广东和广西地区柑橘木虱内生细菌的分离鉴定及多样性分析

[目的] 基于广东和广西地区柑橘木虱内生细菌的分离培养及分子鉴定,明确柑橘木虱可培养内生细菌的多样性,为研究内生细菌与柑橘木虱互作、筛选潜在的共生控制候选细菌提供基础。[方法] 采用虫体捣碎和涂布平板法分离柑橘木虱内生细菌,在线BLAST分析菌株的16S rDNA序列,鉴定内生细菌的种属,并构建优势菌群的系统发育进化树和韦恩图。[结果] 共获得114株柑橘木虱内生细菌,归为细菌界的3个门的15个属,其中芽孢杆菌属59株为优势菌群,占分离细菌总数的51.75%;假单胞菌属14株,占分离细菌总数的12.28%;泛菌属10株,占分离细菌总数的8.77%;其他细菌占分离细菌总数的27.19%。[结论] 芽孢杆菌属细菌广泛分布在两广地区的柑橘木虱体内,值得作为潜在的候选细菌进行共生控制柑橘木虱的研究。     

Quantification and Qualification of Bacteria Trapped in Chewed Gum

Chewing of gum contributes to the maintenance of oral health. Many oral diseases, including caries and periodontal disease, are caused by bacteria. However, it is unknown whether chewing of gum can remove bacteria from the oral cavity. Here, we hypothesize that chewing of gum can trap bacteria and remove them from the oral cavity. To test this hypothesis, we developed two methods to quantify numbers of bacteria trapped in chewed gum. In the first method, known numbers of bacteria were finger-chewed into gum and chewed gums were molded to standard dimensions, sonicated and plated to determine numbers of colony-forming-units incorporated, yielding calibration curves of colony-forming-units retrieved versus finger-chewed in. In a second method, calibration curves were created by finger-chewing known numbers of bacteria into gum and subsequently dissolving the gum in a mixture of chloroform and tris-ethylenediaminetetraacetic-acid (TE)-buffer. The TE-buffer was analyzed using quantitative Polymerase-Chain-Reaction (qPCR), yielding calibration curves of total numbers of bacteria versus finger-chewed in. Next, five volunteers were requested to chew gum up to 10 min after which numbers of colony-forming-units and total numbers of bacteria trapped in chewed gum were determined using the above methods. The qPCR method, involving both dead and live bacteria yielded higher numbers of retrieved bacteria than plating, involving only viable bacteria. Numbers of trapped bacteria were maximal during initial chewing after which a slow decrease over time up to 10 min was observed. Around 10⁸ bacteria were detected per gum piece depending on the method and gum considered. The number of species trapped in chewed gum increased with chewing time. Trapped bacteria were clearly visualized in chewed gum using scanning-electron-microscopy. Summarizing, using novel methods to quantify and qualify oral bacteria trapped in chewed gum, the hypothesis is confirmed that chewing of gum can trap and remove bacteria from the oral cavity.     

家蚕肠道产蛋白酶细菌的分离筛选与分子鉴定

目的肠道细菌对家蚕具有重要的生理作用,探明家蚕肠道产蛋白酶细菌菌群对家蚕肠道细菌的高效开发与利用具有十分重要的意义。方法从菁松×皓月品种4龄家蚕肠液中分离与纯化肠道细菌,获得一株产高活力蛋白酶细菌,对该菌菌落进行形态学鉴定及菌体的显微镜检并结合16S rDNA方法进行了鉴定。结果该菌为革兰阴性杆菌,属于嗜麦芽寡养单胞菌(Stenotrophom onas maltophilia)。结论该产蛋白酶细菌产酶能力较高,可进一步开发研究并用作微生态制剂。     

北京城市空气细菌群落结构与动态变化特征

在北京市选择3个典型的功能区,通过定点系统取样,运用BIOLOG鉴定技术,着重研究了北京城市空气细菌的群落结构与动态变化特征。结果表明:北京市空气中革兰氏阳性菌明显多于革兰氏阴性菌,约占80%~85%,其中阳性球菌占总数的50%~55%。不同功能区共发现47属空气细菌,其中革兰氏阳性菌31属,革兰氏阴性菌16属。优势菌属依次为微球菌属(Micrococcus)、葡萄球菌属(Staphylococcus)、芽孢杆菌属(Bacillus)、棒杆菌属(Corynebacterium)和假单胞菌属(Pseudomonas),它们总和约占50%。在优势菌属中,微球菌属约占总数的20%~30%,是北京市空气中比例最大的菌属,假单胞菌属约占2.5%~5.0%。文教区和交通干线细菌浓度明显高于公园绿地(P<0.01);并且文教区和交通干线空气细菌浓度四季变化特征显著,夏季和秋季较高,春季和冬季较低,公园绿地空气细菌浓度四季没有显著差异;3个功能区13:00时的细菌浓度明显低于9:00时和17:00。     

