Morphoanalysis of Bacterially Precipitated Subaqueous Calcium Carbonate from Weebubbie Cave,Australia

In this article, we present a previously unreported morphology of bacterially precipitated calcite (determined using XRD, FTIR, and SAED) occurring subaqueously in Weebubbie Cave. Observations using FESEM and TEM revealed spindle-shaped crystals with curved [hk.0] faces lying parallel to the c-axis. Calcite precipitated under conditions designed to mimic the inorganic solution chemistry of the cave revealed a different morphology. These differences between the crystals suggest that the formation of the cave crystals is a consequence of biologically activity.     

Evidences for Microbial Precipitation of Calcite in Speleothems from Krem Syndai in Jaintia Hills,Meghalaya, India

Speleothems from Krem Syndai, Meghalaya in Northeast India were studied for their microbial diversity using 16S rDNA-based phylogenetic approach and conventional microbiological techniques along with geochemistry, mineralogy and in vitro experiments to understand participation of microorganisms in CaCO₃ precipitation. Speleothems imaged by scanning electron microscopy showed round coccoid-like, sporangia-like and spinose calcified structures, numerous broken cocci shells with spotted interiors inside a calcite crystal, honeycomb long reticulate, smooth, flat, twisted, ribbon-like, tubular, beaded, microbe-mineralized filaments and extracellular polymeric substances (EPS). Fourier spectroscopy indicated the presence of various organic compounds. δ¹³C and δ¹⁸O isotopic ratios of speleothems ranged from ?4.65 to ?7.34‰ and ?3.06 to ?6.80‰, respectively. Total number of microbial cells using SYBR Gold was high. Fluorescence in situ hybridization (FISH) indicated approximately 3 × 10⁵ to 5 × 10⁵ cells g sed^–1 in the speleothems out of which the number of microbes belonging to Eubacteria ranged from 1.8 × 10⁵ to 3.6 × 10⁵ cells, g sed^–1. FISH showed ～45% active microbial cells of the total cell number in samples. DNA-based high-throughput amplicon sequencing revealed 19 bacterial phyla in the speleothem. Approximately 42% of the sequences were similar to Proteobacteria (Alphaproteobacteria: 22.4%, Betaproteobacteria: 8.9%, Gammaproteobacteria: 8.6%). Sequences similar to Nitrospiraceae (22.8%) had the highest proportion of sequences belonging to a single family. Bacterial strains isolated from the speleothems raised alkalinity and precipitated calcite in the laboratory cultures which was confirmed by X-ray diffraction (XRD) analyses. These isolates belonged to Bacillus spp., Actinomycetes spp., Streptomyces spp., Pseudomonas spp., Micrococcus spp., Staphylococcus spp., Xanthobacter spp. and Arthrobacter spp. Overall, the results showed unequivocal evidence of bacterial fingerprints during CaCO₃ precipitation in the cave.     

Mineralogical Footprints of Bacterial Biofilms Associated with Labit Cave,a Part of the Longest Cave System in India

The present study was an attempt to demonstrate the capabilities of the microbial strains from the unexplored Labit cave in India to precipitate calcite providing evidence for biotic processes involved in formation of speleothem deposits. Six calcifying bacterial strains majority belonging to genus Bacillus were isolated from the cave. SEM studies revealed an array of various in vitro crystal polymorphs generated by the isolated bacteria which are similar to microscopic observations on natural formations in speleothems. The EDX spectrum of the precipitated crystals predominately composed of calcium carbonate indicating the relevance of bacterial biofilm in cave geomicrobiology and biogenic evolution of cave formations in the studied cave, which is further supported by XRF analysis and Raman spectroscopy.     

