphid predators and ants. The promising data presented in this study may pave the way for alternative drugs to overcome the continued emergence of multidrug-resistant bacteria, and find alternative drugs to conventional cancer therapies.

Sulochrins and alkaloids from a fennel endophyte Aspergillus sp. FVL2

The fungal endophyte Aspergillus sp. strain FVL2, isolated from the traditional medicinal fennel plant, Foeniculum vulgare, was investigated for secondary metabolites. Fermentation on rice medium followed by chromatographic separation delivered three new natural products, 7-demethyl-neosulochrin (1), fumigaclavine I (3) and N-benzoyl-tryptophan (6) together with further 14 known metabolites, 1-O-methyl-sulochrin-4'-sulfate, questin, laccaic acid, isorhodoptilometrin, fumigaclavine A, fumigaclavine C, fumitremorgin C, fumigaquinazoline C, tryptoquivaline J, trypacidin, 3'-O-demethyl-sulochrin, 1-O-methyl-sulochrin, protocatechuic acid, and vermelone. The chemical structures of the new metabolites were determined by NMR spectroscopy and ESI HR mass spectrometry. For fumigaclavine I, we observed the partial deuterium transfer from the solvent to the enol form with a remarkable high stereo selectivity. The discovery of the new seco-anthraquinone 7-demethyl-neosulochrin (1) revealed a second type of ring cleavage by a questin oxygenase. The discovery of diverse secondary metabolites broadens the chemical space of Aspergillus.

Recent Advances of Marine Natural Indole Products in Chemical and Biological Aspects

The ocean has always been one of the important sources of natural products. In recent years, many natural products with different structures and biological activities have been obtained, and their value has been clearly recognized. Researchers have been deeply engaged in the field of separation and extraction, derivative synthesis, structural studies, biological evaluation, and other fields of research for marine natural products. Thus, a series of marine indole natural products which have structural and biological prospect have caught our eyes. In this review, we summarize some of these marine indole natural products with relatively good pharmacological activity and research value, and discuss issues concerning chemistry, pharmacological activity, biological evaluation, and synthesis, including monomeric indoles, indole peptides, bis-indoles, and annelated indoles. Most of the compounds have cytotoxic, antiviral, antifungal, or anti-inflammatory activities.

Characterization of the antimicrobial activity produced by Bacillus sp. isolated from wetland sediment

Bacteria of the genus Bacillus sp. present the potential for inhibiting various pathogens, making them a promising starting point in the search for new antimicrobial substances. In this study, bacteria were isolated from sediment samples from humid areas of a Natural Conservation Unit in the state of Rio Grande do Sul, Brazil. The isolate Bacillus sp. sed 1.4 was selected for production of antimicrobial activity, and was characterized by MALDI-TOF and 16S rDNA sequencing. Phylogenetic analysis showed that Bacillus sed 1.4 was closely related to Bacillus altitudinis and Bacillus pumilus. The cell-free supernatant was partially purified using ammonium sulfate precipitation, gel filtration chromatography (Sephadex G-200) and an ultrafiltration membrane. Partial purification resulted in specific activity of 769.23 AU/mg, with a molecular mass of approximately 148 kDa. This antimicrobial substance showed stability at 100°C for 5 min, and was inactivated by proteolytic enzymes. An antimicrobial effect against Listeria species was observed. Considering the importance of the Listeria genus in the area of food safety, this antimicrobial activity should be further explored, specifically in the field of dairy products and with a focus on food biopreservation studies.

Novel Antibacterial Strategies for Combating Bacterial Multidrug Resistance

BACKGROUND

Antibacterial multidrug resistance has emerged as one of the foremost global problems affecting human health. The emergence of resistant infections with the increasing number of multidrug-resistant pathogens has posed a serious problem, which required innovative collaborations across multiple disciplines to address this issue.

METHODS

In this review, we will explain the mechanisms of bacterial multidrug resistance and discuss different strategies for combating it, including combination therapy, the use of novel natural antibiotics, and the use of nanotechnology in the development of efflux pump inhibitors.

RESULTS

While combination therapy will remain the mainstay of bacterial multi-drug resistance treatment, nanotechnology will play critical roles in the development of novel treatments in the coming years.

CONCLUSION

Nanotechnology provides an encouraging platform for the development of clinically relevant and practical strategies to overcome drug resistance in the future.

