This reveals that mutant cells do not die in the presence of GlcNAc and only their growth has been inhibited. Atomic force microscopy was employed to analyze cell morphology and no significant changes were observed between wild type and mutant cells. In the present study, we report a genomic DNA fragment belonging to N-acetylglucosamine 6-phosphate deacetylase from cellulose producing bacterium G. xylinus. In E. coli and other prokaryotes, nagA is demonstrated to be involved in GlcNAc metabolisms by deacetylating GlcNAc-6-P to Gln-6-P. Therefore we sought to investigate the role of nagA in N-acetylglucosamine assimilation in G. xylinus by disrupting nagA. Since nagA mutants were able to grow on glucosamine, this clearly indicates that deacetylase is not involved in glucosamine degradation. Due to the fact that UDP-GlcNAc was almost undetectable in DnagA cells under either glucose or GlcNAc feed, we not only conclude that nagA is essential for conversion of GlcNAc supplements in to UDP-GlcNAc but also that G. xylinus lacks the enzyme AGM, as in presence AGM bacteria would be able to synthesize UDP-GlcNAc even in the absence of nagA. Based on our results and the GlcNAc metabolic pathway from both prokaryotes and eukaryotes, we believed that following steps occurred in G. xylinus: i) conversion of GlcNAc-6-phosphate into glucosamine-6-phosphate by NagA; ii) conversion of GlcN-6-P into glucosamine-1-phosphate ; iii) acetylation of GlcN-1-P to produce N-acetylglucosamine-1-phosphate ; and iv) synthesis of UDP-GlcNAc from GlcNAc-1- P and UTP. The overall pathway is illustrated in Fig. 6. The growth characteristics of deacetylaseless mutants confirm the catabolic routes for glucosamine and GlcNAc in G. xylinus. The inhibited growth of mutants in presence of GlcNAc was due to lack of adequate UDP-GlcNAc in cytoplasm for peptidoglycan cell wall synthesis; as a result the bacteria could not multiply. Earlier studies have shown that G. xylinus is able to incorporate GlcNAc in cellulose while grown under GlcNAc fed conditions. Therefore we sought to evaluate the chemical composition of cellulose produced by both wild type and mutant cells and the role of nagA in this procedure. We did not observe any GlcNAc content in cellulose produced by mutant cells while a small fraction of GlcNAc was observed in wild type cells as reported earlier.

Furthermore, these late-spawning species and/or colonies may be at greater risk from the combined effects of high SST and pollution from flood plumes. To quantify this risk, both field studies and laboratory approaches are needed to understand the combined effects of climate change and pollution. A recent field study indicated that wastewater discharge has increased the susceptibility of coral communities in the Florida Keys to thermal bleaching. Similarly, the occurrence of coral bleaching on the GBR can be more accurately predicted when dissolved inorganic nitrogen concentration is included in the modelling framework. Such models indicate that reducing DIN by 50% –80% would help to protect inshore corals of the GBR by increasing the bleaching threshold by 2uC. Successful coral recruitment is important for the maintenance and recovery of coral communities under pressure from climate change and other anthropogenic influences. The profound effect that Cu has on exacerbating the negative effects of thermal stress on coral larval metamorphosis in the laboratory illustrates that water quality can be a particularly pressing issue for the health of coral reefs as SSTs increase due to climate change. The larval metamorphosis model developed here from experimental data demonstrates that reducing water contamination can have positive effects on coral recruitment. At a seawater temperature of 28uC, 50% of Acropora millepora and A. tenuis larvae successfully metamorphosed when Cu concentrations were approximately equal to 25 and 30 mg L21 respectively. However, halving Cu concentrations from these values resulted in more than 3.5uC increase in the temperature threshold for both species. Indeed, for each of the percentage metamorphosis thresholds depicted in Fig. 3, halving Cu concentrations from the value corresponding to the control temperature led to an increase in the temperature tolerance by 3–5uC. This study therefore provides empirical evidence to support government programs that aim to improve water quality to mitigate the negative effects of increasing seawater temperatures due to global change.