Biomineralization Potential of Bacillus subtilis,Rummeliibacillus Stabekisii and Staphylococcus Epidermidis Strains In Vitro Isolated from Speleothems,Khasi Hill Caves,Meghalaya, India

Microorganisms were isolated and identified from speleothems at Khasi hill caves, Meghalaya. The aim was to understand their biomineralization potential. Analyses of the speleothems from Krem Soitan, Krem Mawpun, and Krem Lawbah using scanning electron microscope (SEM) showed evidences for microbe–mineral interactions. SEM showed microbial reticulate and beaded filaments, cells, fiber calcites, and clusters of coccoid-like structures. A total of 113 bacterial strains were isolated and identified by a combination of conventional and molecular based tools. 105 strains that were sequenced belonged to the genus: Bacillus, Rummeliibacillus, Staphylococcus, and Brevibacterium. The BLASTn sequence search of 16S rRNA sequences with the National Centre for Biotechnology Information database to establish the identity of the strains yielded similarity scores of ≥99% with the respective organisms. The strains were identified as Bacillus simplex, Bacillus gaemokensis, Bacillus subtilis, Bacillus thuringiensis, Bacillus albus, Bacillus cereus, Bacillus anthracis, Bacillus weihenstephanensis, Rummeliibacillus stabekisii, Bacillus wiedmannii, Staphylococcus epidermidis, Rummeliibacillus pycnus, Kurthia zopfii, and Brevibacterium frigoritolerans. These strains were tested for biomineralization on B-4 medium. Five strains (B. subtilis, R. stabekisii, Staphylococcus epiderdimis, B. cereus, and B. wiedmannii) had the capability to precipitate biominerals in vitro. B. subtilis, R. stabekisii, and S. epidermidis precipitated 0.24, 0.36, and 0.35 g/L of biominerals at 22°C at the end of the four week experiment period. These strains increased the pH of the medium from 7 to 8.95. The precipitated biominerals were imaged using an ultra-high resolution field emission SEM. X-ray diffraction of the biomineral precipitated by R. stabekisii showed that it was composed of vaterite and jungite. Whereas S. epidermidis showed that it was composed of calcite, vaterite, and jungite. B. subtilis produced small, circular calcite crystals. This is the first comprehensive report on the possible evidences about the role of R. stabekisii and S. epidermidis in calcite precipitation isolated from speleothems in the Indian caves. These results allow us to postulate that the identified strains have biomineralization potential. Further evidences of the coexistence of exopolysaccharides, whisker fiber calcites, microbial filaments, and coccoid-like forms point to biogenic inputs in the cave mineral formations.     

Geomicrobiological Study of the Grotta dei Cervi,Porto Badisco,Italy

Speleothems (active stalactites, wall concretions), rock walls, ceiling, and soils from the galleries of Grotta dei Cervi, Porto Badisco, Italy, were sampled to investigate the culturable heterotrophic microbial communities present in this cave. Sampling was carried out in a transect of about 230 m from the entrance to the central gallery where numerous Gram-positive bacteria were isolated from all studied sites. Members of the genera Agromyces, Arthrobacter, Rhodococcus , and particularly Streptomyces , of the order Actinomycetales, are spread throughout the whole cave. The ability of actinomycetes, and particularly of Nocardiopsis , to colonize salt-stressed environments is favored by the presence of ectoine, a compatible solute for osmotic adaptation. Selected actinomycete isolates were tested for the formation of crystals. Strains from all tested genera, except isolates of Gordonia and Nocardia , produced vaterite and/or calcite. Production of Mgcalcite was restricted to strains of Brachybacterium, Rhodococcus , and Streptomyces , whereas struvite was only precipitated by an unidentified isolate. These findings indicate that actinomycetes may play a role in the formation of mineral deposits in caves.     