Antimicrobial activity of bacteria from marine sponge Suberea mollis and bioactive metabolites of Vibrio sp. EA348

Discovery of potential bioactive metabolites from sponge-associated bacteria have gained attraction in recent years. The current study explores the potential of sponge (Suberea mollis) associated bacteria against bacterial and fungal pathogens. Sponge samples were collected from Red sea in Obhur region, Jeddah, Saudi Arabia. Of 29 isolated bacteria belong to four different classes i.e. Firmicutes (62%), γ-Proteobacteria (21%), α-Proteobacteria (10%) and Actinobacteria (7%). Among them nineteen (65%) bacterial strains showed antagonistic activity against oomycetes and only 3 (10%) bacterial strains were active against human pathogenic bacteria tested. Most bioactive genera include Bacillus (55%), Pseudovibrio (13%) and Ruegeria (10%). Enzyme production (protease, lipase, amylase, cellualse) was identified in 12 (41%) bacterial strains where potential strains belonging to γ-Proteobacteria and Firmicutes groups. Production of antimicrobial metabolites and hydrolysates in these bacteria suggest their potential role in sponge against pathogens. Further bioactive metabolites from selected strain of Vibrio sp. EA348 were identified using LC-MS and GC–MS analyses. We identified many active metabolites including antibiotics such as Amifloxacin and fosfomycin. Plant growth hormones including Indoleacetic acid and Gibberellin A3 and volatile organic compound such as methyl jasmonate were also detected in this strain. Our results highlighted the importance of marine bacteria inhabiting sponges as potential source of antimicrobial compounds and plant growth hormones of pharmaceutical and agricultural significance.

Future directions for the discovery of antibiotics from actinomycete bacteria

Antimicrobial resistance (AMR) is a growing societal problem, and without new anti-infective drugs, the UK government-commissioned O'Neil report has predicted that infectious disease will claim the lives of an additional 10 million people a year worldwide by 2050. Almost all the antibiotics currently in clinical use are derived from the secondary metabolites of a group of filamentous soil bacteria called actinomycetes, most notably in the genus Streptomyces. Unfortunately, the discovery of these strains and their natural products (NPs) peaked in the 1950s and was then largely abandoned, partly due to the repeated rediscovery of known strains and compounds. Attention turned instead to rational target-based drug design, but this was largely unsuccessful and few new antibiotics have made it to clinic in the last 60 years. In the early 2000s, however, genome sequencing of the first Streptomyces species reinvigorated interest in NP discovery because it revealed the presence of numerous cryptic NP biosynthetic gene clusters that are not expressed in the laboratory. Here, we describe how the use of new technologies, including improved culture-dependent and -independent techniques, combined with searching underexplored environments, promises to identify a new generation of NP antibiotics from actinomycete bacteria.

Characterization of cellulose degrading bacteria from the larval gut of the white grub beetle Lepidiota mansueta (Coleoptera: Scarabaeidae)

The goal of this study is to identify and characterize the cellulose degrading microorganisms in the larval gut of the white grub beetle, Lepidiota mansueta. Thirty bacterial strains were isolated and tested for cellulolytic activity using soluble carboxymethyl cellulose (CMC) degrading assays. Of these strains, five (FGB1, FB2, MB1, MB2, and HB1) degrade cellulose. Cellulolytic activity was determined based on formation of clear zone and cellulolytic index on CMC plate media. The highest cellulolytic index (2.14) was found in FGB1. Partial 16S rDNA sequencing, morphological, and biochemical tests were used to identify and characterize the five isolates, all Citrobacter sp. (Enterobacteriaceae). This study identifies new cellulose degrading microorganisms from the larval gut of L. mansueta. The significance of identifying these strains lies in possible application in cellulose degradation.

