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PubMed1995

Impact of carbon and flooding on the metabolic diversity of microbial communities in soils.

The assumption that carbon and soil water content are major determinants of microbial community structure and function is rarely questioned because of substantial evidence of the impacts of these variables on specific populations and functions. The significance of carbon and water for metabolic diversity at the microbial community level was tested on the field scale in agricultural plots varying in carbon inputs and in whether they were flooded. Surface soils in which rice straw was incorporated or burned and which were flooded or unflooded were sampled at monthly intervals three times during the flooded winter period (January to March) and again 1 month postdraining. Biomass carbon and nitrogen were not affected by treatments, active bacterial counts showed slight increases, and respiration rates were increased by carbon inputs and flooding. Biolog microplates were inoculated with soil extracts to quantify the metabolic diversity of the soil microbial community. Canonical correspondence analysis and the Monte Carlo permutation testing showed that differences in substrate utilization patterns were significantly related (P < 0.001) to carbon and flooding treatments. Biolog substrates whose metabolism was altered by the treatments were consistent across dates and tended to be positively related (utilization enhancement) to carbon inputs and negatively related to winter flooding. The importance of carbon as an environmental variable increased over time after straw treatment, whereas the importance of water became evident after flooding and decreased after drainage. The effect of long-term rice straw incorporation on substrate utilization patterns at another field site was consistent with these results despite the dissimilarities of the two soils.

Journal Article↗

PubMed2007

Quantitative and qualitative beta diversity measures lead to different insights into factors that structure microbial communities.

The assessment of microbial diversity and distribution is a major concern in environmental microbiology. There are two general approaches for measuring community diversity: quantitative measures, which use the abundance of each taxon, and qualitative measures, which use only the presence/absence of data. Quantitative measures are ideally suited to revealing community differences that are due to changes in relative taxon abundance (e.g., when a particular set of taxa flourish because a limiting nutrient source becomes abundant). Qualitative measures are most informative when communities differ primarily by what can live in them (e.g., at high temperatures), in part because abundance information can obscure significant patterns of variation in which taxa are present. We illustrate these principles using two 16S rRNA-based surveys of microbial populations and two phylogenetic measures of community beta diversity: unweighted UniFrac, a qualitative measure, and weighted UniFrac, a new quantitative measure, which we have added to the UniFrac website (http://bmf.colorado.edu/unifrac). These studies considered the relative influences of mineral chemistry, temperature, and geography on microbial community composition in acidic thermal springs in Yellowstone National Park and the influences of obesity and kinship on microbial community composition in the mouse gut. We show that applying qualitative and quantitative measures to the same data set can lead to dramatically different conclusions about the main factors that structure microbial diversity and can provide insight into the nature of community differences. We also demonstrate that both weighted and unweighted UniFrac measurements are robust to the methods used to build the underlying phylogeny.

Animals↗

PubMed2026

Climate and soil shape Daqu wheat quality and seed microbiome via rhizosphere taxa and microbial assembly.

The grain quality and seed microbiome of Daqu wheat are fundamental determinants of Daqu fermentation performance; however, the mechanisms by which cultivation environments influence these traits via rhizosphere microbial communities remain unclear. Bacterial and fungal communities across the bulk soil-rhizosphere-seed continuum of three wheat cultivars grown in four ecoregions were characterized using absolute quantitative amplicon sequencing. The rhizosphere microbiome was treated as a central intermediary, while the response variables were seed microbial diversity and grain-quality traits, including starch content, protein content, and grain hardness. Twelve physicochemical properties of soil and 11 climatic factors were integrated into a multidimensional association framework. Environmental conditions exerted stronger influences on both seed quality traits and microbial diversity than cultivar identity. Distinct regional signatures were also evident in rhizosphere microbiomes, with environmental gradients explaining community variation more effectively than geographic distance. Bacterial communities exhibited greater sensitivity to environmental fluctuations than fungi. Mantel analyses identified available nitrogen, precipitation, and atmospheric pressure as significant drivers of core rhizosphere taxa (P < 0.05). iCAMP revealed that stochastic processes predominantly governed rhizosphere bacterial assembly, whereas stochastic and deterministic mechanisms jointly shaped fungal assembly. Partial least squares path modeling further uncovered a rhizosphere-mediated environment-seed cascade, wherein sunlight intensity and duration, atmospheric pressure, and soil nitrogen directly or indirectly affected seed wet gluten content, grain hardness, and seed microbial diversity through their influences on rhizosphere microbiota. Rhizosphere bacterial diversity was negatively associated with seed bacterial diversity (path coefficient = -0.118, P < 0.05), indicating that rhizosphere communities may shape seed endophytic bacterial assemblages via environmental filtering and competitive interactions. Collectively, these findings elucidate how environments shape the quality and seed microbiomes of Daqu wheat, providing scientific guidance for optimal site selection and the standardized production of high-quality brewing wheat for industrial Baijiu.

