Antibiotic resistance of bacteria isolated from shrimp hatcheries and cultural ponds on Donghai Island, China

The resistance of bacteria to 12 different antibiotics was investigated in shrimp farms on Donghai Island, China. Antibiotic-resistant bacteria were found to be widespread in shrimp farms, indicating a high environmental risk. Further, significant differences were found in bacterial strains among farms (ANOVA, p < 0.05), showing resistance to antibiotics such as ampicillin, trimethoprim, compound sinomi, tetracycline, chloramphenicol and cefazolin. No significant differences in antibiotic resistance were found among 6 hatcheries evaluated in this study (ANOVA, p > 0.05), between exalted and traditional shrimp ponds (ANOVA, p > 0.05), and between cultural ponds and corresponding control water source sites (T-test, p > 0.05). In cultural ponds, no significant difference in bacterial resistance to antibiotics was found between water and sediment (T-test, p > 0.05), and antibiotic resistance of bacteria from water showed a significant positive correlation with that from sediment (p < 0.05). Therefore, our study indicates that bacterial multiple antibiotic resistance (MAR) is more widespread in shrimp hatcheries than ponds.     

Isolation and characterization of alkane degrading bacteria from petroleum reservoir waste water in Iran (Kerman and Tehran provenances)

Petroleum products spill and leakage have become two major environmental challenges in Iran. Sampling was performed in the petroleum reservoir waste water of Tehran and Kerman Provinces of Iran. Alkane degrading bacteria were isolated by enrichment in a Bushnel–Hass medium, with hexadecane as sole source of carbon and energy. The isolated strains were identified by amplification of 16S rDNA gene and sequencing. Specific primers were used for identification of alkane hydroxylase gene. Fifteen alkane degrading bacteria were isolated and 8 strains were selected as powerful degradative bacteria. These 8 strains relate to Rhodococcus jostii, Stenotrophomonas maltophilia, Achromobacter piechaudii, Tsukamurella tyrosinosolvens, Pseudomonas fluorescens, Rhodococcus erythropolis, Stenotrophomonas maltophilia, Pseudomonas aeruginosa genera. The optimum concentration of hexadecane that allowed high growth was 2.5%. Gas chromatography results show that all strains can degrade approximately half of hexadecane in one week of incubation. All of the strains have alkane hydroxylase gene which are important for biodegradation. As a result, this study indicates that there is a high diversity of degradative bacteria in petroleum reservoir waste water in Iran.     

Visualisation of bacterial degradation and mobilisation of oil in a porous medium

 Bacterial interaction with oil and sea water, in a porous medium, was studied using a transparent micro model mounted on a cybernetic-controlled positioning board of an inverted microscope. This was interfaced with computer-operated image analysis and surveillance equipment. Consecutive flooding of the model allowed oil to become trapped by capillary forces. Hydrocarbonoclastic bacteria were inoculated. The interaction of biofilm and oil was monitored during a period of 25 days, while mineral salts were supplied intermittently. A unique feature of biofilm behaviour was discovered. The phenomenon is discussed, and calculations are presented. A possible explanation of the phenomenon appears to be local reductions of the surface tension. The phenomenon helps explain why bacteria are able to mobilise oil trapped by capillary forces without reducing the interfacial tension to a level that leads to an increase in the capillary number sufficient to explain incremental oil recovery. The experimental design is believed to be suitable for studying biofilm behaviour on the pore level. Received: 26 January 1998 · Accepted: 9 July 1998     

Primary production and microbial activity in the euphotic zone of Lake Baikal (Southern Basin) during late winter

Three years of regular weekly/biweekly monitoring of seasonal changes in temperature, transparency, chlorophyll a (CHL) and bacteria [erythrosine-stained microscopic counts and cultivable colony forming units (CFUs)] at the vertical profile in the South basin of Lake Baikal (51°54′195″N, 105°04′235″E, depth 800 m) were evaluated. In more detail, the structure and function of phytoplankton and the microbial loop in the euphotic layer at the same site were investigated during the late-winter–early-spring period under the ice. The depth of euphotic zone (up to 1% of surface irradiation) was 35 to 40 m. Primary production was measured three times a week with the ¹⁴C method in 2, 10, 20, 30 and 40 m. Maximum production was found in 10 m, with lower values towards the surface (light inhibition) and towards the lower layers. The total production in cells larger than 1 μm in the column (0–40 m) was 204–240 mg C d⁻¹ m⁻², 30–40% of it being in cells 1–3 μm (mostly picocyanobacteria), which represented roughly 9% of the total chlorophyll a (estimated from pigment analyses). A major part of phytoplankton biomass was formed by diatoms (Synedra acus Hust., Asterionella formosa Hass. and Stephanodiscus meyerii Genkal & Popovskaya). Total production (including extracellular, dissolved organic matter) was 235–387 mg C day⁻¹ m⁻², and the exudates were readily used by bacteria (particles 0.2–1 μm). This part amounted to 1–5% of cellular production in 2 to 20 m and 11–77% of cellular production in 20–40 m, i.e., in light-limited layers. From 0 to 30 m, chlorophyll a concentration was 0.8 to 1.3 μg l⁻¹, wherefrom it decreased rapidly to 0.1 μg l⁻¹ towards the depth of 40 m. Bacteria (DAPI-stained microscopic counts) reached 0.5–1.4×10⁶ ml⁻¹; their cell volumes measured via image analysis were small (average 0.05 μm⁻³), often not well countable when erythrosine stain was used. Bacterial biomasses were in the range of 6–21 μg C l⁻¹. Numbers of colony forming units (CFUs) on nutrient fish-agar were c. 3–4 orders lower than DAPI counts. The amounts of heterotrophic protists were low, whereby flagellates reached 6 to 87 ml⁻¹ and ciliates, 0.2–1.2 ml⁻¹ (mostly Oligotrichida). Bacterial production was measured in the same depths as primary production using ³H-thymidine (Thy) and ¹⁴C-leucine (Leu) uptake. Consistently, bacterial abundances, biomasses, thymidine and leucine production were higher by 30–50% in layers 2, 10 and 20 m compared with that in the deeper 30 and 40 m, where cellular primary production was negligible. Leucine uptake in the deeper layers was even three times lower than in the upper ones. From the comparison of primary and bacterial production, bacteria roughly use 20–40% of primary production during 24 h in the layers 2 to 20 m.     