Isolation and Characterization of a Broad Spectrum Bacteriocin from Bacillus amyloliquefaciens RX7

We isolated a Bacillus strain, RX7, with inhibitory activity against Listeria monocytogenes from soil and identified it as Bacillus amyloliquefaciens based on 16S rRNA gene sequencing. The inhibitory activity was stable over a wide range of pH and was fully retained after 30 min at 80°C, after which it decreased gradually at higher temperatures. The activity was sensitive to the proteolytic action of α-chymotrypsin, proteinase-K, and trypsin, indicating its proteinaceous nature. This bacteriocin was active against a broad spectrum of bacteria and the fungus Candida albicans. Direct detection of antimicrobial activity on a sodium dodecyl sulfate-polyacrylamide gel suggested an apparent molecular mass of approximately 5 kDa. Ammonium sulfate precipitation and anion-exchange and gel permeation chromatography integrated with reverse phase-high-performance liquid chromatography were used for bacteriocin purification. Automated N-terminal Edman degradation of the purified RX7 bacteriocin recognized the first 15 amino acids as NH2-X-Ala-Trp-Tyr-Asp-Ile-Arg-Lys-Leu-Gly-Asn-Lys-Gly-Ala, where the letter X in the sequence indicates an unknown or nonstandard amino acid. Based on BLAST similarity search and multiple alignment analysis, the obtained partial sequence showed high homology with the two-peptide lantibiotic haloduracin (HalA1) from Bacillus halodurans, although at least two amino acids differed between the sequences. A time-kill study demonstrated a bactericidal mode of action of RX7 bacteriocin.

Detection of carboxylesterase and esterase activity in culturable gut bacterial flora isolated from diamondback moth, Plutella xylostella (Linnaeus), from India and its possible role in indoxacarb degradation

Diamondback moth (DBM), Plutella xylostella (Linnaeus), is a notorious pest of brassica crops worldwide and is resistant to all groups of insecticides. The insect system harbors diverse groups of microbiota, which in turn helps in enzymatic degradation of xenobiotic-like insecticides. The present study aimed to determine the diversity of gut microflora in DBM, quantify esterase activity and elucidate their possible role in degradation of indoxacarb. We screened 11 geographic populations of DBM in India and analyzed them for bacterial diversity. The culturable gut bacterial flora underwent molecular characterization with 16S rRNA. We obtained 25 bacterial isolates from larvae (n=13) and adults (n=12) of DBM. In larval gut isolates, gammaproteobacteria was the most abundant (76%), followed by bacilli (15.4%). Molecular characterization placed adult gut bacterial strains into three major classes based on abundance: gammaproteobacteria (66%), bacilli (16.7%) and flavobacteria (16.7%). Esterase activity from 19 gut bacterial isolates ranged from 0.072 to 2.32μmol/min/mg protein. Esterase bands were observed in 15 bacterial strains and the banding pattern differed in Bacillus cereus - KC985225 and Pantoea agglomerans - KC985229. The bands were characterized as carboxylesterase with profenofos used as an inhibitor. Minimal media study showed that B. cereus degraded indoxacarb up to 20%, so it could use indoxacarb for metabolism and growth. Furthermore, esterase activity was greater with minimal media than control media: 1.87 versus 0.26μmol/min/mg protein. Apart from the insect esterases, bacterial carboxylesterase may aid in the degradation of insecticides in DBM.

Bioactive natural products from novel microbial sources

Despite the importance of microbial natural products for human health, only a few bacterial genera have been mined for the new natural products needed to overcome the urgent threat of antibiotic resistance. This is surprising, given that genome sequencing projects have revealed that the capability to produce natural products is not a rare feature among bacteria. Even the bacteria occurring in the human microbiome produce potent antibiotics, and thus potentially are an untapped resource for novel compounds, potentially with new activities. This review highlights examples of bacteria that should be considered new sources of natural products, including anaerobes, pathogens, and symbionts of humans, insects, and nematodes. Exploitation of these producer strains, combined with advances in modern natural product research methodology, has the potential to open the way for a new golden age of microbial therapeutics.

Antimicrobial activity of heterotrophic bacterial communities from the marine sponge Erylus discophorus (Astrophorida, Geodiidae)