Bacterial tolerances to metals and antibiotics in metal-contaminated and reference streams

Anthropogenic-derived sources of selection are typically implicated as mechanisms for maintaining antibiotic resistance in the environment. Here we report an additional mechanism for maintaining antibiotic resistance in the environment through bacterial exposure to metals. Using a culture-independent approach, bacteria sampled along a gradient of metal contamination were more tolerant of antibiotics and metals compared to bacteria from a reference site. This evidence supports the hypothesis that metal contamination directly selects for metal tolerant bacteria while co-selecting for antibiotic tolerant bacteria. Additionally, to assess how antibiotic and metal tolerance may be transported through a stream network, we studied antibiotic and metal tolerance patterns over three months in bacteria collected from multiple stream microhabitats including the water column, biofilm, sediment and Corbicula fluminea (Asiatic clam) digestive tracts. Sediment bacteria were the most tolerant to antibiotics and metals, while bacteria from Corbicula were the least tolerant. Differences between microhabitats may be important for identifying reservoirs of resistance and for predicting how these genes are transferred and transported in metal-contaminated streams. Temporal dynamics were not directly correlated to a suite of physicochemical parameters, suggesting that tolerance patterns within microhabitats are linked to a complex interaction of the physicochemical characteristics of the stream.     

Distribution of Purple Photosynthetic Bacteria in Wetland and Woodland Habitats of Central and Northern Minnesota

Enrichment cultures for purple nonsulfur and sulfur photosynthetic bacteria were prepared from soil samples collected in central and northern Minnesota. The purple nonsulfur bacteria were found in most wetland soils sampled but were uncommon in woodland and grassland soils. The pH range of the soils in which these bacteria occurred was 3.8 to 7.8, and the oxidation-reduction potential (E(h)) range was +510 to -65 mV. Soils with a pH below 5.0 or an E(h) above +370 mV had few purple nonsulfur bacteria (<10/g of soil). Rhodopseudomonas viridis, a photosynthetic bacterium containing bacteriochlorophyll b, and the purple sulfur bacteria were common only in low-acidity wetland soils that were usually being reduced.     

Diel and Seasonal Variations in Abundance,Activity, and Community Structure of Particle-Attached and Free-Living Bacteria in NW Mediterranean Sea

Diel and seasonal variations in abundance, activity, and structure of particle-attached vs free-living bacterial communities were investigated in offshore NW Mediterranean Sea (0–1000 m). Attached bacteria were always less abundant and less diverse but generally more active than free-living bacteria. The most important finding of this study was that the activity of attached bacteria showed pronounced diel variations in the upper mixed water column with higher activities at night. Under mesotrophic conditions, the contribution of attached bacteria to total bacterial activity increased from less than 10% at day time to 83% at night time. At high chlorophyll a concentration, the highest cell-specific activities and contribution to total bacterial activity were due to free-living bacteria at day and to attached bacteria at night. Under summer oligotrophic conditions, free-living bacteria dominated and contributed to the most important part of the bacterial activity at both day and night, whereas attached bacteria were much less abundant but presented the highest cell-specific activities. These diel and seasonal variations in activities were concomitant to changes in bacterial community structure, mainly in the upper layer. The number of attached ribotypes was fairly constant suggesting that particles are colonized by a relatively limited number of ubiquitous ribotypes. Most of these ribotypes were also free-living ribotypes suggesting that attached bacteria probably originate from colonization of newly formed particles by free-living bacteria in the upper layer. These results reinforce the biogeochemical role of attached bacteria in the cycling of particulate organic carbon in the NW Mediterranean Sea and the importance of diel variability in these processes.     

