Plant growth-promoting rhizobacteria are important contributors to rice yield in karst soils.

The difficulty of releasing nutrients from soils in karst areas limits the yield of local crops and leads to poverty. In this study, two strains of plant growth-promoting rhizobacteria (PGPR) were isolated from the rhizosphere soil of typical plants in karst areas, which were both identified as Bacillus sp. and named GS1 and N1. And two isolates were used to construct a composite PGPR named MC1. These three strains of PGPR were used for soil inoculation in the pot experiment and field trial and their capacity to promote rice development was assessed. The results showed that MC1 inoculation exhibited notable rice growth-promoting ability in pot experiments, and, respectively, had an increment of 16.96, 18.74, and 11.50% in shoot biomass, total biomass, and rice height compared with control. This is largely attributed to PGPR's capacity to secrete phytohormones and soil enzymes, particularly urease (UE) in GS1, whose secreted UE content was significantly higher by 12.18% compared to the control. When applied to the field, MC1 inoculation not only increased rice yield by 8.52% and the available nutrient content in rice rhizosphere soil, such as available phosphorus (AP) and exchangeable magnesium (EMg); but also improved the abundance of beneficial rhizobacteria and the diversity of microbial communities in rice rhizosphere soil. Results in this study revealed that inoculated PGPR played a major role in promoting rice growth and development, and a new strategy for facilitating the growth of rice crops in agriculture was elucidated. Supplementary Information: The online version contains supplementary material available at 10.1007/s13205-023-03593-0.

Response Surface Methodology for the Optimization of Zn-Contaminated Soil Remediation by Soil Washing with Water-Soluble Chitosan.

Soil washing is an important method for the remediation of contaminated soil. This research presents the optimization of soil washing conditions in the remediation of Zn-contaminated soils with water-soluble chitosan (WSCS). Response surface methodology (RSM) was used to optimized the washing conditions after single factor experiments. The central composite design (CCD) with three factors and five levels was applied to the optimization of the removal efficiency of Zn from soils, and WSCS concentration, pH value, and washing time were evaluated variables in the washing process. Results indicated that the pH value (p < 0.0001) was the most significant factor which mainly affected the distribution and content of metal species in aqueous solution, ion exchange and adsorption/desorption behavior of metals, solubility of chelating agent, as well as readsorption of metal complexes. The optimal conditions for the Zn removal from soils were WSCS concentration of 1.5%, pH of 3.3, and washing time of 72 min. The removal efficiency could reach 65.4% under the optimized conditions, which was close to the predicted value of 68.3% by the response surface method. Therefore, it could be found that the response surface methodology was an effective method to determine the optimal conditions for the removal of metals from contaminated soils by soil washing.

Community characteristics of autotrophic CO2-fixing bacteria in karst wetland groundwaters with different nitrogen levels.

Karst wetlands are important in the global carbon and nitrogen cycles as well as in security of water resources. Huixian wetland (Guilin) is the largest natural karst wetland in China. In recent years, groundwater nitrogen pollution has increasingly affected the wetland ecosystem integrity due to anthropogenic activities. In this study, it was hypothesized that autotrophic microbial diversity is impacted with the advent of pollution, adversely affecting autotrophs in the carbon and nitrogen cycles. Autotrophic microbes have important roles in abating groundwater nitrogen pollution. Thus, it is of great significance to study the characteristics of autotrophic bacterial communities and their responses to environmental parameters in nitrogen-polluted karst groundwaters. The abundances of the Calvin-Benson cycle functional genes cbbL and cbbM as well as the autotrophic CO2-fixing bacterial communities were characterized in the karst groundwater samples with different levels of nitrogen pollution. The cbbM gene was generally more abundant than the cbbL gene in the groundwater samples. The cbbL gene abundance was significantly positively correlated with dissolved inorganic nitrogen (DIN) concentration (P < 0.01). In the autotrophic CO2-fixing bacterial communities, Alphaproteobacteria, Betaproteobacteria, and Gammaproteobacteria of the phylum Proteobacteria were predominant. At the genus level, Rubrivivax and Methylibium were the dominant cbbL gene containing genera, while Halothiobacillus and Endothiovibrio were the dominant genera for the cbbM gene. The abundance of autotrophic CO2-fixing bacterial communities increased but their diversity decreased with the inflow of nitrogen into the karst groundwater system. The community structure of autotrophic CO2-fixing bacteria in the groundwaters was also significantly affected by environmental factors such as the carbonic anhydrase (CA) activity, dissolved inorganic carbon (DIC) concentration, temperature, and oxidation-reduction potential (ORP). Nitrogen inflow significantly changed the characteristics of autotrophic CO2-fixing bacterial communities in the karst groundwaters. Some key genera such as Nitrosospira and Thiobacillus were clearly abundant in the karst groundwaters with high nitrogen levels. Their respective roles in nitrification and denitrification impact nitrogen removal in this ecosystem. The findings in this study provide an important reference for biological abatement of nitrogen pollution in the karst groundwater system.