Heterotrophic bacteria associated with two specimens of the marine sponge Erylus discophorus were screened for their capacity to produce bioactive compounds against a panel of human pathogens (Staphylococcus aureus wild type and methicillin-resistant S. aureus (MRSA), Bacillus subtilis, Pseudomonas aeruginosa, Acinetobacter baumanii, Candida albicans and Aspergillus fumigatus), fish pathogen (Aliivibrio fischeri) and environmentally relevant bacteria (Vibrio harveyi). The sponges were collected in Berlengas Islands, Portugal. Of the 212 isolated heterotrophic bacteria belonging to Alpha- and Gammaproteobacteria, Actinobacteria and Firmicutes, 31% produced antimicrobial metabolites. Bioactivity was found against both Gram positive and Gram negative and clinically and environmentally relevant target microorganisms. Bioactivity was found mainly against B. subtilis and some bioactivity against S. aureus MRSA, V. harveyi and A. fisheri. No antifungal activity was detected. The three most bioactive genera were Pseudovibrio (47.0%), Vibrio (22.7%) and Bacillus (7.6%). Other less bioactive genera were Labrenzia, Acinetobacter, Microbulbifer, Pseudomonas, Gordonia, Microbacterium, Micrococcus and Mycobacterium, Paenibacillus and Staphylococcus. The search of polyketide I synthases (PKS-I) and nonribosomal peptide synthetases (NRPSs) genes in 59 of the bioactive bacteria suggested the presence of PKS-I in 12 strains, NRPS in 3 strains and both genes in 3 strains. Our results show the potential of the bacterial community associated with Erylus discophorus sponges as producers of bioactive compounds.

DGGE Identification of Microorganisms Associated with Borrelia burgdorferi Sensu Lato- or Anaplasma phagocytophilum-Infected Ixodes ricinus Ticks from Northwest Norway

Ticks acquire a wide range of microorganisms as a natural part of their lifecycle. Bacteria, viruses, and protozoa can be transmitted to ticks during feeding and free-living phases. DGGE profiling is a molecular method to describe the microbial population associated with ticks and demonstrate some of the complexity and variety of tick-borne microorganisms. The present study profiled a total of 120 I. ricinus ticks, which were divided into three equally sized groups. We found that B. burgdorferi s.l.-infected ticks presented a pattern consisting of bacterial Pseudomonas spp. (67.5%), Bacillus spp. (50%), and Sphingomonas spp. (77.5%), while A. phagocytophilum-infected ticks were associated with Pseudomonas spp. (82.5%) and Sphingomonas spp. (57.5%). All profiles had one or more Pseudomonas species present, and the intramitochondrial endosymbiont Candidatus Midichloria mitochondrii was present in more than 25% of the samples. Statistical analysis demonstrated that the microbial communities were not significantly different between the groups and that the groups could not be characterised by a specific microbial population.

Cattle tick-associated bacteria exert anti-biofilm and anti-Tritrichomonas foetus activities

Research on microbiota in cattle tick and the evaluation of its activity against other microorganisms can contribute to identify new molecules potentially useful to control infections caused by bacteria and protozoa. Biofilms pose increasing problems worldwide, mainly due to their resistance to antimicrobial therapies and host immune response. In this study we investigate the ability Rhipicephalus (Boophilus) microplus-associated bacteria may exhibit to produce anti-biofilm and trichomonicidal compounds. Gut, ovary, salivary glands, and Gené organ were collected from engorged R. microplus female. Homogenates of each tissue were inoculated onto 15 distinct culture media. Anti-biofilm and trichomonicidal activities were analyzed by culturing each bacterium isolated in a liquid medium. Results showed that R. microplus cattle tick microflora varies for different tissues. Bacteria belonging to different genera (Aeromonas, Bacillus, Brevibacillus, Castelaniella, Comamonas, Kocuria, and Microbacterium) were identified. Interestingly, all bacterial species found displayed pronounced activity against Staphylococcus epidermidis and Pseudomonas aeruginosa biofilms, and also against the cattle pathogen Tritrichomonas foetus, confirming the hypothesis that cattle tick could be a source of bacteria active against pathogens. This is the first study showing that bacteria isolated from a tick exert anti-biofilm and trichomonicidal activities.

Antibacterial activity of halophilic bacterial bionts from marine invertebrates of mandapam-India

Marine ecosystem and its organisms, particularly the invertebrates are recent targets of bioprospecting and mining for a large group of structurally unique natural products encompassing a wide variety of chemical classes such as terpenes, polyketides, acetogenins, peptides and alkaloids of varying structures, having pronounced pharmacological activities. In view of the limited reports on the antibacterials produced by bacteria, isolated from marine sponges, corals and bivalves of Indian origin, the present study is aimed at investigating the antagonistic activities of 100 heterotrophic, halophilic bacterial bionts isolated from 9 sponges, 5 corals and one bivalve. Culture broths of 46 of these bionts were active against human pathogenic bacteria namely Staphylococcus citreus, Proteus vulgaris, Serratio marcesans, Salmonella typhi, Aerobacter aerogenes and Escherichia coli. Further, the ethyl acetate extracts of cell free supernatant confirmed the presence of extracellular bioactive factor, by agar cup diffusion method. Interestingly, highest number of bionts having activity was isolated from corals followed by sponges and bivalve. The study clearly demonstrates that bacterial bionts of marine invertebrates are a rich source of bioactive secondary metabolites against human bacterial pathogens.