呼吸机相关性肺炎的常见病原菌耐药性分析

目的:探讨呼吸机相关性肺炎(VAP)的常见病原菌并分析其耐药性,为临床治疗提供依据。方法:选取我院收治的135例VAP患者的临床资料,分析其病原菌分布以及抗菌药物的耐药性。结果:135例患者中共分离出183株病原菌,其中革兰氏阴性菌135株(占73.77%),革兰氏阳性细菌33株(占18.03%),真菌15株(占8.20%)。革兰氏阴性菌主要为鲍曼不动杆菌,占35.52%,革兰氏阳性细菌主要为金黄色葡萄球菌,占9.84%,革兰阳性菌无一对万古霉素耐药,除了米诺环素总耐药率为42.42%外,其余病原菌对于常用的药物总耐药率均大于60.0%,革兰阴性菌普遍存在多药耐药现象。结论:引起VAP患者感染的主要致病菌为革兰阴性菌群,且存在严重的多重耐药现象,在临床上应加强对VAP疾病的预防和控制,合理应用抗菌药物。     

Total counts, culturable and viable, and non-culturable microflora of a French mineral water: a case study

The changes in bacterial counts during the storage of a natural mineral water from a French spring were studied. Samples were taken from the spring and the bottling line. Viable cultivable (VC) bacteria were counted on R2A medium. Total counts, viable and dead bacteria were counted using the LIVE/DEAD Bac Light VIABILITY kit and epifluorescence microscopy. Viable but non-cultivable (VNC) bacteria were estimated by difference between viable and VC counts. Isolates were clustered by phenotype. The microflora in the spring water increased from < 10-3 x 10(5) bacteria ml-1 after 6 d in storage and then stabilized. Mechanical bottling increased the allochthonous bacteria in the water that stabilized at 10(5) bacteria ml-1. Maximal growth is controlled by the low concentration of nutrients in the mineral water and the lysis of dead cells. The allochthonous bacteria came from the aquifer and colonized the filling line. The changes in the VC and VNC populations showed that the bacteria used starvation-survival and entry into the VNC state to adapt to the bottling stress and the enclosed oligotrophic environment.     

胸腹水培养中的病原菌分布及耐药性分析

目的了解胸腹水培养中病原菌的分布和耐药情况,为临床合理用药提供依据。方法通过回顾性分析中山市第二人民医院住院部自2011年1月至2013年11月送检的胸腹水标本细菌培养及药敏资料。结果在494份胸腹水标本中共检出47株病原菌,总阳性率为9.5%;其中326例胸水分离出病原菌28例,阳性率为8.59%,胸水培养中革兰阳性菌占67.86%,革兰阴性菌占32.12%,菌种较为分散;168例腹水分离出病原菌19例,阳性率为11.31%,腹水培养中革兰阴性菌占73.68%,革兰阳性菌占26.32%。检出革兰阴性病原菌对氨苄西林和四环素耐药率较高,对阿米卡星、美罗培南和亚胺培南敏感。检出革兰阳性病原菌对氨苄西林、头孢西丁和红霉素耐药率高,对万古霉素、替考拉宁和吗啉噁酮敏感。结论应重视胸腹水标本的细菌学检查,依据药敏试验合理使用抗菌药物,减少细菌的耐药率。     

In vivo humoral and cellular reactions, and fate of injected bacteria Aeromonas hydrophila in freshwater prawn Macrobrachium rosenbergii

Live non-opsonized and opsonized Aeromonas hydrophila were injected into juveniles of freshwater prawn Macrobrachium rosenbergii to study the cells involved in phagocytosis, distribution of bacteria, cellular reactions and clearance of both forms of bacteria from the system. The bacteria were rapidly distributed to various tissues viz., gills, heart, hepatopancreas within 1h, and the tissues revealed haemocytic nodule formation after 3 h of injection. There was rapid clearance of both the forms of bacteria from the circulation. However, clearance efficiency was significantly (P < 0.05) faster in the case of opsonized bacteria at 12 h after injection. Similarly, the nodule formation, that was prominent in cardiac musculature, was rapidly eliminated from the tissues of the group injected with opsonized bacteria as compared to non-opsonized bacteria injected group, thus confirming the existence of opsonic factors in haemolymph of this prawn. In another experiment, various dose levels of bacteria were injected intramuscularly into prawns and haemolymph was collected after 1, 6, 24, 72 h and 7 days of injection to study various immune parameters. Although, no major alterations in the total and differential haemocyte counts were observed in bacteria injected prawns compared to control, there was a significant decline in phenoloxidase activity in the highest dose bacteria injected group at the earlier phase and a rise in agglutinin levels at the later phase of the experimental period in the higher dose groups.     