Laboratory studies on the coprecipitation of phosphate with calcium carbonate in the Salton Sea, California

The Salton Sea is a hypereutrophic, saline lake in the desert of southern California. Like many lakes, the primary productivity of the Sea is limited by phosphorus. However, unlike most lakes, the release of P from the sediments is not controlled by the reductive dissolution of Fe(III)-oxide minerals. Most of the iron in the sediments of the Salton Sea is present as Fe(II)-sulfides and silicates. Rather, the sediments are dominated by calcite which is actively precipitating due to alkalinity production via sulfate reduction reactions. We hypothesized that calcite could be an important sink for phosphorus released from the decomposing organic matter. In this work we evaluated the potential for phosphate to coprecipitate with calcite formed in simulated Salton Sea sediment pore water. At calcite precipitation levels and P concentrations typical for the Salton Sea pore water, coprecipitation of P removed 82–100% of the dissolved phosphorus. The amount of P incorporated into the calcite was independent of temperature. The results of this work indicate that the internal loading of P within the Salton Sea is being controlled by calcite precipitation. Management of external P loading should have an immediate impact on reducing algae blooms in the Salton Sea. Guest editor: S. H. Hurlbert The Salton Sea Centennial Symposium. Proceedings of a Symposium Celebrating a Century of Symbiosis Among Agriculture, Wildlife, and People, 1905–2005, held in San Diego, California, USA, March 2005     

Structure and seasonal dynamics of humid tropical grasslands in Meghalaya,India

Abstract. Four humid grassland communities at three different locations in Meghalaya, India were analysed during 1988 and 1989 for species and life-form composition, diversity and dominance in relation to altitude, soil and prevailing disturbances. Due to the adverse interactive influences of exceptionally high annual rainfall (> 10 000 mm), topography and human interference on soil fertility, the grassland at Cherrapunji, at 1300 m altitude, had a low species diversity (H'= 1.74) and was dominated by three perennial grass species. Similar grasslands, at both higher and lower altitudes on fertile soil and with lower rainfall (ca. 2000 mm), showed higher diversity values (H'= 2.28 at Burnihat and 2.31 at Upper Shillong). The proportion of perennial species and chamaephytes increased with elevation. At the high altitude site a grassland under short-term protection from fires and grazing had a higher species richness, density and basal cover than an unprotected grassland. All grasslands show a clear seasonality, albeit with different patterns, with a maximum in density and basal cover in August. The differences in structure and seasonality are discussed in terms of different levels of stress.     

Tree diversity in sacred groves of the Jaintia hills in Meghalaya, northeast India

Biodiversity of woody species was investigated in Ialong and Raliangsacred groves of the Jaintia hills in Meghalaya, northeast India. These grovesrepresent the climax subtropical broad-leaved forest of the area. A total of 738individuals belonging to 82 species, 59 genera and 39 families was identified ina 0.5 ha plot of the Ialong sacred grove, whereas the same area in theRaliang sacred grove had 469 individuals of 80 species, 62 genera and 41families. About 32% species were common to both groves. Lauraceae, with10–17 species, was the dominant family. The canopy and subcanopy stratawere respectively composed of 28 and 33% of the total tree species in theforest. The number of species as well as stem density were greater for the treesof lower dbh (5–15 cm) class compared to the higher (> 66cm) dbh class. The majority of the species showed a contagiousdistribution pattern and low frequency. The basal area varied from 57.4 to 71.4m² ha^–1. Species richness within theforest varied from 3 to 15 per 100 m² in Ialong and 3 to 12 per 100m² in Raliang. The dominance–distribution curves showed highequitability and low dominance in both groves.     

Iron Oxidation and Deposition in the Biofilm Covering Montacuta ferruginosa (Mollusca,Bivalvia)

The shell of the bivalve Montacuta ferruginosa is covered with a rust-colored biofilm. This biofilm includes filamentous bacteria and protozoa encrusted with a mineral, rich in ferric ion and phosphate. The aim of this research was to study two possible microbial iron precipitation pathways in the biofilm, namely, microbial iron oxidation and microbial degradation of organic Fe(III) complexes. The iron-oxidizing activity was assayed spectrophotometrically by monitoring the formation of the dye Wurster blue in biofilm extracts. Iron-oxidizing activity was effectively detected in extracts obtained by oxalic acid treatment of biofilm fragments. Extracts obtained without oxalic acid treatment, heated extracts, or extracts supplemented with HgCl 2 did not show any activity. This suggests that an iron-oxidizing factor (IOF), possibly an enzyme, coprecipitated with the mineral. Additional information gathered by using sodium dodecyl sulfate-polyacrylamide gel electrophoresis, gel-filtration chromatography, and UV spectrophotometry indicate that the IOF would be a small peptide or glycopeptide (1,350 Da). Microbial degradation of organic Fe(III) complexes was assayed with biofilm fragments incubated in a medium containing ferric citrate. Analysis of the supernatants after various intervals revealed that the complex was degraded by living microorganisms much faster than in the heat-killed negative controls. We conclude that ferric iron precipitation in the biofilm may proceed by way of microbial Fe(II) oxidation as well as microbial degradation of organic Fe(III) complexes.     