Clostridium weizhouense sp. nov., an anaerobic bacterium isolated from activated sludge of petroleum wastewater.

A Gram-stain-positive, anaerobic, spore-forming, rod-shaped (0.4-0.6 µm×2.5-3.2 µm), flagellated bacterium, designated strain YB-6T, was isolated from activated sludge of an anaerobic tank at Weizhou marine oil mining wastewater treatment plant in Beihai, Guangxi, PR China. The culture conditions were 25-45 °C (optimum, 37 °C), pH 4-12 (pH 7.0) and NaCl concentration of 0-7 % w/v (0%). Strain YB-6T grew slowly in petroleum wastewater and removed 68.2 % of the total organic carbon in petroleum wastewater within 10 days. Concentrations of naphthalene, anthracene and phenanthrene at an initial concentration of 50 mg l-1 were reduced by 32.8, 40.4 and 14.6 %, respectively, after 7 days. Phylogenetic analysis of the 16S rRNA gene sequence indicated that strain YB-6T belongs to Clostridium cluster I and is most closely related to Clostridium uliginosum CK55T (98.5 % similarity). The genome size of strain YB-6T was 3.96 Mb, and the G+C content was 26.5 mol%. The average nucleotide identity value between strain YB-6T and C. uliginosum CK55T was 81.9 %. The major fatty acids in strain YB-6T were C14 : 0 FAME, C16 : 0 FAME and summed feature 4 (unknown 14.762 and/or C15 : 2 FAME). The main polar lipids were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, five unidentified aminophospholipids, one unidentified glycolipid and one unidentified aminolipid. Diaminopimelic acid was not detected in the strain YB-6T cell walls. Whole-cell sugars mainly consisted of ribose and galactose. Based on the results of phenotypic and genotypic analyses, strain YB-6T represents a novel species of the genus Clostridium, for which the name Clostridium weizhouense sp. nov. is proposed. The type strain is YB-6T (=GDMCC 1.2529T=JCM 34754T).

Contribution of microalgae to carbon sequestration in a natural karst wetland aquatic ecosystem: An in-situ mesocosm study.

Carbonate rock weathering coupled with aquatic photosynthesis in karst areas is an important part in the formation of terrestrial carbon sinks. The capacity of photosynthetic carbon sequestration by aquatic microalgae and carbonic anhydrase (CA) is integral in the estimation of carbon sink potential of karst aquatic ecosystems. To date, carbon sequestration by aquatic microalgae in karst areas has been investigated in laboratory experiments. In the present work, the capacity of carbon sequestration by microalgae and CA under natural karst aquatic conditions and the main environmental factors were investigated in field in-situ mesocosms. The Sizhitan Pond of the Huixian karst wetland in Guilin City, Guangxi Province, China, was selected as a typical karst natural water body for this study. The capacity of photosynthetic carbon sequestration varied with microalgal community composition. The microalgal communities with active extracellular CA showed high capacity of carbon sequestration. The average conversion of inorganic carbon to relatively stable organic carbon by microalgae in the Huixian karst wetland aquatic ecosystem was estimated as 4207.5 t C/a. Approximately 28.7% of the bicarbonate fed by the karst underground river was fixed into organic carbon by microalgal photosynthesis. The major environmental factors affecting the capacity of carbon sequestration by microalgae in the karst wetland aquatic ecosystem were the water CA activity, illumination, temperature, total phosphorus and total nitrogen. This study is the first to address the contribution of aquatic microalgae and CA to carbon sequestration under natural karst aquatic conditions. The findings contribute to establishing groundwork for substantiating the carbon sink potential in global karst ecosystems.

