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Denitrification and nitrate-ammonification are the responsible processes for nitrate removal in the estuaries. Temperature, nitrate and organic carbon availability are key factors controlling a rate of the nitrate reduction processes. This mixed cultures chemostat study investigates the competition ability and their nitrate reduction end-products of the bacteria isolated from an estuary at different temperatures. This study will help us to understand the seasonal nitrate reduction processes in an estuary. The experiments showed that a nitrate-ammonifier was the predominant process in the steady-state chemostat at high temperature. While a facultative denitrifier-nitrate ammonifier was the predominant process at low temperature. However, the main end products of nitrate reduction at high temperature were up to 61% N2 indicating a denitrifier still had an important role in the end products of nitrate reduction in the estuary. The data also showed that a nitrite respiring bacterium reduced nitrite to N2, that responsible for approximately 6-9% of total N2 produced in the culture. This study confirmed that nitrate ammonifiers out-compete denitrifiers at high temperature, however, denitrifiers still had an important role in end products of nitrate reduction. [ABSTRACT FROM AUTHOR]

Certain strains of V. parahaemolyticus carry a gene that encodes a toxin that causes Acute hepatopancreatic necrosis disease (AHPND) in P. vannamei. AHPND attacks shrimp post larvae within 20-30 days after stocking causing up to 100% mortality. The expression of these virulent genes is controlled by the quorum sensing system. This system is inhibited by an anti-quorum sensing (AQS) mechanism. Several Bacillus strains have AQS mechanism by producing AHLLactonase enzyme. Therefore, this study aimed to obtain Bacillus spp. having AQS activity for controlling AHPND. The study was conducted from isolation and selection of Bacillus isolates, as well as determination of AQS activity. From 22 samples consisting of shrimp intestines, water and pond sediment samples, a total of 151 isolates of Bacillus spp. were isolated. The screening test for AQS activity obtained 11 isolates that showed AQS activity on Cromobacterium violaceum. Determination of violacein pigment in liquid cultures of C. violaceum showed the index value of the pigment formation was between 0.025-0.166 and 0.026-0.567 at 24-hour and between 48-hour incubations, respectively. The quantitative analysis of violacein production showed that there were six isolates of Bacillus could inhibit the pigment production more than 75%. The isolates were identified as Bacillus cereus (four isolates), Bacillus thuringiensis (one isolate), and Bacillus velezensis (one isolate), respectively. The molecular analysis had confirmed that the isolates have aiiA genes encoding AHL-lactonase enzyme. These Bacillus isolates have potential application for controlling AHNPD disease. [ABSTRACT FROM AUTHOR]

Research has been conducted on the nitrate and nitrite concentrations in water and nitrous oxide and nitrite oxide fluxes across sediment-water interface. The rates of the N (Sub)2 O flux from the estuary bottom sediments have been measured in investigating the relationship between N (sub)2 O emission and nitrate and nitrite concentrations in water.

Prebiotic administration is one method to increase growth performance, improve intestinal microbiota composition, inhibit pathogen growth and induce immunity in fishes. Honey consists of oligosaccharides as the major content that can be used as a prebiotic. This study investigated the effects of administration of dietary prebiotic from honey at different doses on growth performance, digestive enzyme activities, intestinal microvilli, short‐chain fatty acid contents and microbiota diversity in the digestive tract of Nile tilapia (Oreochromis niloticus). Four diet treatments were applied, namely control (without honey administration) and honey administration at 0.25%, 0.5% and 1% doses (g/kg diet). Nile tilapia weighing 20 ± 1.72 g were reared with these diet treatments for 30 days. Results demonstrated that honey prebiotic administration could increase growth performance; provide a lower feed conversion ratio; induce digestive enzyme activities (amylase, protease and lipase); increase microvilli length, perimeter ratio, density of intestinal microvilli and short‐chain fatty acid contents (propionate, iso butyrate, iso‐valerate and N‐valerate); and improve microbiota diversity in the digestive tract of Nile tilapia at the best dietary dose of 1%. [ABSTRACT FROM AUTHOR]

Pathogenic bacteria use quorum sensing (QS) mechanism to express virulence gene. QS mechanism is induced by acyl homoserine lactone (AHL) as universal QS autoinducer in Gram negative bacteria. Inhibition of virulence genes expression can be done by degrading the AHL compounds using AHL-lactonase encoding aiiA gene. The study aimed to clone and express aiiA gene of Bacillus cereus B10 into E.coli BL21 (DE3) pLysS. The aiiA gene was cloned into DH5α through pGEMT-easy vector and expressed using pETt15b vector. The aiiA sequences and 3D structure of AiiA protein were analyzed with ORF finder, swiss model program and PyMOL software. Overexpression of aiiA gene in E.coli BL21 (DE3) pLysS was induced by 0.1 mM, 0.5 mM, and 1 mM IPTG through SDS PAGE method. The result showed that aiiA gene consisted of 250 amino acids and had high similarity with AiiA proteins in Bacillus cereus AAL98271. AHL lactonase of B.cereus B10 showed high homology with zinc metallo-beta-lactamase family with HXHXDH motif. The SDS- PAGE analysis showed that AiiA proteins of Bacillus cereus B10 had a molecular weight of 28,18 Kda. The aiiA gene from B.cereus B10 was successfully expressed into E.coli BL21(DE3). [ABSTRACT FROM AUTHOR]

Paddy field is one of the anthropogenic sources that produce greenhouse gases emission. This study aimed to investigate the impact of methanotrophic and N2Oreducing bacterial inoculation on CH4 and N2O emissions, paddy growth and bacterial community structure in paddy field. Two treatments of 100% synthetic fertilizer (250 kg urea/ha) without biofertilizer and 50% synthetic fertilizer (125 kg urea/ha) with biofertilizer consisted of methanotrophic and N2O-reducing bacteria were applied in the paddy field. Inoculation of methanotrophic and N2O-reducing bacteria was able to reduce CH4 and N2O emission up to 4.19 mg CH4/m2/day and 351.29 µg N2O/m2/day, respectively. Those bacterial applications were also able to increase paddy growth and yield productivity. According to DGGE profile, inoculation of the biofertilizer seemed to have a transient impact on bacterial communities in paddy soil at 36 days after transplanting (DAT) which showed the lowest similarity with all samples (a similarity index of 0.68). DGGE bands successfully excised have closest relative to uncultured bacteria which comprised 5 phyla, i.e. Proteobacteria (Alphaproteobacteria and Deltaproteobacteria), Nitrospirae, Actinobacteria, Firmicutes, and Acidobacteria. In this study, Alphaproteobacteria was the most dominant phylum. We provide basic information for developing the biofertilizer which supports sustainable agriculture. [ABSTRACT FROM AUTHOR]