Triticum↗

PubMed2003

Relationships between flavoring capabilities, bacterial composition, and geographical origin of natural whey cultures used for traditional water-buffalo mozzarella cheese manufacture.

Natural whey cultures (NWC) (n = 29) used for traditional water-buffalo Mozzarella cheese manufacture and arising from different geographical areas of production were characterized and grouped on the basis of their capability to develop neutral volatile compounds and according to their microbial diversity as revealed by molecular analysis. The flavoring properties of NWC were studied in dairy microcosms resembling the specific technological procedure used in the traditional water-buffalo Mozzarella cheese-making. Neutral volatile compounds were identified by high-resolution gas chromatography (HRGC)-mass spectrometry analysis while information on the microbial diversity occurring in the NWC was retrieved by PCR-denaturing gradient gel electrophoresis (DGGE) analysis of 16S rDNA after direct DNA extraction. Neoformation volatile substances (n = 27) were found; 23 were identified and some of them recognized as odor-conferring molecules. Eight different bands, referable to eight microbial species, were obtained by PCR-DGGE analysis of the NWC. Statistical analyses were applied to PCR-DGGE and HRGC data. Interestingly, the flavoring capabilities and the microbial diversity of the NWC proved to be closely linked and both related to the geographical origin of the NWC. These results suggested a possible use of the molecular characterization of the dairy products to support the traceability criteria of typical dairy products like water-buffalo Mozzarella cheese.

Animals↗

PubMed2026

Urban soil multifunctionality and seasonal variability of carbon-linked soil traits.

Urban soils can play a significant role in climate change mitigation due to their capacity to store carbon (C) and support microbial biodiversity. In this context, this study evaluated the effects of different fertilization strategies on soil quality, greenhouse gas emissions, and microbial communities in two urban green areas located in the Campania region (Southern Italy) over a three-year period. Mineral fertilization (MIN), micronized vermicompost (CMP), micronized biochar (BCH), vermicompost plus biochar (CMP + BCH) were compared to an unfertilized control (CNT). The results showed that soil physicochemical properties were mainly influenced by site-specific conditions and temporal variability, whereas cation exchange capacity was the soil parameter most responsive to fertilization treatments. The QBS-ar index, used as an indicator of soil biological quality based on soil arthropods, was primarily affected by seasonality, with higher values recorded during spring-summer and no significant effects attributable to fertilization treatments. Vermicompost, BCH, and their combination were associated with lower net soil-vegetation CO2 fluxes and smaller temporal increases in the measured flux compared with the control and mineral fertilization treatments. All treatments exhibited a negative estimated annualized net C balance, indicating that, under the adopted temporal upscaling procedure, the estimated gaseous exchanges exceeded the annual increase in soil organic carbon stocks. Nevertheless, BCH showed the least negative estimated annualized balance. Analyses of microbial diversity revealed that bacterial and fungal communities were mainly shaped by temporal and seasonal factors, while fertilization treatments had limited effects on microbial diversity and community composition. Overall, the findings indicate that biochar showed the most favorable estimated carbon balance and the lowest measured net CO2 fluxes under the conditions investigated. However, its effects on soil biological and microbial properties were limited in the short term, and none of the tested treatments achieved net carbon sequestration. These results suggest that biochar may contribute to climate change mitigation as part of long-term, site-specific management strategies rather than as a standalone solution for improving soil multifunctionality.

Biochar↗

PubMed1999

Use of the 16S--23S ribosomal genes spacer region in studies of prokaryotic diversity.

The description of microbial diversity by molecular culture-independent techniques most often involves the amplification of the 16S rRNA by PCR gene and either analysis of the diversity of amplified molecules (community fingerprinting) that allows the simultaneous study of many samples or the cloning and sequencing of a significant amount of amplification products. The fact that between the 16S and the 23S genes in the ribosomal operon there is a spacer extremely variable in both sequence and length provides an excellent tool to simplify both approaches. The spacer can be amplified almost as easily as the 16S rDNA taking advantage of conserved nucleotide stretches at the 5' end of the 23S gene and the amplicon can contain different amounts of the 16S rDNA choosing primers at the different conserved areas within this gene. Identified by the acronym RISA (rDNA internal spacer analysis), the spacer addition provides a marker of highly variable size allowing standard separation of the amplification products and the sequence of this hypervariable region is useful in the fine discrimination of operational taxonomic units.