Ethnobiological notes on the Khasi and Garo tribes of Meghalaya,Northeast India

A total of 105 plants used for food and medicine and 11 animals hunted and gathered for meat by the Khasis and Garos of Meghalaya were identified. Of the total plants recorded, 85 were used by the Garos alone, only three by the Khasis whereas the other 17 were used by both tribes. In addition to fresh use in-season many plant products were processed for storage and use off-season. Although all adults were familiar with various uses of plants and animals, the village elders were more knowledgeable. Garos have especially knowledgeable curers. Wild foods are of particular value for tiding over lean periods when resources from agriculture and animal husbandry systems are scarce, especially for the poorer sections of society. The importance of recording the use of plants and animals in this region is especially important because of rapid loss of rain forest habitats.     

Assessing the effectiveness of community managed forests for plant diversity conservation in Meghalaya,Northeast India

In the state Meghalaya, northeast India, >80% of the forest lands are owned by local communities and managed by traditional institutions. These forests are under severe threats due to a number of human disturbances. The present study was conducted to assess the plant diversity and identify the community forests for priority conservation in Khasi Hills of Meghalaya. Floristic explorations carried out in the 87 forests reveals the presence of 1300 plant species of which 400 are either rare, endemic or threatened. Of the different forest categories, reserve forests had the highest number of species (1190), followed by sacred forests (987 species) and village forests (786 species). Majority of the forests (56) had high-species richness, irreplaceability level (42 forests) and vulnerability level (54). In terms of area, 13.8% (1666.8 ha) fall under low risk while 1855 ha under high risk zone. High risk zone was mostly represented by village forests. An area of 7661.56 ha of community forests falls under high priority category and hence calls for immediate conservation actions. The conservation priority map generated in the present study will help to concentrate the protection strategy to the demarcated and adjoining areas and help conservationists and planners to evolve effective strategies for conservation of the community forests.     

Planktonic foraminiferal succession in late Cretaceous to early Palaeocene strata in Meghalaya, India

A roughly 10.5-m-thick succession within the Langpar Formation of the Um Sohryngkew River section, Meghalaya, India, constrained by the last occurrence of Globotruncanita stuarti and the first occurrence of Parasubbotina pseudobulloides , spans the K/T (Cretaceous–Tertiary) transition. The unit is divisible into three parts with the lower consisting of shaly limestone, weakly calcareous shale and silty shale with coal streaks. The middle part is dominated by calcareous shale with mud flakes, coprolites, burrows and pyrite nodules, followed by alternating limestone and marlite at the top. Planktonic foraminifera are rare to frequent within the unit. Based on the distribution of zonal indices, seven successive planktonic foraminiferal zones are recognized from across the K/T boundary. From base to top, these are CF4, CF3, CF2 and CF1 in the upper Maastrichtian part and Zone P0, Zone Pα and Subzone P1a in the lower Danian part. The biozones indicate that the section is biostratigraphically continuous across the K/T boundary. A similar foraminiferal succession and K/T transition is observed in the Langpar of the Cherrapunji-Mahadeo road section at a distance of over 5km. These K/T outcrops from Meghalaya provide the first record of a continuous K/T sequence in the Indian subcontinent with respect to planktonic foraminifera.     

