We investigated the temporal variation of bacterial production, respiration, and growth efficiency in the tropical coastal waters of Peninsular Malaysia. We selected five stations including two estuaries and three coastal water stations. The temperature was relatively stable (averaging around 29.5°C), whereas salinity was more variable in the estuaries. We also measured dissolved organic carbon and nitrogen (DOC and DON, respectively) concentrations. DOC generally ranged from 100 to 900 M, whereas DON ranged from 0 to 32 M. Bacterial respiration ranged from 0.5 to 3.2 M O 2 h ؊1 , whereas bacterial production ranged from 0.05 to 0.51 M C h ؊1 . Bacterial growth efficiency was calculated as bacterial production/(bacterial production ؉ respiration), and ranged from 0.02 to 0.40. Multiple correlation analyses revealed that bacterial production was dependent upon primary production (r 2 ‫؍‬ 0.169, df ‫؍‬ 31, and P < 0.02) whereas bacterial respiration was dependent upon both substrate quality (i.e., DOC/DON ratio) (r 2 ‫؍‬ 0.137, df ‫؍‬ 32, and P ‫؍‬ 0.03) and temperature (r 2 ‫؍‬ 0.113, df ‫؍‬ 36, and P ‫؍‬ 0.04). Substrate quality was the most important factor (r 2 ‫؍‬ 0.119, df ‫؍‬ 33, and P ‫؍‬ 0.04) for the regulation of bacterial growth efficiency. Using bacterial growth efficiency values, the average bacterial carbon demand calculated was from 5.30 to 11.28 M C h ؊1 . When the bacterial carbon demand was compared with primary productivity, we found that net heterotrophy was established at only two stations. The ratio of bacterial carbon demand to net primary production correlated significantly with bacterial growth efficiency (r 2 ‫؍‬ 0.341, df ‫؍‬ 35, and P < 0.001). From nonlinear regression analysis, we found that net heterotrophy was established when bacterial growth efficiency was <0.08. Our study showed the extent of net heterotrophy in these waters and illustrated the importance of heterotrophic microbial processes in coastal aquatic food webs.As our understanding of the marine food web evolves, we recognize the importance of microorganisms in aquatic ecosystems. Bacteria are the main respirers and recycle a large pool of dissolved organic matter to higher trophic levels (6, 13). Therefore, bacterial production is a key process in dissolved organic matter flux. However, the transfer of dissolved organic matter to bacteria is more accurately reflected by bacterial carbon demand (BCD) or carbon consumption (23). One way to obtain BCD from bacterial production is through bacterial growth efficiency (BGE) or growth yield. BGE is an important parameter to evaluate the fate of organic carbon inputs and to determine whether bacteria act as a link (recyclers) or sink (mineralizers). Therefore, understanding the patterns of variation in BGE is fundamental for our knowledge of carbon cycling (14).BGE is essentially the ratio of carbon converted to biomass relative to all the carbon consumed, where carbon consumption is either measured as the sum of bacterial production and respiration (5, 24), dissolved organic ...

In the present study, the relationship between bacteria and phytoplankton in tropical coastal waters was investigated. The bacterial abundance, bacterial production, chlorophyll a concentration and net primary production were measured at several locations in the coastal waters of Peninsular Malaysia. Chlorophyll a concentration ranged from 0.40 to 32.81 μg L–1, whereas bacterial abundance ranged from 0.1 to 97.5 × 106 cells mL–1. Net primary production ranged from 8.49 to 55.95 μg C L–1 h–1, whereas bacterial production ranged from 0.17 to 70.66 μg C L–1 h–1. In the present study, the carbon conversion factor used to convert bacterial production (cells mL–1 h–1) into carbon units ranged from 10 to 32.8 fg C cell–1, and was estimated from the bacterial size distribution measured at each location. Both phototrophic and heterotrophic biomass (bacteria–chlorophyll a) and activity (bacterial production–net primary production) were significantly correlated, although their correlation coefficients (r2) were relatively low (r2 = 0.188 and r2 = 0.218 respectively). Linear regression analyses provided the following equations to represent the relationship between: bacteria and chlorophyll a (Chl a), log Bacteria = 0.413 log Chl a + 6.057 (P = 0.003); and between bacterial production (BP) and net primary production (NPP), log BP = 0.896 log NPP – 0.394 (P = 0.004), which fitted with published results well. Comparison of annual carbon fluxes confirmed the prevalence of net heterotrophy in these coastal waters, and together with the low correlation coefficients, suggested the role of allochthonous organic matter in supporting heterotrophic activity.