Bacterial Colonization and Ectoenzymatic Activity in Phytoplankton-Derived Model Particles: Cleavage of Peptides and Uptake of Amino Acids

Abstract Phytoplankton-derived model particles were created in laboratory from a mixture of autoclaved diatom cultures. These particles were colonized by a marine bacterial community and incubated in rolling tanks in order to examine the relationship between aminopeptidase activity and leucine uptake. Bacteria inhabiting particles and ambient water were characterized for abundance, biovolume, aminopeptidase activity, leucine uptake, and growth rate. Particles were a less favorable habitat than ambient water for bacterial growth since growth rates of particle-attached bacteria were similar or even lower than those of free-living bacteria. During the first ∼100 h of the particle decomposition process, there were not statistically significant differences in the aminopeptidase activity:leucine uptake ratio between attached and free-living bacteria. From ∼100 h to ∼200 h, this ratio was higher for attached bacteria than for free-living bacteria. This indicates an uncoupling of aminopeptidase activity and leucine uptake. During this period, attached and free-living bacteria showed similar hydrolytic activities on a cell-specific basis. In the free-living bacterial community, variations in aminopeptidase activity per cell were associated with variations in leucine uptake per cell and growth rates. However, in the attached bacterial community, when leucine uptake and growth rates decreased, aminopeptidase activity remained constant. Thus, after ∼100 h, particle-attached bacteria were not taking advantage of their high aminopeptidase activity; consequently the hydrolysed amino acids were released into the ambient water, supporting the growth of free-living bacteria. These results demonstrate that over the particle decomposition process, the relationship between hydrolysis and uptake of the protein fraction shows different patterns of variation for attached and free-living bacterial communities. However, in our experiments, this uncoupling was not based on a hyperproduction of enzymes by attached bacteria, but on lower uptake rates when compared to the free-living bacteria. Received: 4 February 1997; Accepted: 9 May 1997     

Enumeration and isolation of cellulolytic and hemicellulolytic bacteria from human feces

The fibrolytic microbiota of the human large intestine was examined to determine the numbers and types of cellulolytic and hemicellulolytic bacteria present. Fecal samples from each of five individuals contained bacteria capable of degrading the hydrated cellulose in spinach and in wheat straw pretreated with alkaline hydrogen peroxide (AHP-WS), whereas degradation of the relatively crystalline cellulose in Whatman no. 1 filter paper (PMC) was detected for only one of the five samples. The mean concentration of cellulolytic bacteria, estimated with AHP-WS as a substrate, was 1.2 X 10(8)/ml of feces. Pure cultures of bacteria isolated on AHP-WS were able to degrade PMC, indicating that interactions with other microbes were primarily responsible for previous low success rates in detecting fecal cellulolytic bacteria with PMC as a substrate. The cellulolytic bacteria included Ruminococcus spp., Clostridium sp., and two unidentified strains. The mean concentration of hemicellulolytic bacteria, estimated with larchwood xylan as a substrate, was 1.8 X 10(10)/ml of feces. The hemicellulose-degrading bacteria included Butyrivibrio sp., Clostridium sp., Bacteroides sp., and two unidentified strains, as well as four of the five cellulolytic strains. This work demonstrates that many humans harbor intestinal cellulolytic bacteria and that a hydrated cellulose source such as AHP-WS is necessary for their consistent detection and isolation.     

Spatial and Temporal Variation of Enterobacter Genotypes in Sediments and the Underlying Hyporheic Zone of an Agricultural Stream

Population studies of enteric bacteria in an agriculturally impacted stream (Ledbetter Creek, Murray, Kentucky, USA) were conducted over a period of 2 years. Total number of bacteria, cultivated heterotrophic aerobic bacteria, and enteric bacteria showed significant differences between winter and summer. The cultivated numbers of heterotrophic aerobic bacteria and enteric bacteria were significantly more abundant in summer than in winter. The abundance of enteric bacteria was 12.9% in an upwelling zone and 9.8% in a downwelling zone in summer. Most of the enteric bacterial strains isolated on MacConkey agar were assigned to Enterobacter cloacae and E. agglomerans by API 20E and an analysis of the restriction patterns produced by amplified DNA coding for 16S rRNA (ARDRA) with the enzyme Hpa II. E. cloacae and E. agglomerans genotypes isolated from three hyporheic and gravel bar depth intervals (0-10 cm, 15-25 cm, and 30-40 cm) in summer and fall showed significant spatial variation and were heterogeneously distributed along the stream. Temperature, inorganic nutrients, and occurrence of anoxic zones affected the distribution of enteric bacteria. These techniques can be used as a model to monitor shifts among different species in the stream ecosystem.     