Ecological Assessment and Geological Significance of Microbial Communities from Cesspool Cave,Virginia

Microbial mats from hydrogen sulfide-rich waters and cave-wall biofilms were investigated from Cesspool Cave, Virginia, to determine community composition and potential geomicrobiological functioning of acid-producing bacteria. Rates of microbial mat chemoautotrophic productivity were estimated using [ 14 C]-bicarbonate incorporations and microbial heterotrophy was determined using [ 14 C]-leucine incubations. Chemoautotrophic fixation was measured at 30.4 - 12.0 ng C mg dry wt -1 h -1 , whereas heterotrophic productivity was significantly less at 0.17 - 0.02 ng C mg dry wt -1 h -1 . The carbon to nitrogen ratios of the microbial mats averaged 13.5, indicating that the mats are not a high quality food source for higher trophic levels. Ribosomal RNA-based methods were used to examine bacterial diversity in the microbial mats, revealing the presence of at least five strains of bacteria. The identity of some of the strains could be resolved to the genus Thiothrix and the Flexibacter - Cytophaga - Bacteriodes phylum, and the identity of the remaining strains was to either the Helicobacter or Thiovulum group. Two of 10 sulfur-oxidizing, chemoautotrophic pure cultures of Thiobacillus spp. (syn. Thiomonas gen. nov.) demonstrated the ability to corrode calcium carbonate, suggesting that the colonization and metabolic activity of these bacteria may be enhancing cave enlargement.     

Biogenic Origin of Polymetallic Nodules from the Clarion-Clipperton Zone in the Eastern Pacific Ocean: Electron Microscopic and EDX Evidence

Polymetallic/ferromanganese nodules (Mn-nodules) have been assigned a huge economic potential since they contain considerable concentrations of manganese, copper, nickel, iron, and cobalt. It has been assumed that they are formed by, besides hydrogenous, nonbiogenic processes, biogenic processes based on metabolic processes driven by microorganisms. In the present study, we applied the techniques of digital optical microscopy and high-resolution scanning electron microscopy to search for microorganisms in Mn-nodules. They were collected from the Clarion-Clipperton Zone in the Eastern Pacific Ocean and are composed of Mn (23.9%), Cu (0.69%), Ni (1.02%), Fe (10.9%), and Co (0.29%). These Mn-nodules, between 2.3 and 4.8 cm, show a distinct lamination; they are composed of small-sized micronodules, 100 to 450 μm in size, which are bound together by an interstitial whitish material. In the micronodules, a dense accumulation of microorganisms/bacteria could be visualized. Only two morphotypes exist: (1) round-shaped cocci and (2) elongated rods. The cocci (diameter: ≈3.5 μm) are arranged in bead-like chains, while the rods (≈2 × 0.4 μm) are arranged either as palisades or in a linear row. Energy-dispersive X-ray spectroscopy analyses showed that the areas rich in microorganisms/bacteria are also rich in Mn, while in regions where no microorganisms are found, the element Si is dominant. We suggest that growth of the Mn-nodules starts with the formation of “micronodules.” The formation of micronodules is assumed to be mediated by microorganisms. After accretion of biogenic and additional nonbiogenic minerals, the micronodules assemble to large nodules on the sea floor through additional inclusion of nonbiogenic material.     

Speleothems from Sahastradhara Caves in Siwalik Himalaya,India: Possible Biogenic Inputs