New alkaloid from Streptomyces koyangensis residing in Odontotermes formosanus

A new alkaloid was isolated from the ethyl acetate extract of the culture of a termite-associated Streptomyces koyangensis BY-4. The structure of 1 was elucidated by using MS, NMR, electronic circular dichroism data, and computational approaches. Compound 1 showed weak antimicrobial activities against a panel of test microbes.

Thermostable Bacteriocin BL8 from Bacillus licheniformis isolated from marine sediment

AIM

To isolate and characterize bacteriocin, BL8, from the bacteria identified as Bacillus licheniformis from marine environment.

METHODS AND RESULTS

One-hundred and twelve bacterial isolates from sediment and water samples collected off the coast of Cochin, India, were screened for antibacterial activity. Strain BTHT8, identified as Bacillus licheniformis, inhibited the growth of Gram-positive test organisms. The active component labelled as bacteriocin BL8 was partially purified by ammonium sulphate fractionation and was subjected to glycine SDS-PAGE. The band exhibiting antimicrobial activity was electroeluted and analysed using MALDI-TOF mass spectrometry, and the molecular mass was determined as 1.4 kDa. N-terminal amino acid sequencing of BL8 gave a 13 amino acid sequence stretch. Bacteriocin BL8 was stable even after boiling at 100 °C for 30 min and over a wide pH range of 1-12.

CONCLUSION

A novel, pH-tolerant and thermostable bacteriocin BL8, active against the tested Gram-positive bacteria, was isolated from Bacillus licheniformis.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study reports a stable, low molecular weight bacteriocin from Bacillus licheniformis. This bacteriocin can be used to address two important applications: as a therapeutic agent and as a biopreservative in food processing industry.

Diversity and applications of Bacillus bacteriocins

Members of the genus Bacillus are known to produce a wide arsenal of antimicrobial substances, including peptide and lipopeptide antibiotics, and bacteriocins. Many of the Bacillus bacteriocins belong to the lantibiotics, a category of post-translationally modified peptides widely disseminated among different bacterial clades. Lantibiotics are among the best-characterized antimicrobial peptides at the levels of peptide structure, genetic determinants and biosynthesis mechanisms. Members of the genus Bacillus also produce many other nonmodified bacteriocins, some of which resemble the pediocin-like bacteriocins of the lactic acid bacteria (LAB), while others show completely novel peptide sequences. Bacillus bacteriocins are increasingly becoming more important due to their sometimes broader spectra of inhibition (as compared with most LAB bacteriocins), which may include Gram-negative bacteria, yeasts or fungi, in addition to Gram-positive species, some of which are known to be pathogenic to humans and/or animals. The present review provides a general overview of Bacillus bacteriocins, including primary structure, biochemical and genetic characterization, classification and potential applications in food preservation as natural preservatives and in human and animal health as alternatives to conventional antibiotics. Furthermore, it addresses their environmental applications, such as bioprotection against the pre- and post-harvest decay of vegetables, or as plant growth promoters.

Formation and characterization of acyl carrier protein-linked polyketide synthase extender units

Polyketide natural products are assembled by the condensation of an initiating precursor, or starter unit, with a series of additional precursors referred to as extender units. While there are a number of polyketide synthase starter units, there are currently only seven known polyketide synthase extender units. Polyketide synthase extender units thioesterified to coenzyme A have been known for some time; however, polyketide synthase extender units thioesterified to acyl carrier proteins (ACPs) have been identified only recently. Two of them, (2R)-hydroxymalonyl-ACP and (2S)-aminomalonyl-ACP, are found in the biosynthetic pathway of the antibiotic zwittermicin A in Bacillus cereus UW85. The focus of this chapter is the in vitro formation of (2R)-hydroxymalonyl-ACP and (2S)-aminomalonyl-ACP and the characterization of these extender units using high performance liquid chromatography and matrix-assisted laser desorption ionization time-of-flight mass spectrometry.