Bacteria↗

PubMed1998

Phylogenetic diversity of mesophilic and thermophilic granular sludges determined by 16S rRNA gene analysis.

The microbial diversity of two types of methanogenic granular sludge, mesophilic (35 degrees C) and thermophilic (55 degrees C), which had been treating sucrose/propionate/acetate-based artificial wastewater were compared. 16S rDNA clone libraries were constructed by PCR with a prokaryote-specific primer set, and partial sequencing of the clonal 16S rDNAs was conducted for phylogenetic analysis. Of 115 mesophilic granule and 110 thermophilic granule clones sequenced, 19 and 22%, respectively, were phylogenetically affiliated with the domain Archaea, and the remainder in each case were assigned to the domain Bacteria. Within the domain Archaea, the 16S rDNA clones in both libraries showed relatively close relationships with those of methanogens. Within the Bacteria, a major group represented in the mesophilic clone library was the delta subclass of the Proteobacteria (27%), in which high degrees of relatedness were observed between the clonal 16S rDNA sequences and those of previously identified syntrophic bacteria and sulfate-reducing bacteria. In contrast, in the thermophilic clone library, the Thermodesulfovibrio group (19%), the green non-sulfur bacteria (18%) and the low G + C subclass of the Gram-positive bacteria (18%) were predominant. A significant difference between the two libraries was that no clone affiliated with the Proteobacteria was detected in the thermophilic clone library, whereas the Proteobacteria was detected in the thermophilic clone library, whereas the Proteobacteria was the most predominant group in the mesophilic clones. Thirty-six and 24 different sequences were found in the mesophilic and thermophilic clones, respectively, suggesting that the microbial diversity of the thermophilic granule was lower than that of the mesophilic granule.

Archaea↗

PubMed2006

An assessment of the hypervariable domains of the 16S rRNA genes for their value in determining microbial community diversity: the paradox of traditional ecological indices.

Amplicon length heterogeneity PCR (LH-PCR) was investigated for its ability to distinguish between microbial community patterns from the same soil type under different land management practices. Natural sagebrush and irrigated mouldboard-ploughed soils from Idaho were queried as to which hypervariable domains, or combinations of 16S rRNA gene domains, were the best molecular markers. Using standard ecological indices to measure richness, diversity and evenness, the combination of three domains, V1, V3 and V1+V2, or the combined V1 and V3 domains were the markers that could best distinguish the undisturbed natural sagebrush communities from the mouldboard-ploughed microbial communities. Bray-Curtis similarity and multidimensional scaling were found to be better metrics to ordinate and cluster the LH-PCR community profiling data. The use/misuse of traditional ecological indices such as diversity and evenness to study microbial community profiles will remain a major point to consider when performing metagenomic studies.

Biodiversity↗

PubMed2006

Unexpected diversity and complexity of the Guerrero Negro hypersaline microbial mat.

We applied nucleic acid-based molecular methods, combined with estimates of biomass (ATP), pigments, and microelectrode measurements of chemical gradients, to map microbial diversity vertically on a millimeter scale in a hypersaline microbial mat from Guerrero Negro, Baja California Sur, Mexico. To identify the constituents of the mat, small-subunit rRNA genes were amplified by PCR from community genomic DNA extracted from layers, cloned, and sequenced. Bacteria dominated the mat and displayed unexpected and unprecedented diversity. The majority (1,336) of the 1,586 bacterial 16S rRNA sequences generated were unique, representing 752 species (> or =97% rRNA sequence identity) in 42 of the main bacterial phyla, including 15 novel candidate phyla. The diversity of the mat samples differentiated according to the chemical milieu defined by concentrations of O(2) and H(2)S. Bacteria of the phylum Chloroflexi formed the majority of the biomass by percentage of bulk rRNA and of clones in rRNA gene libraries. This result contradicts the general belief that cyanobacteria dominate these communities. Although cyanobacteria constituted a large fraction of the biomass in the upper few millimeters (>80% of the total rRNA and photosynthetic pigments), Chloroflexi sequences were conspicuous throughout the mat. Filamentous Chloroflexi bacteria were identified by fluorescence in situ hybridization within the polysaccharide sheaths of the prominent cyanobacterium Microcoleus chthonoplastes, in addition to free living in the mat. The biological complexity of the mat far exceeds that observed in other polysaccharide-rich microbial ecosystems, such as the human and mouse distal guts, and suggests that positive feedbacks exist between chemical complexity and biological diversity. The sequences determined in this study have been submitted to the GenBank database and assigned accession numbers DQ 329539 to DQ 331020, and DQ 397339 to DQ 397511.