Stalactites and moonmilk from Sahastradhara caves in Siwalik Himalayas were studied to understand the role of microbes in their genesis. Fourier spectroscopy in the moonmilk indicates a complex milieu of organic compounds that is unusual for inorganic formations. Stable C and O isotopes show trends in the moonmilk and stalactite, which suggest biogenic input; the geochemical inference is consistent with evidence from microscopy and laboratory-based microbial cultures. Light microscopy of moonmilk samples show the presence of a number of microbial forms similar to Cyanobacteria, and scanning electron microscope (SEM) images show microbial structures similar to Spirulina. The total number of microbial cells using SYBR Gold is 6.5 × 10⁵ cells, g sed^?1in moonmilk and 3.2 × 10⁵ cells, g sed^?1 in stalactites. FISH indicates approximately 3.5 × 10⁵ cells, g sed^?1 in moonmilk and 2 × 10⁵ cells, g sed^?1 in stalactites. SEM images of the moonmilk indicate a large network of microbial filaments along with minerals, which are identified as calcite based on their x-ray diffraction pattern. In vitro laboratory cultures with pure monogenic strains isolated from the moonmilk and stalactites raise pH in the medium, which facilitate calcite precipitation. The mineral precipitating isolates were identified as: Bacillus pumilis, B. cereus, B. anthracis, B. lentus, B. sphaericus, B. circulans and Actinomycetes. The Sahastradhara moonmilk and statactites are colonized by a diverse microbial community and the isolated bacterial strains induce biomineralization on different nutrient media, supporting their biogenic origin.     

Fire activity across Cretaceous/Paleogene transition: Evidence from pyrogenic biomarkers preserved in the Mahadeo-Cherrapunji section,Meghalaya, India

Previous studies on high concentrations of polycyclic aromatic hydrocarbon (PAHs) present in the shallow-marine Um-Sohryngkew River (USR) Cretaceous/Paleogene Boundary (KPB) section suggested regional fire incidences and biotic stress on life. However, such observations at the USR site have not been confirmed so far anywhere else in the region, we, therefore, do not know whether the signal was local or regional. Thus, to find out charred organic markers associated with the shelf facies KPB outcrop (at a distance of over 5 km) of the Mahadeo-Cherrapunji road (MCR) section, PAHs were analyzed using gas chromatography–mass spectroscopy. Data show a notable rise in the PAHs and exhibit maximum abundance in the shaly KPB transition layer (in biozone P0) and the immediately underlying layer. The PAH excursions match well with the major incidences of the Deccan volcanic episodes and convergence of the Indian plate with the Eurasian and Burmese plates. These events were responsible for seawater disturbances and eustatic and depositional changes, including the retreat of the Tethys. The incidence of high amount of pyogenic PAHs unrelated to the total organic carbon content is suggestive of wind-blown or aquatic system transportation. A down-thrown shallow-marine facies of the Therriaghat block was responsible for an early accumulation of PAHs. However, the spike of perylene in the immediately underlying KPB transition layer is plausibly linked to the Chicxulub impact crater core. Anomalous concentrations of combustion-derived PAHs together with the high fragmentation and dissolution of the planktonic foraminifer shells show marine biodiversity and biotic distress. Significantly, the pyrogenic PAH excursions are restricted to either the KPB layer itself or strictly below or above it, indicating regional fire incidences and attendant KPB transition (66.016 ± 0.050 Ma).     

Actinobacteria Isolated from an Underground Lake and Moonmilk Speleothem from the Biggest Conglomeratic Karstic Cave in Siberia as Sources of Novel Biologically Active Compounds

Actinobacteria isolated from unstudied ecosystems are one of the most interesting and promising sources of novel biologically active compounds. Cave ecosystems are unusual and rarely studied. Here, we report the isolation and characterization of ten new actinobacteria strains isolated from an ancient underground lake and moonmilk speleothem from the biggest conglomeratic karstic cave in Siberia with a focus on the biological activity of the obtained strains and the metabolite dereplication of one active strain. Streptomyces genera isolates from moonmilk speleothem demonstrated antibacterial and antifungal activities. Some of the strains were able to inhibit the growth of pathogenic Candida albicans.     

Enzymatic activity of fungi endophytic on five medicinal plant species of the pristine sacred forests of Meghalaya,India

Fungal species that establish an endophytic role inside the tissues of medicinal plants are known to produce a wide range of biologically active metabolites and enzymes. In the present study, the most dominant and representative endophytic fungal species of five ethno-medicinal plants prevalent in the pristine sacred forests of Meghalaya, were screened for their ability to produce amylase, cellulase, protease, lipase, and xylanase. Each of endophytic fungal isolates showed a wide range of enzyme activity. Mycelial biomass generation and root colonization, in addition to the enzyme activity of the endophytic fungal isolates, provided insights into their probable origin and ecological roles within the plant host.     