楚科奇海和加拿大海盆表层沉积物中好气异养细菌的地理分布

本文用MPN法测定楚科奇海和加拿大海盆表层沉积物中好气异养细菌(GAB)的含量,并对其地理学分布进行分析。结果表明,研究区GAB的检出率高达100%。4℃时GAB的含量范围、平均含量为4.00×102-2.40×106个.g-1、1.71×106个.g-1。25℃时GAB的含量范围、平均含量为2.40×105-2.40×107个.g-1、1.10×107个.g-1。无论是含量范围,还是平均含量,均是25℃时的培养结果大于4℃时的培养结果。GAB含量的地理分布趋势是随纬度增高,含量呈降低趋势。在经度变化上则为由东向西,含量呈降低趋势。对沉积物所处水深的分析,表明其在4℃培养得出来的GAB含量随水深增加有下降的趋势,25℃培养出来的GAB含量受环境影响较小,与水深变化关系不明显。     

Biodegradation of Crude Oil by Individual Bacterial Strains and a Mixed Bacterial Consortium Isolated from Hydrocarbon Contaminated Areas

A preliminary study was undertaken to determine the optimal conditions for the biodegradation of a crude oil. Among 57 oil‐degrading bacterial cultures isolated from oil‐contaminated soil samples, Bacillus sp. IOS1‐7, Corynebacterium sp. BPS2‐6, Pseudomonas sp. HPS2‐5, and Pseudomonas sp. BPS1‐8 were selected for the study based on the efficiency of crude oil utilization. Along with the selected individual strains, a mixed bacterial consortium prepared using the above strains was also used for degradation studies. The mixed bacterial consortium showed more growth and degradation than did individual strains. At 1% crude oil concentration, the mixed bacterial consortium degraded a maximum of 77% of the crude oil. This was followed by 69% by Pseudomonas sp. BPS1‐8, 64% by Bacillus sp. IOS1‐7, 45% by Pseudomonas sp. HPS2‐5, and 41% by Corynebacterium sp. BPS2‐6. The percentage of degradation by the mixed bacterial consortium decreased from 77 to 45% as the concentration of crude oil was increased from 1 to 12%. Temperature of 35°C and pH 7 were found to be optimum for maximum degradation.     

石斑鱼烂尾病的病理组织学观察

对点带石斑鱼【Epinethelus malabaricus(Block et Schreider)】烂尾病进行了病理组织学观察。结果表明:烂尾病的病因是病原菌侵袭病鱼,而产生一系列的炎症反应,在病原菌的影响下,病鱼的尾柄部鳞片松脱,皮肤裸露、溃烂,最后鳍条脱落,鳃、肝脏、肾脏、心脏、肠等器官均有不同程度的病变。还对烂尾病产生的原因和病变过程进行了探讨,并提出控制烂尾病发生的一些途径。     

Soil microbial population dynamics along a chronosequence of moist evergreen broad-leaved forest succession in southwestern China

Little is known about whether soil microbial population dynamics are correlated with forest succession.To test the hypotheses that(1) soil microbial composition changes over successional stages,and(2) soil microbial diversity is positively correlated with plant species diversity,we determined the soil microbial populations,community composition,and microflora diversity in evergreen broad-leaved forests along a chronosequence of vegetation succession from 5 to 300 years in southwestern China.The soil microbi...     

Inorganic and organic nitrogen cycling in the Southern California Bight

On the basis of mass balance calculations performed for nitrogen (N) uptake experiments in the Southern California Bight (SCB), it has been suggested that a significant portion of dissolved inorganic N (DIN) uptake results in the production of dissolved organic N (DON). To investigate this process, the fate of ammonium (NH₄⁺) and nitrate (NO₃⁻) uptake was quantified within the euphotic zone at three coastal stations in the SCB using ¹⁵N tracer techniques. Several trends in the fate of DIN and the production of DON were observed. First, production of particulate N (PN), from both NH₄⁺ and NO₃⁻, was quantitatively more important in near surface waters, while DON release dominated within the nitracline. Second, the percentage of gross N uptake released as DON was generally higher when NO₃⁻, rather than NH₄⁺, was the substrate. Third, the percentage of N released as DON was higher at night, relative to the day. Fourth, rates of DON release were significantly correlated to NH₄⁺ regeneration, suggesting that similar mechanisms are responsible for both processes—presumably grazing. The results of this study indicate that the DON pool is a sink for DIN uptake on the time scale of hours. One implication of this finding is that new production estimates based on ¹⁵NO₃⁻ uptake rates will likely underestimate particle flux out of the surface layer because the rate of NO₃⁻ uptake is underestimated due to loss of DO¹⁵N during the incubation. On time scales of months to years, however, the N that is taken up as NO₃⁻ and released as DON will likely contribute to export flux via incorporation of the dissolved phase during seasonal mixing into sinking particles or transport. The export of DON on these time scales argues for the use of gross uptake rates to calculate f-ratios.