Bacteria↗

PubMed2006

UniFrac--an online tool for comparing microbial community diversity in a phylogenetic context.

BACKGROUND: Moving beyond pairwise significance tests to compare many microbial communities simultaneously is critical for understanding large-scale trends in microbial ecology and community assembly. Techniques that allow microbial communities to be compared in a phylogenetic context are rapidly gaining acceptance, but the widespread application of these techniques has been hindered by the difficulty of performing the analyses. RESULTS: We introduce UniFrac, a web application available at http://bmf.colorado.edu/unifrac, that allows several phylogenetic tests for differences among communities to be easily applied and interpreted. We demonstrate the use of UniFrac to cluster multiple environments, and to test which environments are significantly different. We show that analysis of previously published sequences from the Columbia river, its estuary, and the adjacent coastal ocean using the UniFrac interface provided insights that were not apparent from the initial data analysis, which used other commonly employed techniques to compare the communities. CONCLUSION: UniFrac provides easy access to powerful multivariate techniques for comparing microbial communities in a phylogenetic context. We thus expect that it will provide a completely new picture of many microbial interactions and processes in both environmental and medical contexts.

Bacteria↗

PubMed2025

Contribution of the Brain-Gut-Microbiome Axis to Intergenerational Abnormalities in a Rat Model of Perioperative Neurocognitive Disorder.

BACKGROUND: The brain-gut-microbiome (BGM) axis is a communication network through which the brain and gastrointestinal microbiota interact via neural, hormonal, immune, and gene expression mechanisms. Gut microbiota dysbiosis is thought to contribute to neurocognitive disorders, including perioperative neurocognitive disorder, and to various metabolic abnormalities. Recently, the authors reported that sevoflurane induces neurocognitive deficits in exposed rats as well as their future offspring, with male offspring being particularly affected (intergenerational perioperative neurocognitive disorder). In this study, the authors examined in the same animals whether the intergenerational effects of sevoflurane involve abnormalities in the BGM axis, and whether they are mitigated by paternal pretreatment with either the Na + -K + -Cl - (NKCC1) Cl - transporter inhibitor bumetanide or the glucocorticoid receptor inhibitor RU486, as previously demonstrated for neurocognitive deficits. METHODS: Male Sprague-Dawley rats (F0 generation) were exposed to 2.1% sevoflurane for 3 h on postnatal days 56, 58, and 60 (F0M_S group). Before each sevoflurane exposure, distinct experimental groups of F0 males received bumetanide (F0M_BS group) or RU486 (F0M_RS group). These males were mated on postnatal day 90 to produce offspring (F1 generation). Gut microbiota were profiled using 16S rRNA gene sequencing, and brain changes analyzed via RNA sequencing of hippocampal samples. RESULTS: F1 male offspring of F0M_S sires exhibited heightened corticosterone responses to stress, increased inflammatory markers, altered hippocampal transcriptomes, gut microbiota dysbiosis, elevated serum low-density lipoprotein cholesterol levels, and increased body weight. The only abnormality observed in F1 females was a shift in microbial diversity. F0M_S displayed profound alterations in hippocampal transcriptome, while microbial diversity was the only parameter affected in their gut microbiota. Bumetanide or RU486 mitigated most abnormalities, except increased body weight in F1 males. CONCLUSIONS: Paternal sevoflurane exposure in rats induces BGM axis abnormalities, particularly in male offspring, despite the absence of direct anesthetic exposure. Pretreatment with bumetanide or RU486 showed therapeutic efficacy.

Animals↗

PubMed2026

Long-Term Warming Reduces Bacterial Diversity and Functional Potential in Temperate Forest Soil.