New phytotoxic metabolites from Pestalotiopsis sp. HC02, a Fungus Residing in Chondracris rosee gut

Two new phytotoxic gamma-lactones, pestalotines A and B (1 and 2, resp.), along with 4-oxo-4H-pyran-3-acetic acid (3) and 6-hydroxyramulosin (=3,4,4a,5,6,7-hexahydro-6,8-dihydroxy-3-methyl-1H-2-benzopyran-1-one; 4), were isolateded from the culture of Pestalotiopsis sp. HC02, a fungus residing in the Chondracris rosee gut. Structures of the new metabolites were elucidated on the basis of their IR, NMR, and MS data. Pestalotines A and B (1 and 2, resp.) significantly inhibited the radical growth of Echinochloa crusgalli with IC(50) values of 1.85 x 10(-4) and 2.50 x 10(-4) M, respectively, comparable to that of 2-(2,4-dichlorophenoxy)acetic acid (0.94 x 10(-4) M) used as a positive control.

Biosynthesis of polyketide synthase extender units

This review covers the biosynthesis of extender units that are utilized for the assembly of polyketides by polyketide synthases. The metabolic origins of each of the currently known polyketide synthase extender units are covered.

Biodiversity, chemical diversity and drug discovery

Drugs developed from microbial natural products are in the fundaments of modern pharmaceutical companies. Despite decades of research, all evidences suggest that there must remain many interesting natural molecules with potential therapeutic application yet to be discovered. Any efforts to successfully exploit the chemical diversity of microbial secondary metabolites need to rely heavily on a good understanding of microbial diversity, being the working hypothesis that maximizing biological diversity is the key strategy to maximizing chemical diversity. This chapter presents an overview of diverse topics related with this basic principle, always in relation with the discovery of novel secondary metabolites. The types of microorganisms more frequently used for natural products discovery are briefly reviewed, as well as the differences between terrestrial and marine habitats as sources of bioactive secondary metabolite producers. The concepts about microbial diversity as applied to prokaryotes have evolved in the last years, but recent data suggest the existence of true biogeographic patterns of bacterial diversity, which are also discussed. Special attention is dedicated to the existing strategies to exploit the microbial diversity that is not easy to tackle by conventional approaches. This refers explicitly to the current attempts to isolate and cultivate the previously uncultured bacteria, including the application of high throughput techniques. Likewise, the advances of microbial molecular biology has allowed the development of metagenomic approaches, i.e., the expression of biosynthetic pathways directly obtained from environmental DNA and cloned in a suitable host, as another way of accessing microbial genetic resources. Also, approaches relying on the genomics of metabolite producers are reviewed.

New strategies for combating multidrug-resistant bacteria

Antibiotic resistance is a problem that continues to challenge the healthcare sector. In particular, multidrug resistance is now common in familiar pathogens such as Staphylococcus aureus and Mycobacterium tuberculosis, as well as emerging pathogens such as Acinetobacter baumannii. New antibiotics and new therapeutic strategies are needed to address this challenge. Advances in identifying new sources of antibiotic natural products and expanding antibiotic chemical diversity are providing chemical leads for new drugs. Inhibitors of resistance mechanisms and microbial virulence are orthogonal strategies that are also generating new chemicals that can extend the life of existing antibiotics. This new chemistry, coupled with a growing understanding of the mechanisms, origins and distribution of antibiotic resistance, position us to tackle the challenges of antibiotic resistance in the 21st century.

Mass spectrometric analysis of lipopeptides from Bacillus strains isolated from diverse geographical locations

Matrix-assisted laser desorption/ionization time-of-flight MS (MALDI-TOF MS) has been applied to characterize lipopeptide biomarkers from 54 different strains of Bacillis from most taxa within the Bacillis subtilis-Bacillis licheniformis clade, isolated from seven geographic locations on five continents. Even the most narrowly defined taxa are diverse in terms of the lipopeptide profiles. Many strains produce previously identified compounds with known antimicrobial properties (e.g. polymyxins and bacitracins), whereas other compounds represent novel classes that were hitherto unknown. Of particular interest is the novel 942/958 Da biomarkers produced by B. s. spizizeni desert strains and several type strains.