Effects of anthropogenic disturbance on plant diversity and community structure of a sacred grove in Meghalaya, northeast India

This study analyses the effects of anthropogenic disturbance on plant diversity and community attributes of a sacred grove (montane subtropical forest) at Swer in the East Khasi Hills district of Meghalaya in northeast India. The undisturbed, moderately disturbed and highly disturbed stands were identified within the sacred grove on the basis of canopy cover, light interception and tree (cbh 15 cm) density. The undisturbed forest stand had >40% canopy cover, >50% light interception and a density of 2103 trees per hectare, whereas the highly disturbed stand had <10% canopy cover, <10% light interception and 852 trees per hectare. The moderately disturbed stand occupied the intermediate position with respect to these parameters. The study revealed that the mild disturbance favoured species richness, but with increased degree of disturbance, as was the case in the highly disturbed stand, the species richness markedly decreased. The number of families of angiosperms was highest (63) in the undisturbed stand, followed by the moderately (60) and highly disturbed (46) stands. The families Rubiaceae, Asteraceae and Poaceae were the dominant families in the sacred forest. Rubiaceae was represented by 11, 14 and 10 species in the undisturbed, moderately disturbed and highly disturbed stands, respectively, whilst the family Asteraceae had 16 species in the moderately disturbed stand and 14 species in the highly disturbed stand. The number of families represented by a single species was reduced significantly from 33 in the undisturbed stand to 23 in the moderately and 21 in the highly disturbed stand. The similarity index was maximum (71%) between the undisturbed and moderately disturbed stand and minimum (33%) between the undisturbed and highly disturbed stands. The Margalef index, Shannon diversity index and evenness index exhibited a similar trend, with highest values in the moderately disturbed stand. In contrast, the Simpson dominance index was highest in the highly disturbed stand. There was a sharp decline in tree density and basal area from the undisturbed (2103 trees ha^–1 and 26.9 m² ha^–1) to the moderately disturbed (1268 trees ha^–1 and 18.6 m² ha^–1) and finally to the highly disturbed (852 trees ha^–1 and 7.1 m² ha^–1) stand. Density–girth curves depicted a successive reduction in number of trees in higher girth classes from the undisturbed to the moderately and highly disturbed stands. The log-normal dominance–distribution curve in the undisturbed and moderately disturbed stands indicated the complex and stable nature of the community. However, the short-hooked curve obtained for the highly disturbed stand denoted its simple and unstable nature.     

Superintendence of antimicrobial resistance observed in bacterial flora isolated from human faecal carriage in Vellore,India

A frequent cross-sectional study was conducted to determine the patterns of antimicrobial resistance in 296 bacterial strains isolated from in-patient faecal samples of Government Vellore Medical College and Hospital, Vellore. Isolation and identification of bacterial strains were done using enrichment media, selective media, and biochemical tests. Antimicrobial susceptibility testing by the disc diffusion method and minimal inhibitory concentration method was conducted and the strains were subjected to extended spectrum beta-lactamases screening. Antibiotic sensitivity pattern of Staphylococcus spp. showed oxacillin resistance. Almost all the strains were sensitive to linezolid, vancomycin, gentamycin and chloramphenicol. In gram negative isolates ciprofloxacin and tobramycin showed better sensitivity and ceftazidime showed a higher percentage of resistance by MIC. Out of 250 isolates, Enterobacteriaceae showed positive for 86/250, 82/250 and 94/250 isolates and 3/10, 4/10 and 4/10 non-Enterobacteriaceae isolates were found to be positive for CTX-M gene, TEM gene and SHV gene, respectively. This study helps to assess/analyse the relation between the spectrum of microorganisms present in various grades of faecal carriage and their susceptibility pattern in this part of the Vellore town.