Soil microbes are key regulators of forest carbon cycling, yet how their diversity and functional potential respond to long-term warming remains poorly understood. Here, we report a five-year in situ warming experiment in a temperate forest, combining ten repeated measurements of microbial diversity and functional gene potential, as well as continuous monitoring of soil CO2 flux. We found that warming progressively reduced bacterial diversity and induced phylogenetically conserved community reorganization. Under warming, community composition shifted in a phylogenetically conserved manner. Warming generally reduced the abundance of microbial functional genes across most carbon-, nitrogen-, and phosphorus-cycling gene categories, except for genes associated with starch decomposition. Warming also altered the factors associated with soil CO2 flux: microbial diversity showed a stronger association with soil CO2 flux under long-term warming, whereas soil moisture was the dominant predictor in the control treatment. This warming-enhanced biodiversity control over soil CO2 flux was associated with shifts in microbial functional potential, particularly increases in starch-degrading genes and microbial biomass production potential. Together, our results suggest that warming can restructure microbial communities in ways that strengthen biodiversity-dependent regulation of soil carbon cycling, with implications for climate-carbon feedbacks.

Soil Microbiology↗

PubMed2005

Genetic diversity of microbial eukaryotes in anoxic sediment around fumaroles on a submarine caldera floor based on the small-subunit rDNA phylogeny.

Recent culture-independent molecular analyses have shown the diversity and ecological importance of microbial eukaryotes (protists) in various marine environments. In the present study we directly extracted DNA from anoxic sediment near active fumaroles on a submarine caldera floor at a depth of 200 m and constructed genetic libraries of PCR-amplified eukaryotic small-subunit (SSU) rDNA. By sequencing cloned SSU rDNA of the libraries and their phylogenetic analyses, it was shown that most sequences have affiliations with known major lineages of eukaryotes (Cercozoa, Alveolata, stramenopiles and Opisthokonta). In particular, some sequences were closely related to those of representatives of eukaryotic parasites, such as Phagomyxa and Cryothecomonas of Cercozoa, Pirsonia of stramenopiles and Ichthyosporea of Opisthokonta, although it is not clear whether the organisms occur in free-living or parasitic forms. In addition, other sequences did not seem to be related to any described eukaryotic lineages suggesting the existence of novel eukaryotes at a high-taxonomic level in the sediment. The community composition of microbial eukaryotes in the sediment we surveyed was different overall from those of other anoxic marine environments previously investigated.

Animals↗

PubMed2006

Application of sequence-based methods in human microbial ecology.

Ecologists studying microbial life in the environment have recognized the enormous complexity of microbial diversity for many years, and the development of a variety of culture-independent methods, many of them coupled with high-throughput DNA sequencing, has allowed this diversity to be explored in ever-greater detail. Despite the widespread application of these new techniques to the characterization of uncultivated microbes and microbial communities in the environment, their application to human health and disease has lagged. Because DNA-based techniques for defining uncultured microbes allow not only cataloging of microbial diversity but also insight into microbial functions, investigators are beginning to apply these tools to the microbial communities that abound on and within us, in what has aptly been called "the second Human Genome Project." In this review we discuss the sequence-based methods for microbial analysis that are currently available and their application to identify novel human pathogens, improve diagnosis of known infectious diseases, and advance understanding of our relationship with microbial communities that normally reside in and on the human body.

Animals↗

PubMed2026

Effects of Fecal Microbiota Transplantation on Intestinal Microbial Characteristics and Clinical Phenotypes in Patients with Parkinson's Disease.

Alterations in the gut microbiota have been associated with Parkinson's disease (PD), but longitudinal microbial changes after fecal microbiota transplantation (FMT) and their clinical associations remain poorly understood. This single-center retrospective observational study included 6 patients with PD, stratified into high- and low-severity subgroups based on disease duration (>6 years vs ≤6 years). Thirty-six fecal samples were collected before FMT and monthly for five months afterward. Microbial diversity, community structure, taxonomic composition, and predicted functional profiles were assessed using 16S ribosomal RNA gene sequencing. Analyses included alpha and beta diversity, taxonomic abundance, linear discriminant analysis effect size, Tax4Fun2-based functional prediction, and Spearman rank correlations between microbial features and clinical indicators. Descriptive analyses indicated differences in microbial richness, diversity, community structure, and predicted functions between severity subgroups and across post-FMT time points. At baseline, the low-severity subgroup had greater microbial richness and diversity than the high-severity subgroup, with relatively higher abundances of taxa including Bifidobacterium and Lactobacillus. One month after FMT, richness and diversity increased from baseline in the high-severity subgroup, accompanied by changes in taxonomic composition. Both subgroups showed time-associated variation in microbial diversity and predicted Kyoto Encyclopedia of Genes and Genomes pathway enrichment after FMT. Predicted functions included carbohydrate and amino acid metabolism, secondary metabolite biosynthesis, membrane transport, and signal transduction. Several operational taxonomic units correlated with indicators of motor impairment, constipation, sleep quality, functional status, and neuropsychiatric symptoms. FMT was therefore associated with longitudinal changes in gut microbial diversity, composition, and predicted functions, and specific microbial features were associated with motor and non-motor indicators. Given the small retrospective cohort, these findings are preliminary and warrant confirmation in larger controlled studies. Future studies should determine whether these microbial alterations are reproducible, persist beyond five months, reflect donor engraftment, and correspond to measurable clinical improvement after transplantation in PD.