Distribution and characterization of kepone-resistant bacteria in the aquatic environment

Effects of the chlorinated insecticide Kepone on the ecology of Chesapeake Bay and James River bacteria were studied. Kepone-resistant bacteria present in a given environment were found to reflect the degree of fecal and/or high organic pollution of the sampling sites, based on total numbers and generic composition of the populations of Kepone-resistant bacteria. The presence of Kepone-resistant bacteria was found to be correlated (alpha = 0.01) with total coliforms, fecal coliforms, and total aerobic viable heterotrophic bacteria, but not with Kepone concentration, since Kepone-resistant bacteria were present in locations where Kepone could not be detected by the analytical methods used in this study. Only gram-negative bacteria, predominantly Pseudomonas, Vibrio, and Aeromonas spp., were found to be resistant to >/=10 mug of Kepone per ml. Gram-positive bacteria, i.e., Bacillus and Corynebacterium spp., were generally sensitive to >/=0.1 mug of Kepone per ml. From results of cluster analysis of taxonomic data, we determined that characteristics of Kepone-resistant bacteria included: resistance to pesticides and heavy metals; degradation of oil; positive oxidase and catalase reactions; and nitrate reduction. From results of the ecological and taxonomic analyses, we conclude that Kepone resistance in estuarine bacteria is due to the physicochemical composition of the gram-negative cell wall and not prior exposure to Kepone. Therefore, the presence of Kepone-resistant bacteria cannot serve as an indicator of Kepone contamination in the aquatic environment where gram-negative bacteria are predominant.     

The effect of sewage sludge composting on the quantitative state of some groups of bacteria and fungi

Analysis of the quantitative state of disease causing bacteria and of other microbic groups were done on the sewage sludge from a sewage treatment plant. The results of the analysis include the ammonifying bacteria, nitrifying and denitrifying bacteria. The general quantity of bacteria and fungi in a secondary dehydrated sludge, fermented secondary dehydrated sludge, and in composted secondary dehydrated sludge was deterinated. Composts were prepared from dehydrated secondary sludge with the addition of sawdust. Microbiological analysis of sewage sludge showed, that the quantities of the fecal coli bacteria were 6500; 220 and 150 cells per cm3 of the secondary dehydrated sludge, fermented secondary dehydrated sludge and composted dehydrated secondary sludge, respectively. The numbers of Salmonella were respectively 67.80; 6.48 and 6.60 cells per cm3. The general numbers of bacteria were 2.98 x 10(7); 2.79 x 10(7); 2.15 x 10(7) cells per cm3 of sludge. The cell numbers of fungi were: 6.20x 10(2); 19.60 x 10(2); 7.80 x 10(2) per cm3 of sludge. In the three types of sludge, the results show great numbers of the ammonifying, nitrifying and denitrifying bacteria. Of the analysed groups of bacteria, the highest numbers of cells were found for general bacteria; ammonifying and nitrifying bacteria were next in abundance; still fewer were the denitrifying bacteria. Fungi and pathogenic bacteria were the least numerous.     

Survival of coliforms and bacterial pathogens within protozoa during chlorination.

The susceptibility of coliform bacteria and bacterial pathogens to free chlorine residuals was determined before and after incubation with amoebae and ciliate protozoa. Viability of bacteria was quantified to determine their resistance to free chlorine residuals when ingested by laboratory strains of Acanthamoeba castellanii and Tetrahymena pyriformis. Cocultures of bacteria and protozoa were incubated to facilitate ingestion of the bacteria and then were chlorinated, neutralized, and sonicated to release intracellular bacteria. Qualitative susceptibility of protozoan strains to free chlorine was also assessed. Protozoa were shown to survive and grow after exposure to levels of free chlorine residuals that killed free-living bacteria. Ingested coliforms Escherichia coli, Citrobacter freundii, Enterobacter agglomerans, Enterobacter cloacae, Klebsiella pneumoniae, and Klebsiella oxytoca and bacterial pathogens Salmonella typhimurium, Yersinia enterocolitica, Shigella sonnei, Legionella gormanii, and Campylobacter jejuni had increased resistance to free chlorine residuals. Bacteria could be cultured from within treated protozoans well after the time required for 99% inactivation of free-living cells. All bacterial pathogens were greater than 50-fold more resistant to free chlorine when ingested by T. pyriformis. Escherichia coli ingested by a Cyclidium sp., a ciliate isolated from a drinking water reservoir, were also shown to be more resistant to free chlorine. The mechanism that increased resistance appeared to be survival within protozoan cells. This study indicates that bacteria can survive ingestion by protozoa. This bacterium-protozoan association provides bacteria with increased resistance to free chlorine residuals which can lead to persistence of bacteria in chlorine-treated water. We propose that resistance to digestion by predatory protozoa was an evolutionary precursor of pathogenicity in bacteria and that today it is a mechanism for survival of fastidious bacteria in dilute and inhospitable aquatic environments.     