Dimethyl phthalate (DMP), a phthalate ester, is widely used in cosmetics, perfumes, and plasticizers. It has been classified as a suspected endocrine disruptor by many countries. The present study describes the biodegradation of DMP by a new aerobic bacterium, isolated from soil samples of a cotton field by an enrichment culture technique utilizing DMP as the sole source of carbon and energy. The isolate was identified as Bacillus thuringiensis based on the morphological and biochemical characteristics as well as gene sequence analysis. Bacillus thuringiensis grows best in a mineral salt medium of pH 7.0 at 30 C incubation for 48 hours. The effects of temperature, inoculum size, substrate concentration and incubation time on DMP degradation were also studied. Bacillus thuringiensis is able to biodegrade 400 mg L À1 of DMP under aerobic conditions with 99% degradation potential. A combination of GC and GC-MS analysis revealed a complete DMP biodegradation pathway. The results indicate that Bacillus thuringiensis may prove a promising source for DMP bioremediation at a commercial scale.

E.coli, an important vector distributing antimicrobial resistance in the environment, was found to be multi-drug resistant, abundant, and genetically diverse in the Matang mangrove estuaries, Malaysia. One-third (34%) of the estuarine E. coli was multi-drug resistant. The highest antibiotic resistance prevalence was observed for aminoglycosides (83%) and beta-lactams (37%). Phylogenetic groups A and B1, being the most predominant E. coli, demonstrated the highest antibiotic resistant level and prevalence of integrons (integron I, 21%; integron II, 3%). Detection of phylogenetic group B23 downstream of fishing villages indicates human fecal contamination as a source of E. coli pollution. Enteroaggregative E. coli (1%) were also detected immediately downstream of the fishing village. The results indicated multi-drug resistance among E. coli circulating in Matang estuaries, which could be reflective of anthropogenic activities and aggravated by bacterial and antibiotic discharges from village lack of a sewerage system, aquaculture farms and upstream animal husbandry.

One major source of antibiotic contamination in the sea is from aquaculture. We monitored concentration of commonly used antibiotic classes and antibiotic resistance genes (ARGs: tet(M), sul1, sul2 and sul3) in seven main aquaculture production stations in Peninsular Malaysia and detected twenty-three antibiotics. Tetracyclines, sulfonamides and quinolones were the most frequently detected antibiotic classes, 2 indicating a wide distribution of antibiotics in Malaysian aquaculture farms.Oxytetracycline, tetracycline and minocycline were the common tetracyclines (LOQ-2.45× 10 2 ng/L) detected, while sulfamerazine and sulfathiazole were commonly detected sulfonamides (LOQ-2.82× 2 ng/L) among the farms. For quinolones (LOQ-9.58 × 10 5 ng/L), enrofloxacin, nalidixic acid, and ofloxacin were the most 31 common. Relative to Asian aquaculture farms, the residues detected here were at low 32 or moderate levels except for quinolones. The dendrogram and heatmap revealed 33 three groups of antibiotic concentration patterns but with no differences in the types of antibiotics usage among aquaculture farms were observed. The ARGs (10 -3 copies/16S) were detected in more than 90% of the sites except for sul3. There was also high ecological risks of ciprofloxacin, enrofloxacin, norfloxacin and lincomycin for cyanobacteria and algae in Kelantan, Perak and Pahang. This is the first study to shed light on the antibiotic contamination, ARGs in aquaculture systems and its potential ecological risk in the coasts of Malaysia. This study will be useful to develop effective management of aquaculture wastewater in order to mitigate antibiotic pollution and transmission of ARGs to humans through the food chain.