Humans↗

PubMed2006

Diagnostic microbial microarrays in soil ecology.

Soil microbial communities are responsible for important physiological and metabolic processes. In the last decade soil microorganisms have been frequently analysed by cultivation-independent techniques because only a minority of the natural microbial communities are accessible by cultivation. Cultivation-independent community analyses have revolutionized our understanding of soil microbial diversity and population dynamics. Nevertheless, many methods are still laborious and time-consuming, and high-throughput methods have to be applied in order to understand population shifts at a finer level and to be better able to link microbial diversity with ecosystems functioning. Microbial diagnostic microarrays (MDMs) represent a powerful tool for the parallel, high-throughput identification of many microorganisms. Three categories of MDMs have been defined based on the nature of the probe and target molecules used: phylogenetic oligonucleotide microarrays with short oligonucleotides against a phylogenetic marker gene; functional gene arrays containing probes targeting genes encoding specific functions; and community genome arrays employing whole genomes as probes. In this review, important methodological developments relevant to the application of the different types of diagnostic microarrays in soil ecology will be addressed and new approaches, needs and future directions will be identified, which might lead to a better insight into the functional activities of soil microbial communities.

Bacteria↗

PubMed2001

Phylogenetic diversity of bacteria associated with the marine sponge Rhopaloeides odorabile.

Molecular techniques were employed to document the microbial diversity associated with the marine sponge Rhopaloeides odorabile. The phylogenetic affiliation of sponge-associated bacteria was assessed by 16S rRNA sequencing of cloned DNA fragments. Fluorescence in situ hybridization (FISH) was used to confirm the presence of the predominant groups indicated by 16S rDNA analysis. The community structure was extremely diverse with representatives of the Actinobacteria, low-G+C gram-positive bacteria, the beta- and gamma-subdivisions of the Proteobacteria, Cytophaga/Flavobacterium, green sulfur bacteria, green nonsulfur bacteria, planctomycetes, and other sequence types with no known close relatives. FISH probes revealed the spatial location of these bacteria within the sponge tissue, in some cases suggesting possible symbiotic functions. The high proportion of 16S rRNA sequences derived from novel actinomycetes is good evidence for the presence of an indigenous marine actinomycete assemblage in R. odorabile. High microbial diversity was inferred from low duplication of clones in a library with 70 representatives. Determining the phylogenetic affiliation of sponge-associated microorganisms by 16S rRNA analysis facilitated the rational selection of culture media and isolation conditions to target specific groups of well-represented bacteria for laboratory culture. Novel media incorporating sponge extracts were used to isolate bacteria not previously recovered from this sponge.

Actinobacteria↗

PubMed1998

Microbiological profile and potential hazards associated with imported and local brands of tomato paste in Nigeria.

Cans of three tomato paste brands (two of which are imported and one produced locally) showing defective or normal appearance were purchased from various retail outlets and analysed for microbial composition and pH values. Substantially higher total viable counts were observed in samples from defective cans but the lowest population was found in the local brand. Ratio of mesophilic to thermophilic micro-organisms increased in samples obtained from cans showing visible defects. Anaerobic spore counts were higher than the aerobic population in both normal and defective cans, but the counts varied with the brands. Four dominant bacterial genera (Bacillus, Clostridium, Lactobacillus and Leuconostoc) were isolated from the samples with the greater proportion being spore-formers. Percentage occurrence of Clostridium thermosaccharolyticum was appreciably higher in samples from defective cans while a preponderance of Lactobacillus occurred in samples from normal cans. Of the moulds isolated, Absidia and Aspergillus fumigatus showed a higher percentage in defective cans. pH values higher than the critical safe level of 4.6 were found in cans with visible defects and greater microbial diversity with higher microbial load was more often associated with these samples. Imported brands showed more undesirable microbial quality and pH values, making them potentially hazardous.

Bacteria, Aerobic↗