Diversity of commensal Bacillus cereus sensu lato isolated from the common sow bug (Porcellio scaber, Isopoda)

Although Bacillus cereus sensu lato are important both from an ecological and an economical point of view, little is known about their population structure, ecology, and relationships with other organisms. In the present work, the genotypic similarity of arthropod-borne B. cereus s.l. isolates, and their symbiotic relationship with the host are assessed. Bacilli of this group were recovered from the digestive tracts of sow bugs (Porcellio scaber) collected in three closely located sites. Their genotypic diversity was investigated using pulse-field gel electrophoresis (PFGE) following the whole-genome DNA digestions with NotI and AscI, and PCR amplification of virulence genes. The majority of the sow-bug Bacillus cereus sensu stricto isolates originating from the same but also from different sites displayed identical PFGE patterns, virulence gene content and enterotoxicity, indicating strong genetic and genomic relationships. The sow-bug Bacillus mycoides/Bacillus pseudomycoides strains displayed a higher diversity. The isopod-B. cereus s.l. relationship was also evaluated using antibiotic-resistant derivatives of B. cereus s.s., B. mycoides/B. pseudomycoides and Bacillus thuringiensis reintroduced into sow bugs. Both spores and vegetative cells of B. cereus s.l. were recovered from sow bugs over a 30-day period, strongly suggesting that these bacteria are natural residents of terrestrial isopods.

Identification and Characterization of Novel Genetic Markers Associated with Biological Control Activities in Bacillus subtilis

ABSTRACT Suppressive subtractive hybridization (SSH) was used to identify genetic markers associated with biological control of plant pathogens by Bacillus subtilis. The genomes of two commercialized strains, GB03 and QST713, were compared with that of strain 168, which has no defined biocontrol capacities, to obtain a pool of DNA fragments unique to the two biocontrol strains. The sequences of 149 subtracted fragments were determined and compared with those present in GenBank, but only 80 were found to correspond to known Bacillus genes. Of these, 65 were similar to genes with a wide range of metabolic functions, including the biosynthesis of cell wall components, sporulation, and antibiotic biosynthesis. Sixteen subtracted fragments shared a high degree of similarity to sequences found in multiple B. subtilis strains with proven biocontrol capacities. Oligonucleotide primers specific to nine of these genes were developed. The targeted genes included five genes involved in antibiotic synthesis (bmyB, fenD, ituC,srfAA, and srfAB) and four additional genes (yndJ, yngG, bioA, and a hypothetical open reading frame) not previously associated with biological control. All nine markers were amplified from the commercialized B. subtilis strains GB03, QST713, and MBI600, with the exception of ituC, which was not detected in GB03. The markers also were amplified from four other B. subtilis isolates, but they were not amplified from other related Bacillus strains, including the plant growth-promoting rhizobacteria IN937a and IN937b. Sequencing of the amplified markers revealed that all seven of the isolates that scored positive for multiple markers were genotypically distinct strains. Interestingly, strains scored positive for the amplifiable markers generally were more effective at inhibiting the growth of Rhizoctonia solani and Pythium ultimum than other Bacillus isolates that lacked the markers. The potential utility of the defined genetic markers to further define the diversity, ecology, and biocontrol activities of B. subtilis are discussed.

Antimicrobial activity of marine bacteria associated with sponges from the waters off the coast of South East India

Seventy-five marine bacterial strains associated with four species of sponges (Echinodictyum sp., Spongia sp., Sigmadocia fibulatus and Mycale mannarensis) were isolated from the Tuticorin coast, Gulf of Mannar region. The agar-overlay method was used to screen for antibiotic production by these strains against four bacteria, viz., Bacillus subtilis, Escherichia coli, Vibrio parahaemolyticus, and Vibrio harveyi and one fungal pathogen, viz., Candida albicans. Twenty-one per cent of the bacterial strains were found to be antibiotic producers and their activities ranged from broad spectral to species specific. A strain coded SC3 was found to be highly potent and was mass cultured. The ethyl acetate extract of the culture broth was further fractionated by reverse phase HPLC and the active fraction identified. In addition, SC3 was subjected to morphological and physiological characterization. The results of the tests showed SC3 to be a Gram-positive rod, sporulating, motile, catalase and oxidase positive. Phylogenetic analysis based on comparative analysis of sequenced 16s rRNA of the active strains indicated a preponderance of bacteria belonging to Vibrio and Bacillus genera with 95-99% sequence similarities. To our knowledge this is the first report on phylogenetic identification of antibiotic producing bacteria associated with sponges from Indian waters.