Phylogenetic analysis of particle-attached and free-living bacterial communities in the Columbia river, its estuary, and the adjacent coastal ocean.

The Columbia River estuary is a dynamic system in which estuarine turbidity maxima trap and extend the residence time of particles and particle-attached bacteria over those of the water and free-living bacteria. Particle-attached bacteria dominate bacterial activity in the estuary and are an important part of the estuarine food web. PCR-amplified 16S rRNA genes from particle-attached and free-living bacteria in the Columbia River, its estuary, and the adjacent coastal ocean were cloned, and 239 partial sequences were determined. A wide diversity was observed at the species level within at least six different bacterial phyla, including most subphyla of the class Proteobacteria. In the estuary, most particle-attached bacterial clones (75%) were related to members of the genus Cytophaga or of the alpha, gamma, or delta subclass of the class Proteobacteria. These same clones, however, were rare in or absent from either the particle-attached or the free-living bacterial communities of the river and the coastal ocean. In contrast, about half (48%) of the free-living estuarine bacterial clones were similar to clones from the river or the coastal ocean. These free-living bacteria were related to groups of cosmopolitan freshwater bacteria (beta-proteobacteria, gram-positive bacteria, and Verrucomicrobium spp.) and groups of marine organisms (gram-positive bacteria and alpha-proteobacteria [SAR11 and Rhodobacter spp.]). These results suggest that rapidly growing particle-attached bacteria develop into a uniquely adapted estuarine community and that free-living estuarine bacteria are similar to members of the river and the coastal ocean microbial communities. The high degree of diversity in the estuary is the result of the mixing of bacterial communities from the river, estuary, and coastal ocean.     

Isolation and identification of lactic acid bacteria from soil using an enrichment procedure

AIMS: To survey, and identify and classify the ecological distribution of lactic acid bacteria from soil in Japan and Taiwan. METHODS AND RESULTS: Acid-producing bacteria were isolated from 68 soil samples, collected from Japan and Taiwan, in the rhizospheres of fruit trees, from the floor of a henhouse and around a horse farm. All isolates were identified by physiological and genetic tests. Thirty-two of the 54 isolates were identified as lactic acid bacteria (LAB), 16 as spore-forming lactic acid bacteria, five as Clostridium and one as Bacillus. These lactic acid bacteria represent five genera: Lactobacillus, Lactococcus, Enterococcus, Leuconostoc and Weissella. CONCLUSIONS: A high rate of isolating lactic acid bacteria was obtained from soil. SIGNIFICANCE AND IMPACT OF THE STUDY: This study suggests that soil may be a common source for the isolation of lactic acid bacteria.     

Seasonal Variation in Population Density and Heterotrophic Activity of Attached and Free-Living Bacteria in Coastal Waters

The abundance and heterotrophic activity of attached and free-living bacteria were examined seasonally in coastal water. Heterotrophic activity was determined by the uptake of [¹⁴C]glucose. The density of attached bacteria was always minor, not showing a seasonal variation, whereas the free-living bacteria were more numerous and showed a marked seasonal variation, their density being higher under warmer conditions. The contribution of the attached bacteria to the total assimilation of [¹⁴C]glucose (from 10 to 38%) was lower than that of the free-living bacteria, neither of them showing a seasonal variation. On a cellular basis, attached bacteria were more active, since they assimilated more [¹⁴C]glucose and showed, under warmer conditions, a higher cellular volume (0.102 versus 0.047 μm³). We consider that the factors responsible for these observations were the amount and quality of the particulate material, the different availability of organic matter for the two types of bacteria, and in a fundamental way, the variation in water temperature.