[Mechanism of Urban Black Odorous Water Based on Continuous Monitoring: A Case Study of the Erkeng Stream in Nanning].

Black odorous water seriously endangers urban ecological functions. The "Water Pollution Prevention Action Plan" promulgated by the State Council has attached great importance to this issue and set a timetable for achieving the goal of pollution remediation of the urban black odorous water problem. However, in the process of managing the city's black odorous water, we found that the apparent governance effect is not sustainable. Many of the urban waters that have been treated to become clear have returned to a black odorous state. This problem has constrained the completion of the black odorous water control plan, and urgently needs to be resolved. To explain the reason for this phenomenon, we chose the Erkeng Stream in Nanning as the research object, which is a water body that returns to a black odorous state after treatment. We used a multi-parameter water quality tester and chemical analysis method to carry out daily continuous monitoring for 24 h and monthly dynamic monitoring of the water body. The results showed that the rainfall process was significantly correlated with the ammonia nitrogen concentration in the water (P<0.01), and the temperature was positively correlated with the trend of ammonia nitrogen concentration in the water (r=0.23, P<0.05), which in turn was negatively correlated with the change trend of water transparency (r=-0.33, P<0.01). The above results show that the return of the black odorous state may be related to the microbial degradation of endogenous pollutants and the input of external pollutants. The reason may be:① The microorganisms are driven by light and temperature to promote the development of water in the direction of the black odorous state; ② Contaminants carried by rainfall promote the formation of black odor in water bodies. In short, in the context that internal pollution cannot be completely eradicated and external pollutants are difficult to control effectively, to prevent the treated urban water body from returning to a black odorous state, attention should be paid to endogenous pollutants such as river sediment and its control technology. Moreover, ecological control measures should be comprehensively adopted to reduce the input of external source indicators.

Comparative study of carbonic anhydrase activity in waters among different geological eco-environments of Yangtze River basin and its ecological significance.

This study provides the presence of carbonic anhydrase (CA) activity in waters of the Yangtze River basin, China, as well as the correlation of CA activity with HCO(3)(-) concentration and CO(2) sink flux. Different degrees of CA activity could be detected in almost all of the water samples from different geological eco-environments in all four seasons. The CA activity of water samples from karst areas was significantly higher than from non-karst areas (P<0.01), indicating that the geological type of river basin affected the CA activity of waters. Distinct seasonal changes in CA activity were found, and the variational trend differed among different sampling sites. Generally, CA activity in summer and autumn was higher than in spring (P<0.01) for karst areas. The correlation analysis showed that water CA activity was positively correlated with HCO(3)(-) [corrected] concentration (r=0.672, P<0.01), and that the annual average water CA activity was positively correlated with the CO(2) [corrected] sink flux (r=0.602, P=0.076) in karst areas. This suggests that CA in waters might have a promoting effect on carbon sinks for atmospheric CO(2) in karst river basins. In conditions of similar geological type, higher CA activity was generally detected in water samples taken from areas that exhibited better eco-environments, implying that the CA activity index of waters could be used as an indicator for monitoring ecological environments and protection of river basins. These findings suggest that the role of CA in waters in the karst carbon sink potential of river basins is worthy of further in-depth studies.